Invention of an Online Interactive Virtual Neurosurgery Simulator With Audiovisual Capture for Tactile Feedback

Operative Neurosurgery 24:194–200, 2023

BACKGROUND: Present neurosurgical simulators are not portable.

OBJECTIVE: To maximize portability of a virtual surgical simulator by providing online learning and to validate a unique psychometric method (“audiovisual capture”) to provide tactile information without force feedback probes.

METHODS: An online interactive neurosurgical simulator of a posterior petrosectomy was developed. The difference in the hardness of compact vs cancellous bone was presented with audiovisual effects as inclinations of the drilling speed and sound based on engineering perspectives. Three training methods (the developed simulator, lectures and review of slides, and dissection of a 3-dimensional printed temporal bone model [D3DPM]) were evaluated by 10 neurosurgical residents. They all first attended a lecture and were randomly allocated to 2 groups by the training D3DPM (A: simulator; B: review of slides, no simulator). In D3DPM, objective measures (required time, quality of completion, injury scores of important structures, and the number of instructions provided) were compared between groups. Finally, the residents answered questionnaires.

RESULTS: The objective measures were not significantly different between groups despite a younger tendency in group A (graduate year À2.4 years, 95% confidence interval À5.3 to 0.5, P = .081). The mean perceived hardness of cancellous bone on the simulator was 70% of that of compact bone, matching the intended profile. The simulator was superior to lectures and review of slides in feedback and repeated practices and to D3DPM in adaptability to multiple learning environments.

CONCLUSION: A novel online interactive neurosurgical simulator was developed, and satisfactory validity was shown. Audiovisual capture successfully transmitted the tactile information.

Stereotactic radiosurgery for intracranial chordomas: an international multiinstitutional study

J Neurosurg 137:977–984, 2022

The object of this study was to evaluate the safety, efficacy, and long-term outcomes of stereotactic radiosurgery (SRS) in the management of intracranial chordomas.

METHODS This retrospective multicenter study involved consecutive patients managed with single-session SRS for an intracranial chordoma at 10 participating centers. Radiological and neurological outcomes were assessed after SRS, and predictive factors were evaluated via statistical methodology.

RESULTS A total of 93 patients (56 males [60.2%], mean age 44.8 years [SD 16.6]) underwent single-session SRS for intracranial chordoma. SRS was utilized as adjuvant treatment in 77 (82.8%) cases, at recurrence in 13 (14.0%) cases, and as primary treatment in 3 (3.2%) cases. The mean tumor volume was 8 cm 3 (SD 7.3), and the mean prescription volume was 9.1 cm 3 (SD 8.7). The mean margin and maximum radiosurgical doses utilized were 17 Gy (SD 3.6) and 34.2 Gy (SD 6.4), respectively. On multivariate analysis, treatment failure due to tumor progression (p = 0.001) was associated with an increased risk for post-SRS neurological deterioration, and a maximum dose > 29 Gy (p = 0.006) was associated with a decreased risk. A maximum dose > 29 Gy was also associated with improved local tumor control (p = 0.02), whereas the presence of neurological deficits prior to SRS (p = 0.04) and an age > 65 years at SRS (p = 0.03) were associated with worse local tumor control. The 5- and 10-year tumor progression-free survival rates were 54.7% and 34.7%, respectively. An age > 65 years at SRS (p = 0.01) was associated with decreased overall survival. The 5and 10-year overall survival rates were 83% and 70%, respectively.

CONCLUSIONS SRS appears to be a safe and relatively effective adjuvant management option for intracranial chordomas. The best outcomes were obtained in younger patients without significant neurological deficits. Further well-designed studies are necessary to define the best timing for the use of SRS in the multidisciplinary management of intracranial chordomas.

Hakuba’s triangle: a cadaveric study detailing its anatomy and neurovascular contents with vascular and skull base implications

Neurosurgical Review (2022) 45:2087–2093

Hakuba’s triangle is a superior cavernous sinus triangle that allows for wide and relatively safe exposure of vascular and neoplastic lesions.

This study provides cadaveric measurements of the borders of Hakuba’s triangle and describes its neurovascular contents in order to enrich the available literature.

