Novel embalming solution for neurosurgical simulation in cadavers

The Use of Technology-Based Simulation among Medical Students as a Global Innovative Solution for Training

BACKGROUND

Technological advancements have been rapidly integrated within the neurosurgical education track since it is a high-risk specialty with little margin for error. Indeed, simulation and virtual reality during training can improve surgical performance and technical skills. Our study aims to investigate the impact of neurosurgical technology-based simulation activities on medical students.

METHODS AND MATERIALS

The "Suturing Mission-The Symposium" was a three-day event held at Humanitas University. Participants had access to live-streamed conferences held by worldwide experts in several fields of neurosurgery and practical simulations of dura mater sutures, microvascular anastomosis, and augmented reality neurosurgical approaches. An anonymous survey was conducted at the beginning and end of the event.

RESULTS

141 medical students with a mean age of 21 participated. After the course, 110 participants (77.5%) showed interest in pursuing a surgical path, with a great prevalence in those who had planned to have a surgical career before the event (88.7% vs. 41.4%, p < 0.001). Participants were also asked about their comfort levels while handling surgical instruments, and a good outcome was reached in 72.7% of participants, with a significant difference between those who had previously attended a suture course (87.8% vs. 66.3%, p = 0.012).

CONCLUSION

Training sessions on surgical simulators were effective in increasing participants' interest in pursuing a surgical path, improving their understanding of postgraduate orientation, and boosting their confidence with surgical instruments.

Simulation to become a better neurosurgeon. An international prospective controlled trial: The Passion study

Introduction

Surgical training traditionally adheres to the apprenticeship paradigm, potentially exposing trainees to an increased risk of complications stemming from their limited experience. To mitigate this risk, augmented and virtual reality have been considered, though their effectiveness is difficult to assess.

Research question

The PASSION study seeks to investigate the improvement of manual dexterity following intensive training with neurosurgical simulators and to discern how surgeons' psychometric characteristics may influence their learning process and surgical performance.

Material and methods

Seventy-two residents were randomized into the simulation group (SG) and control group (CG). The course spanned five days, commencing with assessment of technical skills in basic procedures within a wet-lab setting on day 1. Over the subsequent core days, the SG engaged in simulated procedures, while the CG carried out routine activities in an OR. On day 5, all residents' technical competencies were evaluated. Psychometric measures of all participants were subjected to analysis.

Results

The SG demonstrated superior performance (p < 0.0001) in the brain tumour removal compared to the CG. Positive learning curves were evident in the SG across the three days of simulator-based training for all tumour removal tasks (all p-values <0.05). No significant differences were noted in other tasks, and no meaningful correlations were observed between performance and any psychometric parameters.

Discussion and conclusion

A brief and intensive training regimen utilizing 3D virtual reality simulators enhances residents' microsurgical proficiency in brain tumour removal models. Simulators emerge as a viable tool to expedite the learning curve of in-training neurosurgeons.

Cadaver preservative properties of a solution composed of honey, ethyl alcohol, liquid paraffin, distilled water and citric acid: Experiments on rabbit cadavers

The objective of this study is to assess the efficacy of a solution including honey, ethyl alcohol, liquid paraffin, distilled water and citric acid (HEFS) as a preservative for rabbit cadavers, serving as a potential substitute for formaldehyde. The cadavers underwent preservation using three distinct solutions: 10% formalin, 35% alcohol and HEFS. The cadavers were subjected to a total of four sampling events, occurring at 4-month intervals, in order to collect specimens for microanatomical, histological, microbiological, mycological, colourimetric, texture and odour analysis. In terms of hardness, suitability for dissection and joint mobility metrics, the cadavers fixed with HEFS had superior qualities to those fixed with formalin. The fixation quality of HEFS for histological analyses was deemed acceptable, except kidney and intestinal tissues. In texture analysis, differences only in the elasticity parameter (p < 0.05) in the same sampling period. A total of 10 (13.9) bacteria isolates were identified among which, Metasolibacillus meyeri 3 (30%) was predominantly followed by Staphylococcus aureus 2 (20%), Bacillus siamensis, Bacillus subtilis, Pseudarthrobacter oxydans, Bacillus licheniformis, Bacillus subtilis subsp. subtilis with a proportion of 1 (10%), respectively, by both microbiological and molecular analysis. However, no anaerobic bacteria and fungi were isolated. A considerable percentage of the students had the perception that HEFS was appropriate for utilization in laboratory settings due to its absence of unpleasant odours and detrimental impact on ocular and respiratory functions. In conclusion, we consider that HEFS may serve as a viable substitute for formalin solution in the preservation of rabbit cadavers.

Toward an optimal cadaveric brain model for neurosurgical education: assessment of preservation, parenchyma, vascular injection, and imaging

OBJECTIVE

We assessed types of cadaveric head and brain tissue specimen preparations that are used in a high throughput neurosurgical research laboratory to determine optimal preparation methods for neurosurgical anatomical research, education, and training.

METHODS

Cadaveric specimens (N = 112) prepared using different preservation and vascular injection methods were imaged, dissected, and graded by 11 neurosurgeons using a 21-point scale. We assessed the quality of tissue and preservation in both the anterior and posterior circulations. Tissue quality was evaluated using a 9-point magnetic resonance imaging (MRI) scale.

RESULTS

Formalin-fixed specimens yielded the highest scores for assessment (mean ± SD [17.0 ± 2.8]) vs. formalin-flushed (17.0 ± 3.6) and MRI (6.9 ± 2.0). Cadaver assessment and MRI scores were positively correlated (P < 0.001, R2 0.60). Analysis showed significant associations between cadaver assessment scores and specific variables: nonformalin fixation (β = -3.3), preservation within ≤72 h of death (β = 1.8), and MRI quality score (β = 0.7). Formalin-fixed specimens exhibited greater hardness than formalin-flushed and nonformalin-fixed specimens (P ≤ 0.006). Neurosurgeons preferred formalin-flushed specimens injected with colored latex.

CONCLUSION

For better-quality specimens for neurosurgical education and training, formalin preservation within ≤72 h of death was preferable, as was injection with colored latex. Formalin-flushed specimens more closely resembled live brain parenchyma. Assessment scores were lower for preparation techniques performed > 72 h postmortem and for nonformalin preservation solutions. The positive correlation between cadaver assessment scores and our novel MRI score indicates that donation organizations and institutional buyers should incorporate MRI as a screening tool for the selection of high-quality specimens.

Comparison of histological procedures and antigenicity of human post-mortem brains fixed with solutions used in gross anatomy laboratories

Background

Brain banks provide small tissue samples to researchers, while gross anatomy laboratories could provide larger samples, including complete brains to neuroscientists. However, they are preserved with solutions appropriate for gross-dissection, different from the classic neutral-buffered formalin (NBF) used in brain banks. Our previous work in mice showed that two gross-anatomy laboratory solutions, a saturated-salt-solution (SSS) and an alcohol-formaldehyde-solution (AFS), preserve antigenicity of the main cellular markers (neurons, astrocytes, microglia, and myelin). Our goal is now to compare the quality of histology and antigenicity preservation of human brains fixed with NBF by immersion (practice of brain banks) vs. those fixed with a SSS and an AFS by whole body perfusion, practice of gross-anatomy laboratories.

Methods

We used a convenience sample of 42 brains (31 males, 11 females; 25-90 years old) fixed with NBF (N = 12), SSS (N = 13), and AFS (N = 17). One cm3 tissue blocks were cut, cryoprotected, frozen and sliced into 40 μm sections. The four cell populations were labeled using immunohistochemistry (Neurons = neuronal-nuclei = NeuN, astrocytes = glial-fibrillary-acidic-protein = GFAP, microglia = ionized-calcium-binding-adaptor-molecule1 = Iba1 and oligodendrocytes = myelin-proteolipid-protein = PLP). We qualitatively assessed antigenicity and cell distribution, and compared the ease of manipulation of the sections, the microscopic tissue quality, and the quality of common histochemical stains (e.g., Cresyl violet, Luxol fast blue, etc.) across solutions.

Results

Sections of SSS-fixed brains were more difficult to manipulate and showed poorer tissue quality than those from brains fixed with the other solutions. The four antigens were preserved, and cell labeling was more often homogeneous in AFS-fixed specimens. NeuN and GFAP were not always present in NBF and SSS samples. Some antigens were heterogeneously distributed in some specimens, independently of the fixative, but an antigen retrieval protocol successfully recovered them. Finally, the histochemical stains were of sufficient quality regardless of the fixative, although neurons were more often paler in SSS-fixed specimens.

Conclusion

Antigenicity was preserved in human brains fixed with solutions used in human gross-anatomy (albeit the poorer quality of SSS-fixed specimens). For some specific variables, histology quality was superior in AFS-fixed brains. Furthermore, we show the feasibility of frequently used histochemical stains. These results are promising for neuroscientists interested in using brain specimens from anatomy laboratories.

