A quantitative comparative surgical analysis of the endoscopic transorbital approach and frontotemporal-orbitozygomatic approach for extradural exposure of the cavernous sinus

OBJECTIVE

Recently, the endoscopic superior eyelid transorbital approach (SETA) has emerged as a potential alternative to access the cavernous sinus (CS). Several previous studies have attempted to quantitatively compare the traditional open anterolateral skull base approaches with transorbital exposure; however, these comparisons have been limited to the area of exposure provided by the bone opening and trajectory, and fail to account for the main avenues of exposure provided by subsequent requisite surgical maneuvers. The authors quantitatively compare the surgical access provided by the frontotemporal-orbitozygomatic (FTOZ) approach and the SETA following applicable periclinoid surgical maneuvers, evaluate the surgical exposure of key structures in each, and discuss optimal approach selection.

METHODS

SETA and FTOZ approaches were performed with subsequent applicable surgical maneuvers on 8 cadaveric heads. The lengths of exposure of cranial nerves (CNs) II-VI and the cavernous internal carotid artery; the areas of the space accessed within the supratrochlear, infratrochlear, and supramaxillary (anteromedial) triangles; the total area of exposure; and the angles of attack were measured and compared.

RESULTS

Exposure of the extradural CS was comparable between approaches, whereas access was significantly greater in the FTOZ approach compared with the SETA. The lengths of extradural exposure of CN III, V1, V2, and V3 were comparable between approaches. The FTOZ approach provided marginally increased exposure of CNs IV (20.9 ± 2.36 mm vs 13.4 ± 3.97 mm, p = 0.023) and VI (14.1 ± 2.44 mm vs 9.22 ± 3.45 mm, p = 0.066). The FTOZ also provided significantly larger vertical (44.5° ± 6.15° vs 18.4° ± 1.65°, p = 0.002) and horizontal (41.5° ± 5.40° vs 15.3° ± 5.06°, p < 0.001) angles of attack, and thus significantly greater surgical freedom, and provided significantly greater access to the supratrochlear (p = 0.021) and infratrochlear (p = 0.007) triangles, and significantly greater exposure of the cavernous internal carotid artery (17.2 ± 1.70 mm vs 8.05 ± 2.37 mm, p = 0.001). Total area of exposure was also significantly larger in the FTOZ, which provided wide access to the lateral wall of the CS as well as the possibility for intradural access.

CONCLUSIONS

This is the first study to quantitatively identify the relative advantages of the FTOZ and transorbital approaches at the target region following requisite surgical maneuvers. Understanding these data will aid in selecting an optimal approach and maneuver set based on target lesion size and location.

The complete anterior petrosectomy: an expanded extended-middle fossa approach with removal of the infratrigeminal petrous apex and drilling of the lateral clivus

Intradural exposure in the extended middle fossa anterior transpetrosal approach is traditionally limited to the inferior petrosal sinus inferomedially. Expanding bone removal of the petrous apex around the petrous internal carotid artery (ICA), underneath the trigeminal ganglion/mandibular nerve, and into the lateral component of the clivus can significantly expand the limits of this approach beyond the inferior petrosal sinus and allows for exposure of the midline structures, aspects of the contralateral inferior clival region, and, when high riding, the vertebrobasilar junction. To date, no descriptive techniques for drilling into the lateral clivus in this approach have been published. The authors provide a detailed stepwise description of their complete anterior petrosectomy, in use at their institution, that involves skeletonization of the posteromedial petrous ICA, gentle elevation of the trigeminal ganglion/mandibular nerve, removal of the infratrigeminal petrous apex, and two techniques for drilling into the lateral clivus along the petroclival fissure. These techniques provide a direct and unobstructed corridor to the midpetroclival region and ventral brainstem with greater maneuverability and enhanced control of the midline structures, which is especially useful for resection of petroclival meningiomas, chondrosarcomas, and giant vascular lesions of the mid- and upper basilar artery and its proximal branches.

Quantitative analysis of external carotid artery bypass donor vessels by recipient and approach

INTRODUCTION

Utilization an in-situ pedicle of the external carotid artery (ECA) as an arterial donor can allow for the successful augmentation or replacement of flow to a large vascular territory. We propose a mathematical model for quantitatively analyzing and grading the suitability of donor and recipient bypass vessels based on a set of anatomical and surgical variables in order to predict which pair has the greatest possibility for success. Using this method, we analyze all of the potential donor-recipient pairs for each ECA donor vessel-including the superficial temporal (STA), middle meningeal (MMA), and occipital (OA) arteries.

METHODS

The ECA pedicles were dissected in frontotemporal, middle fossa, subtemporal, retrosigmoid, far lateral, suboccipital, supracerebellar, and occipital transtentorial approaches. For each approach, every potential donor-recipient pair was identified, and donor length and diameter were measured as well as depth of field, angle of exposure, ease of proximal control, maneuverability, and length and diameter of the recipient segment. Anastomotic pair scores were determined by adding the weighted donor and recipient.

RESULTS

The best overall anastomotic pairs were OA-vertebral artery (V3, 17.1) and STA-insular (M2, 16.3) and STA-sylvian (M3, 15.9) segments of the middle cerebral artery. Other strong anastomotic combinations were OA- telovelotonsillar (15) and OA- tonsilomedullary (14.9) segments of the posterior inferior cerebellar artery, and MMA-lateral pontomesencephalic segment of the superior cerebellar artery (14.2).