The anatomical borders of the Hakuba’s triangle (lateral, medial, and posterior borders) were defined based on Hakuba’s description and identified. Then the triangle was dissected to reveal its morphology and relationship with adjacent neurovascular structures in Embalmed Caucasian cadaveric specimens.

The oculomotor nerve occupied roughly one-third of the area of the triangle and the nerve was more or less parallel to its medial border. The mean lengths of the lateral border, posterior border, and medial border were 17 mm ± 0.5 mm, 12.2 mm ± 0.4 mm, and 10.6 mm ± 0.4 mm, respectively. The mean area of Hakuba’s triangle was 63.9 mm 2 ± 4.4 mm 2 .

In this study, we provided cadaveric measurements of the borders of Hakuba’s triangle along with descriptions of its neurovascular contents.

Anatomical relationship between the foramen ovale and the lateral plate of the pterygoid process: application to percutaneous treatments of trigeminal neuralgia

Neurosurgical Review (2022) 45:2193–2199

Our aim was to clarify the variations in the positional relationship between the base of the lateral plate of the pterygoid process and the foramen ovale (FO), which block inserted needles during percutaneous procedures to the FO usually used for the treatment of trigeminal neuralgia.

Ninety skulls were examined. The horizontal relationship between the FO and the posterior border of the base of the lateral plate of the pterygoid process was observed in an inferior view of the skull base. Skulls that showed injury to either the FO or the lateral plate of the pterygoid process on either side were excluded.

One hundred and sixty sides of eighty skulls were eligible. The relationship between the FO and the posterior border of the base of the lateral plate was classified into four types. Among the 160 sides, type III (direct type) was the most common (35%), followed by type I (lateral type, 29%) and type IV (removed type, 21%); type II (medial type) was the least common (15%). Of the 80 specimens, 53 showed the same type bilaterally.

In type IV, the posterior border of the base of the lateral plate is disconnected from the FO, so percutaneous procedures for treating trigeminal neuralgia could fail in patients with this type.

Retrolabyrinthine transsigmoid approach to complex parabrainstem tumors in the posterior fossa

J Neurosurg 136:1097–1102, 2022

The surgical management of large and complex tumors of the posterior fossa poses a formidable challenge in neurosurgery. The standard retrosigmoid craniotomy approach has been performed at most neurosurgical centers; however, the retrosigmoid approach may not provide enough working space without significant retraction of the cerebellum. The transsigmoid approach provides wider and shallower surgical fields; however, there have been few clinical and no cadaveric studies on its usefulness. In the present study, the authors describe the transsigmoid approach in clinical cases and cadaveric specimens.

METHODS For the clinical study, the authors retrospectively reviewed the medical records and operative charts of patients who had been surgically treated for parabrainstem tumors using the transsigmoid approach between 1997 and 2019. They analyzed patient demographic and clinical data, as well as surgical and clinical outcomes. In the cadaveric study, they compared the surgical views obtained in different approaches (retrosigmoid, presigmoid, retrolabyrinthine, and transsigmoid) and measured the sigmoid sinus width at the level of the endolymphatic sac and the distance between the anterior edge of the sigmoid sinus and the endolymphatic sac on 35 sides in 19 cadaveric specimens.

RESULTS A total of 21 patients (6 males and 15 females) with a mean age of 42.2 (range 15–67) years were included in the clinical study. Eleven patients had meningioma, 7 had vestibular schwannoma, 2 had hemangioblastoma, and 1 had epidermoid cyst. Gross-total, near-total, and subtotal removal were achieved in 7 (33.3%), 3 (14.3%), and 11 (52.4%) patients, respectively. In the cadaveric study, 19 cadaveric specimens were used. The sigmoid sinus was cut in the middle, and the incision was extended from the retrosigmoid to the presigmoid dura. The dura was then retracted upward and downward like opening a door. The results indicated that this technique can widen the operative field anteriorly by approximately 2 cm as compared to the retrosigmoid approach and provides a better view anterior to the brainstem.

