The role of apparent diffusion coefficient as a predictive factor for tumor recurrence in patients with cerebellopontine angle epidermoid tumor.

Intracranial epidermoid tumors are slowly growing benign tumors, but due to adjacent critical neurovascular structures, surgical resection is challenging, with the risk of recurrence. The apparent diffusion coefficient (ADC) has been used to evaluate the characteristics of brain tumors, but its utility for intracranial epidermoid tumors has not been specifically explored. This study analyzed the utility of preoperative ADC values in predicting tumor recurrence for patients with intracranial epidermoid tumors. Between 2008 and 2019, 21 patients underwent surgery for cerebellopontine angle (CPA) epidermoid tumor, and their preoperative ADC data were analyzed. The patients were divided into two groups: the recurrence group, defined by regrowth of the remnant tumor or newly developed mass after gross total resection on magnetic resonance imaging (MRI); and the stable group, defined by the absence of growth or evidence of tumor on MRI. Receiver operating characteristic (ROC) analysis was used to obtain the ADC cutoff values for predicting tumor recurrence. The prognostic value of the ADC was assessed using Kaplan-Meier curves. The minimum ADC values were significantly lower in the recurrence group than in the stable tumor group (P = 0.020). ROC analysis showed that a minimum ADC value lower than 804.5 × 10-6 mm2/s could be used to predict higher recurrence risk of CPA epidermoid tumors. Non-total resection and mean and minimum ADC values lower than the respective cutoffs were negative predictors of recurrence-free survival. Minimum ADC values could be useful in predicting the recurrence of CPA epidermoid tumors.

Factors Associated With Abducens Nerve Palsy in Patients Undergoing Surgery for Petroclival Meningiomas.

BACKGROUND: During the surgical resection of petroclival meningiomas, preserving the cranial nerves is crucial. The abducens nerve is particularly vulnerable during surgery. However, the preoperative risk factors and postoperative prognosis of abducens nerve palsy (ANP) are poorly understood. METHODS: We retrospectively analyzed 70 patients who underwent surgery for petroclival meningiomas between May 2010 and December 2019, divided into gross-total resection (GTR) and subtotal resection (STR) groups. The relationship of preoperative clinical factors with the incidence and recovery of postoperative ANP was analyzed. RESULTS: Postoperative ANP was observed in 23 patients (32.9%). Multivariable logistic regression revealed that the tumor-to-cerebellar peduncle T2 imaging intensity index (TCTI) (P < 0.001) and internal auditory canal invasion (P = 0.033) contributed to postoperative ANP. GTR was achieved in 37 patients (52.9%), and 10 (27.0%) of them showed ANP. STR was achieved in 33 patients (47.1%), and 13 (39.4%) of them showed ANP. Recovery from ANP took a median of 6.6 months (range, 4.5-20.3 months). At 6 months after the operation, recovery of the abducens nerve function was observed in 16 patients (69.0%); of whom, 4 (40.0%) were in the GTR group and 12 (92.3%) were in the STR group (P = 0.025). CONCLUSIONS: TCTI and internal auditory canal invasion were the risk factors for postoperative ANP. Although intentional STR did not prevent ANP immediately after the operation, recovery of the abducens nerve function after surgery was observed more frequently in the STR group than in the GTR group.

Clinical applications of the endoscopic transorbital approach for various lesions.

BACKGROUND: The endoscopic transorbital approach (ETOA) was recently added to the neurosurgical armamentarium. Although this approach could result in less injury to normal brain tissue, shorter operation times, and smaller scars, its clinical applications have not been fully investigated. We, therefore, sought to share our unique experiences of exploring the application of this approach in various diseases. METHODS: From June 2017 to March 2019, we conducted ETOAs via the superior eyelid crease in 22 patients for the treatment of lesions confined to the middle fossa with and without slight extension to the posterior fossa. These lesions included 5 gliomas, 11 meningiomas, 3 schwannomas, 1 lymphoma, 1 cavernous hemangioma in the orbital wall, and 1 hemangiopericytoma mimicking schwannoma. Perioperative radiologic findings and clinical outcomes were recorded. RESULTS: Gross total resection was accomplished in three (60%) patients with gliomas, nine (81.8%) with meningiomas, two (66.7%) with schwannomas, and one (33.3%) with another lesion. The mean bleeding count was 1051.4 ± 961.1 cc, and major complications were observed in only two (9.1%) cases (one major cerebral artery infarction and one reoperation due to a large amount of bleeding). A cerebrospinal fluid leak was reported in two (9.1%) patients, and transient eye movement palsy was noted in four (18.2%) patients without permanent disability. CONCLUSIONS: The endoscopic transorbital approach could be considered to be feasible for various lesions with different characteristics. After carefully considering the lesion anatomy, consistency, and vascular relationships, using this approach, we could achieve a satisfactory extent of resection without severe complications.