CONCLUSIONS

This novel model for anastamotic pair scoring can serve as a useful clinical tool for selecting the optimal donor, recipient, and approach combination that can help facilitate a successful bypass.

Anterolateral Routes to the Skull Base—The Frontotemporal Approaches and Exposure of the Sellar and Parasellar Regions

Surgical approaches to the sellar and parasellar regions are highly challenging due to the densely packed nature of the traversing neurovasculature. The frontotemporal-orbitozygomatic approach offers a wide angle of exposure for the management of lesions involving the cavernous sinus, parasellar region, upper clivus, and adjacent neurovascular structures. It combines the pterional approach with different osteotomies that remove the superior and lateral walls of the orbit and zygomatic arch. Extradural exposure and preparation of the periclinoid region, whether as initial preparation for a combined intraextradural approach to deep-seated skull base targets or as the main avenue of surgical exposure, can substantially enlarge surgical corridors and minimize the need for brain retraction in this very confined microsurgical space. We provide a stepwise description of how we perform the fronto-orbitozygomatic approach and an associated series of surgical maneuvers and techniques that can be utilized in a variety of anterior and anterolateral approaches, either alone or in combination, to tailor exposure to a given lesion. These techniques are not limited to traditional skull base approaches and represent a valuable addition to every neurosurgeon's armamentarium as enhancements to common surgical approaches.

Posterolateral Routes to the Skull Base, Craniocervical Junction, and Jugular Foramen—The Far Lateral Transcondylar Approach and Combined Transpetrosal Transcervical Approaches

The far lateral approach provides wide surgical access to the lower third of the clivus, pontomedullary junction, and anterolateral foramen magnum and rarely requires craniovertebral fusion. The most common indications for this approach are posterior inferior cerebellar artery and vertebral arteryaneurysms, brainstem cavernous malformations, and tumors anterior to the lower pons and medulla, including meningiomas of the anterior foramen magnum, schwannomas of the lower cranial nerves, and intramedullary tumors at the craniocervical junction. We provide a stepwise description of how we perform the far lateral approach, as well as how to combine the far lateral approach with other skull base approaches, including the subtemporal transtentorial approach, for lesions involving the upper clivus; the posterior transpetrosal approach, for lesions involving the cerebellopontine angle and/or petroclival region; and/or lateral cervical approaches, for lesions involving the jugular foramen or carotid sheath regions.

Transpetrosal Routes to the Skull Base—Anterior and Posterior Transpetrosal Approaches

The extended middle fossa approach with anterior petrosectomy, or anterior transpetrosal approach, is a highly effective and direct approach to difficult-to-access petroclival tumors and basilar artery aneurysms. This surgical approach exposes a significant window of the posterior fossa dura between the mandibular nerve, internal auditory canal, and petrous internal carotid artery, below the level of the petrous ridge, and provides an unobstructed view of the middle fossa floor to the upper half of the clivus and petrous apex, without requiring removal of the zygoma. The posterior transpetrosal approaches, including the perilabyrinthine, translabyrinthine, and transcochlear approaches, provide direct and wide exposure of the cerebellopontine angle and posterior petroclival region. The translabyrinthine approach is commonly used for the removal of acoustic neuromas and other lesions of the cerebellopontine angle. We provide a stepwise description of how we perform these approaches and how to combine and extend them in order to achieve transtentorial exposure.

A novel 3D surgical neuroanatomy course for medical students: Outcomes from a pilot 6-week elective

BACKGROUND

Developing and maintaining a three-dimensional working knowledge of neuroanatomy is an essential skill in neurosurgery. However, conventional 2D head, neck, and neuroanatomy education is typically characterized by the separate rote learning of constituent tissues and often fails to provide learners with a contextual understanding of the relationships between these highly complex and interconnected structures. This can pose a significant challenge to medical students entering neurosurgery who lack a topographic understanding of intracranial anatomy.

METHODS

We report on the design and efficacy of a novel 6-part 3D surgical neuroanatomy pilot elective for medical students that utilized a navigation-based pedagogical technique with the goal of providing students with a framework for developing a 3D mental map of the skull base, neurovasculature, ventricular system, and associated brain regions. Students took on the perspective of physically traveling along the paths of key structures with a 360-degree view of surrounding anatomy such that they could appreciate the integration and relative spatial relationships of the varying tissues within the cranium. Mental navigation exercises and pre- and post-course surveys were used to assess students' baseline and learned familiarity with the different anatomical regions covered.

RESULTS

At the conclusion of the course, all students were able to successfully complete all of the multifaceted mental navigation exercises. Post-course survey data indicated that respondents perceived significant increases in their knowledge of cranial nerves; anterior, middle, and posterior skull base anatomy; anterior and posterior cranial circulation; and the ventricular system.

CONCLUSION

3D navigation-based fly-through instruction is a novel and effective technique for teaching complex anatomy and can provide learners with the foundational skills for developing and maintaining a 3D mental map of intracranial anatomy.

