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.

Prognostic value of the Simpson grading scale in modern meningioma surgery: Barrow Neurological Institute experience.

OBJECTIVE: Recently, the prognostic value of the Simpson resection grading scale has been called into question for modern meningioma surgery. In this study, the authors analyzed the relationship between Simpson resection grade and meningioma recurrence in their institutional experience. METHODS: This study is a retrospective review of all patients who underwent resection of a WHO grade I intracranial meningioma at the authors' institution from 2007 to 2017. Binary logistic regression analysis was used to assess for predictors of Simpson grade IV resection and postoperative neurological morbidity. Cox multivariate analysis was used to assess for predictors of tumor recurrence. Kaplan-Meier analysis and log-rank tests were used to assess and compare recurrence-free survival (RFS) of Simpson resection grades, respectively. RESULTS: A total of 492 patients with evaluable data were included for analysis, including 394 women (80.1%) and 98 men (19.9%) with a mean (SD) age of 58.7 (12.8) years. The tumors were most commonly located at the skull base (n = 302; 61.4%) or the convexity/parasagittal region (n = 139; 28.3%). The median (IQR) tumor volume was 6.8 (14.3) cm3. Simpson grade I, II, III, or IV resection was achieved in 105 (21.3%), 155 (31.5%), 52 (10.6%), and 180 (36.6%) patients, respectively. Sixty-three of 180 patients (35.0%) with Simpson grade IV resection were treated with adjuvant radiosurgery. In the multivariate analysis, increasing largest tumor dimension (p < 0.01) and sinus invasion (p < 0.01) predicted Simpson grade IV resection, whereas skull base location predicted neurological morbidity (p = 0.02). Tumor recurrence occurred in 63 patients (12.8%) at a median (IQR) of 36 (40.3) months from surgery. Simpson grade I resection resulted in superior RFS compared with Simpson grade II resection (p = 0.02), Simpson grade III resection (p = 0.01), and Simpson grade IV resection with adjuvant radiosurgery (p = 0.01) or without adjuvant radiosurgery (p < 0.01). In the multivariate analysis, Simpson grade I resection was independently associated with no tumor recurrence (p = 0.04). Simpson grade II and III resections resulted in superior RFS compared with Simpson grade IV resection without adjuvant radiosurgery (p < 0.01) but similar RFS compared with Simpson grade IV resection with adjuvant radiosurgery (p = 0.82). Simpson grade IV resection with adjuvant radiosurgery resulted in superior RFS compared with Simpson grade IV resection without adjuvant radiosurgery (p < 0.01). CONCLUSIONS: The Simpson resection grading scale continues to hold substantial prognostic value in the modern neurosurgical era. When feasible, Simpson grade I resection should remain the goal of intracranial meningioma surgery. Simpson grade IV resection with adjuvant radiosurgery resulted in similar RFS compared with Simpson grade II and III resections.

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.

Preoperative embolization versus no embolization for WHO grade I intracranial meningioma: a retrospective matched cohort study.

OBJECTIVE: The controversy continues over the clinical utility of preoperative embolization for reducing tumor vascularity of intracranial meningiomas prior to resection. Previous studies comparing embolization and nonembolization patients have not controlled for detailed tumor parameters before assessing outcomes. METHODS: The authors reviewed the cases of all patients who underwent resection of a WHO grade I intracranial meningioma at their institution from 2008 to 2016. Propensity score matching was used to generate embolization and nonembolization cohorts of 52 patients each, and a retrospective review of clinical and radiological outcomes was performed. RESULTS: In total, 52 consecutive patients who underwent embolization (mean follow-up 34.8 ± 31.5 months) were compared to 52 patients who did not undergo embolization (mean follow-up 32.8 ± 28.7 months; p = 0.63). Variables controlled for included patient age (p = 0.82), tumor laterality (p > 0.99), tumor location (p > 0.99), tumor diameter (p = 0.07), tumor invasion into a major dural sinus (p > 0.99), and tumor encasement around the internal carotid artery or middle cerebral artery (p > 0.99). The embolization and nonembolization cohorts did not differ in terms of estimated blood loss during surgery (660.4 ± 637.1 ml vs 509.2 ± 422.0 ml; p = 0.17), Simpson grade IV resection (32.7% vs 25.0%; p = 0.39), perioperative procedural complications (26.9% vs 19.2%; p = 0.35), development of permanent new neurological deficits (5.8% vs 7.7%; p = 0.70), or favorable modified Rankin Scale (mRS) score (a score of 0-2) at last follow-up (96.0% vs 92.3%; p = 0.43), respectively. When comparing the final mRS score to the preoperative mRS score, patients in the embolization group were more likely than patients in the nonembolization group to have an improvement in mRS score (50.0% vs 28.8%; p = 0.03). CONCLUSIONS: After controlling for patient age, tumor size, tumor laterality, tumor location, tumor invasion into a major dural sinus, and tumor encasement of the internal carotid artery or middle cerebral artery, preoperative meningioma embolization intended to decrease tumor vascularity did not improve the surgical outcomes of patients with WHO grade I intracranial meningiomas, but it did lead to a greater chance of clinical improvement compared to patients not treated with embolization.