Differences in surgical outcome between petroclival meningioma and anterior petrous meningioma.

BACKGROUND: Petroclival meningiomas (PC MNGs) and anterior petrous meningiomas (AP MNGs) have similar locations. However, these are different tumors clearly divided by the trigeminal nerve. There has never been a study on the comparison of the surgical outcomes of these two meningiomas. In this study, we compared and analyzed the surgical outcome of PC MNGs and AP MNGs. METHODS: The charts of 85 patients diagnosed with PC MNGs of AP MNGs who underwent surgical treatment were retrospectively reviewed. And we analyzed the characteristics of 49 PC MNGs (57.6%) and compared them with those of 36 AP MNGs. RESULTS: Preoperative brainstem edema was observed in 11 patients (22.4%) of the PC MNG group and 1 patient (2.8%) of the AP MNG group (p = 0.024). Total tumor removal was achieved in 21 patients (58.3%) of the AP MNG group, but only 17 patients (34.7%) of the PC MNG group were able to completely (p = 0.047). In addition, sixth cranial nerve palsy occurred in 17 patients (34.7%) of the PC MNG group and 4 patients (11.1%) of the AP MNG group (p = 0.025). CONCLUSIONS: In this study, we found that PC MNGs has a worse surgical outcome than AP MNGs, because PC MNGs were difficult to completely remove and were more likely to damage abducens nerve.

Dural Metastasis in Breast Cancer: MRI-Based Morphological Subtypes and Their Clinical Implications.

Purpose: To investigate the clinical factors associated with breast cancer (BRCA) dural metastases (DMs), their impact on prognosis compared to brain parenchymal metastases (BPMs) alone, and differences between DM subtypes, aiming to inform clinical decisions. Materials and Methods: We retrospectively analyzed 119 patients with BRCA with brain metastasis, including 91 patients with BPM alone and 28 patients with DM. Univariate and multivariate analyses were performed to compare the clinical characteristics between the two groups and within subtypes of DM. Overall survival after DM (OSDM) and the interval from DM to leptomeningeal carcinomatosis (LMC) were compared using Kaplan-Meier analysis. Results: DM was notably linked with extracranial metastasis, luminal-like BRCA subtype (p=0.033), and skull metastases (p<0.001). Multiple logistic regression revealed a strong association of DM with extracranial and skull metastases, but not with subtype or hormone receptor (HR) status. Patients with DM did not show survival differences compared with patients with BPM alone. In the subgroup analysis, nodular type DM correlated with HER2 status (p=0.044), whereas diffuse type DM was significantly associated with a higher prevalence of the luminal-like subtype (p=0.048) and the presence of skull metastasis (p=0.002). Patients with diffuse DM did not exhibit a significant difference in OSDM but had a notably shorter interval from DM to LMC compared to those with nodular DM (p=0.049). Conclusion: While the impact of DM on the overall prognosis of patients with BRCA is minimal, our findings underscore distinct characteristics and prognostic outcomes within DM subgroups.

The Anterolateral Approach, Revisited for Benign Jugular Foramen Tumors With Predominant Extracranial Extension: Microsurgical Anatomy and Case Series (SevEN-012).

BACKGROUND AND OBJECTIVES: The anterolateral approach (ALA) enables access to the mid and lower clivus, jugular foramen (JF), craniocervical junction, and cervical spine with added anterior and lateral exposure than the extreme lateral and endoscopic endonasal approach, respectively. We describe the microsurgical anatomy of ALA with cadaveric specimens and report our clinical experience for benign JF tumors with predominant extracranial extension. METHODS: A stepwise and detailed microsurgical neurovascular anatomy of ALA was explored with cadaveric specimens. Then, the clinical results of 7 consecutive patients who underwent ALA for benign JF tumors with predominant extracranial extension were analyzed. RESULTS: A hockey stick skin incision is made along the superior nuchal line to the anterior edge of the sternocleidomastoid muscle (SCM). ALA involves layer-by-layer muscle dissection of SCM, splenius capitis, digastric, longissimus capitis, and superior oblique muscles. The accessory nerve runs beneath SCM and is found at the posterior edge of the digastric muscle. The internal jugular vein (IJV) is lateral to and at the level of the accessory nerve. The occipital artery passes over the longissimus capitis muscle and IJV and into the external carotid artery, which is lateral and superficial to IJV. The internal carotid artery (ICA) is more medial and deeper than external carotid artery and is in the carotid sheath with the vagus nerve and IJV. The hypoglossal and vagus nerves run along the lateral and medial side of ICA, respectively. Prehigh cervical carotid, prejugular, and retrojugular surgical corridors allow deep and extracranial access around JF. In the case series, gross and near-total resections were achieved in 6 (85.7%) patients without newly developed cranial nerve deficits. CONCLUSION: ALA is a traditional and invaluable neurosurgical approach for benign JF tumors with predominant extracranial extension. The anatomic knowledge of ALA increases competency in adding anterior and lateral exposure of extracranial JF.