Anterior Clinoidal Meningiomas: Meningeal Anatomical Considerations and Surgical Implications

Objective: Surgical removal of anterior clinoidal meningiomas (ACMs) remains a challenge because of its complicated relationship with surrounding meninges, major arteries and cranial nerves. This study aims to define the meningeal structures around the anterior clinoid process (ACP) and its surgical implications.

Methods: Five dry skulls and 19 cadavers were used in the anatomical study. Cadavers were prepared as transverse, coronal, and sagittal plastinated sections, and the meningeal architecture around the ACP was studied with dissecting and confocal microscopies. The database of meningiomas in one single center was retrospectively reviewed, and the patients with ACMs were collected for clinical analysis.

Results: The superior, lateral, medial surfaces, and the tip of ACP were covered by different layers and types of meninges. The ACMs were classified into four main types based on the sites of origin, possible extending pathways following meningeal dura. In the retrospective cohort of 131 ACMs, the percentage of types I, IIa, IIb, III, and IV were 42.0% (55/131), 19.8% (26/131), 9.2% (12/131), 16.8% (22/131), and 12.2% (16/131), respectively. We found that types IIa and I had higher chances for achieving Simpson grade 1–2 resection (92.3 and 85.4%, respectively), followed by type III (54.5%) and type IV (31.3%), while type IIb showed little chance of Simpson grade 1–2 resection. Univariate and multivariate analyses revealed ACM classification and tumor size (<3 cm) to be independent risk factors for achieving more extensive resection.

Conclusion: The meningeal architecture around the ACP may guide and determine the origin and extension of ACMs. The classification based on the meningeal architecture helps to understand surgical anatomy as well as predicting surgical outcomes.

Surgical Management of Posterior Communicating Artery Aneurysms in the Presence of a Low-Coursing Internal Carotid Artery and Narrowed Retrocarotid Window

BACKGROUND

Anatomical variations of the course of the internal carotid artery (ICA) may complicate surgical clipping of posterior communicating artery (PCoA) aneurysms by narrowing the retrocarotid window. We evaluated the efficacy of the periclinoid surgical maneuvers for expanding the retrocarotid window and analyzed computed tomography angiography (CTA) data from patients with PCoA aneurysms to define parameters for low-coursing ICAs.

METHODS

Using cadaveric specimens, standard pterional craniotomies were fashioned and extradural or intradural periclinoid surgical maneuvers-cutting of the meningo-orbital band, anterior clinoidectomy, and cutting of the distal dural ring (DDR)-were performed, and their relative advantages for expanding the retrocarotid window were assessed. Additionally, preoperative CTA data from 24 patients with PCoA aneurysms used to calculate the angles of the ICA relative to the skull base.

RESULTS

Periclinoid maneuvers, especially the anterior clinoidectomy, provided additional exposure of the retrocarotid space. Cutting of the DDR allowed for partial mobilization of the ICA and widened the retrocarotid surgical window, enhancing maneuverability. The anterior clinoidectomy with cutting of the DDR allowed for enhanced exposure of the medial, middle, and posterolateral aspects of the retrocarotid space. Cutting the anterior petroclinoid fold and mobilizing cranial nerve III provided wide exposure of the lateral aspect of retrocarotid space.

CONCLUSION

When clipping PCoA aneurysms in the presence of normal-coursing ICAs (approximately ≥30° ICA angle), a standard pterional craniotomy with anterior clinoidectomy and cutting of the DDR allows for substantial expansion of the retrocarotid window.

Characteristics and management of hydrocephalus associated with vestibular schwannomas: a systematic review

Hydrocephalus (HC) can be associated with vestibular schwannoma (VS) at presentation. Although spontaneous resolution of HC after VS removal is reported, first-line treatment is varied including preoperative ventriculoperitoneal (VP) shunt, external ventricular drainage (EVD), or lumbar drainage (LD). We performed a systematic review to clarify optimal management of HC associated with VS at presentation, as well as characteristics of patients with initial and persistent HC after VS removal, and prevalence of HC associated with VS. Fourteen studies were included. Patients were grouped according to the timing of HC treatment. The overall rate of VP shunts was 19.4%. Among patients who received VS removal as first-line treatment, 6.9% underwent permanent shunts. In a subgroup of 132 patients (studies with no-aggregate data), t test analysis for mean tumor size (P = 0.02) and mean CSF protein level (P < 0.001) demonstrated statistically significant differences between patients with resolved HC (3.48 cm and 201 mg/dL) and patients with persistent HC (2.46 cm and 76.8 mg/dL) after VS resection. Transient treatment of HC using EVD or LD further resolved the HC in 87.5% and 82.9% of patients, respectively, before and after VS removal. The overall prevalence of HC associated with VS in a population of 2336 patients was 9.3%. Schwannoma removal as first-line treatment is justified by its low rate of persistent HC requiring VP shunt (roughly 7%). Patients with smaller VS and lower CSF proteins present higher risk of persistent HC after schwannoma removal. Temporary treatment of HC contributes to its resolution, both before and after VS removal.

