Comparison of posterior approaches to the posterior incisural space: microsurgical anatomy and proposal of a new method, the occipital bi-transtentorial/falcine approach

Indocyanine green illuminates the way to cut the tentorium in occipital transtentorial approach: technical note

BACKGROUND AND IMPORTANCE

The occipital transtentorial approach is used to address lesions at the posterior incisural space or upper cerebellum. This approach is rarely used, making standardization of the surgical procedure challenging. Here we describe the effectiveness of indocyanine green (ICG) and dye markings before tentorial incision in charting a safe and bloodless surgical trajectory for improved manoeuvrability.

CLINICAL PRESENTATION

The first case was a 40-year-old man with a residual pineal mass after chemoradiation therapy for pathologically-proven germinoma. Surgical resection was performed via left occipital craniotomy. Incision of the left cerebellar tentorium by a radiofrequency knife was preceded by visualization of the straight sinus and venous lake, which were marked with dye, enabling safe entry into the quadrigeminal cistern. Finally, total-resection of the mature teratoma was achieved. The second case was a 50-year-old man with an enhancing mass at the cerebellar vermis and left hemisphere. Left occipital craniotomy was followed by ICG administration, illuminating the straight sinus and a complex structure of dural venous channels, which were marked with dye. This visualization maximized the tentorial incision by carefully avoiding venous structures and widely exposed the upper cerebellum. Subtotal-resection of the tumor was achieved, with a diagnosis of glioblastoma.

CONCLUSION

ICG administration and dye marking are feasible and useful methods for precise identification/visualization of venous structures. They enable maximization as well as safe and appropriate tentorial incision to provide a sufficient surgical corridor for the occipital transtentorial approach.

The Use of the Suboccipital Transtentorial Approach to the Posterior Inferior Incisural Space

Objective To describe our experience with the microsurgical technique of the suboccipital transtentorial (SOTT) approach in the removal of posterior fossa lesions located in the posterior incisural space. Method Between 2002 and 2020 we reviewed all patients who underwent microsurgical resection of lesions of the posterior incisural space at the Department of Neurosurgery, Essex Neuroscience Centre, London, England (eight patients, male to female 3:5, mean age: 51, range 35-69). We describe the preoperative symptoms, radiological findings, surgical techniques, histology and postoperative outcomes in this cohort of patients. Results Eight patients with tumours located in the posterior incisural space underwent surgery during the study period including four meningiomas (50%), two haemangioblastomas (25%), one metastasis (13%) and one giant prolactinoma (13%). Gross or near total resection was achieved in six patients (75%): the giant prolactinoma could not be radically removed and one of the meningiomas required a small fragment to be left in place to protect the Vein of Galen. No patient developed a visual field deficit due to occipital lobe retraction. One patient developed a temporary trochlear nerve palsy (13%). Five patients had mild disability (Glasgow Outcome Scale (GOS) = 5), and four had moderate disability (GOS = 4). Conclusion In our series, the SOTT approach provided excellent access for all cases of tumours in the posterior incisural space. The tumour's size and relationship to the deep venous system contributed to the choice of approach and in one patient who had previously undergone surgery via the supracerebellar route, the SOTT approach enabled the avoidance of gliotic scar tissue. Success is dependent on careful case selection, though from our series of 8 patients, we conclude that this approach allows safe access to the posterior incisural space, with acceptable outcomes with regard to postoperative disability and cranial nerve palsy. As such, the approach should be in the armamentarium of any neurosurgeon who regularly deals with posterior fossa pathology.

Microsurgical approaches to the cerebellar interpeduncular region: qualitative and quantitative analysis

OBJECTIVE

The cerebellar interpeduncular region (CIPR) is a gate for dorsolateral pontine and cerebellar lesions accessed through the supracerebellar infratentorial approach (SCITa), the occipital transtentorial approach (OTa), or the subtemporal transtentorial approach (STa). The authors sought to compare the exposures of the CIPR region that each of these approaches provided.

METHODS

Three approaches were performed bilaterally in eight silicone-injected cadaveric heads. The working area, area of exposure, depth of the surgical corridor, length of the interpeduncular sulcus (IPS) exposed, and bridging veins were statistically studied and compared based on each approach.

RESULTS

The OTa provided the largest working area (1421 mm2; p < 0.0001) and the longest surgical corridor (6.75 cm; p = 0.0006). Compared with the SCITa, the STa provided a larger exposure area (249.3 mm2; p = 0.0148) and exposed more of the length of the IPS (1.15 cm; p = 0.0484). The most bridging veins were encountered with the SCITa; however, no significant differences were found between this approach and the other approaches (p > 0.05).

CONCLUSIONS

To reach the CIPR, the STa provided a more extensive exposure area and more linear exposure than did the SCITa. The OTa offered a larger working area than the SCIT and the STa; however, the OTa had the most extensive surgical corridor. These data may help neurosurgeons select the most appropriate approach for lesions of the CIPR.

Vascular Lesions of the Pineal Region: A Comprehensive Review of the Therapeutic Options

OBJECTIVE

Vascular lesions of the pineal region comprise aneurysms of the pineal region, arteriovenous malformations, cavernous malformations, and vein of Galen malformations. In the present report, we have offered an extensive review of each vascular pineal region lesion.

METHODS

We performed an extensive literature review, focusing on the current therapeutic options available for the different vascular lesions of the pineal region.

RESULTS

Vascular lesions of the pineal region are rare. Microneurosurgery remains a valid treatment of cavernomas, arteriovenous malformations, and aneurysms. Endovascular treatments seem to be the first option for the vein of Galen malformations, followed by microneurosurgery. Radiosurgery seems beneficial for small-size arteriovenous malformations. Complex and large vascular lesions will require a combination of multiple treatments.

CONCLUSIONS

Vascular lesions of the pineal region are complex, uncommon diseases. Thus, definitive therapeutic modalities for these lesions require further research.

Occipital interhemispheric transtentorial approach to a pineoblastoma in a 4-year-old child

The authors present a pediatric case of a pineoblastoma treated with gross-total removal through an occipital interhemispheric transtentorial approach (OITA). The child presented with acute hydrocephalus that was treated by endoscopic third ventriculostomy (ETV) and tumor biopsy through a single burr hole. Histology revealed a pineoblastoma. Microsurgical total removal was performed 3 months after neoadjuvant chemotherapy. OITA was chosen on the basis of the tumor’s location below the Herophilus-Galen line of sight. In this video, the authors show the positioning, the operating devices, the approach, and the microsurgical dissection, indicating all the neurovascular structures encountered.

The video can be found here: https://stream.cadmore.media/r10.3171/2021.4.FOCVID2122.

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.

Surgical Management of Tentorial Notch Meningioma Guided by Further Classification: A Consecutive Study of 53 Clinical Cases

Background

Management of tentorial notch meningiomas (TNM) remains a challenge for neurosurgeons. We demonstrate the clinical characteristics and surgical experiences of TNM based on our cases according to a proposed further classification.

Methods

We retrospectively analyzed clinical and follow-up data in a consecutive series of 53 TNM patients who underwent microsurgical operation from 2011 to 2019 in our institution. The operations were performed using various approaches. Clinical history, preoperative and postoperative neurofunction, imaging results, and surgical outcomes were collected for further classification of TNM.

