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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Jugular Foramen Tumors: Surgical Strategies and Representative Cases

(1) Background: Jugular foramen tumors are complex lesions due to their relationship with critical neurovascular structures within the skull base. It is necessary to have a deep knowledge of the anatomy of the jugular foramen and its surroundings to understand each type of tumor growth pattern and how it is related to the surrounding neurovascular structures. This scope aims to provide a guide with the primary surgical approaches to the jugular foramen and familiarize the neurosurgeons with the anatomy of the region. (2) Methods and (3) Results: A comprehensive description of the surgical approaches to jugular foramen tumors is summarized and representative cases for each tumor type is showcased. (4) Conclusions: Each case should be carefully assessed to find the most suitable approach for the patient, allowing the surgeon to remove the tumor with minimal neurovascular damage. The combined transmastoid retro- and infralabyrinthine transjugular transcondylar transtubercular high cervical approach can be performed in a stepwise fashion for the resection of complex jugular foramen tumors.

Arteriovenous malformation with unique drainage through the emissary vein of the foramen ovale: illustrative case

BACKGROUND

As part of the laterotrigeminal venous system (LTVS), the emissary vein of the foramen ovale (EVFO) is an underrecognized venous structure communicating between the cavernous sinus and pterygoid plexus. The sphenobasal sinus is an anatomical variation of the sphenoparietal sinus that drains directly into the EVFO. The authors present the case of a ruptured arteriovenous malformation (AVM) with a unique drainage pattern through the sphenobasal sinus and EVFO.

OBSERVATIONS

A 9-year-old female initially presented with loss of consciousness and was subsequently found to have a ruptured AVM in the left basal frontal area. She underwent an immediate decompressive hemicraniectomy, with a computed tomography angiogram demonstrating a unique anatomical variation in which the sphenobasal sinus communicated with the EVFO and LTVS. The final venous drainage returned to the pterygoid plexus and external jugular vein. Postoperatively, the patient made a substantial recovery, with generalized right-sided weakness remaining as the sole deficit.

LESSONS

The authors present the case of a ruptured AVM with unique venous drainage into the sphenobasal sinus and EVFO, for which the current literature remains limited. As exemplified by this illustrative case, technique modification may be warranted in the setting of this unique anatomical variation to avoid venous sinus injury.

Artery of Uchimura: origin and evolution of identification of the vascular supply to the hippocampus

In 1928, neuroscientist Yushi Uchimura (1897-1980) published a landmark study detailing the hippocampal vasculature. Working in Walther Spielmeyer's Munich laboratory (1925-1927), Uchimura sought evidence for a vascular theory of Ammon's horn sclerosis (AHS). He described an artery supplying the vulnerable sector of the hippocampus, where pathognomonic changes of AHS were noted, and characterized the artery as particularly susceptible to circulatory disturbances. Discovery of this artery led to new concepts and new terminology pertaining to the hippocampus. In addition to having a distinguished career in psychiatry and academia (including a position as University of Tokyo dean), Uchimura was, before attending medical school, one of Japan's best baseball pitchers; he was eventually named Nippon Professional Baseball Organization commissioner and inducted into the Japan Baseball Hall of Fame. Uchimura's description of hippocampal vasculature, which is still subject to debate after nearly a century, brought international attention to AHS and epilepsy and showed the hippocampal vasculature to be variable and vulnerable; important considerations for later neurosurgeons in the development of selective mesial temporal surgery. Prominent figures in neurosurgery have since developed classification systems for the hippocampal vasculature in which the artery of Uchimura remains central. Perhaps no other brain artery has been the nexus for such intense investigation and debate about its association to structure, function, disease, and treatment methodology.

Do overlapping neurosurgical procedures affect patient outcomes? A systematic review and meta-analysis

Overlapping surgery (OS) is a common practice in neurosurgery that has recently come under scrutiny. This study includes a systematic review and meta-analysis on articles evaluating the effects of OS on patient outcomes. PubMed and Scopus were searched for studies that analyzed outcome differences between overlapping and non-overlapping neurosurgical procedures. Study characteristics were extracted, and random-effects meta-analyses were performed to analyze the primary outcome (mortality) and secondary outcomes (complications, 30-day readmissions, 30-day operating room returns, home discharge, blood loss, and length of stay). Mantel-Haenszel tests were completed for binary outcomes, whereas the inverse variance tests were conducted for continuous outcomes. Heterogeneity was measured using the I² and X² tests. The Egger's test was conducted to evaluate publication bias. Eight of 61 non-duplicate studies were included. Overall, 21,249 patients underwent non-OS (10,504 female) and 15,863 patients underwent OS (8393 female). OS was associated with decreased mortality (p = 0.002), 30-day returns to OR (p < 0.001), and blood loss (p < 0.001) along with increased home discharges (p < 0.001). High heterogeneity was observed for home discharge (p = 0.002) and length of stay (p < 0.001). No publication bias was observed. OS was not associated with worse patient outcomes compared to non-OS. However, considering multiple sources of limitation in the methodology of the included studies (such as limited number of studies, reports originating from mostly high-volume academic centers, discrepancy in the definition of "critical portion(s)" of the surgery across studies, and selection bias), extra caution is advised in interpretation of our results and further focused studies are warranted.

Surgical Outcomes of Awake Craniotomy for Treatment of Arteriovenous Malformations in Eloquent Cortex: A Systematic Review

OBJECTIVE

Arteriovenous malformations (AVM) located in eloquent brain regions are historically associated with a poor prognosis. Awake craniotomy (AC) with the adjunct of brain mapping has the potential of identifying non-eloquent gyri to maximize resection, thereby theoretically decreasing the risk of neurologic deficits. With limited evidence regarding the efficacy of AC in treatment of eloquent AVMs, this review aims to investigate its surgical outcomes.

METHODS

A systematic search in the PubMed database was performed to identify all relevant studies up to February 2022.

RESULTS

13 studies were extracted for quantitative analysis, yielding a total of 46 patients. The mean age was 34.1 years, and most patients were female (54.8%). Seizures were the most frequently reported presenting symptom (41%, 19/46 cases). Spetzler-Martin Grade III was the most prevalent (45.9%, 17 cases) with a mean nidus size of 32.6 mm. Seventy-four percent of AVMs were located on the left-side, with the frontal lobe being the most common location (30%, 14/46 cases). The most common eloquent regions were language (47.8%, 22/46 cases), motor (17.4%, 8/46 cases), and language + motor cortices (13.1%, 6/46 cases). Complete resection of AVM was achieved in 41 patients (89%). Intraoperative complications occurred in 14/46 cases (30.4%) with transient postoperative neurologic deficits in 14 patients (30.4%).

CONCLUSION

AC may enable precise microsurgical excision of eloquent AVMs with preservation of critical brain functions. Risk factors for poor outcomes include eloquent AVMs located in the language + motor regions and the occurrence of intraoperative complications such as seizures/hemorrhage.