Exploring alternatives for securing anatomical structures in capturing digital images: A comparative analysis

Teaching veterinary anatomy using digital platforms requires improved image quality, which may influence the fixation process. This study aimed to compare four embalming solutions for high-colour-quality images of different tissues compared to the original image. Four equine left pelvic limbs were cut into metameres and divided equally for application of 10% formaldehyde, 96% glycerine, 33% hypersaturated NaCl solution and modified Larssen solution, respectively, which was maintained for 3 days. After drying for 3 days at room temperature, photographs were obtained at time 0 (T0), without any fixation process (original colour); time 1 (T1), immediately after removal from the solutions; and every 24 h for 3 days (T2-T4). The image colour quality was investigated by digitally evaluating the cortical bone, tendon and bone marrow using histograms and CIEDE2000 as well as by 10 specialists in an online survey. CIEDE2000 and histograms revealed that all fixation solutions changed the original tissue colour at all the time points (p < 0.0001). According to the specialists, the 33% saline solution produced the best results compared to the original one. The modified Larssen solution demonstrated better results for the tendon, marrow and cortical bone at T3 (p = 0.0015). Considering the colour of digital images, the modified Larssen solution provided the best results; however, the visual evaluation by the specialists revealed the 33% saline solution as the best.

Petroclival Clinoidal Folds and Arachnoidal Membranes of the Anteromedial Incisural Space: Clinical Anatomy for Neuro Critical Care

A systematic and narrative literature review was performed, focusing attention on the anatomy of the area located at the junction of the sphenoid and the basal portion of the temporal bone (petrous bone, petrous apex, upper petro-clival region) encircled by the free edge of the tentorium, the insertion of the tentorium itself to the petrous apex and the anterior and posterior clinoid processes that give rise to three distinct dural folds or ligaments: the anterior petroclinoid ligament, the posterior petroclinoid ligament and the interclinoid ligament. These dural folds constitute the posterior portion of the roof of the cavernous sinus denominated "the oculomotor triangle". The main purpose of this review study was to describe this anatomical region, particularly in the light of the relationships between the anterior margin of the free edge of the tentorium and the above-mentioned components of the sphenoid and petrous bone.

Combined cone-beam CT imaging and microsurgical dissection of cadaver specimens to study cerebral venous anatomy: a technical note

PURPOSE

Cadaver dissections and X-ray based 3D angiography are considered gold standards for studying neurovascular anatomy. We sought to develop a model that utilize the combination of both these techniques to improve current tools for anatomical research, teaching and preoperative surgical planning, particularly addressing the venous system of the brain.

MATERIALS AND METHODS

Seven ethanol-fixed human cadaveric heads and one arm were injected with a latex-barium mixture into the internal jugular veins and the brachial artery. After the ethanol-based fixation, specimens were scanned by high-resolution cone-beam CT and images were post-processed on a 3D-workstation. Subsequent, microsurgical dissections were performed by an experienced neurosurgeon and venous anatomy was compared with relevant 3D venograms.

RESULTS

Latex-barium mixtures resulted in a homogenous cast with filling of the cerebral venous structures down to 150 μm in diameter. The ethanol-based preparation of the cadaveric brains allowed for near-realistic microsurgical maneuverability during dissection. The model improves assessment of the venous system for anatomical education and hands-on surgical training.

CONCLUSION

To our knowledge we describe the first preparation method which combines near-realistic microsurgical dissection of human heads with high-resolution 3D imaging of the cerebral venous system in the same specimens.

Microsurgical anatomical vascular study of the PICA-PICA bypass

OBJECTIVE

To assess the posterior inferior cerebellar artery (PICA)-PICA bypass possibility.

METHODS

Fifteen adult cadaver heads were used for surgical simulation, and the far-lateral approach was used to expose the surgical field. The bilateral PICA course, diameter, and perforators were observed and measured to evaluate the possibility of a PICA-PICA bypass.

RESULTS

The PICA-PICA bypass was performed in seven (46.7 %) of the 15 specimens; the procedure was performed easily in three specimens, a little difficult in two, and was difficult in two specimens because of the relationship between the tonsil and the short parallel length of the bilateral tonsillomedullary (p3) segment. In eight (53.3 %) of the 15 specimens, PICA-PICA bypass was not feasible for reasons including 1) the caliber of the bilateral p3 was unmatched for bypass, 2) the distance of bilateral p3 in the midline was > 7 mm, 3) the middle segment of p3 perforating direct arteries limited the buffer length, and 4) single caudal loops.

CONCLUSION

The possibility of PICA-PICA bypass was determined by the proximity of the bilateral p3, caliber match, and mobilization of the bilateral caudal loop due to the perforators. The difficulty of the PICA-PICA bypass mainly depends on the relationship between the cerebellar tonsil and the parallel length of the bilateral PICA in the midline.

Petroclival Clinoidal Folds and Relationships with Arachnoidal Membranes of Medial Incisural Space: Old Neuroanatomical Terms for a New Neurosurgical Speech in Cadaver Labs with Limited Resources Era. Part III: Arachnoid Membranes, Cranial Nerves, and Surgical Implications

BACKGROUND Anatomical dissections play an irreplaceable role in the training of new generations of effective neurosurgeons, especially when addressing skull base lesions is required.The Authors describe an inter-laboratory dissection study aimed at improving the knowledge of a complex region of the skull base. The anterior and middle incisural spaces are of remarkable anatomical and surgical interest due to complex relationships between bony, dural, arachnoidal, and neurovascular structures. The primary purposes of this study are to describe the anatomy of this region with particular emphasis on the relationships between the anterior margin of the free edge of the tentorium and the sphenoid and petrous bone; to identify surgical implications in many different types of neurosurgical procedures dealing with this challenging complex anatomic area.METHODS Thirteen anatomical specimens, including five injected specimens, were dissected in this study. In the formalin-fixed specimens, vessels were injected with colored silicone.RESULTS The anatomical study focused on the description of the relationships between bony dural, arachnoid, and neurovascular structures. Surgical implications are described accordingly.CONCLUSIONS Detailed anatomical knowledge of this region finds concrete applications in neurosurgical practice since the anterior and middle incisural spaces are often surgically exposed in neoplastic and vascular diseases. The high-definition pictures reported in this study could represent useful support to understand the anatomy of this complex region.Finally, our study could provide guidance to neurosurgical centers in which resources are limited that are either planning to establish their own cadaver dissection laboratory or failed to do so because of the supposed high-costs.

Petroclival Clinoidal Folds and Relationships with Arachnoidal Membranes and Neural Structures of Anterior and Middle Incisural Spaces: Old Neuroanatomical Terms for a New Neurosurgical Speech in Cadaver Labs with Limited Resources Era. Part I: Osteology and Structural Anatomy of Dura Mater

Purpose The role of cadaver labs in preparing new generations of effective neurosurgeons is of paramount importance. The Authors describe a personal cadaver lab experience aimed at improving the knowledge of a difficult region of the central skull base. The anterior and middle incisural spaces are regions of remarkable anatomical, and surgical interest due to complex relationships between bony, dural, arachnoidal, and neurovascular structures. The primary purpose of this study is (1) to describe the anatomy of this region with particular emphasis on the relationships between the anterior margin of the free edge of the tentorium and the sphenoid and petrous bone; (2) to identify surgical implications in many different types of neurosurgical procedures dealing with this challenging complex anatomic area.Methods Eight fresh, non-formalin-fixed non-silicon-injected adult cadaver heads and five injected formalin-fixed adult cadaver heads were analyzed in this study.Results The anatomical study was focused on the description of the relationships between bony, dural, arachnoid, and neurovascular structures. Surgical implications are described accordingly.Conclusions Detailed anatomical knowledge of this region finds concrete applications in neurosurgical practice since the anterior and middle incisural spaces are often surgically exposed in neoplastic and vascular diseases.

Petroclival Clinoidal Folds and Relationships with Arachnoidal Membranes of Anterior and Middle Incisural Spaces: Old Neuroanatomical Terms for a New Neurosurgical Speech in Cadaver Labs with Limited Resources Era. Part II: Free Edge of the Tentorium, Petroclinoid Folds, and Incisural Spaces

BACKGROUND Anatomical dissections play an irreplaceable role in the training of new generations of effective neurosurgeons, especially when addressing skull base lesions is required.The Authors describe an inter-laboratory dissection study aimed at improving the knowledge of a complex region of the skull base. The anterior and middle incisural spaces are of remarkable anatomical and surgical interest due to complex relationships between bony, dural, arachnoidal, and neurovascular structures. The primary purposes of this study are to describe the anatomy of this region with particular emphasis on the relationships between the anterior margin of the free edge of the tentorium and the sphenoid and petrous bone; to identify surgical implications in many different types of neurosurgical procedures dealing with this challenging, complex anatomic area.METHODS Thirteen anatomical specimens, including five injected specimens, were dissected in this study. In the formalin-fixed specimens, vessels were injected with colored silicone.RESULTS The anatomical study was focused on the description of the relationships between bony dural, arachnoid, and neurovascular structures. Surgical implications are described accordingly.CONCLUSIONS Detailed anatomical knowledge of this region finds concrete applications in neurosurgical practice since the anterior and middle incisural spaces are often surgically exposed in neoplastic and vascular diseases. The high-definition pictures reported in this study could represent useful support to understand the anatomy of this complex region.Finally, our study could provide guidance to neurosurgical centers in which resources are limited that are either planning to establish their own cadaver dissection laboratory or failed to do so because of the supposed high-costs.