On-Demand Intraoperative 3-Dimensional Printing of Custom Cranioplastic Prostheses

BACKGROUND

Currently, implantation of patient-specific cranial prostheses requires reoperation after a period for design and formulation by a third-party manufacturer. Recently, 3-dimensional (3D) printing via fused deposition modeling has demonstrated increased ease of use, rapid production time, and significantly reduced costs, enabling expanded potential for surgical application. Three-dimensional printing may allow neurosurgeons to remove bone, perform a rapid intraoperative scan of the opening, and 3D print custom cranioplastic prostheses during the remainder of the procedure.

OBJECTIVE

To evaluate the feasibility of using a commercially available 3D printer to develop and produce on-demand intraoperative patient-specific cranioplastic prostheses in real time and assess the associated costs, fabrication time, and technical difficulty.

METHODS

Five different craniectomies were each fashioned on 3 cadaveric specimens (6 sides) to sample regions with varying topography, size, thickness, curvature, and complexity. Computed tomography-based cranioplastic implants were designed, formulated, and implanted. Accuracy of development and fabrication, as well as implantation ability and fit, integration with exiting fixation devices, and incorporation of integrated seamless fixation plates were qualitatively evaluated.

RESULTS

All cranioprostheses were successfully designed and printed. Average time for design, from importation of scan data to initiation of printing, was 14.6 min and average print time for all cranioprostheses was 108.6 min.

CONCLUSION

On-demand 3D printing of cranial prostheses is a simple, feasible, inexpensive, and rapid solution that may help improve cosmetic outcomes; significantly reduce production time and cost-expanding availability; eliminate the need for reoperation in select cases, reducing morbidity; and has the potential to decrease perioperative complications including infection and resorption.

Developing a 3D composite training model for cranial remodeling

OBJECTIVE

Craniosynostosis correction, including cranial vault remodeling, fronto-orbital advancement (FOA), and endoscopic suturectomy, requires practical experience with complex anatomy and tools. The infrequent exposure to complex neurosurgical procedures such as these during residency limits extraoperative training. Lack of cadaveric teaching tools given the pediatric nature of synostosis compounds this challenge. The authors sought to create lifelike 3D printed models based on actual cases of craniosynostosis in infants and incorporate them into a practical course for endoscopic and open correction. The authors hypothesized that this training tool would increase extraoperative facility and familiarity with cranial vault reconstruction to better prepare surgeons for in vivo procedures.

METHODS

The authors utilized representative craniosynostosis patient scans to create 3D printed models of the calvaria, soft tissues, and cranial contents. Two annual courses implementing these models were held, and surveys were completed by participants (n = 18, 5 attending physicians, 4 fellows, 9 residents) on the day of the course. These participants were surveyed during the course and 1 year later to assess the impact of this training tool. A comparable cohort of trainees who did not participate in the course (n = 11) was also surveyed at the time of the 1-year follow-up to assess their preparation and confidence with performing craniosynostosis surgeries.

RESULTS

An iterative process using multiple materials and the various printing parameters was used to create representative models. Participants performed all major surgical steps, and we quantified the fidelity and utility of the model through surveys. All attendees reported that the model was a valuable training tool for open reconstruction (n = 18/18 [100%]) and endoscopic suturectomy (n = 17/18 [94%]). In the first year, 83% of course participants (n = 14/17) agreed or strongly agreed that the skin and bone materials were realistic and appropriately detailed; the second year, 100% (n = 16/16) agreed or strongly agreed that the skin material was realistic and appropriately detailed, and 88% (n = 14/16) agreed or strongly agreed that the bone material was realistic and appropriately detailed. All participants responded that they would use the models for their own personal training and the training of residents and fellows in their programs.

CONCLUSIONS

The authors have developed realistic 3D printed models of craniosynostosis including soft tissues that allow for surgical practice simulation. The use of these models in surgical simulation provides a level of preparedness that exceeds what currently exists through traditional resident training experience. Employing practical modules using such models as part of a standardized resident curriculum is a logical evolution in neurosurgical education and training.

On the Surgical Implications of Peritrigeminal Perforating Vessels in Microvascular Decompression

BACKGROUND

Perforating branches arising from the superior cerebellar artery (SCA) or anterior inferior cerebellar artery (AICA) that pierces the brainstem within 5 mm of the trigeminal root may limit offending vessel transposition during microvascular decompression for trigeminal neuralgia.

OBJECTIVE

To investigate the microsurgical anatomy of peritrigeminal perforators and evaluate their effect on the mobility of the SCA and AICA. Additionally, we propose strategies for mitigating the potential complications caused by the presence of short peritrigeminal perforators.

METHODS

Retrosigmoid approaches and exposure of the upper cerebellopontine angle were performed on 11 cadaveric heads (22 sides). The number, origin, and course of perforators were recorded and each was classified as either type I, short straight (<3 mm); type II, long straight perforators (>3 mm); or type III, long circumflex (>3 mm). Transposition of each SCA and AICA away from trigeminal nerve was performed, and degree of mobilization was evaluated and graded.

RESULTS

A total of 123 perforators were identified, of which 44 were considered peritrigeminal. Of these, 19 arose from the AICA, 18 from the SCA, and 7 from the basilar artery. Type I peritrigeminal perforators were the most common at 77.3%. Transposition or interposition of the parent vessel was not possible in 8 (47.1%) instances.