CONCLUSIONS The transsigmoid approach is useful for complex parabrainstem tumors in the posterior fossa because it provides a wider and shallower operative view with less retraction of the cerebellum. This enables safer tumor removal with less damage to important structures in the posterior fossa, resulting in better operative and clinical outcomes.


Anterior transpetrosal approach: experiences in 274 cases over 33 years. Technical variations, operated patients, and approach-related complications

J Neurosurg 136:413–421, 2022

The anterior transpetrosal approach (ATPA) was initially reported in 1985. The authors’ institution has 274 case records of surgery performed with the ATPA during the period from 1984 to 2017. Although many technical advances and modifications in the ATPA have occurred over those 33 years, to the authors’ knowledge no articles to date have reported a detailed analysis of variations and complications of the ATPA. In this study, the authors analyzed their patient series to elucidate improvements over time in ATPA methodology while highlighting unresolved problems and evaluating how to avoid surgical complications.

METHODS All surgical cases (274 patients) using the ATPA at the authors’ institution during the period from 1984 to 2017 were analyzed retrospectively using charts, clinical summaries, operative records, and operative videos. Obtained parameters were patient age and sex, diagnosis, size of tumors, location of disease, operative date, neurological symptoms before and after surgery, radiographically identified brain injury, and other surgical complications. The most common diagnosis was petroclival meningioma (n = 158), followed by trigeminal schwannoma (n = 32), chordoma (n = 25), epidermoid tumor (n = 21), other tumor (n = 27), aneurysm (n = 6), and other (n = 5).

RESULTS The original ATPA was performed in 239 cases. In an additional 35 cases, a modified ATPA was performed. Zygomatic osteotomy with ATPA was a common modification that was used in 19 of the 35 cases to decrease retraction damage to the temporal lobe for high-positioned tumors. Brain injury by temporal lobe retraction without venous hemorrhage still occurred in 8 of the 19 cases (3.1%) with surgical death in 1 of these cases (0.4%) of reoperation with sacrifice of the petrosal vein. Symptomatic CSF leak was the most frequent complication noted and was observed in 35 cases (13.5%). In most of these cases the patients were cured by observation or lumbar drain, but in 6 cases (17.1%) reoperation was needed. Facial nerve damage related to surgical approach decreased from 6.2% to 3.5% after 2010; however, the incidence of CSF leaks (13.5%) has not improved.

CONCLUSIONS There have been several modifications and advancements made in the ATPA to increase tumor removal and decrease surgical complications. However, complications related to surgical approach occurred, such as venous occlusion–related brain injury and facial nerve damage at pyramid resection. CSF leak remained an unsolved problem related to the ATPA procedures. Preoperative assessment of venous variation of the middle fossa, pneumatization of the temporal bone, and intraoperative monitoring of cranial nerves are important procedures to decrease these complications.


Morphometric Study of the Posterior Fossa: Identification of Practical Parameters for Tailored Selection of Surgical Routes to the Petroclival Region

J Neurol Surg B Skull Base 2022;83:37–43

The petroclival region is an integral part of the skull base. It can harbor different pathologies and provides access to the petroclival junction and cerebellopontine angle. We present the results of the morphometric analysis of the posterior fossa and a prediction model to enable skull base surgeons to choose an optimal surgical corridor considering patient’s bony anatomy.

Methods Ninety patients (14 to assess interobserver reliability) with temporal bone computed tomography were selected. Exclusion criteria included patients <18 years of age, radiographic evidence of trauma, infection, or previous surgery. The images were analyzed using OsiriX MD (Bernex, Switzerland). We recorded clival length, vertical angle, and surface area, and petroclival angle, petrous apex, and translabyrinthine corridors volume.

Results The average age was 49.5 years (55%) for males. The mean clival length and surface areas were 44.2mm (standard deviation [SD]   4.1) and 8.1 cm2 (SD   1.3). The mean petrous apex and translabyrinthine corridors volumes were 2.2 cm3 (SD   0.6) and 10.1 cm3 (SD   3.7). The mean petroclival angle at the internal auditory canal (IAC) was 154.9 degrees (SD   9). The clival length correlated positively with clival surface area (rho   0.6, p <0.05), petrous apex volume (rho   0.3, p < 0.05), and translabyrinthine volume (rho   0.3, p < 0.05).