Comprehensive microsurgical anatomy of the middle cranial fossa: Part II-neurovascular anatomy

In order to master the surgical approaches to the middle cranial fossa, the surgeon needs to understand the relevant bony anatomy. However, she/he also needs to have a clear and sound understanding of the neural and vascular anatomy because, oftentimes, the osseous anatomy (except for the optic apparatus) should be removed to expose and protect the neurovascular anatomy. This is the second of a two-part article discussing the neurovascular anatomy of the middle cranial fossa. A brief discussion of the surgical approaches follows.

Comprehensive microsurgical anatomy of the middle cranial fossa: Part I-Osseous and meningeal anatomy

The middle cranial fossa is one of the most complex regions in neurosurgery and otolaryngology-in fact, the practice of skull base surgery originated from the need to treat pathologies in this region. Additionally, great neurosurgeons of our present and past are remembered for their unique methods of treating diseases in the middle fossa. The following article reviews the surgical anatomy of the middle fossa. The review is divided into the anatomy of the bones, dura, vasculature, and nerves-in two parts. Emphasis is paid to their neurosurgical significance and applications in skull base surgery. Part I focuses on the bony and dural anatomy.

Nervus intermedius: Microsurgical and anatomic relationships to the cerebellopontine angle neurovascular complex

Background

The nervus intermedius (NI) comprises fibers originating from the trigeminal, superior salivary, and solitary tract nuclei, which join the facial nerve (cranial nerve [CN] VII). Neighboring structures include the vestibulocochlear nerve (CN VIII), the anterior inferior cerebellar artery (AICA), and its branches. Microsurgical procedures at the cerebellopontine angle (CPA) benefit from understanding NI anatomy and relationships, especially for the microsurgical treatment of geniculate neuralgia, where the NI is transected. This study sought to characterize common relationships between the NI rootlets, CN VII, CN VIII, and the meatal loop of AICA at the internal auditory canal (IAC).

Methods

Seventeen cadaveric heads underwent retrosigmoid craniectomy. Following complete unroofing of the IAC, the NI rootlets were individually exposed to identify their origins and insertion points. The AICA and its meatal loop were traced to assess their relationship with the NI rootlets.

Results

Thirty-three NIs were identified. The median number of NI rootlets was 4 per NI (interquartile range, 3-5). The rootlets mainly originated from the proximal premeatal segment of CN VIII (81 of 141, 57%) and inserted onto CN VII at the IAC fundus (89 of 141, 63%). When crossing the acoustic-facial bundle, the AICA most frequently passed between the NI and CN VIII (14 of 33, 42%). Five composite patterns of neurovascular relationships were identified regarding NI.

Conclusion

Although certain anatomical trends can be identified, the NI has a variable relationship with the adjacent neurovascular complex at the IAC. Therefore, anatomical relationships should not be used as the sole method of NI identification during CPA surgery.

Endoscopic-assisted combined transcrusal anterior petrosal approach for resection of large petroclival meningioma: operative video and nuances of technique

In this illustrative video, the authors demonstrate an endoscopic-assisted combined transcrusal anterior petrosal approach for resection of a large petroclival meningioma with significant brainstem compression involving Meckel’s cave. This unique petrosal variant provides increased petroclival exposure that can potentially preserve hearing by combining a transcrusal labyrinthectomy with anterior petrosectomy (Kawase’s approach). The advantages include multidirectional angles of attack to the brainstem and petroclival region without cerebellar retraction. Endoscopic assistance allows expanded visualization into deep surgical corridors. The surgery was performed in a two-stage fashion, and a near-total resection was achieved with cranial nerve and hearing preservation. The operative nuances are demonstrated.

The video can be found here: https://stream.cadmore.media/r10.3171/2022.1.FOCVID21257

Retrosigmoid approach for giant cystic vestibular schwannoma: subperineural dissection technique for facial nerve preservation

In this illustrative video, the authors demonstrate retrosigmoid resection of a giant cystic vestibular schwannoma using the subperineural dissection technique to preserve facial nerve function. This thin layer of perineurium arising from the vestibular nerves is used as a protective buffer to shield the facial and cochlear nerves from direct microdissection trauma. A near-total resection was achieved, and the patient had an immediate postoperative House-Brackmann grade I facial nerve function. The operative nuances and pearls of technique for safe cranial nerve and brainstem dissection, as well as the intraoperative decision and technique to leave the least amount of residual adherent tumor, are demonstrated.

The video can be found here: https://stream.cadmore.media/r10.3171/2021.7.FOCVID21128

The Vascularized Occipital Fascial Flap (OFF): A Novel Reconstructive Technique for Posterior Fossa Surgery

BACKGROUND

Posterior fossa surgery is particularly prone to cerebrospinal fluid (CSF) leakage. Several methods have been introduced to address and/or prevent this complication. However, to the best of our knowledge, the use of a vascularized fascial flap based on the occipital artery for the purpose of reconstruction has not been reported. We introduce the occipital fascial flap (OFF) for reconstruction of a craniectomy defect after the retrosigmoid approach.

METHODS

A 57-year-old woman with a large cerebellar metastasis underwent gross total resection of the mass followed by reconstruction of the craniectomy defect using OFF.

RESULTS

Postoperative imaging showed flap viability and no CSF leak occurred during follow-up.

CONCLUSIONS

We report the first use of OFF for reconstruction of a craniectomy defect in a retrosigmoid approach. The vascularized fascial flap in posterior fossa surgery is a potentially helpful technique to reduce the risk of CSF leak in high-risk patients.

Coding cerebral bypasses: a proposed nomenclature to better describe bypass constructs and revascularization techniques

OBJECTIVE

Bypass surgery has evolved into a complex surgical art with a variety of donor arteries, recipient arteries, interpositional grafts, anastomoses, and suturing techniques. Although innovation in contemporary bypasses has increased, the literal descriptions of these new bypasses have not kept pace. The existing nomenclature that joins donor and recipient arteries with a hyphen is simplistic, underinformative, and in need of improvement. This article proposes a nomenclature that systematically incorporates anatomical and technical details with alphanumeric abbreviations and is a clear, concise, and practical "code" for bypass surgery.

METHODS

Detailed descriptions and illustrations of the proposed nomenclature, which consists of abbreviations for donor and recipient arteries, arterial segments, arteriotomies, and sides (left or right), with hyphens and parentheses to denote the arteriotomies joined in the anastomosis and brackets and other symbols for combination bypasses, are presented. The literature was searched for articles describing bypasses, and descriptive nomenclature was categorized as donor and recipient arteries (donor-recipient), donor-recipient with additional details, less detail than donor-recipient, and complete, ambiguous, or descriptive text.

RESULTS

In 483 publications, most bypass descriptions were categorized as donor-recipient (335, 69%), with superficial temporal artery-middle cerebral artery bypass described most frequently (299, 62%). Ninety-seven articles (20%) used donor-recipient descriptions with additional details, 45 (9%) were categorized as ambiguous, and none contained a complete bypass description. The authors found the proposed nomenclature to be easily applicable to the more complex bypasses reported in the literature.