Anterior transtemporal endoscopic selective amygdalohippocampectomy: a virtual and cadaveric feasibility study

PURPOSE

Selective amygdalohippocampectomy (SelAH) is one of the most common surgical treatments for mesial temporal sclerosis. Microsurgical approaches are associated with the risk of cognitive and visual deficits due to damage to the cortex and white matter (WM) pathways. Our objective is to test the feasibility of an endoscopic approach through the anterior middle temporal gyrus (aMTG) to perform a SelAH.

METHODS

Virtual simulation with MRI scans of ten patients (20 hemispheres) was used to identify the endoscopic trajectory through the aMTG. A cadaveric study was performed on 22 specimens using a temporal craniotomy. The anterior part of the temporal horn was accessed using a tubular retractor through the aMTG after performing a 1.5 cm corticectomy at 1.5 cm posterior to the temporal pole. Then, an endoscope was introduced. SeIAH was performed in each specimen. The specimens underwent neuronavigation-assisted endoscopic SeIAH to confirm our surgical trajectory. WM dissection using Klingler's technique was performed on five specimens to assess WM integrity.

RESULTS

This approach allowed the identification of collateral eminence, lateral ventricular sulcus, choroid plexus, inferior choroidal point, amygdala, hippocampus, and fimbria. SelAH was successfully performed on all specimens, and CT neuronavigation confirmed the planned trajectory. WM dissection confirmed the integrity of language pathways and optic radiations.

CONCLUSIONS

Endoscopic SelAH through the aMTG can be successfully performed with a corticectomy of 15 mm, presenting a reduced risk of vascular injury and damage to WM pathways. This could potentially help to reduce cognitive and visual deficits associated with SelAH.

Antigenicity is preserved with fixative solutions used in human gross anatomy: A mice brain immunohistochemistry study

Background

Histology remains the gold-standard to assess human brain biology, so ex vivo studies using tissue from brain banks are standard practice in neuroscientific research. However, a larger number of specimens could be obtained from gross anatomy laboratories. These specimens are fixed with solutions appropriate for dissections, but whether they also preserve brain tissue antigenicity is unclear. Therefore, we perfused mice brains with solutions used for human body preservation to assess and compare the tissue quality and antigenicity of the main cell populations.

Materials and methods

Twenty-eight C57BL/6J mice were perfused with 4% formaldehyde (FAS, N = 9), salt-saturated solution (SSS, N = 9), and alcohol solution (AS, N = 10). The brains were cut into 40 μm sections for antigenicity analysis and were assessed by immunohistochemistry of four antigens: neuronal nuclei (NeuN), glial fibrillary acidic protein (GFAP astrocytes), ionized calcium-binding adaptor molecule 1 (Iba1-microglia), and myelin proteolipid protein (PLP). We compared the fixatives according to multiple variables: perfusion quality, ease of manipulation, tissue quality, immunohistochemistry quality, and antigenicity preservation.

Results

The perfusion quality was better using FAS and worse using AS. The manipulation was very poor in SSS brains. FAS- and AS-fixed brains showed higher tissue and immunohistochemistry quality than the SSS brains. All antigens were readily observed in every specimen, regardless of the fixative solution.

Conclusion

Solutions designed to preserve specimens for human gross anatomy dissections also preserve tissue antigenicity in different brain cells. This offers opportunities for the use of human brains fixed in gross anatomy laboratories to assess normal or pathological conditions.

Anatomical Variation of the Sympathetic Trunk and Aberrant Rami Communicantes and their Clinical Implications

Surgical interventions involving the sympathetic trunk are increasingly performed to alleviate symptoms of several disorders such as hyperhidrosis. Anatomical variation has been highlighted as one of the main causes behind surgical failure and symptoms recurrence following surgeries conducted on the chain or its surroundings. This study therefore aimed to record anatomical variants within spinal segments C8-T10 of the sympathetic trunk. Thirty Thiel-embalmed cadavers were investigated bilaterally. The stellate ganglion was recorded on 29 sides. Its size was significantly greater in males and on the right side when the coalescence extended to the subsequent ganglion. The intrathoracic nerve of Kuntz was observed on 21 sides and was significantly more prevalent in males. There was a significant positive association between the presence of this nerve and the descending ramus in the first intercostal space. Aberrant rami found between spinal root C8 and the ventral ramus of the first intercostal nerve were introduced as rami communicantes superi. Aberrant rami communicantes were recorded 50 times in total, of which 70% were found in males. Descending rami showed the highest prevalence in upper intercostal levels, especially in males within the first intercostal space. Aberrant neuronal pathways in upper levels were significantly more prevalent when the stellate ganglion was present. The scientific literature has proven to be stochastic as results were significantly higher in past studies in regard to some sympathetic variants. Anatomical findings of the current study as well as the inconsistency of previous data should be acknowledged and considered for better surgical planning.

Unsuccessful bypass and trapping of a giant dolichoectatic thrombotic basilar trunk aneurysm. What went wrong?

Aneurysms of the basilar trunk represent an exceptional challenge to the neurosurgeon, due to high mortality and surgical morbidity. We present a 69-year-old man with a giant dolichoectatic thrombotic basilar trunk aneurysm (BTA), who underwent right orbitozygomatic craniotomy, posterior cerebral artery (PCA) to right middle cerebral artery (MCA) bypass and trapping of the BTA. Unfortunately, patient died after surgery due to multiple foci of intraparenchymal haemorrhage and thrombosis of a short segment proximal to aneurysm trapped and his body was donated to the hospital, giving us the unique opportunity to compare intraoperative details with anatomical dissection findings, according to our previously published cadaveric neurosurgical research. The great and unique opportunity of this reported case, to learn by watching and watching again what has been done during surgery, to observe small vessels and brainstem perforators and to look at stiches of the bypass, SVG and the position of the clips, permits to refine the theoretical and practical skills for the treatment of complex aneurysms such as that one reported.

A Novel Cadaveric Embalming Technique for Enhancing Visualisation of Human Anatomy

Within the discipline of anatomical education, the use of donated human cadavers in laboratory-based learning activities is often described as the 'gold standard' resource for supporting student understanding of anatomy. Due to both historical and educational factors, cadaveric dissection has traditionally been the approach against which other anatomy learning modalities and resources have been judged. To prepare human donors for teaching purposes, bodies must be embalmed with fixative agents to preserve the tissues. Embalmed cadavers can then be dissected by students or can be prosected or plastinated to produce teaching resources. Here, we describe the history of cadaveric preservation in anatomy education and review the practical strengths and limitations of current approaches for the embalming of human bodies. Furthermore, we investigate the pedagogic benefits of a range of established modern embalming techniques. We describe relevant cadaveric attributes and their impacts on learning, including the importance of colour, texture, smell, and joint mobility. We also explore the emotional and humanistic elements of the use of human donors in anatomy education, and the relative impact of these factors when alternative types of embalming process are performed. Based on these underpinnings, we provide a technical description of our modern Newcastle-WhitWell embalming process. In doing so, we aim to inform anatomy educators and technical staff seeking to embalm human donors rapidly and safely and at reduced costs, while enhancing visual and haptic tissue characteristics. We propose that our technique has logistical and pedagogic implications, both for the development of embalming techniques and for student visualisation and learning.

Comparison of Haptic and Biometric Properties, Bacterial Load, and Student Perception of Fixative Solutions: Formaldehyde Versus Chilean Conservative Fixative Solution with and without Formaldehyde in Pig Kidneys

One of the most widely used solutions to fix and preserve organic tissues is formaldehyde, despite reservations regarding its toxicity and the fact that formaldehyde-embalmed bodies lose their original characteristics. Anatomy laboratories have been replacing formaldehyde with solutions that retain the characteristics of fresh tissue. For this purpose, alternative solutions with a very low concentration of formaldehyde or without any formaldehyde have been analyzed. The objective of this study was to compare biometry, coloration, haptic properties, and bacterial load on animal specimens (pig kidneys) embalmed with formaldehyde, and with Chilean Conservative Fixative Solution with and without formaldehyde (formaldehyde chCFS and formaldehyde-free chCFS). Also, the perception of health and biological science students toward specimens treated with different solutions was assessed. The results indicated that there were no significant differences in specimens' retraction, or bacterial load. Students showed a preference for organs embalmed in formaldehyde chCFS and formaldehyde-free chCFS; indicating that with these treatments they could better visualize structures and that the prosections had greater flexibility and the colors were more similar to those of fresh tissue. Additionally, students recommended the material embalmed in formaldehyde chCFS and formaldehyde-free chCFS for anatomy learning. In contrast, students indicated that formaldehyde-fixation negatively affected their practical experience. In conclusion, embalming with formaldehyde chCFS or formaldehyde-free chCFS provides an advantageous practical experience over the use of formaldehyde and may be an alternative to replace the use of formaldehyde in anatomy laboratories.