Association of MGMT Gene Promoter Methylation With Clinicopathological Parameters in Patients With Wild-type IDH Glioblastoma.

BACKGROUND: The methylation status of the O6-methylguanine-DNA methyltransferase (MGMT) promoter plays a key role in response to temozolomide chemotherapy and disease prognosis in patients with wild-type isocitrate dehydrogenase (IDH) glioblastoma (GBM). PATIENTS AND METHODS: The MGMT promoter methylation status and its association with clinicopathological parameters were retrospectively analysed in a cohort of 316 patients with GBM with wild-type IDH. RESULTS: MGMT methylation was significantly associated with ATRX chromatin remodeler (ATRX) loss and completion of the standard Stupp protocol. The median durations of overall and progression-free survival for the unmethylated, low-methylated (10-39%), and hypermethylated (≥40%) groups were 15, 23, and 30 months and 11, 18, and 21 months, respectively. However, the improvement in the survival of the hypermethylated group was not statistically significant. CONCLUSION: We suggest a possible association between MGMT methylation status and ATRX mutations in GBM with wild-type IDH.

Recent Update on Neurosurgical Management of Brain Metastasis.

Brain metastasis (BM), classified as a secondary brain tumor, is the most common malignant central nervous system tumor whose median overall survival is approximately 6 months. However, the survival rate of patients with BMs has increased with recent advancements in immunotherapy and targeted therapy. This means that clinicians should take a more active position in the treatment paradigm that passively treats BMs. Because patients with BM are treated in a variety of clinical settings, treatment planning requires a more sophisticated decision-making process than that for other primary malignancies. Therefore, an accurate prognostic prediction is essential, for which a graded prognostic assessment that reflects next-generation sequencing can be helpful. It is also essential to understand the indications for various treatment modalities, such as surgical resection, stereotactic radiosurgery, and whole-brain radiotherapy and consider their advantages and disadvantages when choosing a treatment plan. Surgical resection serves a limited auxiliary function in BM, but it can be an essential therapeutic approach for increasing the survival rate of specific patients; therefore, this must be thoroughly recognized during the treatment process. The ultimate goal of surgical resection is maximal safe resection; to this end, neuronavigation, intraoperative neuro-electrophysiologic assessment including evoked potential, and the use of fluorescent materials could be helpful. In this review, we summarize the considerations for neurosurgical treatment in a rapidly changing treatment environment.

Prognostic factors to predict the efficacy of surgical interventions against brain metastasis secondary to thyroid cancer.

Introduction: Brain metastasis in differentiated thyroid cancer (DTC) is rare (frequency < 1%) and has a poor prognosis. Treatment strategies for brain metastasis are not well established. Objectives: We conducted a retrospective analysis to identify predictive factors for patient outcomes and verify surgical indications for patients with brain metastasis and DTC. Methods: The study included 34 patients with pathologically confirmed DTC with brain metastasis from March 2008 to November 2020. The associations between overall survival (OS) and clinical factors were evaluated. Cox regression analysis was used to determine the relationship between clinical factors and OS. To assess the survival benefit of craniotomy, Kaplan-Meier survival analysis was performed for each variable whose statistical significance was determined by Cox regression analysis. Results: The median OS of the entire patient sample was 11.4 months. Survival was affected by the presence of lung metastasis (P = 0.033) and the number of brain metastases (n > 3) (P = 0.039). Only the subgroup with the number of brain metastases ≤3 showed statistical significance in the subgroup analysis of survival benefit following craniotomy (P = 0.048). Conclusions: The number of brain metastases and the existence of lung metastasis were regarded more essential than other clinical factors in patients with DTC in this study. Furthermore, craniotomies indicated a survival benefit only when the number of brain metastases was ≤3. This finding could be beneficial in determining surgical indications in thyroid cancer with brain metastasis.

Surgical Outcomes of Sphenoid Wing Meningioma with Periorbital Invasion.