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.

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.

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.

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.

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.

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.

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.

Contralateral Interhemispheric Transfalcine Approach for Intra-Axial Medial Occipital Lesion: 2-Dimensional Operative Video.

Safe access to intra-axial mesial cortical lesions is challenging. When approached through standard transcortical approaches, normal white matter tracts such as the superior longitudinal fasciculus, corona radiata, and optic radiations may be violated en route to the lesion. Conversely, use of ipsilateral interhemispheric approaches necessitates retraction and manipulation of edematous and friable perilesional tissue. The contralateral interhemispheric transfalcine (CIHTF) approach may circumvent these challenges. The CIHTF approach uses a gravity-created window between the ipsilateral hemisphere and the falx and allows direct access contralaterally by opening the falx. We demonstrate the CIHTF approach for an intra-axial, medial occipital/precuneus lesion in a 69-yr-old man presenting with left homonymous hemianopia. MRI revealed a heterogeneously enhancing intra-axial lesion in the right mesial occipital lobe. After the patient gave voluntary informed consent, a CIHTF approach was planned, with the patient positioned laterally, right side up (IRB approval was unnecessary). A lumber drain facilitated gravity autoretraction of the ipsilateral lobe. Within the created trajectory, the falx was opened with use of a nerve hook attached to monopolar electrocautery. The contralateral lesion was visualized and removed piecemeal with the assistance of fluorescence imaging. Postoperative MRI showed complete removal. The patient reported a significant vision improvement. The diagnosis was metastatic adenocarcinoma from the lung; subsequent radiosurgery was recommended. MRI at the 8-mo follow-up revealed no recurrence of the lesion. The CIHTF approach is feasible for a mesial intra-axial lesion because it offers gravity autoretraction, a large working angle, and avoidance of parenchymal swelling. Used with permission from Barrow Neurological Institute.

Efficient harvest of the occipital artery in the retrosigmoid approach: Technical note.

The occipital artery (OA) can be used as a donor artery in many types of bypasses; however, harvesting this artery in the depths of its course is challenging. In order to safely harvest the OA, a large hockey-stick-shaped incision is often used, even when only a retrosigmoid approach is needed for the intracranial procedure. In this article, we describe a detailed technique whereby the OA is harvested via a suboccipital subperiosteal-transperiosteal dissection technique. In this technique, the occipital groove is identified via a small linear incision. With the technique described, the OA can be localized and harvested effectively for bypass in the subsequent retrosigmoid approach.

Anatomical assessment of the digastric branch of the facial nerve as a landmark to localize the extratemporal facial nerve trunk.

PURPOSE: Localization of the facial nerve trunk (FNT) [i.e., the portion of the facial nerve between the stylomastoid foramen (SMF) and pes anserinus] may be required during various surgical interventions such as parotidectomy and hypoglossal-facial anastomosis. Several landmarks have been proposed for efficient identification of the FNT. We sought to assess the anatomical features of the digastric branch of the facial nerve (DBFN) and its potential as a landmark to identify FNT. METHODS: Fifteen sides of eight cadaveric heads were dissected to find the DBFN. Anatomic features of DBFN including its point of origin relative to SMF, length, and important relationships, as well as the distance between the insertion point on the digastric muscle and mastoid tip were recorded. RESULTS: DBFN was found in all specimens originating from the FNT outside the SMF with an average length (± standard deviation) of 15.4 ± 3.4 mm. In all specimens, the DBFN inserted on the superomedial aspect of the posterior belly of the digastric muscle (PBD). In 8/15 specimens, DBFN was accompanied by the stylomastoid artery on its anteromedial side. Average distance (± standard deviation) between the mastoid tip and the nerve insertion point on PBD was 13.6 ± 2.0 mm (range 10-17). CONCLUSIONS: The DBFN is a reliable landmark for identifying the FNT. It could be consistently identified within 15-20 mm of the mastoid tip on the superomedial aspect of the PBD. The DBFN may be used as a supplementary landmark for efficient localization of the FNT. LEVEL OF EVIDENCE: Not applicable (anatomic study).

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.

Anatomical Analysis of the Vagoaccessory Triangle and the Triangles Within: The Suprahypoglossal, Infrahypoglossal, and Hypoglossal-Hypoglossal Triangles.