Practical Arachnoid Anatomy for the Technical Consideration of Galen Complex Dissection: Cadaveric and Clinical Evaluation

BACKGROUND

The occipital transtentorial approach (OTA) is a very useful but challenging approach to expose the pineal region because the deep-seated arachnoid membranes usually fold and extend over the great vein of Galen (GVG), leading to dense and poor visibility. In addition, the practical aspects of arachnoid anatomy are not well understood. We aimed to develop a safe surgical procedure for the OTA according to the practical aspects of arachnoid anatomy.

METHODS

The procedure is shown through an illustrative video of surgery and cadaver. Five cadavers were analyzed for their arachnoid structures and the surgical procedures via the OTA, in strict compliance with legal and ethical requirements.

RESULTS

All cadavers showed a 2-layered arachnoid structure-one belonging to the occipital lobe, and the other to the cerebellum. According to our cadaveric analysis, the arachnoid attachment of the tentorial apex can be peeled bluntly, with an average distance of 10.2 mm. For our clinical presentation, a pineal tumor with hydrocephalus was detected in a 14-year-old boy. While using the OTA and expanding the deep surgical field, we detached the membrane from the tentorial apex and bluntly peeled it to reveal the deep veins. Finally, gross total removal of the tumor was achieved.

CONCLUSIONS

A 2-layered arachnoid structure interposes the GVG from above and below the tentorium. The arachnoid membrane below the tentorium can be peeled off bluntly from the GVG to the attachment bundle limited by the penetrating veins. This detachment technique is useful for safe enlargement of the surgical field for the OTA.

The Usefulness of Saturated Salt Solution Embalming Method for Oral Surgical Skills Training: A New Cadaveric Training Model for Bone Harvesting

The purpose of this study was to assess the usefulness of saturated salt solution-embalmed cadavers for oral surgical skills training related to bone graft harvesting. Two half-day surgical skills training workshops were held at the Tokyo Medical University utilizing eight cadavers embalmed with the saturated salt solution. A total of 22 participants including oral surgeons, residents, and dentists attended the workshop. Surgical training consisted of six procedures related to intraoral and extraoral bone harvesting. The participants were surveyed to assess self-confidence levels for each surgical procedure before and after completion of each workshop. The Wilcoxon signed-rank test was used to compare the differences between each median score before and after the workshop. There were statistically significant increases in the self-assessed confidence scores in bone harvesting procedures for the zygomatic bone (P = 0.003), maxillary tuberosity (P = 0.002), and other sites (P < 0.001). The anatomical features of saturated salt solution-embalmed cadavers were also examined. The textures of the oral mucosa and skin were similar to those of living individuals. The structure of bone tissues was well-preserved and the hardness was realistic. Consequently, all procedures were performed with sufficient realism. The saturated salt solution method has a relatively low cost of preparation and storage, and almost no odor. The authors suggest that saturated salt solution-embalmed cadavers could provide a new model for oral surgical skills training in bone harvesting.

A novel ex vivo, in situ method to study the human brain through MRI and histology

BACKGROUND

MRI-histology correlation studies of the ex vivo brain mostly employ fresh, extracted (ex situ) specimens, aldehyde fixed by immersion, which has several disadvantages for MRI scanning (e.g. deformation of the organ). A minority of studies are done ex vivo-in situ (unfixed brain), requiring an MRI scanner readily available within a few hours of the time of death.

NEW METHOD

We propose a new technique, exploited by anatomists, for scanning the ex vivo brain: fixation by whole body perfusion, which implies fixation of the brain in situ. This allows scanning the brain surrounded by fluids, meninges, and skull, preserving the structural relationships of the brain in vivo. To evaluate the proposed method, five heads perfused-fixed with a saturated sodium chloride solution were employed. Three sequences were acquired on a 1.5 T MRI scanner: T1weighted, T2weighted-FLAIR, and Gradient-echo. Histology analysis included immunofluorescence for myelin basic protein and neuronal nuclei.

RESULTS

All MRIs were successfully processed through a validated pipeline used with in vivo MRIs. All cases exhibited positive antigenicity for myelin and neuronal nuclei.

COMPARISON WITH EXISTING METHODS

All scans registered to a standard neuroanatomical template in pseudo-Talairach space more accurately than an ex vivo-ex situ scan. The time interval to scan the ex vivo brain in situ was increased to at least 10 months.

CONCLUSIONS

MRI and histology study of the ex vivo-in situ brain fixed by perfusion is an alternative approach that has important procedural and practical advantages over the two standard methods to study the ex vivo brain.

Revascularization of the Posterior Inferior Cerebellar Artery Using the Occipital Artery: A Cadaveric Study Comparing the p3 and p1 Recipient Sites

BACKGROUND

Revascularization of the posterior inferior cerebellar artery (PICA) is typically performed with the occipital artery (OA) as an extracranial donor. The p3 segment is the most accessible recipient site for OA-PICA bypass at its caudal loop inferior to the cerebellar tonsil, but this site may be absent or hidden due to a high-riding location.

OBJECTIVE

To test our hypothesis that freeing p1 PICA from its origin, transposing the recipient into a shallower position, and performing OA-p1 PICA bypass with an end-to-end anastomosis would facilitate this bypass.

METHODS

The OA was harvested, and a far lateral craniotomy was performed in 16 cadaveric specimens. PICA caliber and number of perforators were measured at p1 and p3 segments. OA-p3 PICA end-to-side and OA-p1 PICA end-to-end bypasses were compared.

RESULTS

OA-p1 PICA bypass with end-to-end anastomosis was performed in 16 specimens; whereas, OA-p3 PICA bypass with end-to-side anastomosis was performed in 11. Mean distance from OA at the occipital groove to the anastomosis site was shorter for p1 than p3 segments (30.2 vs 48.5 mm; P < .001). Median number of perforators on p1 was 1, and on p3, it was 4 (P < .001).

CONCLUSION

Although most OA-PICA bypasses can be performed using the p3 segment as the recipient site for an end-to-side anastomosis, a more feasible alternative to conventional OA-p3 PICA bypass in cases of high-riding caudal loops or aberrant anatomy is to free the p1 PICA, transpose it away from the lower cranial nerves, and perform an end-to-end OA-p1 PICA bypass instead.

Virtual reality technology for teaching neurosurgery of skull base tumor

BACKGROUND

Neurosurgery represents one of the most challenging and delicate of any surgical procedure. Skull base tumors in particular oftentimes present as a very technically difficult procedures in the setting of neurosurgical teaching. Virtual reality technology is one of the most promising surgical planning tools. It can perform fast three-dimensional (3D) reconstruction of computed tomography (CT), magnetic resonance imaging (MRI) and other imaging data sets under conditions of virtual reality (VR). Surgical simulation can more intuitively understand the anatomical relationship of the surgical area in significantly greater detail.

METHODS

Thirty clinical undergraduates from the class of 2016 were randomly divided into two groups: the traditional teaching group and the virtual reality teaching group. After the study concluded, the teaching effectiveness was evaluated by combining basic theoretical knowledge, case analysis and questionnaire survey methods.

RESULTS

Comparative analysis between both groups showed the response effect of the virtual reality teaching group was better than that of the traditional teaching group (P < 0.05). There was also no difference between both groups in terms of the design of the surgical approach and the listing of surgical matters that required attention (P > 0.05).The results of theoretical knowledge assessment between both groups showed that the scores of basic theory, location, adjacent structure, clinical manifestation, diagnosis and analysis, surgical methods and total scores in the VR group exceeded those in the traditional teaching group (P < 0.05).

CONCLUSIONS

This study showed that VR technology might improve neurosurgical skull base teaching quality, which should be promoted in the teaching of clinical subjects.

Facial Nerve Preservation for Supraorbital Approaches: Anatomical Mapping Based on Consistent Landmarks

BACKGROUND

The supraorbital keyhole approach (SOKA) provides a safe and advantageous access to the anterior cranial fossa. The implemented skin incision varies depending on surgeon's preferences and requirements. Facial nerve (FN) injury might appear in up to 5.6% of patients. There is a lack of validated tenets for avoiding FN injury.

OBJECTIVE

To define a safety area for FN preservation during a SOKA.

METHODS

Ten dried skulls and 5 injected cadaveric heads (10 sides) were used. A Cartesian frame was created with its horizontal axis at the level of the supraorbital notch and the vertical axis just lateral to the frontozygomatic junction (FZj). FNs were dissected and points along their course were registered and transferred to the Cartesian frame.