Results

All TNM cases were divided into anterior (T1), middle (T2), and posterior notch (T3). According to the direction of tumor extension and correlation with the neurovascular structures, detailed subtypes of anterior TNMs were identified as the central (T1a), posterior (T1b), and medial type (T1c). The middle TNMs were divided into the infratentorial (T2a), supratentorial (T2b), and supra-infratentorial type (T2c). The posterior TNMs were divided into superior (T3a), inferior (T3b), lateral (T3c), and straight sinus type (T3d) in reference to Bassiouni’s classification. Total removal of the tumor was achieved in 46 cases, with five cases of subtotal and two cases of partial removal without any recorded deaths in our series. In total, five subtotal resected cases underwent gamma-knife treatment and achieved stable disease. Postoperative aggravation or new onset cranial nerve dysfunction occurred in some individual cases, with incidences ranging from 3.77 to 15.10% and improved preoperative neurological deficits ranging from 0 to 100%.

Conclusion

Further, TNM classification based on the intracranial location, extension direction, relationship with brainstem, and neurovascular structures guides preoperative evaluation, rational surgical approach selection, and surgical strategy formulation. Taking microsurgery as the main body, a satisfactory outcome of TNM treatment can be achieved for complicated tumors by combining stereotactic radiotherapy. This study demonstrates the surgical outcomes and complications in detail. Further classification might be helpful for treatment decisions in the future.

Quantitative analysis of ipsilateral and contralateral supracerebellar infratentorial and occipital transtentorial approaches to the cisternal pulvinar: laboratory anatomical investigation

OBJECTIVE

The cisternal pulvinar is a challenging location for neurosurgery. Four approaches for reaching the pulvinar without cortical transgression are the ipsilateral supracerebellar infratentorial (iSCIT), contralateral supracerebellar infratentorial (cSCIT), ipsilateral occipital transtentorial (iOCTT), and contralateral occipital transtentorial/falcine (cOCTF) approaches. This study quantitatively compared these approaches in terms of surgical exposure and maneuverability.

METHODS

Each of the 4 approaches was performed in 4 cadaveric heads (8 specimens in total). A 6-sided anatomical polygonal region was configured over the cisternal pulvinar, defined by 6 reachable anatomical points in different vectors. Multiple polygons were subsequently formed to calculate the areas of exposure. The surgical freedom of each approach was calculated as the maximum allowable working area at the proximal end of a probe, with the distal end fixed at the posterior pole of the pulvinar. Areas of exposure, surgical freedom, and the working distance (surgical depth) of all approaches were compared.

RESULTS

No significant difference was found among the 4 different approaches with regard to the surgical depth, surgical freedom, or medial exposure area of the pulvinar. In the pairwise comparison, the cSCIT approach provided a significantly larger lateral exposure (39 ± 9.8 mm2) than iSCIT (19 ± 10.3 mm2, p < 0.01), iOCTT (19 ± 8.2 mm2, p < 0.01), and cOCTF (28 ± 7.3 mm2, p = 0.02) approaches. The total exposure area with a cSCIT approach (75 ± 23.1 mm2) was significantly larger than with iOCTT (43 ± 16.4 mm2, p < 0.01) and iSCIT (40 ± 20.2 mm2, p = 0.01) approaches (pairwise, p ≤ 0.01).

CONCLUSIONS

The cSCIT approach is preferable among the 4 compared approaches, demonstrating better exposure to the cisternal pulvinar than ipsilateral approaches and a larger lateral exposure than the cOCTF approach. Both contralateral approaches described (cSCIT and cOCTF) provided enhanced lateral exposure to the pulvinar, while the cOCTF provided a larger exposure to the lateral portion of the pulvinar than the iOCTT. Medial exposure and maneuverability did not differ among the approaches. A short tentorium may negatively impact an ipsilateral approach because the cingulate isthmus and parahippocampal gyrus tend to protrude, in which case they can obstruct access to the cisternal pulvinar ipsilaterally.

Parietal interhemispheric transfalcine transtentorial approach for posterior incisural space lesions: from the lab to the operative room

The operative approach to the posterior incisural space is challenging because of its deep location, the surrounding eloquent areas, and the intimate relationship with the deep veins. Several approaches have been proposed to manage the lesions in this region: supratentorial, infratentorial and a combination of them. Brain retraction, injury to the occipital lobe and corpus callosum, and venous bleeding are the principle drawbacks of these routes. We performed anatomical dissection study using 10 embalmed human cadaver specimens injected with colored latex exploring a different route, parietal interhemispheric transfalcine transtentorial (PITT). Then we used a PITT approach on two patients with posterior incisural space (PIS) lesions. The PITT approach led to successful and safe complete removal of PIS lesions in our cases. No complications were reported. The present approach could be a valuable option in case of PIS lesions, especially those associated with downward displacement of the deep venous complex; thanks to the gravity it reduce the complications related to the occipital lobe retraction and manipulation. Moreover, cutting the superior-anterior edge of the tentorium, the sub-tentorial space could be reached.

Endoscopic Endonasal Transclival Approach to the Ventral Brainstem: Anatomic Study of the Safe Entry Zones Combining Fiber Dissection Technique with 7 Tesla Magnetic Resonance Guided Neuronavigation

BACKGROUND

Treatment of intrinsic lesions of the ventral brainstem is a surgical challenge that requires complex skull base antero- and posterolateral approaches. More recently, endoscopic endonasal transclival approach (EETA) has been reported in the treatment of selected ventral brainstem lesions.

OBJECTIVE

In this study we explored the endoscopic ventral brainstem anatomy with the aim to describe the degree of exposure of the ventral safe entry zones. In addition, we used a newly developed method combining traditional white matter dissection with high-resolution 7T magnetic resonance imaging (MRI) of the same specimen coregistered using a neuronavigation system.

METHODS

Eight fresh-frozen latex-injected cadaver heads underwent EETA. Additional 8 formalin-fixed brainstems were dissected using Klingler technique guided by ultra-high resolution MRI.

RESULTS

The EETA allows a wide exposure of different safe entry zones located on the ventral brainstem: the exposure of perioculomotor zone requires pituitary transposition and can be hindered by superior cerebellar artery. The peritrigeminal zone was barely visible and its exposure required an extradural anterior petrosectomy. The anterolateral sulcus of the medulla was visible in most of specimens, although its close relationship with the corticospinal tract makes it suboptimal as an entry point for intrinsic lesions. In all cases, the use of 7T-MRI allowed the identification of tiny fiber bundles, improving the quality of the dissection.

CONCLUSION

Exposure of the ventral brainstem with EETA requires mastering surgical maneuvers, including pituitary transposition and extradural petrosectomy. The correlation of fiber dissection with 7T-MRI neuronavigation significantly improves the understanding of the brainstem anatomy.