CONCLUSIONS

The authors propose a comprehensive nomenclature based on segmental anatomy and additional anastomotic details that allows bypasses to be coded simply, succinctly, and accurately. This alphanumeric shorthand allows greater precision in describing bypasses and clarifying technical details, which may improve reporting in the literature and thus help to advance the field of bypass surgery.

Combined Petrosal Approach for Resection of a Large Trigeminal Schwannoma With Meckel's Cave Involvement-Part II: Microsurgical Approach and Tumor Resection: 2-Dimensional Operative Video

This video is the second part of a 2-part video presentation demonstrating the microsurgical technique of a combined petrosal approach for resection of a large trigeminal schwannoma in a 54-yr-old woman involving multiple cranial fossae extending anteriorly into Meckel's cave. The patient presented with long-standing worsening headache and facial tingling and numbness. After discussing the benefits and risks of the surgery as well as the alternative management strategies, the patient decided to proceed with surgery and informed consent was obtained. The surgery was performed in a single stage. The technical nuances of anterior and posterior (retrolabyrinthine) petrosectomy are demonstrated and discussed. Microsurgical resection of the tumor is also demonstrated emphasizing the important steps of dural opening, arachnoid dissection, identification and preservation of cranial nerves, and exploration of Meckel's cave. Use of endoscopic-assistance for visualization of the cerebellopontine angle and neurovascular structures is also demonstrated.  Table in video reprinted by permission from Copyright Clearance Center: Springer Nature, Acta Neurochirurgica, Frontotemporal epidural approach to trigeminal neurinomas, Dolenc VV, Copyright 1994.

The Glossopharyngo-Cochlear Triangle-Part II: Case Series Highlighting the Clinical Application to High-Riding Posterior Inferior Cerebellar Artery Aneurysms Exposed Through the Extended Retrosigmoid Approach

BACKGROUND

Use of the far lateral transcondylar (FL) approach and vagoaccessory triangle is the standard exposure for clipping most posterior inferior cerebellar artery (PICA) aneurysms. However, a distal PICA origin or high-lying vertebrobasilar junction can position the aneurysm beyond the vagoaccessory triangle, making the conventional FL approach inappropriate.

OBJECTIVE

To demonstrate the utility of the extended retrosigmoid (eRS) approach and a lateral trajectory through the glossopharyngo-cochlear triangle as the surgical corridor for these cases.

METHODS

High-riding PICA aneurysms treated by microsurgery were retrospectively reviewed, comparing exposure through the eRS and FL approaches. Clinical, surgical, and outcome measures were evaluated. Distances from the aneurysm neck to the internal auditory canal (IAC), jugular foramen, and foramen magnum were measured.

RESULTS

Six patients with PICA aneurysms underwent clipping using the eRS approach; 5 had high-riding PICA aneurysms based on measurements from preoperative computed tomography angiography (CTA). Mean distances of the aneurysm neck above the foramen magnum, below the IAC, and above the jugular foramen were 27.0 mm, 3.7 mm, and 8.2 mm, respectively. Distances were all significantly lower versus the comparison group of 9 patients with normal or low-riding PICA aneurysms treated using an FL approach (P < .01). All 6 aneurysms treated using eRS were completely occluded without operative complications.

CONCLUSION

The eRS approach is an important alternative to the FL approach for high-riding PICA aneurysms, identified as having necks more than 23 mm above the foramen magnum on CTA. The glossopharyngo-cochlear triangle is another important anatomic triangle that facilitates microsurgical dissection.

Dissection of the Petrosal Presigmoid-Retrolabyrinthine Approach for the Petroclival Region on a Cadaver: 2-Dimensional Operative Video

Skull base epidermoid tumors, meningiomas, and schwannomas can be accessed by different techniques depending on the location and size of the lesion. Small lesions located anterior to the internal acoustic meatus (IAM) can be accessed via the subtemporal approach, and lesions located posterior to the IAM can be approached via retrosigmoid craniotomy. However, expansive lesions that are located anterior to the IAM and extend posteriorly toward the lower clivus can be accessed via the petrosal approach. The petrosal approach (presigmoid-retrolabyrinthine) is centered on the petrous ridge of the temporal bone and is mainly performed for intradural lesions located at the clivus and petroclivus junction area. Patients with intact hearing can benefit from this technique, as the labyrinth is untouched and yet the middle and posterior fossa compartments are connected. Additionally, extension of the lesion from the suprasellar area/cavernous sinus to the foramen magnum can be dissected and removed. There are variations of the petrosal approach, such as translabyrinthine, transotic, and transchoclear, with which hearing cannot be preserved, and the "transcrusal" approach, wherein posterior and superior semicircular canals are sacrificed yet hearing preserved. The endolymphatic duct is usually transected and not reapproximated. Neurotology input is always helpful when dealing with inner ear structures. This complex approach demands exhaustive practice with temporal bone dissection in a cadaver laboratory. Although this approach can be extended anteriorly, combination with an anterior petrosal approach permits more rostral exposure. In this video, we demonstrate the stepwise dissection of the posterior petrosal approach only, showing procedure nuances in a cadaver.1-8Used with permission from Barrow Neurological Institute, Phoenix, Arizona.

Combined Petrosal Approach for Resection of a Large Trigeminal Schwannoma With Meckel's Cave Involvement-Part I: Anatomic Rationale and Analysis: 2-Dimensional Operative Video

Resection of large trigeminal schwannomas involving both posterior and middle cranial fossae is challenging. The depth of the surgical target in the superomedial corner of the cerebellopontine angle and the petrous apex makes for a difficult lesion to favorably access, expose, and safely resect. Judicious planning of a skull base approach is therefore the most crucial step in successful management of these formidable tumors. When properly chosen, planned, and executed, the combined petrosal approach sets the stage for an optimal exposure of such tumors that involve both posterior and middle cranial fossae. The present video is the first of a 2-part video presentation that explains the anatomic rationale of selecting a combined petrosal approach (anterior petrosectomy and retrolabyrinthine petrosectomy) for the resection of a large trigeminal schwannoma involving the posterior and middle cranial fossae with an extension into Meckel's cave in a 54-yr-old female presenting with 5-yr history of increasing headaches, left-sided face numbness, and disequilibrium. The benefits, risks, and alternatives of the surgical procedure were discussed in detail with the patient and she consented to proceed with surgery. Part I also discusses the important nuances of positioning the patient, as well as planning and execution of the skin incision, including pericranial flap harvesting.  Of note, the patient consented to the publication of images obtained from her.

The Glossopharyngo-Cochlear Triangle-Part I: Quantitative Anatomic Analysis of High-Riding Posterior Inferior Cerebellar Artery Aneurysms Exposed Through the Extended Retrosigmoid Approach

BACKGROUND

An extended retrosigmoid approach can offer sufficient space for clip reconstruction of some high-riding posterior inferior cerebellar artery (PICA) aneurysms.