BACKGROUND: Rootlets of the lower cranial nerves create a web that limits microsurgical maneuverability in the cerebellomedullary cistern (CMC). The vagoaccessory triangle (VAT) and 2 triangles within it were defined to identify surgical routes to aneurysms of the posterior inferior cerebellar artery (PICA). Dividing the VAT into 2 triangles (suprahypoglossal [SHT] and infrahypoglossal [IHT]), although elegant, oversimplifies CMC anatomy. The triangle formed by the superior and inferior hypoglossal rootlets (hypoglossal-hypoglossal triangle [HHT]) needs consideration as well. METHODS: Far-lateral craniotomy was performed on 10 cadaveric heads bilaterally. Areas of CMC triangles were calculated. Relationships between the PICA origin and the adjacent triangles were analyzed. Vertebral artery (VA) exposure and clipping lengths were recorded for each triangle. RESULTS: The area of SHT was almost twice those of IHT and HHT. The average VA depth relative to VAT increased significantly when moving distally from proximal VA (P < 0.001), but VA exposure and clipping lengths were not significantly different between triangles. IHT, HHT, and SHT defined VA subsegments (V4i, V4h, and V4s), with PICA most commonly originating from V4h. Based on our cadaveric measurements, the V4 subsegments were identified with 76% accuracy in angiograms. CONCLUSIONS: Based on this study, VAT should be divided into 3 triangles, not 2. Splayed rootlets of cranial nerve XII and multiple outlet foramina create an important space different from the previously recognized SHT and IHT. These triangles provide corridors to vascular pathologies. V4 subsegments may be approximated from imaging studies and may help with preoperative planning.

Interdural course of the ophthalmic artery in the optic canal.

OBJECTIVE: In the current neurosurgical and anatomical literature, the intracanalicular segment of the ophthalmic artery (OphA) is usually described to be within the optic nerve dural sheath (ONDS), implying direct contact between the nerve and the artery inside the optic canal. In the present study, the authors sought to clarify the exact relationship between the OphA and ONDS. METHODS: Ten cadaveric heads were subjected to endoscopic endonasal and transcranial exposures of the OphA in the optic canal (5 for each approach). The relationship between the OphA and ONDS was assessed. Histological examination of one specimen of the optic nerve and the accompanying OphA was also performed to confirm the relationship with the ONDS. RESULTS: In all specimens, the OphA coursed between the two layers of the dura (endosteal and meningeal) and was not in direct contact with the optic nerve, except for the first few millimeters of the proximal optic canal before it pierced the ONDS. Upon reaching the orbit, the two layers of the dura separated and allowed the OphA to literally float within the orbital fat. The meningeal dura continued as the ONDS, whereas the endosteal dura became the periorbita. CONCLUSIONS: This study clarifies the interdural course of the OphA within the optic canal. This anatomical nuance has important neurosurgical implications regarding safe exposure and manipulation of the OphA.

Double Origin of the Posterior Inferior Cerebellar Artery: Anatomic Case Report.

BACKGROUND: Double origin of the posterior inferior cerebellar artery is rare. It has important clinical implications especially in cases of aneurysms of the vertebral artery or the posterior inferior cerebellar artery. Several radiologic reports of this variant exist. However, no anatomic illustration of this rarity exists in the literature. This brief report provides the first anatomic illustration of this important variation of the vertebrobasilar system. CASE DESCRIPTION: A cadaveric specimen was prepared for dissection. A far lateral craniotomy was performed on the right side. While exploring the right cerebellomedullary cistern, 2 separate origins of the posterior inferior cerebellar artery were found from the vertebral artery as the caudal and rostral trunks that joined to form the distal posterior inferior cerebellar artery trunk at the tonsillomedullary segment. Microscopic and endoscopic illustrations are provided. CONCLUSIONS: To the best of our knowledge, this is the first anatomic report on the double origin of the posterior inferior cerebellar artery. Cadaveric illustration of this variant helps with understanding its anatomic relationship with adjacent neurovascular structures of the cerebellomedullary cistern including the perforating arteries and the lower cranial nerves.

Quantitative Endoscopic Comparison of Contralateral Interhemispheric Transprecuneus and Supracerebellar Transtentorial Transcollateral Sulcus Approaches to the Atrium.

OBJECTIVE: The contralateral interhemispheric transprecuneus approach (CITP) and the supracerebellar transtentorial transcollateral sulcus approach (STTC) are 2 novel approaches to access the atrium of the lateral ventricle. We quantitatively compared the 2 approaches. METHODS: Both approaches were performed in 6 sides of fixed and color-injected cadaver heads. We predefined the 6 targets in the atrium for measurement and standardization of the approaches. Using a navigation system, we quantitatively measured the working distance, cortical transgression, angle of attack, area of exposure, and surgical freedom. RESULTS: The distances from the craniotomy edge to the posterior pole of the choroid plexus of the CITP (mean ± standard deviation, 67 ± 5.3 mm) and STTC (mean, 57 ± 4.0 mm) differed significantly (P < 0.01). Cortical transgression with the CITP (mean, 27 ± 2.8 mm) was significantly greater than that with the STTC (mean, 21 ± 6.7 mm; P = 0.03). The CITP showed a significantly wider rostrocaudal angle of attack than that with the STTC (P = 0.01). The STTC showed a significantly wider mediolateral angle (P < 0.01). No significant difference was found for surgical freedom of any target except for point E, for which the CITP was larger. The exposure area did not differ significantly between the 2 approaches (P = 0.07). CONCLUSIONS: Both approaches were feasible for accessing the atrium. The STTC provided a shorter working distance and wider mediolateral angle, CITP provided a wider rostrocaudal angle of attack and better exposure and maneuverability to the anterior and superior atrium. In contrast, the STTC was more favorable for the inferior and posterior regions.