Different strategies in the management of thalamic space-occupying lesions

Introduction

Thalamic space-occupying lesions (SOL) are considered challenging for microsurgical removal. Unfortunately, the pathological features of lesions occurring in the thalamic region are different with a wide variation in clinical behavior and outcome. Although microsurgery is still the gold standard in the management of these lesions through different approaches, questions remain whether surgery is feasible and safe in these patients and what are the alternatives? It is well known that stereotactic techniques may be favorable especially in cystic, small, multiple lesions and in combination with adjuvant therapy. Transventricular endoscopic approach is also an alternative technique to combine tumor biopsy and treatment of hydrocephalus.

Aim of the study

The identification of the different procedures for the management of thalamic SOL in respect to the age of the patient, the clinical condition, and the site of the lesion as well as its extent and pathology.

Patients and methods

This prospective study included 35 patients having thalamic lesions with a mean age of 27 years old who were treated with different approaches including microsurgical, stereotactic, and endoscopic approaches. The clinical outcome was assessed as the same, improved, deteriorated, or died in comparison to the initial clinical status, while the radiological control was measured as no gross residual, residual < 10% and residual > 10%. Chi-square test was used to test the association between two categorical variables.

Results

Thirty-five patients were included in this study, 20 were males and 15 were females. Eight cases were children, and 27 cases were adults. The most common clinical presentation was contralateral hemiparesis. The most common pathology was pilocytic astrocytoma. Radiological studies showed that the total thalamic type was the most common topographic variant and that 10 cases had hydrocephalus treated with CSF diversion procedures. For the definitive lesion, 2 cases underwent endoscopic biopsy and cystoventriculostomy and 18 cases had stereotactic technique in the form of biopsy, aspiration, and ommaya reservoir application, while 15 cases had microsurgery through different approaches with stereotactic technique preceding surgery in 2 of them.

Conclusion

The main factors involved in choosing the appropriate approach included nature of the lesion (solid or cystic, multiplicity), suspected pathological type, and diffusion tensor imaging. Abscesses are best treated with stereotaxy, while non-neoplastic cystic lesions (other than abscesses) related to the ventricles are best treated with endoscopy. For the remaining pathologies, maximum surgical removal is the best management. Best lesion control was provided by microsurgery.

Trial registration

ISRCTN 1380 registered 6/11/2018

Safe handling of veins in the pineal region-a mixed method study

Surgical experience in pineal surgery is largely confined to a few experienced surgeons and may be lost when they stop their practice. The objective of this study is to systematically preserve and analyze valuable practical knowledge of pineal region surgical venous anatomy. A survey was constructed to obtain experienced surgeons' perception of estimated risks and individual experience following occlusion of veins during pineal surgery. Data were qualitative and analyzed with a mixed methods approach. Of the 126 invited neurosurgeons, 40 submitted completed questionnaires. General agreement existed of which veins were associated with high and low risks following occlusion. The risk of death was estimated to be high with sacrifice of the vein of Galen (83%), both internal cerebral veins (69%) and the basal veins (58%). The risk of death was estimated to be lower with the sacrifice of both superior vermian veins (13%) and one internal occipital vein (10%). Importantly, a sub-group of experienced surgeons reported substantial risk of death and consequences with the sacrifice of cerebellar bridging veins (8-13%). Our findings provide a coherent picture of surgical risk with venous sacrifice, which can inform the surgical community of systematically gathered views from aggregated surgeries of a very large cohort of patients. Extensive presurgical radiological workup and anatomical studies seemed to correlate more cautious risk estimations. Our findings increase available knowledge of risks of venous complications.

Multistaged, multidirectional strategy for safe removal of large meningiomas in the pineal region

OBJECTIVE Pineal region meningiomas are rare and tend to be discovered only after they grow. Several simultaneous multidirectional approaches performed as a single operation have been proposed, but the best strategy to remove these deeply situated large meningiomas involving the deep vital venous system remains to be established. The authors advocate a multistaged, multidirectional approach to safely remove these challenging tumors. METHODS Four consecutive cases of meningioma in the pineal region were treated between April 2013 and June 2016. The 3 large (> 40 mm diameter) tumors were removed via multistaged, multidirectional approaches (2 surgeries in 2 patients and 3 surgeries in 1 patient) with gravity retraction of the occipital or parietal lobe. The large occipital skin incision extending bilaterally was used for the next operation from the contralateral side. Combinations of the occipital transtentorial approach with or without the transfalcine approach, occipital bitranstentorial/falcine approach, combined supra-/infratentorial transsinus approach, and contralateral parietal interhemispheric transcallosal approach were used. RESULTS Transient visual field deficits occurred after 2 of the 8 operations, but all tumors were removed grossly or subtotally without permanent surgery-related morbidity. The galenic venous system and straight sinus remained intact in all patients. During the follow-up period (mean 29.5 months [range 13-52 months]), there were no recurrences after the final operation. CONCLUSIONS A multistaged, multidirectional strategy with an intentional large occipital scalp incision and gravity retraction of the occipital lobe is a good choice for the safe removal of large meningiomas in the pineal region.

Unilateral Occipital Transtentorial Approach with Multimodal Assistance for Resection of Large Supracerebellar Hemangioblastomas: Preliminary Experience of 2 Cases

BACKGROUND

The surgical resection of large supracerebellar hemangioblastomas (SHBs) is exceptionally challenging due to their vascularity and deep anatomic location and is associated with a high risk of postoperative complications and mortality. Access to the posterior incisural space can be achieved by either an infratentorial supracerebellar approach or occipital transtentorial approach (OTA). However, the optimal surgical strategy has not yet been established. Here, we report 2 cases of large SHBs that were successfully and safely resected via a unilateral OTA with multimodal assistance.

CASE DESCRIPTION

Two patients presented to our hospital with ataxia due to large, solid SHBs. After preoperative embolization, gross total resection of the SHBs was achieved via an OTA. Furthermore, endoscopic assistance was used to resect the remnant portion of the tumor in the second patient. Both patients experienced transient ataxia but were discharged from the hospital without serious complications.

CONCLUSIONS

The combination of an OTA with preoperative embolization and endoscopic assistance may reduce the intraoperative risk and contribute to improved outcome in patients with such clinically challenging tumors.

Supracerebellar Infratentorial and Occipital Transtentorial Approaches to the Pulvinar: Ipsilateral Versus Contralateral Corridors

BACKGROUND

Due to the critical neurovascular structures that surround the pulvinar, deciding the best surgical approach can be challenging, with multiple options available.

OBJECTIVE

To analyze and compare the ipsilateral vs the contralateral version of the 2 main approaches to the cisternal pulvinar surface: paramedian supracerebellar infratentorial (PSCI) and interhemispheric occipital transtentorial (IOT).

METHODS

The PSCI and IOT approaches were performed on 7 formalin-fixed adult cadaveric heads to evaluate qualitatively and quantitatively the microsurgical exposure of relevant anatomic structures. We quantitatively measured the corridor distance to our target with each approach.

RESULTS

The ipsilateral PSCI approach provided an easier access and a better exposure of the anteromedial portion of the cisternal pulvinar surface. The contralateral approach provided a wider and more accessible exposure of the posterolateral portion of the cisternal pulvinar surface. When protrusion of the posterior parahippocampal gyrus above the free edge of the tentorium was present, the contralateral PSCI approach provided an unobstructed view to both areas. The IOT approach provided a better view of the anteromedial portion of the cisternal pulvinar surface, especially with a contralateral approach.