OBJECTIVE

To quantitatively investigate the glossopharyngo-cochlear triangle (GCT) and anatomic structures within it.

METHODS

Extended retrosigmoid craniotomies were performed on 10 sides of cadaveric heads, and the GCT was identified in each specimen. The length of the base and the area of the GCT were measured. The depth of the vertebrobasilar system and the abducens nerve to the GCT were measured. The proximal and distal exposable and controllable points on the vertebrobasilar system were identified. Two imaging-based patient selection algorithms are provided using the lengths from those points to the vertebral artery dural entry point and the superoinferior distances from those points to the inferior edge of the foramen magnum. Other factors related to accessibility via the GCT were investigated.

RESULTS

The mean (standard deviation [SD]) area of the GCT was 45.7 (12.55) mm2. The mean (SD) depth of the abducens nerve was 14.3 (1.42) mm. The mean (SD) superoinferior distances from the foramen magnum to those points were 23.1 (7.39), 24.7 (8.25), 30.0 (9.56), and 32.6 (7.79) mm, respectively. The lower segment of the vertebrobasilar system was more superficial in the setting of a high-lying vertebrobasilar junction (VBJ) than a low-lying VBJ.

CONCLUSION

We describe the GCT in an extended retrosigmoid approach for high-riding PICA aneurysms and evaluate the spatial relationship of the neurovascular structures within it. Two potential algorithms are offered for preoperative patient selection.

Learning microvascular anastomosis: Analysis of practice patterns

BACKGROUND

Performing a successful microsurgical vascular anastomosis (MVA) is challenging and requires lots of practice. However, the most efficient practice protocol is yet to be found. We aimed to compare and analyze two major practice patterns for fine motor tasks as applied to learning MVA: distributed and mass practice protocols. Ten neurosurgeons with comparable experience in microsurgery (but no experience in vascular anastomosis) were randomized to practice MVA either using a distributed (1 session/day) or a mass practice (6 sessions/day) protocol. A total of 24 sessions of practice and 2 recall test sessions were given. Anastomosis score, time to complete a single stitch and the total time to complete an anastomosis were recorded. Mass practice protocol caused a clear fatigue effect observed toward the end of each mass practice trial block. Statistical comparison using one-way analysis of variance showed significantly higher anastomosis scores and shorter times to place a single stitch as well as to complete the anastomosis in distributed practice group for the last 3 acquisition practice trials, and the 2 recall tests (p < 0.05). The relative advantage of the distributed practice protocol could be attributed to forgetting/spacing effect. Although mass practice protocol resulted in worse performance, it still showed a gradual improvement trend in performance from beginning to the end. Therefore, certain adjustments to a mass practice protocol (such as increasing the number of practice blocks) could potentially lead to an eventual performance level comparable to a distributed protocol. This point is a subject of further investigation.

Using the Post-Descendens Hypoglossal Nerve in Hypoglossal-Facial Anastomosis: An Anatomic and Histologic Feasibility Study

BACKGROUND

Hypoglossal-facial anastomosis (HFA) is a popular facial reanimation technique. Mobilizing the intratemporal segment of the facial nerve and using the post-descendens hypoglossal nerve (ie, the segment distal to the take-off of descendens hypoglossi) have been proposed to improve results. However, no anatomic study has verified the feasibility of this technique.

OBJECTIVE

To assess the anatomic feasibility of HFA and the structural compatibility between the 2 nerves when the intratemporal facial and post-descendens hypoglossal nerves are used.

METHODS

The facial and hypoglossal nerves were exposed bilaterally in 10 sides of 5 cadaveric heads. The feasibility of a side-to-end (ie, partial end-to-end) HFA with partial sectioning of the post-descendens hypoglossal nerve and the mobilized intratemporal facial nerve was assessed. The axonal count and cross-sectional area of the facial and hypoglossal nerves at the point of anastomosis were assessed.

RESULTS

The HFA was feasible in all specimens with a mean (standard deviation) 9.3 (5.5) mm of extra length on the facial nerve. The axonal counts and cross-sectional areas of the hypoglossal and facial nerves matched well. Considering the reduction in the facial nerve cross-sectional area after paralysis, the post-descendens hypoglossal nerve can provide adequate axonal count and area to accommodate the facial nerve stump.

CONCLUSION

Using the post-descendens hypoglossal nerve for side-to-end anastomosis with the mobilized intratemporal facial nerve is anatomically feasible and provides adequate axonal count for facial reanimation. When compared with use of the pre-descendens hypoglossal nerve, this technique preserves C1 fibers and has a potential to reduce glottic complications.

Far Lateral Craniotomy and Occlusion In Situ of a Lateral Medullary Arteriovenous Malformation: 2-Dimensional Operative Video

Lateral medullary arteriovenous malformations (AVMs) are located in the pia on the lateral medullary surface.1 They are supplied by arterial feeders from the V4 segment of the vertebral artery or posterior inferior cerebellar artery. A 64-yr-old man presented with leg spasms and progressively worsening gait. Angiography demonstrated a lateral medullary AVM. Patient consent was obtained for the surgical treatment of this lesion. Owing to its eloquent location, an occlusion in situ was performed without resection.1,2 This technique relies on the interruption of the arterial blood supply and occlusion of the draining vein to occlude the AVM. Intraoperative neurophysiological monitoring of motor and somatosensory evoked potentials was used, and the elimination of arteriovenous shunt flow was confirmed using indocyanine green videoangiography. Occlusion in situ preserves the flow to the delicate brainstem perforators and is safer than resection in selected cases like this one. Used with permission from Barrow Neurological Institute, Phoenix, Arizona.

Cognard Grade IV Tentorial Dural Arteriovenous Fistula Presenting as Trigeminal Neuralgia: Endovascular Management

Tentorial dural arteriovenous fistulas have an increased risk of rupture and hemorrhage, and therefore require urgent treatment to occlude the fistula and proximal venous drainage. This is usually accomplished via endovascular treatment. We present a case of a Cognard grade IV dural arteriovenous fistula that presented as trigeminal neuralgia. This video showcases the angiographic vascular composition of the lesion with main feeders coming from the middle meningeal artery and the tentorial artery of Bernasconi and Cassinari. Details, benefits, and risks of the procedure were thoroughly discussed with the patient and consent was obtained prior to the procedure. We performed endovascular Onyx embolization through a distal branch of the right middle meningeal artery. We were able to successfully occlude the lesion using Onyx embolization and the patient had significant improvement of her pretreatment trigeminal neuralgia.

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

BACKGROUND

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Contralateral interoptic approach to paraclinoid aneurysms: a patient-selection algorithm based on anatomical investigation and clinical validation

OBJECTIVE

Aneurysms that arise on the medial surface of the paraclinoid segment of the internal carotid artery (ICA) are surgically challenging. The contralateral interoptic trajectory, which uses the space between the optic nerves, can partially expose the medial surface of the paraclinoid ICA. In this study, the authors quantitatively measure the area of the medial ICA accessible through the interoptic triangle and propose a potential patient-selection algorithm that is based on preoperative measurements on angiographic imaging.