Conclusion The petroclival region is complex and with high variability of surgical significance. The use of preoperative measurements of the clival length and petroclival angle as part of surgical planning that could help the surgeon to choose an optimal surgical corridor by overcoming the anatomical variability elements.

Surgery versus radiosurgery for facial nerve schwannoma

J Neurosurg 135:542–553, 2021

Intracranial facial nerve schwannomas (FNS) requiring treatment are frequently recommended for surgery or stereotactic radiosurgery (SRS). The objective of this study was to compare facial nerve function outcomes between these two interventions for FNS via a systematic review and meta-analysis.

METHODS A search of the Ovid EMBASE, PubMed, SCOPUS, and Cochrane databases from inception to July 2019 was conducted following PRISMA guidelines. Articles were screened against prespecified criteria. Facial nerve out- comes were classified as improved, stabilized, or worsened by last follow-up. Incidence was pooled by random-effects meta-analysis of proportions.

RESULTS Thirty-three articles with a pooled cohort of 519 patients with FNS satisfied all criteria. Twenty-five articles described operative outcomes in 407 (78%) patients; 10 articles reported SRS outcomes in 112 (22%). In the surgical cohort, facial nerve function improved in 23% (95% CI 15%–32%), stabilized in 41% (95% CI 32%–50%), and worsened in 30% (95% CI 21%–40%). In the SRS cohort, facial nerve function was improved in 20% (95% CI 9%–34%), stable in 66% (95% CI 54%–78%), and worsened in 9% (95% CI 3%–16%). Compared with SRS, microsurgery was associated with a significantly lower incidence of stable facial nerve function (p < 0.01) and a significantly higher incidence of wors- ened facial nerve function (p < 0.01). Tumor progression and complication rates were comparable. Outcome certainty assessments were very low to moderate for all parameters.

CONCLUSIONS Unfavorable facial nerve function outcomes are associated with surgical treatment of intracranial FNS, whereas stable facial nerve function outcomes are associated with SRS. Therefore, SRS should be recommended to patients with FNS who require treatment, and surgery should be reserved for patients with another indication, such as decompression of the brainstem. Further study is required to definitively optimize and validate management strategies for these rare skull base tumors.

Tumor Growth Rate as a New Predictor of Progression-Free Survival After Chordoma Surgery

Neurosurgery 89:291–299, 2021

Currently, different postoperative predictors of chordoma recurrence have been identified. Tumor growth rate (TGR) is an image-based calculation that provides quantitative information of tumor’s volume changing over time and has been shown to predict progression-free survival (PFS) in other tumor types.

OBJECTIVE: To explore the usefulness of TGR as a new preoperative radiological marker for chordoma recurrence.

METHODS: A retrospective single-institution study was carried out including patients reflecting these criteria: confirmed diagnosis of chordoma on pathological analysis, no history of previous radiation, and at least 2 preoperative thin-slice magnetic resonance images available to measure TGR. TGR was calculated for all patients, showing the percentage change in tumor size over 1 mo.

RESULTS: A total of 32 patients were retained for analysis. Patients with a TGR ≥ 10.12%/m had a statistically significantly lower mean PFS (P<.0001). TGR≥10.12%/m (odds ratio=26, P=.001) was observed more frequently in recurrent chordoma. In a subgroup analysis, we found that the association of Ki-67 labeling index≥6% and TGR≥10.12%/m was correlated with recurrence (P = .0008).

CONCLUSION: TGR may be considered as a preoperative radiological indicator of tumor proliferation and seems to preoperatively identify more aggressive tumors with a higher tendency to recur. Our findings suggest that the therapeutic strategy and clinical radiological follow-up of patients with chordoma can be adapted also according to this new parameter.

Endoscopic endonasal approach for suprasellar meningiomas

J Neurosurg 135:113–125, 2021

The endoscopic endonasal approach (EEA) has gained increasing popularity for the resection of suprasellar meningiomas (SSMs). Appropriate case selection is critical in optimizing patient outcome. Long-term outcome data are lacking. The authors systematically identified preoperative factors associated with extent of resection (EOR) and determined the relationship between EOR and long-term recurrence after EEA for SSMs.