CONCLUSION

Multiple approaches to the pulvinar have been described, modified, and improved. Based on this anatomic study we believe that although the corridor distance with a contralateral approach is longer, the surgical view and access can be better. We recommend the use of a PSCI contralateral approach especially when a significant protrusion of the posterior parahippocampal gyrus is present.

Surgical Management of Anterolateral and Posteromedial Incisural Tentorial Meningioma

BACKGROUND

Tentorial meningiomas are a broad and consistent category of tumors but their definition is still unclear and their classification uncertain.

OBJECTIVE

To report the clinical and surgical characteristics of tentorial hiatus meningiomas based on a revised classification of tentorial meningiomas.

METHODS

We reviewed the records of 14 patients who had undergone microsurgical removal of incisural tentorial meningioma. Two tumor subgroups, anterolateral (AL) and posteromedial (PM), were distinguished according to their site of attachment: the middle third and the posterior third of the tentorial free margin, respectively. Clinical presentation, radiological findings, surgical approaches, extent of resection, and outcome were compared.

RESULTS

The 2 subgroups differed by tumor size (larger in PM), incidence of the direction of growth (infratentorial in PM), and hydrocephalus (only in PM), as well as by some clinical aspects. Surgical approach depended on tumor location: lateral (pterional, subtemporal, and retromastoid) for AL lesions; medial (occipital or supracerebellar infratentorial) for PM lesions. Total removal (Simpson grade I-II) was performed in 64% of cases and complications occurred in 14%. Stereotactic radiosurgery was performed in cases of incomplete resection. At a mean follow-up of 104.5 mo, clinical improvement with low recurrence (9%) was achieved.

CONCLUSION

Reallocation of tentorial edge meningiomas is the premise to compare treatment and further improve the approach case-by-case. In spite of their deep site, good outcomes can be achieved in both AL and PM tentorial meningiomas. Also of note is the indolent behavior of residual tumor.

Transtentorial transcollateral sulcus approach to the ventricular atrium: an endoscope-assisted anatomical study

OBJECTIVE

Conventional approaches to the atrium of the lateral ventricle may be associated with complications related to direct cortical injury or brain retraction. The authors describe a novel approach to the atrium through a retrosigmoid transtentorial transcollateral sulcus corridor.

METHODS

Bilateral retrosigmoid craniotomies were performed on 4 formalin-fixed, colored latex–injected human cadaver heads (a total of 8 approaches). Microsurgical dissections were performed under 3× to 24× magnification, and endoscopic visualization was provided by 0° and 30° rigid endoscope lens systems. Image guidance was provided by coupling an electromagnetic tracking system with an open source software platform. Objective measurements on cortical thickness traversed and total depth of exposure were recorded. Additionally, the basal occipitotemporal surfaces of 10 separate cerebral hemisphere specimens were examined to define the surface topography of sulci and gyri, with attention to the appearance and anatomical patterns and variations of the collateral sulcus and the surrounding gyri.

RESULTS

The retrosigmoid approach allowed for clear visualization of the basal occipitotemporal surface. The collateral sulcus was identified and permitted easy endoscopic access to the ventricular atrium. The conical corridor thus obtained provided an average base working area of 3.9 cm2 at an average depth of 4.5 cm. The mean cortical thickness traversed to enter the ventricle was 1.4 cm. The intraventricular anatomy of the ipsilateral ventricle was defined clearly in all 8 exposures in this manner. The anatomy of the basal occipitotemporal surface, observed in a total of 18 hemispheres, showed a consistent pattern, with the collateral sulcus abutted by the parahippocampal gyrus medially, and the fusiform and lingual gyrus laterally. The collateral sulcus was found to be caudally bifurcated in 14 of the 18 specimens.

CONCLUSIONS

The retrosigmoid supracerebellar transtentorial transcollateral sulcus approach is technically feasible. This approach has the potential advantage of providing a short and direct path to the atrium, hence avoiding violation of deep neurovascular structures and preserving eloquent areas. Although this approach appears unconventional, it may provide a minimally invasive option for the surgical management of selected lesions within the atrium of the lateral ventricle.

Occipital transtentorial/falcine approach, a "cross-court" trajectory to accessing contralateral posterior thalamic lesions: case report

Surgical treatment of lesions in the posterior thalamus, especially those extending laterally, is technically challenging because of a deep surgical field, narrow operative corridor, and the surrounding critical neurovascular structures. The authors describe an occipital transtentorial/falcine approach (OTFA) that was successfully used in the treatment of a cavernous malformation (CM) extending laterally from thalamus to midbrain. A 40-year-old man complained of progressive right hemiparesis and numbness. Radiological evaluation revealed a large CM in the left thalamus, surfacing on the pulvinar thalami, and extending 4 cm laterally from the midline. In addition to the usual procedures of a right-sided occipital transtentorial approach, the authors incised the falx cerebri to expand the operative corridor to the left thalamus. They achieved generous exposure of the left thalamus through a "cross-court" oblique trajectory while avoiding excessive retraction on the occipital lobe. The CM was completely removed, and no newly developed or worsening deficits were detected postoperatively. To better understand the OTFA and its application, the authors performed a cadaveric dissection. The OTFA provides increased exposure of the posterior thalamus without cortical incision and facilitates lateral access to this area through the "cross-court" operative corridor. This approach adds to the armamentarium for neurosurgeons treating thalamic lesions.

[The paramedian supracerebellar transtentorial approach to the mediobasal temporal region]

The mediobasal temporal region (MTR) is located near the brain stem and surrounded by the eloquent neurovascular structures. The supracerebellar transtentorial approach (STA) is safe access to the posterior MTR structures, however its use for resection of anterior MTR lesions still remains controversial. The article describes the technique and outcome of surgery for different MTR structures using STA.

MATERIAL AND METHODS

The paramedian STA was used in 18 patients (13 females and 5 males) for 7 years. Ten patients presented with glial MTR tumors, 3 patients with cavernomas, 2 patients with arteriovenous malformations (AVMs), 2 patients with intraventricular meningiomas, and 1 patient with mesial temporal sclerosis. The patient age ranged from 19 to 57 years. In 10 cases, lesions were localized on the left. Epilepsy was the leading symptom in 14 cases. Patients underwent preoperative high-resolution MRI, electroencephalography video monitoring before and after surgery, intraoperative corticography (if necessary), and postoperative CT and MRI.

RESULTS

Lesions were located in the anterior third of MTR in 5 patients, in the anterior and middle thirds in 2 patients, in the middle third in 5 patients, in the middle and posterior thirds in 2 patients, in the posterior third in 1 patient, in the anterior, middle, and posterior thirds in 1 patient, and in the ventricular triangle area in 2 patients. In all patients with intraventricular tumors, AVMs, and cavernous malformations and in 8 patients with glial MTR tumors, the lesions were totally resected. Two patients with intracerebral tumors underwent subtotal resection. A patient with intractable epilepsy and mesial temporal sclerosis underwent resection of the anterior two-thirds of the hippocampus and parahippocampal gyrus and, partially, amygdala using intraoperative corticography. There was no surgical mortality; 2 patients developed a transient neurological deficit, and 1 patient had a cerebellar hematoma that was successfully removed during surgery.