METHODS

The contralateral interoptic trajectory was studied on 10 sides of 5 cadaveric heads, through which the medial paraclinoid ICA was identified. The falciform ligament medial to the contralateral optic canal was incised, the contralateral optic nerve was gently elevated, and the medial surface of the paraclinoid ICA was inspected via different viewing angles to obtain maximal exposure. The accessible area on the carotid artery was outlined. The distance from the distal dural ring (DDR) to the proximal and distal borders of this accessible area was measured. The superior and inferior borders were measured using the clockface method relative to a vertical line on the coronal plane. To validate these parameters, preoperative measurements and intraoperative findings were reviewed in 8 clinical cases.

RESULTS

In the sagittal plane, the mean (SD) distances from the DDR to the proximal and distal ends of the accessible area on the paraclinoid ICA were 2.5 (1.52) mm and 8.4 (2.32) mm, respectively. In the coronal plane, the mean (SD) angles of the superior and inferior ends of the accessible area relative to a vertical line were 21.7° (14.84°) and 130.9° (12.75°), respectively. Six (75%) of 8 clinical cases were consistent with the proposed patient-selection algorithm.

CONCLUSIONS

The contralateral interoptic approach is a feasible route to access aneurysms that arise from the medial paraclinoid ICA. An aneurysm can be safely clipped via the contralateral interoptic trajectory if 1) both proximal and distal borders of the aneurysm neck are 2.5-8.4 mm distal to the DDR, and 2) at least one border of the aneurysm neck on the coronal clockface is 21.7°-130.9° medial to the vertical line.

Concomitant Reversible Cerebral Vasoconstriction and Hyperperfusion Syndromes Following Carotid Endarterectomy

Cerebral hyperperfusion syndrome (CHS) and reversible cerebral vasoconstriction syndrome (RCVS) are two syndromes characterized by disordered vascular autoregulatory mechanisms of brain. These may be seen after carotid endarterectomy (CEA). We present a patient who developed both syndromes after CEA which is a rare occurrence.

Virtual Exploration of Safe Entry Zones in the Brainstem: Comprehensive Definition and Analysis of the Operative Approach

BACKGROUND

A detailed and accurate understanding of the intrinsic brainstem anatomy and the interrelationship between its internal tracts and nuclei and external landmarks is of paramount importance for safe and effective brainstem surgery. Using anatomical models can be an important step in increasing such understanding. In the present study, we have shown the applicability of our developed virtual 3-dimensional (3D) model in depicting the safe entry zones (SEZs) to the brainstem.

METHODS

Accurate 3D virtual models of brainstem elements were created using high-resolution magnetic resonance imaging and computed tomography to depict the brainstem SEZs.

RESULTS

All the described SEZs to different parts of the brainstem were successfully depicted using our 3D virtual models.

CONCLUSIONS

The virtual models provide an immersive experience of brainstem anatomy, allowing users to understand the intricacies of the microdissection that is necessary to appropriately work through the brainstem nuclei and tracts toward a particular target. The models provide an unparalleled learning environment to understand the SEZs into the brainstem that can be used for training and research.

Microsurgical Anatomy of the Meningeal Branch of the Dorsolateral Medullary Plexus

BACKGROUND

Meningeal branches originating from intradural arteries may be involved in several diseases such as meningeal tumors and arteriovenous lesions. These "pial-dural" arterial connections have been described for anterior cerebral, posterior cerebral, and cerebellar arteries. However, to the best of our knowledge, meningeal supply originating from the arterial plexus over the dorsolateral aspect of the medulla oblongata (dorsolateral medullary plexus [DLMP]) has not been described.

OBJECTIVE

To define the microsurgical anatomy of the meningeal branch of DLMP.

METHODS

A total of 20 cadaver heads (40 sides) underwent far-lateral craniotomy and the cerebellomedullary cisterns were explored to find the DLMP and any meningeal branches. Additionally, de-identified intraoperative images of 85 patients with vertebral artery (VA)/posterior inferior cerebellar artery aneurysms who had undergone far-lateral craniotomy were studied to find any meningeal branches of DLMP.

RESULTS

The meningeal branches of DLMP were identified in 4 cadavers/sides. These branches reached the region of jugular tubercle (JT) after crossing the accessory nerve. In 3 specimens, these branches were joined by a small twig from V4-VA before penetrating the dura. DLMP meningeal branches were found in 12 patients of the studied cohort (14%) with similar anatomical features as those found in the cadaveric study.

CONCLUSION

DLMP may give rise to meningeal branches to the adjacent dura of JT. The actual prevalence of this anatomic variation is difficult to estimate using our data. However, when present, these branches may have important clinical implications, ie, diseases such as dural arteriovenous fistulas, pial arteriovenous malformations (AVMs), and meningeal-based tumors.

Rapid Recovery of Cranial Nerve Deficits After Anterior Petrosal (Kawase) Approach for Medically Refractory Petrous Apicitis

BACKGROUND

The mainstay treatment for petrous apicitis (Gradenigo's syndrome) is medical management with antibiotics, steroids, and placement of pressure equalization tubes. The role for surgery is limited as second-line treatment if conservative methods have failed.

CASE DESCRIPTION

We report 2 cases of medically refractory petrous apicitis presenting with progressive cranial neuropathies who underwent petrous apex resection and debridement via an anterior petrosal (Kawase) approach. Both patients had improvement of their preoperative cranial nerve deficits within 24-48 hours of surgery, that previously did not improve after 2 weeks of medical management.

CONCLUSIONS

To our knowledge, the use of the Kawase approach for petrous apicitis has not been previously reported. In addition, we postulate that surgical intervention can potentially result in quicker recovery of preexisting cranial nerve deficits in medically refractory petrous apicitis. This raises the potential role of earlier surgical intervention.

Zygomatic-Meatal Perpendicular Projection Lines: Bony Landmarks for Early Identification of the Temporal Horn of the Lateral Ventricle

OBJECTIVE

Localization of the temporal horn of the lateral ventricle (TH) may be required during temporal lobe and ambient cistern surgery. Most available anatomic landmarks for TH localization are based on adjacent cortical landmarks that are inherently variable or subtle. This study aimed to localize the anterior tip of the TH relative to adjacent bony landmarks.

METHODS

The TH was exposed on 21 sides of 11 cadaveric heads via removal of the middle temporal gyrus. Two lines were defined: (1) a perpendicular line to the zygomatic arch projected from the anterior concavity of the posterior zygomatic root (line A), and (2) a parallel line passing through the anterosuperior corner of the external auditory canal (line B). Sagittal distances from lines A and B to a parallel line passing through the anterior recess of the TH (line H) were measured.

RESULTS

Mean (standard deviation) distances from lines A and B to line H were 13.3 (2.5) mm and 11.9 (2.2) mm, respectively. Line H was at 53% (8%) of the line A-line B interval measured from line A. The best way to search for the TH was to start approximately 15 mm posterior to line A and progress posteriorly such that a more posteriorly located TH tip would not be missed.