RESULTS

Ten microscopic dissections of the FN were performed preserving all branches. A safety area could be defined 8 mm superior and 10 mm inferior to the FZj extending medially to the supraorbital notch and beyond. A 20 mm2 area superior and lateral to the FZj provided low probability (≤10%) of injuring the FN. Similarly, starting 4 mm inferior to the FZj, a lateral safety area was also found. A probabilistic colored heat map was built to represent the results.

CONCLUSION

We provide a "safety zone" for a SOKA incision in which the probability to encounter the FN is low. Clinical studies following our method may validate our findings and add evidence to the tenets for minimizing morbidity related to the SOKA incision.

Perfusion fixation in brain banking: a systematic review

Background

Perfusing fixatives through the cerebrovascular system is the gold standard approach in animals to prepare brain tissue for spatial biomolecular profiling, circuit tracing, and ultrastructural studies such as connectomics. Translating these discoveries to humans requires examination of postmortem autopsy brain tissue. Yet banked brain tissue is routinely prepared using immersion fixation, which is a significant barrier to optimal preservation of tissue architecture. The challenges involved in adopting perfusion fixation in brain banks and the extent to which it improves histology quality are not well defined.

Methodology

We searched four databases to identify studies that have performed perfusion fixation in human brain tissue and screened the references of the eligible studies to identify further studies. From the included studies, we extracted data about the methods that they used, as well as any data comparing perfusion fixation to immersion fixation. The protocol was preregistered at the Open Science Framework: https://osf.io/cv3ys/.

Results

We screened 4489 abstracts, 214 full-text publications, and identified 35 studies that met our inclusion criteria, which collectively reported on the perfusion fixation of 558 human brains. We identified a wide variety of approaches to perfusion fixation, including perfusion fixation of the brain in situ and ex situ, perfusion fixation through different sets of blood vessels, and perfusion fixation with different washout solutions, fixatives, perfusion pressures, and postfixation tissue processing methods. Through a qualitative synthesis of data comparing the outcomes of perfusion and immersion fixation, we found moderate confidence evidence showing that perfusion fixation results in equal or greater subjective histology quality compared to immersion fixation of relatively large volumes of brain tissue, in an equal or shorter amount of time.

Conclusions

This manuscript serves as a resource for investigators interested in building upon the methods and results of previous research in designing their own perfusion fixation studies in human brains or other large animal brains. We also suggest several future research directions, such as comparing the in situ and ex situ approaches to perfusion fixation, studying the efficacy of different washout solutions, and elucidating the types of brain donors in which perfusion fixation is likely to result in higher fixation quality than immersion fixation.

Electronic supplementary material

The online version of this article (10.1186/s40478-019-0799-y) contains supplementary material, which is available to authorized users.

The Endoscopic Endonasal Transmaxillary Approach to Meckel's Cave Through the Inferior Orbital Fissure

BACKGROUND

Surgical access to Meckel's Cave (MC) is challenging due to its deep location and surrounding important neurovascular structures. Currently existing endoscopic endonasal (EE) approaches require dissecting near the internal carotid artery (ICA) or require transposition of the pterygopalatine neurovascular bundle.

OBJECTIVE

To describe a novel approach to access the anterolateral aspect of the MC using a minimally invasive EE route.

METHODS

The EE transmaxillary transinferior orbital fissure approach was simulated in 10 specimens. The approach included an ethmoidectomy followed by an extended medial maxillectomy with transposition of the nasolacrimal duct. The infraorbital fissure was opened, and the infraorbital neurovascular bundle was transposed inferiorly. A quadrilateral space, bound by the maxillary nerve inferomedially, ophthalmic nerve superomedially, infraorbital nerve inferolaterally, and floor of the orbit superolaterally, was exposed. The distances from the foramen rotundum (FR) to the ICA, orbital apex (OA), and infratemporal crest (ITC) and from the OA to the ICA and ITC were measured.

RESULTS

The distances obtained were FR-ICA = 19.42 ± 2.03 mm, FR-ITC = 18.76 ± 1.75 mm, FR-OA = 8.54 ± 1.34 mm, OA-ITC = 19.78 ± 2.63 mm, and OA-ICA = 20.64 ± 142 mm. Two imaginary lines defining safety boundaries were observed between the paraclival ICA and OA, and between the OA and ITC (safety lines 1 and 2).

CONCLUSION

The reported approach provides a less invasive route compared to contemporary approaches, allowing expanded views and manipulation anteromedial and anterolateral to MC. It may be safer than the existing approaches as it does not require transposition of the ICA, infratemporal fossa, and pterygopalatine fossa, and allows access to tumors located anteriorly on the floor of the middle cranial fossa.

Sequential Extradural Release of the V3 Vertebral Artery to Facilitate Intradural V4 Vertebral Artery Reanastomosis: Feasibility of a Novel Revascularization Technique

BACKGROUND

Revascularization of the intradural vertebral artery (VA) usually involves V3-V4 bypass using an interposition graft. The interposition of a graft increases surgical time, adds risks, and requires 2 suture lines.

OBJECTIVE

To assess the feasibility of an excision-reanastomosis of V4 by sequentially releasing V3.

METHODS

Twenty specimens were prepared for surgical simulation of a far-lateral approach. The third and fourth segments of the VA were exposed through the far-lateral approach bilaterally. The V3 segment was divided into three subsegments: (1) V3 f : from entry to C1 transverse foramen to the point of exit from C1 transverse foramen; (2) V3 s : from V3 f to the distal point of V3 within the sulcus arteriosus; and (3) V3 d : from point V3 leaves the sulcus arteriosus to its dural entrance. After transecting the VA 2 mm proximal to the posterior inferior cerebellar artery origin, each subsegment was released sequentially. We measured the lengths obtained before and after releasing each segment by pulling the VA along its main axis to recreate a V3-V4 excision-reanastomosis.

RESULTS

The V3 could not be effectively mobilized without release. When totally released, an average length of 13.15 mm was available for completing V3-V4 reanastomosis.

CONCLUSION

Complete release of V3 from all its adhesions in its extracranial course can provide an average length of 13.15 mm for excision-reanastomosis. The present study shows the anatomic feasibility of the use of V3 segment in primary anastomosis after excision of a diseased segment of the intradural VA, laying the basis for future clinical application.

Assessment of the endoscopic endonasal approach to the basilar apex region for aneurysm clipping

OBJECTIVE

The expanded endoscopic endonasal approach (EEA) has shown promising results in treatment of midline skull base lesions. Several case reports exist on the utilization of the EEA for treatment of aneurysms. However, a comparison of this approach with the classic transcranial orbitozygomatic approach to the basilar apex (BAX) region is missing.The present study summarizes the results of a series of cadaveric surgical simulations for assessment of the EEA to the BAX region for aneurysm clipping and its comparison with the transcranial orbitozygomatic approach as one of the most common approaches used to treat BAX aneurysms.

METHODS

Fifteen cadaveric specimens underwent bilateral orbitozygomatic craniotomies as well as an EEA (first without a pituitary transposition [PT] and then with a PT) to expose the BAX. The following variables were measured, recorded, and compared between the orbitozygomatic approach and the EEA: 1) number of perforating arteries counted on bilateral posterior cerebral arteries (PCAs); 2) exposure and clipping lengths of the PCAs, superior cerebellar arteries (SCAs), and proximal basilar artery; and 3) surgical area of exposure in the BAX region.

RESULTS

Except for the proximal basilar artery exposure and clipping, the orbitozygomatic approach provided statistically significantly greater values for vascular exposure and control in the BAX region (i.e., exposure and clipping of ipsilateral and contralateral SCAs and PCAs). The EEA with PT was significantly better in exposing and clipping bilateral PCAs compared to EEA without a PT, but not in terms of other measured variables. The surgical area of exposure and PCA perforator counts were not significantly different between the 3 approaches. The EEA provided better exposure and control if the BAX was located ≥ 4 mm inferior to the dorsum sellae.

CONCLUSIONS

For BAX aneurysms located in the retrosellar area, PT is usually required to obtain improved exposure and control for the bilateral PCAs. However, the transcranial approach is generally superior to both endoscopic approaches for accessing the BAX region. Considering the superior exposure of the proximal basilar artery obtained with the EEA, it could be a viable option when surgical treatment is considered for a low-lying BAX or mid-basilar trunk aneurysms (≥ 4 mm inferior to dorsum sellae).

The pterygoclival ligament: a novel landmark for localization of the internal carotid artery during the endoscopic endonasal approach

OBJECTIVE

The transpterygoid extension of the endoscopic endonasal approach provides exposure of the petrous apex, Meckel's cave, paraclival area, and the infratemporal fossa. Safe and efficient localization of the lacerum segment of the internal carotid artery (ICA) is a crucial part of such exposure. The aim of this study is to introduce a novel landmark for localization of the lacerum ICA.