In this retrospective cohort study, the authors identified preoperative clinical and imaging characteristics associated with EOR and built on the recently published University of California, San Francisco resectability score to propose a score more specific to the EEA. They then examined the relationship between gross-total resection (GTR; 100%), near-total resection (NTR; 95%–99%), and subtotal resection (STR; < 95%) and recurrence or progression with Kaplan-Meier survival analysis.

A total of 51 patients were identified. Radiographic GTR was achieved in 40 of 47 (85%) patients in whom it was the surgical goal. Significant independent risk factors for incomplete resection were prior surgery (OR 25.94, 95% CI < 2.00 to 336.49, p = 0.013); tumor lateral to the optic nerve (OR 13.41, 95% CI 1.82–98.99, p = 0.011); and complete internal carotid artery (ICA) encasement (OR 15.12, 95% CI 1.17–194.08, p = 0.037). Tumor size and optic canal invasion were not significant risk factors after adjustment for other variables. A resectability score based on the multivariable model successfully predicted the likelihood of GTR; a score of 0 had a positive predictive value of 97% for GTR, whereas a score of 2 had a negative predictive value of 87.5% for incomplete resection. After a mean follow-up of 40.6 ± 32.4 months (mean ± SD), recurrence was 2.7% after GTR (1 patient with atypical histology), 44.4% after NTR, and 80% after STR (p < 0.0001). Vision was stable or improved in 93.5% and improved in 67.4% of patients with a preoperative deficit. There were 5 (9.8%) postoperative CSF leaks, of which 4 were managed with lumbar drains and 1 required a reoperation.

The EEA is a safe and effective approach to SSMs, with favorable visual outcomes in well-selected cases. The combination of postoperative MRI-based EOR with direct endoscopic inspection can be used in lieu of Simpson grade to predict recurrence. GTR dramatically reduces recurrence and can be achieved regardless of tumor size, proximity or encasement of the anterior cerebral artery, or medial optic canal invasion. Risk factors for incomplete resection include prior surgery, tumor lateral to the optic nerve, and complete ICA encasement.

Comparative anatomical analysis between the minipterional and supraorbital approaches

J Neurosurg 134:1276–1284, 2021

Keyhole approaches, namely the minipterional approach (MPTa) and the supraorbital approach (SOa), are alternatives to the standard pterional approach to treat lesions located in the anterior and middle cranial fossae. Despite their increasing popularity and acceptance, the indications and limitations of these approaches require further assessment. The purpose of the present study was to determine the differences in the area of surgical exposure and surgical maneuverability provided by the MPTa and SOa.

METHODS The areas of surgical exposure afforded by the MPTa and SOa were analyzed in 12 sides of cadaver heads by using a microscope and a neuronavigation system. The area of exposure of the region of interest and surgical freedom (maneuverability) of each approach were calculated.

RESULTS The area of exposure was significantly larger in the MPTa than in the SOa (1250 ± 223 mm2 vs 939 ± 139 mm2, p = 0.002). The MPTa provided larger areas of exposure in the ipsilateral and midline compartments, whereas there was no significant difference in the area of exposure in the contralateral compartment. All targets in the anterior circulation had significantly larger areas of surgical freedom when treated via the MPTa versus the SOa.

CONCLUSIONS The MPTa provides greater surgical exposure and better maneuverability than that offered by the SOa. The SOa may be advantageous as a direct corridor for treating lesions located in the contralateral side or in the anterior cranial fossa, but the surgical exposure provided in the midline region is inferior to that exposed by the MPTa.

Sphenoparietal sinus transposition technique: optimization of the surgical corridor with preservation of prominent bridging veins between the brain and the cranial base during aneurysm clipping via the pterional approach

J Neurosurg 134:999–1005, 2021

The sylvian bridging veins between the brain and the dura on the inner surface of the sphenoid wing can restrict brain retraction for widening of the lateral retrocarotid space during clipping surgery for internal carotid artery (ICA)–posterior communicating artery (PCoA) and basilar apex (BX) aneurysms. In such cases, the authors perform extradural anterior clinoidectomy with peeling of the temporal dura propria from the periosteal dura and inner cavernous membrane around the superior orbital fissure, with the incision of the dura mater stretching from the base of the temporal side to just before the distal dural ring of the ICA (termed by the authors as the sphenoparietal sinus transposition [SPST] technique). This technique displaces the bridging segment of the sylvian vein posteriorly and enables widening of the surgical space without venous injury. In this study, the authors observed the operative nuances and investigated the usefulness of this technique.