CONCLUSIONS

The zygomatic-meatal landmark is a reliable tool to localize TH during various approaches. It is independent from the approach trajectory. This landmark may be used as an ancillary tool in conjunction with other cortical landmarks and image guidance.

The Inferior Nuchal Line as a Simple Landmark for Identifying the Vertebral Artery During the Retrosigmoid Approach

BACKGROUND

The V3 segment of the vertebral artery (V3-VA) is at risk during various approaches to the craniovertebral junction. Several landmarks have been defined to identify V3-VA, but these landmarks are not routinely exposed during a retrosigmoid (RS) approach, where musculocutaneous dissection inferiorly towards the foramen magnum can threaten this arterial segment.

OBJECTIVE

To find a landmark that will identify the V3-VA during the RS approach, and analyze the inferior nuchal line (INL) as this novel landmark.

METHODS

The anatomic relationships between the INL and the V3-VA were assessed in 7 cadaveric heads through RS exposure in the lateral position.

RESULTS

The INL is an L-shaped bony ridge with horizontal (medial) and vertical (lateral) arms, with the vertical arm being more conspicuous in all specimens (INLV). The mean depths of the V3-VA relative to the medial and lateral ends of the INLV were (mean ± standard deviation) 24.9 ± 7.1 mm, and 8.3 ± 3.2 mm, respectively. In all specimens, the V3-VA was located inferior and anterior to the INLV.

CONCLUSION

The INL provides an important landmark during RS approach that can protect the V3-VA from inadvertent injury or identify it for use in an interpositional bypass. The INLV identifies the region of the suboccipital triangle where the V3-VA is embedded. INLV is routinely seen during the RS approach, making it more relevant than other classic landmarks such as the transverse process of C1, C1 posterior arch, and the atlantomastoid line that are not exposed during the RS approach.

Venous anatomy of the supratentorial compartment

The cerebral venous drainage system in humans has several unique characteristics that set it apart from its arterial counterpart. The intracranial drainage system can be broadly divided into supra- and infratentorial components. The supratentorial venous drainage is further subclassified into superficial and deep systems, each with a unique set of features. A thorough knowledge of the normal and variant venous drainage pathways is important to understand the different pathologic processes involving the venous vasculature, to identify and anticipate the different venous channels encountered during surgery and also to predict the possible sequelae of intentional or inadvertent venous sacrifice during surgery. This chapter summarizes the anatomic and radiologic characteristics of the venous supply of the supratentorial compartment of the brain, reviews its general characteristics, sheds light on the different classifications and nomenclature used for its descriptions, and briefly discusses its embryologic development.

Exposure of the V1 Segment of the Vertebral Artery: Stepwise Cadaveric Surgical Simulation

BACKGROUND

Surgical exposure of the V1 segment of the vertebral artery (V1-VA) at the lower neck may be necessary to address intravascular (atherosclerotic) and extravascular (external compression by neoplastic or degenerative) pathologies. The adjacent anatomy at the lower cervical region is complex and relatively unfamiliar to neurosurgeons compared to that of upper cervical levels. High-quality cadaveric images simulating the surgical approach to V1-VA are important for learning the relevant anatomy.

OBJECTIVE

To provide a brief stepwise depiction of the exposure of the V1-VA using a cadaveric surgical simulation.

METHODS

A cadaveric surgical simulation was performed on the left side to expose the V1-VA using the retrojugular and interjugular carotid approaches. The important adjacent anatomic structures en route to the V1-VA were identified.

RESULTS

A stepwise photographic demonstration of the surgical exposure of the V1-VA is provided.

CONCLUSION

Exposure of the V1-VA can be challenging and requires a clear anatomic understanding of the relevant anatomy. The present work attempts to facilitate this objective.

Anatomical assessment of the endoscopic endonasal approach for the treatment of paraclinoid aneurysms

OBJECTIVE

Endoscopic endonasal approaches (EEAs) are increasingly being incorporated into the neurosurgeon’s armamentarium for treatment of various pathologies, including paraclinoid aneurysms. However, few anatomical assessments have been performed on the use of EEA for this purpose. The aim of the present study was to provide a comprehensive anatomical assessment of the EEA for the treatment of paraclinoid aneurysms.

METHODS

Five cadaveric heads underwent an endonasal transplanum-transtuberculum approach to expose the paraclinoid area. The feasibility of obtaining proximal and distal internal carotid artery (ICA) control as well as the topographic location of the origin of the ophthalmic artery (OphA) relative to dural landmarks were assessed. Limitations of the EEA in exposing the supraclinoid ICA were also recorded to identify favorable paraclinoid ICA aneurysm projections for EEA.

RESULTS

The extracavernous paraclival and clinoidal ICAs were favorable segments for establishing proximal control. Clipping the extracavernous ICA risked injury to the trigeminal and abducens nerves, whereas clipping the clinoidal segment put the oculomotor nerve at risk. The OphA origin was found within 4 mm of the medial opticocarotid point on a line connecting the midtubercular recess point to the medial vertex of the lateral opticocarotid recess. An average 7.2-mm length of the supraclinoid ICA could be safely clipped for distal control. Assessments showed that small superiorly or medially projecting aneurysms were favorable candidates for clipping via EEA.

CONCLUSIONS

When used for paraclinoid aneurysms, the EEA carries certain risks to adjacent neurovascular structures during proximal control, dural opening, and distal control. While some authors have promoted this approach as feasible, this work demonstrates that it has significant limitations and may only be appropriate in highly selected cases that are not amenable to coiling or clipping. Further clinical experience with this approach helps to delineate its risks and benefits.

Transcavernous Approach to the Upper Basilar and Retroclival Area-Cadaveric Surgical Simulation Video: 2-Dimensional Operative Video

The transcavernous approach (TcA) is an extension of the pterional approach that widens access to the central and lateral skull base regions. Through working between the nerves and vascular structures within the cavernous sinus, the TcA enables enhanced exposure of areas and structures including but not limited to the retrosellar area, Meckel's cave, and the basilar trunk. When the basilar apex and retrosellar regions are targeted, the TcA offers a valuable solution to the problem of the restricted space between the neurovascular structures of the central skull base through opening and widening the 2 major triangles of the cavernous sinus roof: the clinoidal and oculomotor triangles. Mastery of this approach requires careful review of the anatomy and much time spent in the cadaver lab. Although many quantitative studies and illustrative papers exist on the technical nuances of the TcA to the basilar apex region, the TcA is still difficult to understand, learn, and undertake. This cadaveric surgical simulation attempts to facilitate this objective. Of note, we have demonstrated and discussed the specific variant of the TcA that aims to reach the basilar apex area, and this video does not include the full TcA that also involves complete exposure of the lateral aspect of the cavernous sinus and the Meckel's cave.