METHODS

Ten cadaveric heads were prepared for transnasal endoscopic dissection. The floor of the sphenoid sinus was drilled to expose an extension of the pharyngobasilar fascia between the sphenoid floor and the pterygoid process (the pterygoclival ligament). Several features of the pterygoclival ligament were assessed. In addition, 31 dry skulls were studied to assess features of the bony groove harboring the pterygoclival ligament.

RESULTS

The pterygoclival ligament was identified bilaterally during drilling of the sphenoid floor in all specimens. The ligament started a few millimeters posterior to the posterior end of the vomer alae and invariably extended posterolaterally and superiorly to blend into the fibrous tissue around the lacerum ICA. The mean length of the ligament was 10.5 ± 1.7 mm. The mean distance between the anterior end of the ligament and midline was 5.2 ± 1.2 mm. The mean distance between the posterior end of the ligament and midline was 12.3 ± 1.4 mm. The bony pterygoclival groove was identified at the confluence of the vomer, pterygoid process of the sphenoid, and basilar part of the occipital bone, running from posterolateral to anteromedial. The mean length of the groove was 7.7 ± 1.8 mm. Its posterolateral end faced the anteromedial aspect of the foramen lacerum medial to the posterior end of the vidian canal. A clinical case illustration is also provided.

CONCLUSIONS

The pterygoclival ligament is a consistent landmark for localization of the lacerum ICA. It may be used as an adjunct or alternative to the vidian nerve to localize the ICA during endoscopic endonasal surgery.

Anatomical Assessment of the Temporopolar Artery for Revascularization of Deep Recipients

BACKGROUND

Intracranial-intracranial and extracranial-intracranial bypass options for revascularization of deep cerebral recipients are limited and technically demanding.

OBJECTIVE

To assess the anatomical feasibility of using the temporopolar artery (TPA) for revascularization of the anterior cerebral artery (ACA), posterior cerebral artery (PCA), and superior cerebellar arteries (SCA).

METHODS

Orbitozygomatic craniotomy was performed bilaterally on 8 cadaveric heads. The cisternal segment of the TPA was dissected. The TPA was cut at M3-M4 junction with its proximal and distal calibers and the length of the cisternal segment measured. Feasibility of the TPA-A1-ACA, TPA-A2-ACA, TPA-SCA, and TPA-PCA bypasses were assessed.

RESULTS

A total of 17 TPAs were identified in 16 specimens. The average distal TPA caliber was 1.0 ± 0.2 mm, and the average cisternal length was 37.5 ± 9.4 mm. TPA caliber was ≥ 1.0 mm in 12 specimens (70%). The TPA-A1-ACA bypass was feasible in all specimens, whereas the TPA reached the A2-ACA, SCA, and PCA in 94% of specimens (16/17). At the point of anastomosis, the average recipient caliber was 2.5 ± 0.5 mm for A1-ACA, and 2.3 ± 0.7 mm for A2-ACA. The calibers of the SCA and PCA at the anastomosis points were 2.0 ± 0.6 mm, and 2.7 ± 0.8 mm, respectively.

CONCLUSION

The TPA-ACA, TPA-PCA, and TPA-SCA bypasses are anatomically feasible and may be used when the distal caliber of the TPA stump is optimal to provide adequate blood flow. This study lays foundations for clinical use of the TPA for ACA revascularization in well-selected cases.

Anterior clinoidectomy using an extradural and intradural 2-step hybrid technique

In Brief: The authors found a practical intraoperative landmark to localize the optic strut during anterior clinoidectomy and used it as the basis for performing anterior clinoidectomy in two steps: extradural phase and intradural phase. This anatomically based technique can increase the safety of anterior clinoidectomy by providing easily identifiable landmarks and reducing intradural bone drilling, which could put the adjacent neurovauscular structures at risk.

Minimally Invasive Exposure of the Maxillary Artery at the Anteromedial Infratemporal Fossa

BACKGROUND

The maxillary artery (MA) has been described as a reliable donor for extracranial-intracranial high-flow bypass. Existing techniques to harvest MA require brain retraction and drilling of the middle fossa (with or without a zygomatic osteotomy), carrying the potential risks of venous bleeding, injury to the branches of the maxillary or mandibular nerves, muscular transection, or temporomandibular junction disorders.

OBJECTIVE

To describe a novel technique to expose the MA without bony drilling and with minimal impact to surrounding structures.

METHODS

A conventional curvilinear incision was performed in 10 cadaveric specimens, prior to elevating the scalp to expose the zygomatic root and lateral orbital rim. The sphenozygomatic suture was followed to the anterolateral edge of the inferior orbital fissure (IOF) to locate and harvest the pterygoid segment of the MA. Topographic anatomy was assessed using surrounding landmarks and 3D Cartesian coordinates to define the surgical area. The number of visible MA branches and their lengths were recorded.

RESULTS

The MA was successfully exposed in all specimens. This approach allowed 6 branches of MA to be exposed. The average length of exposure was 23.3 ± 8.3 mm and the average surgical area was 2.8 ± 0.9 cm2. The IOF was 11.5 ± 4.2 mm from the MA.

CONCLUSION

Our technique provides landmarks to identify the distal pterygoid segment of MA as a donor for extracranial-intracranial bypasses without the need for additional craniectomies. Clear anatomical landmarks, including the sphenozygomatic suture, anterolateral edge of IOF, infraorbital artery, and the pterygomaxillary fissure defined a trajectory to efficiently localize the MA with minimal risk to surrounding structures.

The transperiosteal "inside-out" occipital artery harvesting technique

OBJECTIVE The occipital artery (OA) is a frequently used donor vessel for posterior circulation bypass procedures due to its proximity to the recipient vessels and its optimal caliber, length, and flow rate. However, its tortuous course through multiple layers of suboccipital muscles necessitates layer-by-layer dissection. The authors of this cadaveric study aimed to describe a landmark-based novel anterograde approach to harvest OA in a proximal-to-distal "inside-out" fashion, which avoids multilayer dissection. METHODS Sixteen cadaveric specimens were prepared for surgical simulation, and the OA was harvested using the classic (n = 2) and novel (n = 14) techniques. The specimens were positioned three-quarters prone, with 45° contralateral head rotation. An inverted hockey-stick incision was made from the spinous process of C-2 to the mastoid tip, and the distal part of the OA was divided to lift up a myocutaneous flap, including the nuchal muscles. The OA was identified using the occipital groove (OG), the digastric muscle (DM) and its groove (DG), and the superior oblique muscle (SOM) as key landmarks. The OA was harvested anterogradely from the OG and within the flap until the skin incision was reached (proximal-to-distal technique). In addition, 35 dry skulls were assessed bilaterally (n = 70) to study additional craniometric landmarks to infer the course of the OA in the OG. RESULTS The OA was consistently found running in the OG, which was found between the posterior belly of the DM and the SOM. The mean total length of the mobilized OA was 12.8 ± 1.2 cm, with a diameter of 1.3 ± 0.1 mm at the suboccipital segment and 1.1 ± 0.1 mm at the skin incision. On dry skulls, the occipitomastoid suture (OMS) was found to be medial to the OG in the majority of the cases (68.6%), making it a useful landmark to locate the OG and thus the proximal OA. CONCLUSIONS The anterograde transperiosteal inside-out approach for harvesting the OA is a fast and easy technique. It requires only superficial dissection because the OA is found directly under the periosteum throughout its course, obviating tedious layer-by-layer muscle dissection. This approach avoids critical neurovascular structures like the vertebral artery. The key landmarks needed to localize the OA using this technique include the OMS, OG, DM and DG, and SOM.

Analysis of Surgical Freedom Variation Across the Basilar Artery Bifurcation: Towards a Deeper Insight Into Approach Selection for Basilar Apex Aneurysms

BACKGROUND

The orbitozygomatic approach is generally advocated over the pterional approach for basilar apex aneurysms. However, the impact of the extensions of the pterional approach on the obtained maneuverability over multiple vascular targets (relevant to basilar apex surgery) has not been studied before.

OBJECTIVE

To analyze the patterns of surgical freedom change across the basilar bifurcation between the pterional, orbitopterional, and orbitozygomatic approaches.

METHODS

Surgical freedom was assessed for 3 vascular targets important in basilar apex aneurysm surgery (ipsilateral and contralateral P1-P2 junctions, and basilar apex), and compared between the pterional, orbitopterional, and orbitozygomatic approaches in 10 cadaveric specimens.

RESULTS

Transitioning from the pterional to orbitopterional approach, the surgical freedom increased significantly at all 3 targets (P < .05). However, the gain in surgical freedom declined progressively from the most superficial target (60% for ipsilateral P1-P2 junction) to the deepest target (35% for contralateral P1-P2 junction). Conversely, transitioning from the orbitopterional to the orbitozygomatic approach, the gain in surgical freedom was minimal for the ipsilateral P1-P2 and basilar apex (<4%), but increased dramatically to 19% at the contralateral P1-P2 junction.