CONCLUSION

STA enables resection of lesions localized in all parts of the MTR, without damage to the surrounding nerve and vascular structures.

Quantification and comparison of neurosurgical approaches in the preclinical setting: literature review

There is a growing awareness of the need for evidence-based surgery and of the issues that are specific to research in surgery. Well-conducted anatomical studies can represent the first, preclinical step for evidence-based surgical innovation and evaluation. In the last two decades, various reports have quantified and compared neurosurgical approaches in the anatomy laboratory using different methods and technology. The aim of this study was to critically review these papers. A PubMed and Scopus search was performed to select articles that quantified and compared different neurosurgical approaches in the preclinical setting. The basic characteristics that anatomically define a surgical approach were defined. Each study was analyzed for measured features and quantification method and technique. Ninety-nine papers, published from 1990 to 2013, were included in this review. A heterogeneous use of terms to define the features of a surgical approach was evident. Different methods to study these features have been reported; they are generally based on quantification of distances, angles, and areas. Measuring tools have evolved from the simple ruler to frameless stereotactic devices. The reported methods have each specific advantages and limits; a common limitation is the lack of 3D visualization and surgical volume quantification. There is a need for a uniform nomenclature in anatomical studies. Frameless stereotactic devices provide a powerful tool for anatomical studies. Volume quantification and 3D visualization of the surgical approach is not provided with most available methods.

Japanese neurosurgeons and microsurgical anatomy: a historical review

Research in microneurosurgical anatomy has contributed to great advances in neurosurgery in the last 40 years. Many Japanese neurosurgeons have traveled abroad to study microsurgical anatomy and played major roles in advancing and spreading the knowledge of anatomy, overcoming their disadvantage that the cadaver study has been strictly limited inside Japan. In Japan, they initiated an educational system for surgical anatomy that has contributed to the development and standardization of Japanese neurosurgery. For example, the Japanese Society for Microsurgical Anatomy started an annual educational meeting in the middle of 1980s and published its proceedings in Japanese every year for approximately 20 years. These are some of the achievements that bring worldwide credit to Japanese neurosurgeons. Not only should Japanese neurosurgeons improve their educational system but they should also contribute to the international education in this field, particularly in Asia.

Quantitative study of the opticocarotid and carotid-oculomotor windows for the interpeduncular fossa, before and after internal carotid artery mobilization and posterior communicating division

BACKGROUND

The management of basilar apex (BX) aneurysms remains problematic.

OBJECTIVE

We quantified the surgical exposure of the BX through the opticocarotid window (OCW) and the carotid-oculomotor window (COW), before and after mobilization of the internal carotid artery and division of the posterior communicating artery (PCoA).

METHODS

Eleven silicone-injected cadaveric heads were dissected bilaterally. The surgical dissection was divided into 4 major steps: (1) supraorbital modified orbitozygomatic craniotomy, (2) mobilization of the internal carotid artery after drilling out the anterior clinoid process intradurally and cutting the distal dural ring, (3) drilling out the posterior clinoid process and dorsum sellae, and (4) dividing the PCoA from the posterior third portion of the vessel. A frameless navigation system was used to quantify the surgical exposure area of the BX through the OCW and COW.

RESULTS

The total surgical area increased significantly from steps 1 to 4 (P < .001) in both OCW and COW groups. Overall, there was a larger total surgical area obtained in the COW compared with the OCW (P = .010). ICA mobilization increased the surgical area for temporary (P < .001) and permanent (P < .003) clip application in both windows. The division of PCoA significantly increased the overall surgical area for permanent clip application (P < .003). Compared with the OCW, the COW had a significantly increased change in the area for permanent clip application in the low-lying group (P = .03).

CONCLUSION

When approaching the BX via the pterion route, the appropriate surgical step and window should be selected according to characteristics of the PCoA and height of the BX.

The superior transvelar approach to the fourth ventricle and brainstem

Objective The superior transvelar approach is used to access pathologies located in the fourth ventricle and brainstem. The surgical path is below the venous structures, through the superior medullary velum. Following splitting the tentorial edge, near the tentorial apex, the superior medullary velum is split in the cerebello-mesencephalic fissure. Using the supracerebellar infratentorial, transtentorial or parietal interhemispheric routes, the superior medullary velum is approached. Splitting this velum provides a detailed view of the fourth ventricle and its floor. Materials and Methods A total of 10 formalin-fixed specimens were dissected in a stepwise manner to simulate the superior transvelar approach to the fourth ventricle. The exposure gained the distance from the craniotomy site and the ease of access was assessed for each of the routes. We also present an illustrative case, operated by the senior author (AN). Results The superior transvelar approach provides access to the entire length of the fourth ventricle floor, from the aqueduct to the obex, when using the parietal interhemispheric route. In addition, this approach provides access to the entire width of the floor of the fourth ventricle; however, this requires retracting the superior cerebellar peduncle. Using the supracerebellar infratentorial route gives a limited exposure of the superior part of the fourth ventricle. The occipital interhemispheric route is a compromise between these two. Conclusion The superior transvelar approach to the fourth ventricle provides a route for approaching the fourth ventricle from above. This approach does not require opening the posterior fossa in the traditional way, and provides a reasonable alternative for accessing the superior fourth ventricle.

Meningioma of the pineal region

Meningiomas rarely occur in the pineal region, but they can reach huge diameters. We presented the case of a patient with a very large meningioma of the pineal region (6x5x4 cm). The tumor, developed from the falcotentorial junction, was totally removed via an occipital interhemispheric transtentorial approach with minimal postoperative neurological deficits. The postoperative course was complicated with an acute internal hydrocephalus that needed temporary placement of an external ventricular drainage. The supratentorial surgical corridors allow for increased exposure and are best suited for falcotentorial meningiomas.

Posterior cranial fossa tumors: Results and prognostic factors in a consecutive series of 14 operated patients by occipital transtentorial approach

BACKGROUND

The objective of our study was to determine the safety and usefulness of performing surgery via occipital transtentorial approach to treat posterior cranial fossa tumors, which is well known as an approach to the pineal region (Poppen's approach).

METHODS

Fourteen patients with posterior cranial fossa tumors were successfully treated using occipital transtentorial approach between 2007 and 2012. The lesions included five meningiomas, three astrocytomas, two metastases, two hemangioblastomas, one cavernoma, and one dysgerminoma.

RESULTS

Lesions were <3 cm in 12 cases and ≥3 cm in two cases. Average Karnofsky Performance Status (KPS) scoring at admission was 88.5. Eleven patients scored ≥70 and seven patients <70. Average age was 43.1 years. All patients underwent surgical treatment by the same surgical team. All tumors were completely removed surgically without any injury to the venous complex and the adjoining structures. There was no incidence of mortality or morbidity in all patients, and all functional outcomes were good to excellent postoperatively. Postoperative computed tomography (CT) imaging revealed that none of the patients had suffered brain damage or infarction around the cerebellum, brainstem, or occipital lobe.