CONCLUSION

Identification of inhibiting perforators is essential before performing microvascular decompression to avoid ischemic injury to the brainstem. The presence of type I perforators may necessitate extensive arachnoid dissection and use of an interpositioning technique with minimal repositioning of the offending vessel.

Shunt-dependent hydrocephalus after aneurysmal subarachnoid hemorrhage

INTRODUCTION

Shunt-dependent hydrocephalus (SDHC) after aneurysmal subarachnoid hemorrhage (aSAH) is the occurrence of symptomatic ventriculomegaly requiring permanent shunt diversion. Although several studies investigated the predictors of SDHC, the role of many of these factors, as well as the prevalence of SDHC and patients' clinical outcome, remain a matter of controversy.

EVIDENCE ACQUISITION

According to PRISMA guidelines we performed a systematic search looking into four databases with the purpose of clarifying the prevalence of SDHC after aSAH, the predictors of SDHC, the mortality rate and clinical outcome of patients with and without SDHC.

EVIDENCE SYNTHESIS

Our analysis included 23 studies involving 22,264 patients. The overall prevalence of SDHC was 22.3% (95% CI: 17.9-26.6%). The predictors of SDHC included radiological hydrocephalus at presentation (OR 6.3, 95% CI: 2.27-17.51%), external ventricular drainage insertion (OR 5.7, 95% CI: 3.77-8.61%), high Hunt and Hess scale score (HHS 3-5: OR 3.3, 95% CI: 2.64-4.15%; HHS 4-5: OR 3.2, 95% CI: 2.4-4.2%), high Fisher grade (OR 3.1, 95% CI: 2.58-3.72%), intraventricular blood (OR 3.1, 95% CI: 2.60-3.71%), vasospasm (OR 1.9, 95% CI: 1.30-2.81%), intraparenchymal hemorrhage (OR 1.8, 95% CI: 1.2-2.78%), female gender (OR 1.3, 95% CI: 1.14-1.65%) and posterior circulation aneurysms (OR 1.4, 95% CI: 1.11-1.71%). The modality of aneurysm repair did not affect the rate of permanent shunt diversion. Patients with SDHC were more likely to be associated with a poor clinical outcome (mRS 3-6) (OR 4.3), even if mortality rate was similar between shunted and non-shunted patients (9%, 95% CI: 2-16% vs. 10.8%, 95% CI: 3.2-18.5%) (P=0.09).

CONCLUSIONS

The prevalence of SDHC is 22.3%. Our analysis identified several predictors of SDHC that can assist clinicians in monitoring patients with an aSAH. Shunt dependency is not related to the treatment modality of the ruptured aneurysm, whereas the occurrence of SDHC is a predictor of poor clinical outcome.

Preoperative identification of the initial burr hole site in retrosigmoid craniotomies: A teaching and technical note

BACKGROUND

When fashioning a retrosigmoid craniotomy, precise placement of the initial burr hole is crucial to avoid iatrogenic sinusal injury and to facilitate a corridor that allows for minimal cerebellar retraction.

METHODS

3D CT reconstructions of 16 cadaveric sides were used to identify and measure three discrete anatomical points. These three points and distances between them were plotted onto the surface of the skull using a digital caliper to identify the optimal burr hole location. This technique was subsequently applied in 20 clinical cases.

RESULTS

Optimal burr hole placement was achieved in 87.5% of specimens and, with minor refinement, 100% of clinical cases with no significant increase in operative time. Preoperative planning took an average of 10 minutes.

CONCLUSION

This technique for localizing the location of the initial retrosigmoid burr hole is a simple, safe, reliable, rapid, and inexpensive solution for surgeons who do not have regular access to neuronavigation.

The rectus capitis lateralis and the condylar triangle: important landmarks in posterior and lateral approaches to the jugular foramen

OBJECTIVE

The rectus capitis lateralis (RCL) is a small posterior cervical muscle that originates from the transverse process of C-1 and inserts onto the jugular process of the occipital bone. The authors describe the RCL and its anatomical relationships, and discuss its utility as a surgical landmark for safe exposure of the jugular foramen in extended or combined skull base approaches. In addition, the condylar triangle is defined as a landmark for localizing the vertebral artery (VA) and occipital condyle.

METHODS

Four cadaveric heads (8 sides) were used to perform far-lateral, extended far-lateral, combined transmastoid infralabyrinthine transcervical, and combined far-lateral transmastoid infralabyrinthine transcervical approaches to the jugular foramen. On each side, the RCL was dissected, and its musculoskeletal, vascular, and neural relationships were examined.

RESULTS

The RCL lies directly posterior to the internal jugular vein—only separated by the carotid sheath and in some cases cranial nerve (CN) XI. The occipital artery travels between the RCL and the posterior belly of the digastric muscle, and the VA passes medially to the RCL as it exits the C-1 foramen transversarium and courses posteriorly toward its dural entrance. CNs IX–XI exit the jugular foramen directly anterior to the RCL. To provide a landmark for identification of the occipital condyle and the extradural VA without exposure of the suboccipital triangle, the authors propose and define a condylar triangle that is formed by the RCL anteriorly, the superior oblique posteriorly, and the occipital bone superiorly.