OBJECTIVE: The aim of this study was to evaluate the clinical outcome of sphenoid wing meningioma with periorbital invasion (PI) after operation. METHODS: Sixty one patients with sphenoid wing meningioma were enrolled in this study. Their clinical conditions were monitored after the operation and followed up more than 5 years at the outpatient clinic of a single institution. Clinical and radiologic information of the patients were all recorded including the following parameters : presence of PI, presence of peri-tumor structure invasion, pathologic grade, extents of resection, presence of hyperostosis, exophthalmos index (EI), and surgical complications. We compared the above clinical parameters of the patients with sphenoid wing meningioma in the presence or absence of PI (non-PI), then linked the analyzed data with the clinical outcome of the patients. RESULTS: Of 61 cases, there were 14 PI and 47 non-PI patients. PI group showed a significantly higher score of EI (1.37±0.24 vs. 1.00±0.01, p<0.001), more frequent presence of hyperostosis (85.7% vs. 14.3%, p<0.001), and lower rate of gross total resection (GTR) (35.7% vs. 68.1%, p=0.032). The lower score of pre-operative EI, the absence of both PI and hyperostosis, smaller tumor size, and the performance of GTR were associated with lower recurrence rates in the univariate analysis. However, in the multivariate analysis, the performance of GTR was the only significant factor to determine the recurrence rate (p=0.043). The incidences of surgical complications were not statistically different between the subtotal resection (STR) and GTR groups, but it was strongly associated tumor size (p=0.017). CONCLUSION: The GTR group showed lower recurrence rate than the STR group without differences in the surgical complications. Therefore, the GTR is strongly recommended to treat sphenoid wing meningioma with PI for the better clinical outcome.

Endoscopic transorbital extradural anterior clinoidectomy: A stepwise surgical technique and case series study [SevEN-013].

Background: Anterior clinoidectomy is an important procedure for approaching the central skull base lesions. However, anterior clinoidectomy through the endoscopic transorbital approach (ETOA) still has limitations due to technical difficulties and the structural complexity of the anterior clinoid process (ACP). Therefore, the authors designed a stepwise surgical technique of extradural anterior clinoidectomy through the ETOA. The purpose of this study was to evaluate the feasibility of this technique. Methods: Anatomical dissections were performed in 6 cadaveric specimens using a neuroendoscope and neuro-navigation system. The extradural anterior clinoidectomy through the ETOA was performed stepwise, and based on the results, this surgical technique was performed in the 7 clinical cases to evaluate its safety and efficiency. Results: Endoscopic extradural anterior clinoidectomy was successfully performed in all cadaveric specimens and patients using the proposed technique. This 5-step technique enabled detachment of the lesser wing of sphenoid bone from the ACP, safe unroofing of the optic canal, and resection of the optic strut without injuring the optic nerve and internal carotid artery. Since the sequential resection of the 3 supporting roots of the ACP was accomplished safely, anterior clinoidectomy was then successfully performed in all clinical cases. Furthermore, no complications related to the anterior clinoidectomy occurred in any clinical case. Conclusion: We designed a stepwise surgical technique that allows safe and efficient anterior clinoidectomy through the ETOA. Using this technique, extradural anterior clinoidectomy can be accomplished under direct endoscopic visualization with low morbidity. Since this technique is applicable to the central skull base surgery where anterior clinoidectomy is necessary, it expands the application of the ETOA.

Regrowth factors of WHO grade I skull base meningiomas following incomplete resection.