CONCLUSIONS

We found that the use of occipital transtentorial approach is strongly supported by the successful removal of posterior cranial fossa tumors without serious complications. Open microneurosurgery is probably still the most effective therapy in improving survival and KPS in patients with posterior cranial fossa tumors, given that the proper surgical technique is used and complications do not occur. This case study has strongly suggested that this approach is very useful, safe, and accurate for removing the tumors of posterior fossa and evaluating the surrounding anatomy, as well as for determining operative strategy.

Identification of venous variants in the pineal region with three-dimensional preoperative magnetic resonance imaging navigation in patients harbouring tumors in this area: significance for surgical approach to the lesion

OBJECT

The purpose of this study was to identify the anatomy of pineal region venous complex using neuronavigation software when distorted by the presence of a space-occupying lesion and to describe the anatomical relationship between lesion and veins. Moreover we discuss its influence on the choice of the surgical strategy.

METHODS

Of the 33 patients treated at our Institute for pineal region tumors between 2003 and 2008 we used the neuronavigation software to depict the venous system of the pineal region in 14 patients. We focused on depiction of the basal vein of Rosenthal (BV), the internal cerebral vein (ICV) and the vein of Galen: connection patterns between the veins and the type of anatomical distortion caused by the lesion were investigated and classified.

RESULTS

Using the neuronavigation software for three-dimensional (3D) reconstruction of MRI images the ICV was clearly depicted in all patients on both sides (100%). Last segment of the BV was identified in 25 sides on a total of 28 (89.3%) and absent in 3 of the 28 sides (10.7%). Studying the distortion effect of the tumor on the galenic venous system, three directions of displacement were observed: craniocaudal, anteroposterior and lateral. Seven patients presented a cranial dislocation, 5 patients caudal dislocation and there was no craniocaudal shift in 2 patients. Considering the anteroposterior displacement: 3 subjects showed an anterior shift of the veins, 5 subjects posterior shift and no anterioposterior shift was present in 6 patients. Only 2 of the 14 patients presented lateral displacement of the veins. The principal approaches used in this series were: supracerebellar infratentorial and interhemispheric parieto-occipital. The craniocaudal displacement of the pineal veins seems to be the most important for the choice of the approach.

CONCLUSION

The galenic venous system has a central role in the surgery pineal region tumors. Our study demonstrates that the architecture of the pineal veins and their anatomical relationship with the lesion can be depicted with great accuracy by using 3D neuronavigation software in order to facilitate surgical planning and intraoperative orientation.

The craniocaudal extension of posterolateral approaches and their combination: a quantitative anatomic and clinical analysis

OBJECTIVE

The aim of this study was to describe quantitatively the properties of the posterolateral approaches and their combination.

METHODS

Six silicone-injected cadaveric heads were dissected bilaterally. Quantitative data were generated with the Optotrak 3020 system (Northern Digital, Waterloo, Canada) and Surgiscope (Elekta Instruments, Inc., Atlanta, GA), including key anatomic points on the skull base and brainstem. All parameters were measured after the basic retrosigmoid craniectomy and then after combination with a basic far-lateral extension. The clinical results of 20 patients who underwent a combined retrosigmoid and far-lateral approach were reviewed.

RESULTS

The change in accessibility to the lower clivus was greatest after the far-lateral extension (mean change, 43.62 +/- 10.98 mm2; P = .001). Accessibility to the constant landmarks, Meckel's cave, internal auditory meatus, and jugular foramen did not change significantly between the 2 approaches (P > .05). The greatest change in accessibility to soft tissue between the 2 approaches was to the lower brainstem (mean change, 33.88 +/- 5.25 mm2; P = .0001). Total removal was achieved in 75% of the cases. The average postoperative Glasgow Outcome Scale score of patients who underwent the combined retrosigmoid and far-lateral approach improved significantly, compared with the preoperative scores.

CONCLUSION

The combination of the far-lateral and simple retrosigmoid approaches significantly increases the petroclival working area and access to the cranial nerves. However, risk of injury to neurovascular structures and time needed to extend the craniotomy must be weighed against the increased working area and angles of attack.

Anatomic Study of the Quadrigeminal Cistern in Patients With 3-Dimensional Magnetic Resonance Cisternography

OBJECT

The aim of this study was to demonstrate the anatomy of the quadrigeminal cistern, define the anatomic landmarks, and measure the extension of the cistern in the living by using magnetic resonance (MR) cisternography with 3-dimensional reconstruction.

METHODS

The quadrigeminal cistern was examined in 38 patients. We focused on measurements of the superior, posterior, and lateral limits; the anterior and posterior maximal rostrocaudal diameter; the distance between the right and left superior colliculus and the right and left inferior colliculus; and the angle between the quadrigeminal plate and pineal gland.

RESULTS

The highest variability was observed for the posterior rostrocaudal diameter with a standard deviation of 3.1 and a range from 8 to 21.1 mm followed by the anterior-posterior diameter with a standard deviation of 2.8 and a range from 6.4 to 16.5 mm. In all cases the distance between the right and left superior colliculus (13.3 ± 1.8 mm; mean ± SD) was longer than the distance between the right and left inferior colliculus (11.4 ± 1.3 mm; mean ± SD). We classified 2 types of cisterns: closed cisterns with angles between the quadrigeminal plate and the pineal gland ranging from 39° to 63° and open cisterns with angles ranging from 63° to 76°. The analysis of variability by age and sex showed no significant differences.

CONCLUSIONS

The MR cisternography with 3-dimensional reconstruction was a simple and noninvasive tool providing detailed anatomic information in the living. It allowed measurement of the high variability of morphology of the quadrigeminal cistern. We defined the lateral landmarks and identified the lateral limit of the cistern. We classified the different shapes of the quadrigeminal cistern as open or closed cisterns. This can be helpful in the choice of the surgical approach to the lesions arising in this area.

OCCIPITAL TRANSTENTORIAL APPROACH TO THE PRECENTRAL CEREBELLAR FISSURE AND POSTERIOR INCISURAL SPACE

OBJECTIVE

To describe the surgical techniques and postoperative clinical outcomes with the occipital transtentorial (OT) approach in patients harboring lesions arising from the precentral cerebellar fissure, posterior incisural space, and adjoining structures.

METHODS

Twenty-two patients underwent microsurgical resection of intra-axial lesions arising within the precentral cerebellar fissure and posterior incisural space between 1997 and 2006. Patient demographics, presenting symptoms, pathology, and neurological outcomes were retrospectively reviewed. Pre- and postoperative magnetic resonance imaging scans were evaluated to determine the anatomic extensions of the lesion and the degree of surgical resection. Patients with lesions primarily confined to the pineal and posterior third ventricle approached by a supracerebellar infratentorial trajectory were excluded from this study.

RESULTS

Of the 22 patients reported in this series, 17 (77%) had contrast-enhancing lesions, and 5 (23%) had nonenhancing lesions arising from the precentral cerebellar fissure and posterior incisural space. The lesions were oriented dorsomedial to the midbrain and diencephalon in 6 patients (27%), dorsolateral in 14 patients (64%), and lateral in 2 patients (9%). A lateral OT approach directed under the occipitotemporal junction was used in 16 patients (73%), and an interhemispheric OT approach was used in 6 patients (27%). Transient visual field loss occurred in 3 patients (14%); it resolved by the third follow-up month. Gross total resection or near-total resection of the imaging-defined lesion volume was achieved in 19 patients (86%).