CONCLUSIONS

The RCL is an important surgical landmark that allows for early identification of the critical neurovascular structures when approaching the jugular foramen, especially in the presence of anatomically displacing tumors. The condylar triangle is a novel and useful landmark for identifying the terminal segment of the hypoglossal canal as well as the superior aspect of the VA at its exit from the C-1 foramen transversarium, without performing a far-lateral exposure.

The role of alternative anastomosis sites in occipital artery–posterior inferior cerebellar artery bypass in the absence of the caudal loop using the far-lateral approach

OBJECTIVE

Occipital artery–posterior inferior cerebellar artery (OA-PICA) bypass is a technically challenging procedure for posterior fossa revascularization. The caudal loop of the PICA is considered the optimal site for OA-PICA anastomosis, however its absence can increase the technical difficulty associated with this procedure. The use of the far-lateral approach for accessing alternative anastomosis sites in OA-PICA bypass in patients with absent or unavailable caudal loops of PICA is evaluated.

METHODS

A morphometric analysis of OA-PICA bypass with anastomosis on each segment of the PICA was performed on 5 cadaveric specimens through the conventional midline foramen magnum and far-lateral approaches. The difficulty level associated with anastomoses at each segment was qualitatively assessed in each approach for exposure and maneuverability by multiple surgeons. A series of 8 patients who underwent OA-PICA bypass for hemodynamic ischemia or ruptured dissecting posterior fossa aneurysms are additionally reviewed and described, and the clinical significance of the caudal loop of PICA is discussed.

RESULTS

Anastomosis on the caudal loop could be performed more superficially than on any other segment (p < 0.001). A far-lateral approach up to the medial border of the posterior condylar canal provided a 13.5 ± 2.2–mm wider corridor than the conventional midline foramen magnum approach, facilitating access to alternative anastomosis sites. The far-lateral approach was successfully used for OA-PICA bypass in 3 clinical cases whose caudal loops were absent, whereas the midline foramen magnum approach provided sufficient exposure for caudal loop bypass in the remaining 5 cases.

CONCLUSIONS

The absence of the caudal loop of the PICA is a major contributing factor to the technical difficulty of OA-PICA bypass. The far-lateral approach is a useful surgical option for OA-PICA bypass when the caudal loop of the PICA is unavailable.

Selective Patch Angioplasty and Intraoperative Shunting in Carotid Endarterectomy: A Single-Center Review of 141 Procedures

Objective: Open surgical treatment of carotid artery stenosis, namely, carotid endarterectomy (CEA), has evolved since its inception in 1953. Despite improvements in the treatment of carotid occlusive disease through technological and surgical innovations, the use of patch grafting in CEA’s remains controversial. We evaluate the durability of the primary closure and the safety of selective shunting during carotid endarterectomy (CEA) as determined by intraoperative EEG and postoperative outcomes.

Methods: A consecutive series of CEA’s performed by the senior author at a single academic medical center from 2001 to 2012 were reviewed. All cases were performed under continuous intraoperative electroencephalography (EEG). Patch angioplasty was used in cases where there was tortuosity of the vessel within the region of the endarterectomy and narrow vessel diameter at the distal end of the arteriotomy. Shunting was used when intraoperative EEG showed a > 50% reduction in a waveform in any lead. Patients were evaluated for restenosis via imaging or ultrasound at six months and subsequently annual follow-up.

Results: One hundred and forty-one CEA’s were performed on 132 (76 male, 56 female) patients with an average age of 71 years (range: 40–95 years). Four (3%) cases required patch angioplasty and three (2%) required intraoperative shunts. The cross-clamp time ranged from 22 to 74 minutes, and the duration increased with the use of shunts and patches. Complications were rare and included recurrent stenosis (n=2), postoperative transient ischemic attack (n=1), ischemic stroke in (n=1), temporary hypoglossal nerve weakness (n=2), temporary marginal mandibular nerve weakness (n=6), and neck hematoma (n=1).

Conclusion: Intraoperative EEG data suggests that primary closure and selective shunting in CEA can result in outcomes comparable with routine patch angioplasty and shunting.

A 3D endoscopic transtubular transcallosal approach to the third ventricle

OBJECT

Surgical approaches to deep-seated brain pathologies, specifically lesions of the third ventricle, have always been a challenge for neurosurgeons. In certain cases, the transcallosal approach remains the most suitable option for targeting lesions of the third ventricle, although retraction of the fornices and wall of the third ventricle have been associated with neuropsychological and hypothalamic deficits. The authors investigated the feasibility of an interhemispheric 3D endoscopic transcallosal approach through a minimally invasive tubular retractor system for the management of third ventricular lesions.

METHODS

Three-dimensional endoscopic transtubular transcallosal approaches were performed on 5 preserved cadaveric heads (10 sides). A parasagittal bur hole was placed using neuronavigation, and a tubular retractor was inserted under direct endoscopic visualization. Following observation of the vascular structures, fenestration of the corpus callosum was performed and the retractor was advanced through the opening. Transforaminal, interforniceal, and transchoroidal modifications were all performed and evaluated by 3 surgeons.

RESULTS

This approach provided enhanced visualization of the third ventricle and more stable retraction of corpus callosum and fornices. Bayonetted instruments were used through the retractor without difficulty, and the retractor applied rigid, constant, and equally distributed pressure on the corpus callosum.