METHODS The authors retrospectively reviewed the medical charts of 66 consecutive patients with ICA-PCoA and BX aneurysms between January 2016 and July 2018. This technique was performed in 8 patients (5 patients with PCoA aneurysms and 3 with BX aneurysms) in whom the bridging segments of the sylvian veins between the brain and the skull base restricted brain retraction for widening of the surgical space. The surface areas of the lateral retrocarotid space and the aneurysm were measured at the most visible working angle before and after the SPST technique was performed.

RESULTS With the use of the SPST technique, an adequate surgical space for aneurysm clipping was obtained with preservation of the bridging veins in all patients. The mean surface areas of the lateral retrocarotid space (p = 0.002) and aneurysm (p = 0.001) were significantly increased from 18.3 ± 18.8 and 2.8 ± 2.5 cm2 before to 64.2 ± 21.1 and 20.9 ± 20.6 cm2, respectively, after the SPST technique was performed.

CONCLUSIONS The SPST technique enables displacement of the bridging segments of the sylvian veins without venous injury and enables widening of the surgical space around the lateral retrocarotid area.

Cerebrospinal fluid area and syringogenesis in Chiari malformation type I

J Neurosurg 134:825–830, 2021

Syringogenesis in Chiari malformation type I (CM-I) is thought to occur secondary to impaction of the cerebellar tonsils within the foramen magnum (FM). However, the correlation between the CSF area and syringogenesis has yet to be elucidated. The authors sought to determine whether the diminution in subarachnoid space is associated with syringogenesis. Further, the authors sought to determine if syrinx resolution was associated with the degree of expansion of subarachnoid spaces after surgery.

METHODS The authors performed a retrospective review of all patients undergoing posterior fossa decompression for CM-I from 2004 to 2016 at the University of Virginia Health System. The subarachnoid spaces at the FM and at the level of the most severe stenosis were measured before and after surgery by manual delineation of the canal and neural tissue area on MRI and verified through automated CSF intensity measurements. Imaging and clinical outcomes were then compared.

RESULTS Of 68 patients, 26 had a syrinx at presentation. Syrinx patients had significantly less subarachnoid space at the FM (13% vs 19%, p = 0.0070) compared to those without syrinx. Following matching based on degree of tonsillar herniation and age, the subarachnoid space was significantly smaller in patients with a syrinx (12% vs 19%, p = 0.0015). Syrinx resolution was associated with an increase in patients’ subarachnoid space after surgery compared with those patients without resolution (23% vs 10%, p = 0.0323).

CONCLUSIONS Syrinx development in CM-I patients is correlated with the degree to which the subarachnoid CSF spaces are diminished at the cranial outlet. Successful syrinx reduction is associated with the degree to which the subarachnoid spaces are increased following surgery.

How I do it: retrosigmoid intradural inframeatal petrosectomy

Acta Neurochirurgica (2021) 163:649–653

Lesions infiltrating the petrous temporal bone are some of the most complex to treat surgically. Many approaches have been developed in order to address these lesions, including endoscopic endonasal, anterior petrosectomy, posterior petrosectomy, and retrosigmoid.

Method We describe in a stepwise fashion the surgical steps of the retrosigmoid intradural inframeatal petrosectomy.

Conclusion The retrosigmoid intradural inframeatal petrosectomy may afford satisfactory exposure with limited drilling and minimal disruption of perilesional anatomical structures. It can provide excellent surgical results, especially for soft tumors, while minimizing surgical morbidity.

How I do it: anterior interhemispheric approach to tuberculum sellae meningiomas

Acta Neurochirurgica (2021) 163:643–648

Tuberculum sellae meningiomas are deep-seated tumors difficult to access, located in close relation with important neurovascular structures. While the transsphenoidal approach is linked to specific complications, the different reported transcranial approaches are associated with advantages and drawbacks due to the respective angle of attack, with some areas adequately exposed and others partially hidden.