CONCLUSION

The OT approaches provide excellent exposure for lesions of the precentral cerebellar fissure, posterior incisural space, and adjacent structures. The lateral OT approach directed under the occipitotemporal junction provides an inline view for lesions situated posterolateral to the brainstem. It also provides an inferiorly directed view under the venous system into the precentral cerebellar fissure and fourth ventricular roof. Visual field deficits are minimized by directing the trajectory under the occipitotemporal junction instead of retracting along the interhemispheric corridor. The interhemispheric OT approach was primarily used for lesions extending superiorly, in the midline or near midline, above the tentorium and venous system into the splenium of corpus callosum, lateral ventricle, and posterior thalamus, where extensive lateral retraction was not required.

Comparative analysis of posterior approaches to the medial temporal region: supracerebellar transtentorial versus occipital transtentorial

OBJECTIVE

Cortical and subcortical lesions in the posterior portion of the medial temporal region (MTR) are routinely resected through the supracerebellar transtentorial (SCTT) or occipital transtentorial (OCTT) route. We compared the exposures provided by these 2 approaches to this region.

METHODS

Eight sides of injected cadaver heads were dissected using both approaches. Identical deep target points were collected for SCTT and OCTT routes while accepting variations in initial exposures. Data gathered with the P2-P3 junction as an apex created 2 adjoining triangles (anterior and posterior) in the middle and posterior MTR. Real, projected, and freedom areas were calculated for comparison.

RESULTS

The approach-related differences for the real and projected areas were expressed in relative values. There were no differences in the percentage of projected area between the 2 approaches (e.g., working in the middle of the opening, anterior triangle: SCTT, 5.2 +/- 4.1%; OCTT, 8.4 +/- 5.6%; P = 0.313; posterior triangle: SCTT, 8.6 +/- 3.8%; OCTT, 8.8 +/- 6.3%; P = 0.937). Freedom areas for the SCTT approach were smaller than those for the OCTT approach at many deep points (P < 0.05), except in the posterior margin of the MTR (P = 0.21).

CONCLUSION

The SCTT and OCTT approaches provided no differences in surgical views to the MTR. However, the OCTT approach provides a wider corridor for surgical manipulation compared with the SCTT approach in most parts of the MTR. These data may help neurosurgeons to select a favorable approach to specific lesions of the MTR.

DEPICTION OF SMALL VEINS DRAINING INTO THE VEIN OF GALEN USING PREOPERATIVE 3‐DIMENSIONAL NAVIGATION IN LIVING PATIENTS

OBJECTIVE

The purpose of this study was to delineate the anatomy of the precentral cerebellar vein, superior vermian vein, and internal occipital vein using reconstructions of computed tomographic and magnetic resonance imaging scans with navigation software. These data were compared with previous anatomic and angiographic findings to show the resolution and accuracy of the system.

METHODS

We retrospectively reviewed 100 patients with intracranial pathologies (50 computed tomographic scans with contrast and 50 magnetic resonance imaging scans with gadolinium) using a neuronavigation workstation for 3-dimensional reconstruction. Particular attention was paid to depiction of the precentral cerebellar vein, superior vermian vein, and internal occipital vein. The data were reviewed and analyzed.

RESULTS

The precentral cerebellar vein, superior vermian vein, and its tributary, the supraculminate vein, were depicted in 52 (52%) patients. The internal occipital vein was delineated on 99 (49.5%) sides and joined the basal vein and vein of Galen in 39 (39.4%) and 60 (60.6%) hemispheres, respectively. Comparing these results with previous angiographic studies, the ability of the neuronavigation system for depicting these vessels is similar to that of digital subtraction angiography.

CONCLUSION

This study illustrates the possibility of depicting the small vessels draining into the pineal region venous complex using 3-dimensional neuronavigation with an accuracy comparable to that of digital subtraction angiography. This tool provides important information for both surgical planning and intraoperative orientation.

Meningiomas of the falcotentorial junction: selection of the surgical approach according to the tumor type

BACKGROUND

We retrospectively analyzed a series of patients harboring a FT meningioma with regard to clinical presentation, surgical technique, and follow-up results.

METHODS

Clinical data in a consecutive series of 13 patients treated for a meningioma of the FT junction were retrospectively reviewed. Tumors were classified into 4 types according to their dural origin and tumor extent as depicted from preoperative MRI.

RESULTS

Main presenting symptom in 9 women and 4 men (mean age, 56 years) was headache (69%) and gait disturbance (54%). Clinical examination revealed gait ataxia in 62% of the patients. The tumor displaced the vein of Galen inferiorly in 6 patients, superiorly in 2, and medially in 5 cases. The main surgical approach to the meningioma was via an occipital interhemispheric route (10 patients). Additional resection of the falx and/or incision of the tentorium was performed in 6 cases each. A complete resection (Simpson grade 1 and 2) was achieved in 85% of patients. Permanent surgical morbidity was 23%. One tumor recurrence in an atypical meningioma was observed after the mean follow-up period of 6.2 years (range, 1-14 years) with clinical and MRI examination and had to be reoperated. Eighty-five percent of the patients regained full daily activity on follow-up.

CONCLUSIONS

The surgical approach should be tailored to the dural origin and extent of the tumor as depicted from preoperative MRI. Preservation of the straight sinus and Galenic venous system is recommended.

Identification of venous variants in the pineal region with 3D preoperative computed tomography and magnetic resonance imaging navigation

Object

The purpose of this study was to determine the ability of software-assisted 3D reconstruction performed using a neuronavigation system to delineate the anatomy and variation patterns of the pineal region venous complex, and then to compare these data with previous anatomical findings.

Methods

The authors retrospectively reviewed the neuroimages obtained in 100 patients with intracranial lesions (50 computed tomography [CT] scans obtained with contrast agents and 50 magnetic resonance [MR] images obtained with gadolinium) by using a neuronavigation workstation for 3D reconstruction. Particular attention was given to the internal cerebral vein, basal vein (BV), and the vein of Galen. The various connection patterns between the major vessels were classified and statistically analyzed.

Conclusions

The venous system of the pineal region shows a wide range of sex-related variations. In the female patient the absence of a BV (Type 0) is significantly more frequent than in the male. In this study the authors illustrate the ability to depict the venous drainage patterns in the pineal region for all cases studied by using 3D neuronavigation software without the need for additional examinations. This simple tool provides important information for surgical planning and may be of significant help intraoperatively.

Microsurgical approaches to the medial temporal region: an anatomical study

OBJECTIVE

To describe the surgical anatomy of the anterior, middle, and posterior portions of the medial temporal region and to present an anatomic-based classification of the approaches to this area.

METHODS

Twenty formalin-fixed, adult cadaveric specimens were studied. Ten brains provided measurements to compare different surgical strategies. Approaches were demonstrated using 10 silicon-injected cadaveric heads. Surgical cases were used to illustrate the results by the different approaches. Transverse lines at the level of the inferior choroidal point and quadrigeminal plate were used to divide the medial temporal region into anterior, middle, and posterior portions. Surgical approaches to the medial temporal region were classified into four groups: superior, lateral, basal, and medial, based on the surface of the lobe through which the approach was directed. The approaches through the medial group were subdivided further into an anterior approach, the transsylvian transcisternal approach, and two posterior approaches, the occipital interhemispheric and supracerebellar transtentorial approaches.