CONCLUSION

The orbitopterional approach provides a remarkable increase in surgical maneuverability compared to the pterional approach for the basilar apex target and the relevant adjacent arterial targets. However, compared to the orbitopterional, the orbitozygomatic approach adds little maneuverability except for the deepest target (ie, contralateral P1-P2 junction). Therefore, the orbitozygomatic approach may be most efficacious with larger basilar apex aneurysms limiting the control over of the contralateral P1 PCA.

Comprehensive Anatomic Assessment of the Pterional, Orbitopterional, and Orbitozygomatic Approaches for Basilar Apex Aneurysm Clipping

BACKGROUND

The pterional approach, along with its orbitopterional and orbitozygomatic extensions, is among the most common surgical approaches for tackling challenging aneurysms of the basilar artery apex (BAX). There is general consensus that the orbitozygomatic approach provides the best exposure for these lesions. However, there is little objective evidence to support approach selection for surgical treatment of BAX aneurysms.

OBJECTIVE

To compare different features regarding surgical treatment of BAX aneurysms between the pterional, orbitopterional, and orbitozygomatic approaches.

METHODS

The pterional, orbitopterional, and orbitozygomatic approaches were sequentially completed on 10 cadaveric specimens. The visibility of perforators, lengths of exposure, and safe clipping for major BAX branches, surgical area of exposure, and the surgical freedom for the BAX target were assessed.

RESULTS

The orbitopterional approach provided significantly greater values than the pterional approach in all variables, except for exposure of the bilateral P1 posterior cerebral artery (PCA) perforators. When compared to the orbitopterional approach, the orbitozygomatic approach did not provide a statistically significant increase in (1) surgical freedom through the carotid-oculomotor triangle, (2) area of exposure, (3) ipsilateral, and (4) contralateral P1 PCA perforator visibility, and (5) ipsilateral PCA exposure and (6) clipping lengths.

CONCLUSION

The orbitopterional approach provides significantly greater surgical exposure to BAX than the pterional approach. The orbitopterional approach is less invasive while providing similar surgical access to the BAX compared to the orbitozygomatic. The results of this study show that the orbitopterional approach may be optimal for the treatment of most BAX aneurysms, particularly to reduce morbidity resulting from the full orbitozygomatic approach.

Preservation of neural tissue with a formaldehyde-free phenol-based embalming protocol

The adverse effects formaldehyde fixation has on tissues both gross anatomically and histologically are well documented. Consequently, researchers are seeking alternative embalming techniques that better preserve in vivo characteristics of tissues. Phenol-based embalming is one method that has shown promise in its ability to adequately preserve the in vivo qualities of tissues through preliminary explorations at the gross anatomical level. The literature on phenol-based embalming is currently scarce, especially with regard to its effects on tissues at the microscopic level. For the current study we aimed to document the histologic effects of a formaldehyde-free phenol-based embalming solution on neural tissue, with the hope of providing novel insight into the effects of soft-embalming on tissues at the microscopic level. Cerebral and cerebellar tissue obtained from porcine brains was fixed in phenol- and formaldehyde-based fixatives; the latter served as a control. Fixed samples were processed for histological analysis. The phenol-based embalming solution provided excellent preservation of the cerebral and cerebellar tissue morphology. Of note was the decrease in separation artifact seen in both tissue types relative to the control tissue, as well as anomalous circular artifacts in the white matter. The results of this study indicate that the phenol-based embalming solution preserves neural tissue at the histological level, perhaps superiorly in many aspects when compared to the formaldehyde-fixed samples. Further investigations of both gross anatomy and histology are recommended on the basis of these promising new findings to determine its potential utilities within research and education. Clin. Anat. 32:224-230, 2019. © 2018 Wiley Periodicals, Inc.

Technique for Latex Injection and Reuse of Human Heads Preserved in Formaldehyde

Background  Understanding the anatomy of the skull base is paramount for every skull base surgeon, particularly in light of the expanded endoscopic endonasal approaches, and of the refined surgical technique used in both medial and lateral approaches. A comprehensive knowledge of anatomy is the cornerstone for a safe surgery, maximizing resection and minimizing complications. The best study method is the careful dissection of fresh human cadaveric heads in a well-equipped anatomy laboratory. In this study, we describe our protocol for preparing cadaveric specimens without vascular injection, which had been preserved in a formaldehyde solution after treating them with a dimethyldioctadecylammonium chloride/distearyl dimethyl ammonium chloride solution (commercial fabric softener) and injecting the vascular system with latex. Method  Six cadaveric specimens underwent our treatment and subsequent injection of the vascular system and dissection. Results  All specimens showed a good penetration of the latex and a clear improvement of the malleability of the tissues was noticed. The authors agree that this technique improved the quality of the head and facilitated studying. Conclusion  We consider this an effective treatment with latex, reaching small caliber vessels, and a greater malleability and flexibility of tissues, allowing better dissections, and greater anatomical exposure, making them suitable for skull base training, study, and research.

Contralateral Transfalcine Versus Ipsilateral Anterior Interhemispheric Approach for Midline Arteriovenous Malformations: Surgical and Anatomical Assessment

BACKGROUND

The contralateral anterior interhemispheric approach (CAIA) is considered to provide surgical advantages to access deep midline lesions: wider working angle, gravity enhanced dissection and retraction, more efficient lighting, and ergonomics. Our team has previously published on the merits of using a contralateral trajectory for medial frontoparietal arteriovenous malformations (AVMs) compared with the conventional anterior interhemispheric approach (IAIA). In this article, we compare the IAIA and CAIA for the resection of medial frontoparietal AVMs using quantitative surgical and anatomical analysis.

METHODS

Two models were designed mimicking the most common features of midline AVMs. The CAIA and IAIA were performed bilaterally in 10 specimens. Variables to compare technical feasibility (surgical window [SW] and surgical freedom [SF], target exposure, and angle of attack) were independently assessed using stereotactic navigation. The average SW, SF, and angle of attack were compared with the Student t test. Significance threshold was set at 0.05.

RESULTS

The CITA and IAIA were similar in terms of SW, target exposure, and SF in the superior aspect of the AVM. In the depth of the interhemispheric fissure, the CAIA was significantly superior to IAIA in both AVM models: 77% wider AA for the inferior aspect of the AVM (P < 0.01) and greater SF for the draining vein (54%, P = 0.01), ipsilateral (98%, P = 0.02), and contralateral ACA (117%, P < 0.01).

CONCLUSIONS

This study suggests technical superiority of the CAIA for the resection of deep midline AVMs. No objective difference was noted in the superficial areas of our models, denoting that IAIA is a safer choice for superficial AVMs. Our results set the foundation for further clinical analysis comparing both approaches.

Posterior auricular artery as a novel anatomic landmark for identification of the facial nerve: A cadaveric study

BACKGROUND

Despite preservation techniques, performing a parotidectomy carries a transient facial nerve dysfunction rate in up to 65% of cases and a permanent facial nerve weakness rate of 4%-7%.

METHODS

The lateral aspect of the face and neck was exposed in 5 cadaveric heads (10 sides). The relationship of the posterior auricular artery (PAA) and the facial nerve was studied and recorded and descriptive measurements were taken.

RESULTS

In all specimens, the facial nerve trunk crossed the PAA inferior to the stylomastoid foramen and could be identified precisely by tracing the PAA proximally. The distance from the cross point of the PAA and the facial nerve to the external meatal cartilage was 5.2 ± 0.2 mm.

CONCLUSION

The PAA represents a potential new anatomic landmark for facial nerve identification at the main trunk.

Surgical Training for the Implantation of Neocortical Microelectrode Arrays Using a Formaldehyde-fixed Human Cadaver Model

This protocol describes a procedure to assist surgeons in training for the implantation of microelectrode arrays into the neocortex of the human brain. Recent technological progress has enabled the fabrication of microelectrode arrays that allow recording the activity of multiple individual neurons in the neocortex of the human brain. These arrays have the potential to bring unique insight onto the neuronal correlates of cerebral function in health and disease. Furthermore, the identification and decoding of volitional neuronal activity opens the possibility to establish brain-computer interfaces, and thus might help restore lost neurological functions. The implantation of neocortical microelectrode arrays is an invasive procedure requiring a supra-centimetric craniotomy and the exposure of the cortical surface; thus, the procedure must be performed by an adequately trained neurosurgeon. In order to provide an opportunity for surgical training, we designed a procedure based on a human cadaver model. The use of a formaldehyde-fixed human cadaver bypasses the practical, ethical and financial difficulties of surgical practice on animals (especially non-human primates) while preserving the macroscopic structure of the head, skull, meninges and cerebral surface and allowing realistic, operating room-like positioning and instrumentation. Furthermore, the use of a human cadaver is closer to clinical daily practice than any non-human model. The major drawbacks of the cadaveric simulation are the absence of cerebral pulsation and of blood and cerebrospinal fluid circulation. We suggest that a formaldehyde-fixed human cadaver model is an adequate, practical and cost-effective approach to ensure proper surgical training before implanting microelectrode arrays in the living human neocortex.