Method We report the technical aspects of the anterior interhemispheric approach we practice.

Conclusion This approach has the advantage of providing full control over all the vasculo-nervous structures involved and of allowing access to the medial aspect of both optic canals tangentially to the dorsum sellae.

The endoscopic supraorbital translaminar approach

Acta Neurochirurgica (2021) 163:635–641

Resection of lesions located within the third ventricle presents a surgical challenge. Several approaches have been developed in an attempt to obtain maximal resection, while minimizing brain retraction. In this work, we assess the surgical exposure and maneuverability of the endoscopic supraorbital translaminar approach (ESTA), a potential alternative to fenestrate the lamina terminalis and approach the third ventricle by using the endoscope through a keyhole supraorbital-eyebrow craniotomy.

Methods Five cadaveric heads were used to assess the corridor depth, area of exposure, and viewing angles offered by the ESTA. One additional utilized specimen provided a stepwise dissection of the approach.

Results The ESTA was successfully performed in all specimens. Depth of the surgical corridor from the craniotomy to the ipsilateral internal carotid artery (ICA), lamina terminalis, and contralateral carotid were 70.7 ± 2.9 mm, 73.2 ± 2.9 mm, and 78.9 ± 4.1 mm, respectively. Viewing angle referenced to the ipsilateral ICA was 6.5 ± 4.2°, while the viewing angle for the lamina terminalis was 25.8 ± 4.3°. The surgical exposure provided by the ESTA was 1655 ± 255 mm2.

Conclusions The ESTA provides a wide surgical view of the lamina terminalis and may be potentially used to approach lesions located in the anterior third of the third ventricle. As a pure endoscopic approach, the ESTA requires minimal brain retraction, while affords good visualization of targeted lesions around the lamina terminalis. The ESTA uses an anterolateral approach and so provides a short and straightforward approach to these structures.

Sphenoorbital meningioma: a unique skull base tumor. Surgical technique and results

J Neurosurg 133:1044–1051, 2020

Sphenoorbital meningioma (SOM) is a unique skull base tumor, characterized by infiltrative involvement and hyperostosis primarily of the lesser wing of sphenoid bone, with frequent involvement of the orbital compartment. SOM often manifests with proptosis and visual impairment. Surgical technique and outcome are highly variable among studies reported in the literature. The authors present a single-surgeon experience with SOM.

METHODS A retrospective review of a prospectively maintained institutional database was performed. A blinded imaging review by 2 study team members was completed to confirm SOM, after which chart review was carried out to capture demographics and outcomes. All statistical testing was completed using JMP Pro version 14.1.0, with significance defined as p < 0.05.

RESULTS Forty-seven patients who underwent surgery between 2000 and 2017 were included. The median age at surgery was 47 years (range 36–70 years), 81% of patients were female, and the median follow-up was 43 months (range 0–175 months). All operations were performed via a frontotemporal craniotomy, orbitooptic osteotomy, and anterior clinoidectomy, with extensive resection of all involved bone and soft tissue. Preoperatively, proptosis was noted in 44 patients, 98% of whom improved. Twenty-eight patients (60%) had visual deficits before surgery, 21 (75%) of whom improved during follow-up. Visual field defect other than a central scotoma was the only prognostic factor for improvement in vision on multivariate analysis (p = 0.0062). Nine patients (19%) had recurrence or progression during follow-up.

CONCLUSIONS SOM is a unique skull base tumor that needs careful planning to optimize outcome. Aggressive removal of involved bone and periorbita is crucial, and proptosis and visual field defect other than a central scotoma can improve after surgery.

The membrane of Liliequist—a safe haven in the middle of the brain.

Acta Neurochirurgica (2020) 162:2235–2244

The membrane of Liliequist is one of the best-known inner arachnoid membranes and an essential intraoperative landmark when approaching the interpeduncular cistern but also an obstacle in the growth of lesions in the sellar and parasellar regions. The limits and exact anatomical description of this membrane are still unclear, as it blends into surrounding structures and joins other arachnoid membranes.