RESULTS

The anterior portion of the medial temporal region can be reached through the superior, lateral, and basal surfaces of the lobe and the anterior variant of the approach through the medial surface. The posterior group of approaches directed through the medial surface are useful for lesions located in the posterior portion. The middle part of the medial temporal region is the most challenging area to expose, where the approach must be tailored according to the nature of the lesion and its extension to other medial temporal areas.

CONCLUSION

Each approach to medial temporal lesions has technical or functional drawbacks that should be considered when selecting a surgical treatment for a given patient. Dividing the medial temporal region into smaller areas allows for a more precise analysis, not only of the expected anatomic relationships, but also of the possible choices for the safe resection of the lesion. The systematization used here also provides the basis for selection of a combination of approaches.

Posterior interhemispheric approach: surgical technique, application to vascular lesions, and benefits of gravity retraction

OBJECTIVE

To review an experience with the posterior interhemispheric approach applied to vascular lesions in the posterior midline, to examine the effects of patient position and gravity retraction of the occipital lobe, and to identify circumstances requiring increased exposure by sectioning the falx and tentorium.

METHODS

During a 6.5-year period, 46 posterior interhemispheric approaches were performed to treat 28 arteriovenous malformations, 10 dural arteriovenous fistulae, seven cavernous malformations, and one posterior cerebral artery aneurysm. Twenty-three patients were positioned prone and 23 patient were positioned laterally.

RESULTS

A standard posterior interhemispheric approach was used in 38 patients, and the occipital bitranstentorial/falcine approach was used in seven patients. A contralateral occipital transfalcine approach was used with one thalamic cavernous malformation. All lesions were resected completely and/or obliterated angiographically, with good neurological outcomes in 83% of patients and no operative mortality. Blood loss was lower, operative durations were shorter, postoperative cerebral edema was decreased, and visual outcomes were improved in patients positioned laterally.

CONCLUSION

The posterior interhemispheric approach, without additional dural cuts, is appropriate for most vascular lesions in the posterior midline. Gravity retracts the occipital lobes when patients are positioned laterally, enhancing operative exposure and reducing morbidity. Extension of the posterior interhemispheric approach to a transtentorial or transfalcine approach is required for falcotentorial dural arteriovenous fistulae and vein of Galen arteriovenous malformations, but is not usually necessary with cavernous malformations or other arteriovenous malformations.

Anatomical and quantitative description of the transcavernous approach to interpeduncular and prepontine cisterns. Technical note

OBJECT

The management of wide-necked, giant, or unsuccessfully coil-treated basilar apex aneurysms requires a wide exposure, for both working area and linear visualization of the basilar artery (BA). Cranial-based approaches, such as the transcavernous approach, have been proposed to deal with such aneurysms; whether abbreviated forms of this approach might provide similar exposure remains controversial. The authors examine this issue quantitatively.

METHODS

Four alcohol-preserved cadaveric heads injected with pigmented silicone were prepared for bilateral dissection. After completing an orbitozygomatic craniotomy, the surgeons worked in a reverse direction, performing the transcavernous approach in five steps: 1) posterior clinoidectomy; 2) cavernous sinus opening; 3) anterior clinoidectomy; 4) cutting of the distal dural ring; and 5) cutting of the proximal dural ring. Performing the complete transcavernous approach significantly increased the working area and linear exposure of the BA compared with abbreviated forms of the approach (p < 0.05). Opening the roof of the cavernous sinus significantly increased the working area compared with posterior clinoidectomy alone (p = 0.014); however, additional gains in exposure required completing the transcavernous approach. Resection of the anterior clinoid process combined with opening of only the distal dural ring did not significantly increase the working area or linear exposure of the BA.

CONCLUSIONS

The complete transcavernous approach significantly increases the working area and linear exposure of the BA compared with the more conservative forms of approach.

Endoscope-assisted infratentorial–supracerebellar approach to the third ventricle: an anatomical study

OBJECT

The authors studied the microsurgical anatomy and endoscopic features of the pineal region and third ventricle to describe a combined microsurgical-endoscopic infratentorial-supracerebellar approach to the posterior third ventricle. Such an approach exposes the pineal gland and its complex neurovascular structures so that the third ventricle can be reached through a minimally invasive parapineal incision.

METHODS

The approach was studied in 10 adult cadaveric heads, six fresh and four formalin fixed, by using an operative microscope with a magnification level of 6 to 40 and the assistance of an endoscope. The endoscope-assisted infratentorial-supracerebellar approach affords a complete view of the third ventricle from a posterior perspective. The third ventricle is entered through a parapineal incision using the natural space between the internal cerebral vein and the vein of Rosenthal located above the superior colliculi.

CONCLUSIONS

The infratentorial-supracerebellar approach to the third ventricle follows a natural corridor and requires minimal retraction and resection of critical neural structures. With the use of the endoscope, an unsurpassed view into the third ventricle from a posterior perspective is obtained.

Surgical approaches to the atrium of the lateral ventricle: microsurgical anatomy

BACKGROUND

Managing lesions situated in the atrium of the lateral ventricle remains a challenging neurosurgical problem. The purposes of this study were to examine the microsurgical anatomy of the atrium of the lateral ventricle and the optic radiation and to define the differences in the exposure obtained by various surgical approaches.

METHODS

Fifteen adult cadaveric specimens were studied using magnification x3 to x40 after perfusion of the arteries and veins with colored silicone. The microsurgical anatomy of the atrium of the lateral ventricle was examined. The relationship between the optic radiation and the atrium was studied using the white matter fiber dissection technique. Surgical approaches to the atrium of the lateral ventricle were examined in stepwise dissection.

RESULTS

The medial and inferior walls of the atrium were free from optic radiation fibers. Surgical approaches to the atrium of the lateral ventricle are divided into 3 routes: (1) anterior approach: transsylvian approach, (2) posterior approaches: posterior transcortical, posterior transcallosal, occipital, and supracerebellar transtentorial approaches, and (3) lateral approaches: transtemporal and subtemporal approaches.

CONCLUSION

Knowledge of the microsurgical anatomy of the atrium of the lateral ventricle and surrounding vital structures and the choice of an appropriate surgical approach will help surgeons perform safe and minimally invasive surgery.

Occipital bi-transtentorial/falcine approach for falcotentorial meningioma: case report

Lesions located in the bilateral posterior incisural space are difficult to treat due to limited exposure. The classical approaches to this area are limited for lesions located bilaterally and especially when the lesion extends also below the tentorium as it may occur with meningiomas. Kawashima et al. reported, in anatomic studies, a new occipital transtentorial approach: the occipital bi-transtentorial/falcine approach, to treat such lesions. We present a patient with a large falcotentorial meningioma, located bilaterally in the posterior incisural space. The occipital bi-transtentorial/falcine approach allowed an excellent surgical exposure and complete tumor removal with an excellent patient outcome.