The side door and front door to the upper retroclival region: a comparative analysis of the open pretemporal and the endoscopic endonasal transcavernous approaches

OBJECTIVE

The pretemporal transcavernous approach (PTA) and the endoscopic endonasal transcavernous approach (EETA) are both used to access the retroclival region. A direct quantitative comparison of both approaches has not been made. The authors compared the technical nuances of, and surgical exposure afforded by, each approach and identified the key elements of the approach selection process.

METHODS

Fourteen cadaveric specimens underwent either PTA (group A) or EETA with unilateral (group B) followed by bilateral (group C) interdural pituitary gland transposition. The percentage of drilled clivus; length of exposed oculomotor nerve (cranial nerve [CN] III), posterior cerebral artery (PCA), and superior cerebellar artery (SCA); and surgical area of exposure of both cerebral peduncles and the pons for the 3 groups were measured and compared.

RESULTS

Group A had a significantly lower percentage of drilled area than group B (mean [SD], 35.6% [11.2%] vs 91.3% [4.9%], p < 0.01). In group C, 100% of the upper third of the clivus was drilled in all specimens. Significantly longer segments of the ipsilateral PCA (p < 0.01) and SCA (p < 0.01) were exposed in group A than in group B. There was no significant difference in the length of the ipsilateral CN III exposed among the 3 groups. There was also no significant difference between group A and either group B or group C for the contralateral CN III or PCA exposure. However, longer segments of the contralateral SCA were exposed in group C than in group A (p = 0.02). Furthermore, longer segments of CN III (p < 0.01), PCA (p < 0.01), and SCA (p < 0.01) were exposed in group C than in group B. For brainstem exposure, there was greater exposure of the pons in group C than in group A (mean [SD], 211.4 [19.5] mm2 vs 157.7 [25.3] mm2, p < 0.01) and group B (211.4 [19.5] mm2 vs 153.9 [34.1] mm2, p < 0.01). However, significantly greater exposure of the ipsilateral peduncle was observed in group A (mean [SD], 125.6 [43.1] mm2) than in groups B and C (56.3 [6.0] mm2, p < 0.01). Group C had significantly greater exposure of the contralateral peduncle than group B (p = 0.02).

CONCLUSIONS

This study is the first to quantitatively identify the advantages and limitations of the PTA and EETA from an anatomical perspective. Understanding these data may help the skull base surgeon design a maximally effective yet minimally invasive approach to individual lesions.

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

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

Excision and Primary Reanastomosis of the Anterior Inferior Cerebellar Artery for Treatment of a Ruptured Mycotic Aneurysm: 2-Dimensional Operative Video

Anterior inferior cerebellar artery (AICA) aneurysms are rare lesions with a predisposition for distal location and non-saccular morphology.1,2 These aneurysms are less amenable to clipping and may instead require aneurysm trapping with bypass.3 This video reports a novel bypass for a ruptured, fusiform distal AICA aneurysm. A 51-yr-old woman with newly diagnosed acquired immunodeficiency syndrome presented to the hospital with meningitis and experienced an acute neurological decline while admitted. Neuroimaging revealed a fusiform left a2-AICA aneurysm, thought to be mycotic with diffuse subarachnoid and intraventricular hemorrhage (Hunt-Hess Grade-IV). The occipital artery was harvested as an alternative donor in the myocutaneous flap using a hockey-stick incision. An extended retrosigmoid approach exposed the infectious aneurysm. After aneurysm excision, an a2-AICA-a2-AICA end-to-end reanastomosis was performed in between and deep to the vestibulocochlear nerves superiorly and the glossopharyngeal nerve inferiorly. Indocyanine green videoangiography and postoperative angiogram confirmed bypass patency. Postoperatively, she developed epidural and subdural hematomas due to human immunodeficiency virus-associated coagulopathy and/or increased aspirin sensitivity, requiring reoperation. The patient made a complete recovery at late follow-up. AICA reanastomosis is an elegant intracranial-intracranial bypass for treating distal AICA aneurysms. To our knowledge, this is the first report of AICA reanastomosis in the proximal a2-AICA (lateral pontine) segment. This technique has been reported in the literature for distally located aneurysms (a3-AICA).4 Microanastomosis for more medial AICA aneurysms must be performed deep to the lower cranial nerves. OA to a3-AICA bypass is an alternative in cases where primary reanastomosis is not technically feasible. (Published with permission from Barrow Neurological Institute).

An Anatomic Feasibility Study for Revascularization of the Ophthalmic Artery, Part I: Intracanalicular Segment

BACKGROUND

The anatomico-functional complexity of the ophthalmic segment aneurysms is attributable to the presence of critical neurovascular structures in the surgical field. Surgical clipping of the ophthalmic artery (OpA) aneurysms can result in postoperative visual deficit due to the complexity of the aneurysm, vasospasm, or optic nerve manipulation. In this study, we aimed to characterize the feasibility of an intracanalicular OpA (iOpA) revascularization with 2 donor vessels: an intracranial-intracranial (IC-IC) bypass using the anterior temporal artery (ATA) and an extracranial-intracranial (EC-IC) bypass using the superficial temporal artery (STA). We further discuss their potential role in "unclippable" OpA aneurysms.

METHODS

Twenty cadaveric specimens were used to evaluate the operative exposure of the intradural and intracanalicular OpA segments using an extradural-intradural intracanalicular approach. The arterial caliber and length at the anastomotic sites and required donor artery lengths were measured. The feasibility of the bypass using both donors was assessed.

RESULTS

The average length of the intradural and intracanalicular segment of the OpA was 9.5 ± 1.6 mm. The mean caliber of the iOpA was 1.5 ± 0.2 mm. The mean ATA length required for an ATA-OpA anastomosis was 26.7 ± 8.9 mm, with a mean caliber of 1.0 ± 0.1 mm. The mean length of STA required for the bypass was 89.9 ± 9.7 mm, with a mean caliber of 1.92 ± 0.4 mm.

CONCLUSIONS

This study confirms the feasibility of iOpA revascularization using IC-IC and EC-IC bypasses. These techniques could potentially be used for prophylactic or therapeutic neuroprotection from retinal ischemic injury while treating complex OpA aneurysms, infiltrative tumors, or intraoperative arterial injuries.

Surgical treatment of falcotentorial meningiomas: a retrospective review of a single-institution experience

OBJECTIVE

Meningiomas at the falcotentorial junction represent a rare subgroup of complex meningiomas. Debate remains regarding the appropriate treatment strategy for and optimal surgical approach to these tumors, and surgical outcomes have not been well described in the literature. The authors reviewed their single-institution experience in the management, approach selection, and outcomes for patients with falcotentorial meningiomas.

METHODS

From the medical records, the authors identified all patients with falcotentorial meningiomas treated with resection at the Barrow Neurological Institute between January 2007 and October 2017. Perioperative clinical, surgical, and radiographic data were retrospectively collected. For patients who underwent the supracerebellar infratentorial approach, the tentorial angle was defined as the angle between the line joining the nasion with the tuberculum sellae and the tentorium in the midsagittal plane.