Contralateral Approach to Middle Cerebral Artery Aneurysms: An Anatomical-Clinical Analysis to Improve Patient Selection

BACKGROUND

A contralateral approach to aneurysm clipping in cases of bilateral middle cerebral artery (MCA) aneurysms reduces surgical time and cost. However, there is a lack of evidence for objective patient selection. In this study, we assessed the change in surgical freedom along the contralateral MCA to provide objective evidence for patient selection.

METHODS

Sixteen cadaveric specimens were studied. Through a pterional approach, the surgical freedom was calculated moving distally along the contralateral MCA in 5-mm increments. In addition, in a series of 19 MCA aneurysms clipped contralaterally by the senior author, the average length of the MCA from its origin to the aneurysm neck was measured on angiography.

RESULTS

In these patients treated via a contralateral approach, the average length of the MCA segment from its origin to the aneurysm neck was 12.4 mm. Starting at the MCA origin, surgical freedom decreased significantly between all adjacent target points except at 5-10 mm from the MCA origin.

CONCLUSIONS

After the proximal 5 mm, there is no significant decrease in surgical maneuverability within the proximal 10 mm of MCA when approached contralaterally. When compared to the average length of the MCA from its origin to the aneurysm neck in the clinical series, it can be concluded that the first 10 mm (average, 12.4 mm) of the contralateral MCA may be considered a surgical comfort zone for a contralateral approach. This criterion may be useful for patient selection for a contralateral approach in cases of multiple bilateral intracranial aneurysms.

Revascularization of the upper posterior circulation with the anterior temporal artery: an anatomical feasibility study

OBJECTIVE In various disease processes, including unclippable aneurysms, a bypass to the upper posterior circulation (UPC) including the superior cerebellar artery (SCA) and posterior cerebral artery (PCA) may be needed. Various revascularization options exist, but the role of intracranial (IC) donors has not been scrutinized. The objective of this study was to evaluate the anatomical feasibility of utilizing the anterior temporal artery (ATA) for revascularization of the UPC. METHODS ATA-SCA and ATA-PCA bypasses were performed on 14 cadaver specimens. After performing an orbitozygomatic craniotomy and opening the basal cisterns, the ATA was divided at the M₃-M₄ junction and mobilized to the crural cistern to complete an end-to-side bypass to the SCA and PCA. The length of the recipient artery between the anastomosis and origin was measured. RESULTS Seventeen ATAs were found. Successful anastomosis was performed in 14 (82%) of the ATAs. The anastomosis point on the PCA was 14.2 mm from its origin on the basilar artery. The SCA anastomosis point was 10.1 mm from its origin. Three ATAs did not reach the UPC region due to a common opercular origin with the middle temporal artery. The ATA-SCA bypass was also applied to the management of an incompletely coiled SCA aneurysm. CONCLUSIONS The ATA is a promising IC donor for UPC revascularization. The ATA is exposed en route to the proximal SCA and PCA through the pterional-orbitozygomatic approach. Also, the end-to-side anastomosis provides an efficient and straightforward bypass without the need to harvest a graft or perform multiple or difficult anastomoses.

Registration and fusion quantification of augmented reality based nasal endoscopic surgery

This paper quantifies the registration and fusion display errors of augmented reality-based nasal endoscopic surgery (ARNES). We comparatively investigated the spatial calibration process for front-end endoscopy and redefined the accuracy level of a calibrated endoscope by using a calibration tool with improved structural reliability. We also studied how registration accuracy was combined with the number and distribution of the deployed fiducial points (FPs) for positioning and the measured registration time. A physically integrated ARNES prototype was customarily configured for performance evaluation in skull base tumor resection surgery with an innovative approach of dynamic endoscopic vision expansion. As advised by surgical experts in otolaryngology, we proposed a hierarchical rendering scheme to properly adapt the fused images with the required visual sensation. By constraining the rendered sight in a known depth and radius, the visual focus of the surgeon can be induced only on the anticipated critical anatomies and vessel structures to avoid misguidance. Furthermore, error analysis was conducted to examine the feasibility of hybrid optical tracking based on point cloud, which was proposed in our previous work as an in-surgery registration solution. Measured results indicated that the error of target registration for ARNES can be reduced to 0.77 ± 0.07 mm. For initial registration, our results suggest that a trade-off for a new minimal time of registration can be reached when the distribution of five FPs is considered. For in-surgery registration, our findings reveal that the intrinsic registration error is a major cause of performance loss. Rigid model and cadaver experiments confirmed that the scenic integration and display fluency of ARNES are smooth, as demonstrated by three clinical trials that surpassed practicality.

The Infrazygomatic Segment of the Superficial Temporal Artery: Anatomy and Technique for Harvesting a Better Interposition Graft

BACKGROUND

The superficial temporal artery (STA) is underutilized as an interposition graft because current techniques expose and harvest STA above the level of the zygoma. This technique yields a diminutive arterial segment in both length and diameter, which limits its use for extracranial-intracranial bypass.

OBJECTIVE

To introduce a safe and efficient technique for harvesting of the infrazygomatic segment of the STA.

METHODS

Scalp layers, STA, and the facial nerve were studied in 18 specimens. The length of the STA segment harvested below the superior border of the zygomatic arch was measured. Safety of this technique was assessed by measuring the distance between the facial nerve and the STA.

RESULTS

The galea and subgaleal fat pad were the only anatomical planes found between the facial nerve and the STA below the zygomatic arch. A dense subcutaneous band of galea contained the STA and allowed proximal dissection of the artery without exposing the facial nerve. The average length of the artery harvested between the zygomatic arch and the parotid gland was 20 mm.

CONCLUSION

Subcutaneous dissection within the galea below the level of the zygomatic arch and preservation of the dense subcutaneous band surrounding the STA avoids transecting the facial nerve branches while providing increased STA exposure. This anatomical knowledge may increase the use of STA as an interposition graft in cerebrovascular bypass procedures and reduce the need to harvest grafts through additional incisions at remote sites.

Creation of a novel simulator for minimally invasive neurosurgery: fusion of 3D printing and special effects

OBJECTIVE Recent advances in optics and miniaturization have enabled the development of a growing number of minimally invasive procedures, yet innovative training methods for the use of these techniques remain lacking. Conventional teaching models, including cadavers and physical trainers as well as virtual reality platforms, are often expensive and ineffective. Newly developed 3D printing technologies can recreate patient-specific anatomy, but the stiffness of the materials limits fidelity to real-life surgical situations. Hollywood special effects techniques can create ultrarealistic features, including lifelike tactile properties, to enhance accuracy and effectiveness of the surgical models. The authors created a highly realistic model of a pediatric patient with hydrocephalus via a unique combination of 3D printing and special effects techniques and validated the use of this model in training neurosurgery fellows and residents to perform endoscopic third ventriculostomy (ETV), an effective minimally invasive method increasingly used in treating hydrocephalus. METHODS A full-scale reproduction of the head of a 14-year-old adolescent patient with hydrocephalus, including external physical details and internal neuroanatomy, was developed via a unique collaboration of neurosurgeons, simulation engineers, and a group of special effects experts. The model contains "plug-and-play" replaceable components for repetitive practice. The appearance of the training model (face validity) and the reproducibility of the ETV training procedure (content validity) were assessed by neurosurgery fellows and residents of different experience levels based on a 14-item Likert-like questionnaire. The usefulness of the training model for evaluating the performance of the trainees at different levels of experience (construct validity) was measured by blinded observers using the Objective Structured Assessment of Technical Skills (OSATS) scale for the performance of ETV. RESULTS A combination of 3D printing technology and casting processes led to the creation of realistic surgical models that include high-fidelity reproductions of the anatomical features of hydrocephalus and allow for the performance of ETV for training purposes. The models reproduced the pulsations of the basilar artery, ventricles, and cerebrospinal fluid (CSF), thus simulating the experience of performing ETV on an actual patient. The results of the 14-item questionnaire showed limited variability among participants' scores, and the neurosurgery fellows and residents gave the models consistently high ratings for face and content validity. The mean score for the content validity questions (4.88) was higher than the mean score for face validity (4.69) (p = 0.03). On construct validity scores, the blinded observers rated performance of fellows significantly higher than that of residents, indicating that the model provided a means to distinguish between novice and expert surgical skills. CONCLUSIONS A plug-and-play lifelike ETV training model was developed through a combination of 3D printing and special effects techniques, providing both anatomical and haptic accuracy. Such simulators offer opportunities to accelerate the development of expertise with respect to new and novel procedures as well as iterate new surgical approaches and innovations, thus allowing novice neurosurgeons to gain valuable experience in surgical techniques without exposing patients to risk of harm.