CONCLUSIONS

A transtubular approach to the third ventricle is feasible and facilitates blunt dissection of the corpus callosum that may minimize retraction injury. This technique also provides an added degree of safety by limiting the free range of instrumental movement. The combination of 3D endoscopic visualization with a clear plastic retractor facilitates safe and direct monitoring of the surgical corridor.

Optic Nerve Decompression through a Supraorbital Approach

Objective We propose a stepwise decompression of the optic nerve (ON) through a supraorbital minicraniotomy and describe the surgical anatomy of the ON as seen through this approach. We also discuss the clinical applications of this approach. Methods Supraorbital approaches were performed on 10 preserved cadaveric heads (20 sides). First, 3.5-cm skin incisions were made along the supraciliary arch from the medial third of the orbit and extended laterally. A 2 × 3-cm bone flap was fashioned and extradural dissections were completed. A 180-degree unroofing of the ON was achieved, and the length and width of the proximal and distal portions of the optic canal (OC) were measured. Results The supraorbital minicraniotomy allowed for identification of the anterior clinoid process and other surgical landmarks and adequate drilling of the roof of the OC with a comfortable working angle. A 25-degree contralateral head rotation facilitated visualization of the ON. Conclusion The supraorbital approach is a minimally invasive and cosmetically favorable alternative to more extended approaches with longer operative times used for the management of ON decompression in posttraumatic or compressive optic neuropathy from skull base pathologies extending into the OC. The relative ease of this approach provides a relatively short learning curve for developing neurosurgeons.

Expanding the borders: the evolution of neurosurgical approaches

In this article the authors discuss the development of neurosurgical approaches and the advances in science and technology that influenced this development throughout history. They provide a broad overview of this interesting topic from the first attempts of trephination by ancient cultures to the work of the pioneers of neurosurgery and the introduction of microsurgery.

The Pterional Port in Dual-Port Endoscopy: A 2D and 3D Cadaveric Study

Objective We propose a novel dual-port endonasal and pterional endoscopic approach targeting midline lesions of the anterior cranial fossa with lateral extension beyond the optic nerve. Methods Ten dual-port approaches were performed on five cadaveric heads. All specimens underwent an endoscopic transtuberculum/transplanum approach followed by placement of a pterional port. The endonasal port was combined with an endoscopic extradural pterional keyhole craniectomy. The pterional port was placed at the intersection of the sphenoparietal and coronal sutures. The extradural space was explored using two-dimensional and three-dimensional endoscopes. Results The superolateral access provided by the pterional port may improve the ability to achieve a gross total resection of tumors with lateral extensions. The complete opening of the optic canal achieved through the dual-port approach may enable resection of the intracanalicular portion of a tumor, a crucial step in improvement of visual function and reduction of tumor recurrence. Conclusion The pterional port may enhance control of midline anterior skull base lesions with lateral extension beyond the optic nerve and optic canal. Dual-port endoscopy maintains minimally invasiveness and dramatically increases the working limits and control of anatomical structures well beyond what is attainable through single-port neuroendoscopy.

Evolution of cranial epilepsy surgery complication rates: a 32-year systematic review and meta-analysis

Object

Surgical interventions for medically refractory epilepsy are effective in selected patients, but they are underutilized. There remains a lack of pooled data on complication rates and their changes over a period of multiple decades. The authors performed a systematic review and meta-analysis of reported complications from intracranial epilepsy surgery from 1980 to 2012.

Methods

A literature search was performed to find articles published between 1980 and 2012 that contained at least 2 patients. Patients were divided into 3 groups depending on the procedure they underwent: A) temporal lobectomy with or without amygdalohippocampectomy, B) extratemporal lobar or multilobar resections, or C) invasive electrode placement. Articles were divided into 2 time periods, 1980–1995 and 1996–2012.

Results

Sixty-one articles with a total of 5623 patients met the study's eligibility criteria. Based on the 2 time periods, neurological deficits decreased dramatically from 41.8% to 5.2% in Group A and from 30.2% to 19.5% in Group B. Persistent neurological deficits in these 2 groups decreased from 9.7% to 0.8% and from 9.0% to 3.2%, respectively. Wound infections/meningitis decreased from 2.5% to 1.1% in Group A and from 5.3% to 1.9% in Group B. Persistent neurological deficits were uncommon in Group C, although wound infections/meningitis and hemorrhage/hematoma increased over time from 2.3% to 4.3% and from 1.9% to 4.2%, respectively. These complication rates are additive in patients undergoing implantation followed by resection.

Conclusions

Complication rates have decreased dramatically over the last 30 years, particularly for temporal lobectomy, but they remain an unavoidable consequence of epilepsy surgery. Permanent neurological deficits are rare following epilepsy surgery compared with the long-term risks of intractable epilepsy.