RESULTS

Falcotentorial meningiomas occurred in 0.97% (14/1441) of the patients with meningiomas. Most of the patients (13/14) were female, and the mean patient age was 59.8 ± 11.3 years. Of 17 total surgeries (20 procedures), 11 were single-stage primary surgeries, 3 were two-stage primary surgeries (6 procedures), 2 were reoperations for recurrence, and 1 was a reoperation after surgery had been aborted because of brain edema. Hydrocephalus was present in 5 of 17 cases, 4 of which required additional treatment. Various approaches were used, including the supracerebellar infratentorial (4/17), occipital transtentorial/transfalcine (4/17), anterior interhemispheric transsplenial (3/17), parietal transventricular (1/17), torcular (2/17), and staged supracerebellar infratentorial and occipital transtentorial/transfalcine (3/17) approaches. Of the 17 surgeries, 9 resulted in Simpson grade IV resection, and 3, 1, and 4 surgeries resulted in Simpson grades III, II, and I resection, respectively. The tentorial angle in cases with Simpson grade I resection was significantly smaller than in those with an unfavorable resection grade (43.3° ± 4.67° vs 54.0° ± 3.67°, p = 0.04). Complications occurred in 10 of 22 approaches (17 surgeries) and included visual field defects (6 cases, 2 permanent and 4 transient), hemiparesis (2 cases), hemidysesthesia (1 case), and cerebellar hematoma (1 case).

CONCLUSIONS

Falcotentorial meningiomas are challenging lesions. A steep tentorial angle is an unfavorable preoperative radiographic factor for achieving maximal resection with the supracerebellar infratentorial approach. Collectively, the study findings show that versatility is required to treat patients with falcotentorial meningiomas and that treatment goals and surgical approach must be individualized to obtain optimal surgical results.

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.

Exposure of the External Carotid Artery Through the Posterior Neck Triangle, Cadaveric Surgical Simulation: 2-Dimensional Operative Video

The external carotid artery (ECA) is a robust extracranial donor used for high-flow cerebrovascular bypass procedures. It is usually exposed through the anterior triangle of the neck and may be used to revascularize recipients in the anterior or upper posterior cerebral circulations. However, when a high-flow bypass to the posterior circulation is indicated, oftentimes the patient needs to be put in the prone position (or variants thereof). In such situations, accessing the ECA through the anterior triangle of the neck can be challenging. Therefore, using a technique that enables the surgeon to expose the ECA through a posterior approach could be helpful.1 Although we have not yet encountered a case requiring this type of exposure and bypass, this cadaveric surgical simulation video demonstrates the surgical technique of exposing the ECA through the posterior triangle of the neck (as a cadaveric video, no patient consent was necessary). Briefly, this technique involves an inferolateral extension of the muscular stage of the far-lateral approach and exposing the ECA through a plane developed between the parotid gland and the posterior belly of the digastric muscle. The technical details of this technique are described. Also, relevant anatomic information regarding the safety measures taken to protect adjacent neurovascular structures are discussed.

Characterization of Anatomical Landmarks for Exposing the Internal Carotid Artery in the Infratemporal Fossa Through an Endoscopic Transmasticator Approach: A Morphometric Cadaveric Study

BACKGROUND

The Eustachian tube and sphenoid spine have been previously described as landmarks for endonasal surgical identification of the most distal segment of the parapharyngeal internal carotid artery (PhICA). However, the intervening space between the sphenoid spine and PhICA allows for error during exposure of the artery. In the present study, we have characterized endoscopic endonasal transmasticator exposure of the PhICA using the sphenoid spine, vaginal process of the tympanic bone, and the "tympanic crest" as useful anatomical landmarks.

METHODS

Endonasal dissection was performed in 13 embalmed latex-injected cadaveric specimens. Two open lateral dissections and osteologic analysis of 10 dry skulls were also performed.

RESULTS

A novel and palpable bony landmark, the inferomedial edge of the tympanic bone, referred to as the tympanic crest, was identified, leading from the sphenoid spine to the lateral carotid canal. Additionally, the vaginal process of the tympanic bone, viewed endoscopically, was a guide to the PhICA. The sphenoid spine was bifurcate in 20% of the skulls, with an average length of 5.98 mm (range, 3.9-8.2 mm), width of 5.81 mm (range, 3.0-10.6 mm), and distance to the carotid canal of 4.48 mm (range, 2.5-6.1 mm).

CONCLUSION

The sphenoid spine and pericarotid space has variable anatomy. Using an endoscopic transmasticator approach to the infratemporal fossa, we found that the closest landmarks leading to the PhICA were the tympanic crest, sphenoid spine, and vaginal process of the tympanic bone.

Survival Outcomes Among Patients With High-Grade Glioma Treated With 5-Aminolevulinic Acid-Guided Surgery: A Systematic Review and Meta-Analysis

Background: High-grade glioma (HGG) is associated with a dismal prognosis despite significant advances in adjuvant therapies, including chemotherapy, immunotherapy, and radiotherapy. Extent of resection continues to be the most important independent prognosticator of survival. This underlines the significance of increasing gross total resection (GTR) rates by using adjunctive intraoperative modalities to maximize resection with minimal neurological morbidity. 5-aminolevulinic acid (5-ALA) is the only US Food and Drug Administration–approved intraoperative optical agent used for fluorescence-guided surgical resection of gliomas. Despite several studies on the impact of intra-operative 5-ALA use on the extent of HGG resection, a clear picture of how such usage affects patient survival is still unavailable.

Methods: A systematic review was conducted of all relevant studies assessing the GTR rate and survival outcomes [overall survival (OS) and progression-free survival (PFS)] in HGG. A meta-analysis of eligible studies was performed to assess the influence of 5-ALA-guided resection on improving GTR, OS, and PFS. GTR was defined as >95% resection.

Results: Of 23 eligible studies, 19 reporting GTR rates were included in the meta-analysis. The pooled cohort had 998 patients with HGG, including 796 with newly diagnosed cases. The pooled GTR rate among patients with 5-ALA–guided resection was 76.8% (95% confidence interval, 69.1–82.9%). A comparative subgroup analysis of 5-ALA–guided vs. conventional surgery (controlling for within-study covariates) showed a 26% higher GTR rate in the 5-ALA subgroup (odds ratio, 3.8; P < 0.001). There were 11 studies eligible for survival outcome analysis, 4 of which reported PFS. The pooled mean difference in OS and PFS was 3 and 1 months, respectively, favoring 5-ALA vs. control (P < 0.001).

Conclusions: This meta-analysis shows a significant increase in GTR rate with 5-ALA–guided surgical resection, with a higher weighted GTR rate (~76%) than the pivotal phase III study (~65%). Pooled analysis showed a small yet significant increase in survival measures associated with the use of 5-ALA. Despite the statistically significant results, the low level of evidence and heterogeneity across these studies make it difficult to conclusively report an independent association between 5-ALA use and survival outcomes in HGG. Additional randomized control studies are required to delineate the role of 5-ALA in survival outcomes in HGG.