Methods We performed a systematic narrative review by searching for articles describing the anatomy and the relationship of the membrane of Liliequist with surrounding structures in MEDLINE, Embase and Google Scholar. Included articles were crosschecked for missing references. Both preclinical and clinical studies were included, if they detailed the clinical relevance of the membrane of Liliequist.

Results Despite a common definition of the localisation of the membrane of Liliequist, important differences exist with respect to its anatomical borders. The membrane appears to be continuous with the pontomesencephalic and pontomedullary membranes, leading to an arachnoid membrane complex around the brainstem. Furthermore, Liliequist’s membrane most likely continues along the oculomotor nerve sheath in the cavernous sinus, blending into and giving rise to the carotid-oculomotor membrane.

Conclusion Further standardized anatomical studies are needed to clarify the relation of the membrane of Liliequist with surrounding structures but also the anatomy of the arachnoid membranes in general. Our study supports this endeavour by identifying the knowledge hiatuses and reviewing the current knowledge base.

Clinical classification of clival chordomas for transnasal approaches

Neurosurgical Review (2020) 43:1201–1210

Endoscopic endonasal approaches (EEAs) are ideal for most chordomas, but there is little information regarding the practical clinical classification of clival chordomas to guide surgery with EEAs. This article investigates a relatively concise and practical clinical classification system for clival chordomas and summarizes the clinical characteristics and operative key points of different clinical types.

Here, 55 patients with clival chordomas treated through EEAs from 2012 to 2017 were retrospectively reviewed. Depending on the origin of the notochord and the growth pattern of the tumor, with our introduced Wang’s line, these cases of clival chordoma were divided into types I–IV. There were 14 cases of type I-A, 7 cases of type I-B, 10 cases of type II, 10 cases of type III-A, 7 cases of type III-B, and 7 cases of type IV. The gross total resection (GTR) rate of primary and recurrent type I tumors was 64% and 25%, and residual tumors were found mainly in cases with involvement of the cavernous sinus or the posterior upper part of the dorsum sella. The GTR rate of primary and recurrent type II tumors was 85% and 66.6%, respectively. Residual tumors were found in cases with involvement of the petrous apex. The GTR rate of primary and recurrent type III tumors was 75%and 20%, and residual tumors were found in cases with involvement of the parapharyngeal space and dorsal side of C1– 2. Residual type I-B and type III-B tumors were found when there was BA or VA adhesion or brain stem invasion.

Our new classification method proposed here can be used to guide the resection of clival chordomas through EEAs.

Surgical outcomes of anterior cerebellopontine angle meningiomas using the anterior transpetrosal approach compared with the lateral suboccipital approach

Acta Neurochirurgica (2020) 162:1243–1248

Anterior transpetrosal approach (ATPA) and lateral suboccipital approach (LSO) are the major surgical approaches for cerebellopontine angle (CPA) meningiomas. Particularly, anterior CPA meningiomas are challenging lesions to be treated surgically. To date, only a few studies have directly compared the outcomes of both approaches focusing on the anterior CPA meningiomas.

Methods For the comparative analysis, anterior CPA meningiomas that were eligible for both APTA and LSO were collected in our hospital from April 2005 to March 2017. Anterior CPA meningiomas targeted for this study were defined as follows: (1) without cavernous sinus, clivus, and middle cranial fossa extension, (2) the posterior edge is 1 cm behind the posterior wall of the internal auditory canal, and (3) the inferior edge is above the jugular tuberculum. Based on these criteria, the operative outcomes of 17 patients and 13 patients who were operated via ATPA and LSO were evaluated.

Results The complication rate of the LSO group was significantly higher than that of the ATPA group (30.7% vs. 0%, p = 0.033). The removal rate did not differ between the ATPA and LSO groups (97.35% vs. 99.23%, p = 0.12). The operative time was significantly shorter in the LSO group than in the ATPA group (304.3 min vs. 405.8 min, p = 0.036).

Conclusions Although the LSO is more widely used for CPA meningiomas, ATPA is also considered for these anterior CPA meningiomas.

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