Interhemispheric Endoscopic Fenestration of the Lamina Terminalis through a Single Frontal Burr Hole

Objective We evaluate the feasibility and safety of performing a novel interhemispheric endoscopic fenestration of the lamina terminalis (IEFLT) through a single frontal burr hole immediately lateral to the superior sagittal sinus. Methods Five cadaveric heads underwent IEFLT. Sequential burr holes were made beginning above the glabella and progressed cranially to caudally until the frontal sinus. An endoscope was inserted, and interhemispheric dissection of the arachnoid membranes was completed with endoscopic instruments in a straight direction from the point of entry to the lamina terminalis (LT). Angled optics (0 and 30 degrees) were used to study the neurovascular structures and surgical landmarks. Results The IEFLTs were successfully completed in all specimens and allowed for good visualization of the inferior portion of the LT. The arachnoid dissections were achieved uneventfully. The endoscope provided good surface control of the LT and excellent stereoscopic visualization of the neurovascular complexes. Improved circumferential visualization of the superior part of the anterior portion of the third ventricle was attained. Conclusion IEFLT is a potential alternative to the classic endoscopic third ventriculostomy and a simpler alternative to the subfrontal EFLT, although surgical maneuverability is still limited due to the size of the probe in relation to the narrow surgical corridor.

Dual-Port 2D and 3D Endoscopy: Expanding the Limits of the Endonasal Approaches to Midline Skull Base Lesions with Lateral Extension

Objective To investigate a novel dual-port endonasal and subtemporal endoscopic approach targeting midline lesions with lateral extension beyond the intracavernous carotid artery anteriorly and the Dorello canal posteriorly. Methods Ten dual-port approaches were performed on five cadaveric heads. All specimens underwent an endoscopic endonasal approach from the sella to middle clivus. The endonasal port was combined with an anterior or posterior endoscopic extradural subtemporal approach. The anterior subtemporal port was placed directly above the middle third of the zygomatic arch, and the posterior port was placed at its posterior root. The extradural space was explored using two-dimensional and three-dimensional endoscopes. Results The anterior subtemporal port complemented the endonasal port with direct access to the Meckel cave, lateral sphenoid sinus, superior orbital fissure, and lateral and posterosuperior compartments of the cavernous sinus; the posterior subtemporal port enhanced access to the petrous apex. Endoscopic dissection and instrument maneuverability were feasible and performed without difficulty in both the anterior and posterior subtemporal ports. Conclusion The anterior and posterior subtemporal ports enhanced exposure and control of the region lateral to the carotid artery and Dorello canal. Dual-port neuroendoscopy is still minimally invasive yet dramatically increases surgical maneuverability while enhancing visualization and control of anatomical structures.

The intracranial facial nerve as seen through different surgical windows: an extensive anatomosurgical study

BACKGROUND

The facial nerve has a short intracranial course but crosses critical and frequently accessed surgical structures during cranial base surgery. When performing approaches to complex intracranial regions, it is essential to understand the nerve's conventional and topographic anatomy from different surgical perspectives as well as its relationship with surrounding structures.

OBJECTIVE

To describe the entire intracranial course of the facial nerve as observed via different neurosurgical approaches and to provide an analytical evaluation of the degree of nerve exposure achieved with each approach.

METHODS

Anterior petrosectomies (middle fossa, extended middle fossa), posterior petrosectomies (translabyrinthine, retrolabyrinthine, transcochlear), a retrosigmoid, a far lateral, and anterior transfacial (extended maxillectomy, mandibular swing) approaches were performed on 10 adult cadaveric heads (20 sides). The degree of facial nerve exposure achieved per segment for each approach was assessed and graded independently by 3 surgeons.

RESULTS

The anterior petrosal approaches offered good visualization of the nerve in the cerebellopontine angle and intracanalicular portion superiorly, whereas the posterior petrosectomies provided more direct visualization without the need for cerebellar retraction. The far lateral approach exposed part of the posterior and the entire inferior quadrants, whereas the retrosigmoid approach exposed parts of the superior and inferior quadrants and the entire posterior quadrant. Anterior and anteroinferior exposure of the facial nerve was achieved via the transfacial approaches.

CONCLUSION

The surgical route used must rely on the size, nature, and general location of the lesion, as well as on the capability of the particular approach to better expose the appropriate segment of the facial nerve.

The Meningo-Orbital Band: Microsurgical Anatomy and Surgical Detachment of the Membranous Structures through a Frontotemporal Craniotomy with Removal of the Anterior Clinoid Process

Objective To describe the microanatomy of the meningo-orbital band (MOB) and its associated membranes, and propose a stepwise method for their detachment while minimizing potential complications. Design Cadaveric and prospective clinical. Setting Microneurosurgery Skull Base Laboratory, Weill Cornell Medical College (New York, NY) and Shiroyama Hospital (Osaka, Japan). Participants Five preserved cadaveric heads (10 sides) and five patients requiring surgical detachment of the MOB in 2012. Results MOB detachment and subsequent extradural anterior clinoidectomies were successfully performed on five clinical cases. Detachment of the MOB was accomplished using a four-step dissection based on the structure's detailed microanatomy and included (1) partial removal of the lateral wall of the superior orbital fissure, (2) incising of the lateral periosteal dura of the superior orbital fissure, (3) peeling off the dura propria of the temporal lobe from the inner cavernous membrane, and (4) fully detaching the exposed MOB from the periorbita. Conclusion Understanding the complex microanatomy of these structures enabled a safe and effective stepwise detachment of the MOB. We recommend that surgeons possess sufficient anatomical knowledge before surgically manipulating this structure.