OBJECTIVE: The role of adjuvant radiation therapy following incomplete resection of WHO grade I skull base meningiomas (SBMs) is controversial, and little is known regarding the behavior of residual tumors. The authors investigated the factors that influence regrowth of residual WHO grade I SBMs following incomplete resection. METHODS: From 2005 to 2019, a total of 710 patients underwent surgery for newly diagnosed WHO grade I SBMs. The data of 115 patients (16.2%) with incomplete resection and without any adjuvant radiotherapy were retrospectively assessed during a mean follow-up of 78 months (range 27-198 months). Pre-, intra-, and postoperative clinical and molecular factors were analyzed for relevance to regrowth-free survival (RFS). RESULTS: Eighty patients were eligible for analysis, excluding those who were lost to follow-up (n = 10) or had adjuvant radiotherapy (n = 25). Regrowth occurred in 39 patients (48.7%), with a mean RFS of 50 months (range 3-191 months). Significant predictors of regrowth were Ki-67 proliferative index (PI) ≥ 4% (p = 0.017), Simpson resection grades IV and V (p = 0.005), and invasion of the cavernous sinus (p = 0.027) and Meckel's cave (p = 0.027). After Cox regression analysis, only Ki-67 PI ≥ 4% (hazard ratio [HR] 9.39, p = 0.003) and Simpson grades IV and V (HR 8.65, p = 0.001) showed significant deterioration of RFS. When stratified into 4 scoring groups, the mean RFSs were 110, 70, 38, and 9 months for scores 1 (Ki-67 PI < 4% and Simpson grade III), 2 (Ki-67 PI < 4% and Simpson grades IV and V), 3 (Ki-67 PI ≥ 4% and Simpson grade III), and 4 (Ki-67 PI ≥ 4% and Simpson grades IV and V), respectively. RFS was significantly longer for score 1 versus scores 2-4 (p < 0.01). Tumor consistency, histology, location, peritumoral edema, vascular encasement, and telomerase reverse transcriptase promoter mutation had no impact on regrowth. CONCLUSIONS: Ki-67 PI and Simpson resection grade showed significant associations with RFS for WHO grade I SBMs following incomplete resection. Ki-67 PI and Simpson resection grade could be utilized to stratify the level of risk for regrowth.

The Extent of Necrosis in Brain Metastases May Predict Subtypes of Primary Cancer and Overall Survival in Patients Receiving Craniotomy.

Although necrosis is common in brain metastasis (BM), its biological and clinical significances remain unknown. We evaluated necrosis extent differences by primary cancer subtype and correlated BM necrosis to overall survival post-craniotomy. We analyzed 145 BMs of patients receiving craniotomy. Necrosis to tumor ratio (NTR) was measured. Patients were divided into two groups by NTR: BMs with sparse necrosis and with abundant necrosis. Clinical features were compared. To investigate factor relevance for BM necrosis, multivariate logistic regression, random forests, and gradient boosting machine analyses were performed. Kaplan−Meier analysis and log-rank tests were performed to evaluate the effect of BM necrosis on overall survival. Lung cancer was a more common origin for BMs with abundant necrosis (42/72, 58.33%) versus sparse necrosis (23/73, 31.51%, p < 0.01). Primary cancer subtype and tumor volume were the most relevant factors for BM necrosis (p < 0.01). BMs harboring moderately abundant necrosis showed longer survival, versus sparse or highly abundant necrosis (p = 0.04). Lung cancer BM may carry larger necrosis than BMs from other cancers. Further, moderately abundant necrosis in BM may predict a good prognosis post-craniotomy.

Delirium-related factors and their prognostic value in patients undergoing craniotomy for brain metastasis.

Background: Delirium is characterized by acute brain dysfunction. Although delirium significantly affects the quality of life of patients with brain metastases, little is known about delirium in patients who undergo craniotomy for brain metastases. This study aimed to identify the factors influencing the occurrence of delirium following craniotomy for brain metastases and determine its impact on patient prognosis. Method: A total of 153 patients who underwent craniotomy for brain metastases between March 2013 and December 2020 were evaluated for clinical and radiological factors related to the occurrence of delirium. Statistical analysis was conducted by dividing the patients into two groups based on the presence of delirium, and statistical significance was confirmed by adjusting the clinical characteristics of the patients with brain metastases using propensity score matching (PSM). The effect of delirium on patient survival was subsequently evaluated using Kaplan-Meier analysis. Results: Of 153 patients, 14 (9.2%) had delirium. Age (P = 0.002), sex (P = 0.007), and presence of postoperative hematoma (P = 0.001) were significantly different between the delirium and non-delirium groups. When the matched patients (14 patients in each group) were compared using PSM, postoperative hematoma showed a statistically significant difference (P = 0.036) between the delirium and non-delirium groups. Kaplan-Meier survival analysis revealed that the delirium group had poorer prognosis (log-rank score of 0.0032) than the non-delirium group. Conclusion: In addition to the previously identified factors, postoperative hematoma was identified as a strong predictor of postoperative delirium. Also, the negative impact of delirium on patient prognosis including low survival rate was confirmed.

Endoscopic transorbital approach to the cavernous sinus: Cadaveric anatomy study and clinical application (‡SevEN-009).

Objective: Cavernous sinus (CS) invasion is frequently encountered in the management of skull base tumors. Surgical treatment of tumors in the CS is technically demanding, and selection of an optimal surgical approach is critical for maximal tumor removal and patient safety. We aimed to evaluate the feasibility of an endoscopic transorbital approach (ETOA) to the CS based on a cadaveric study. Methods: Five cadaveric heads were used for dissection under the ETOA in the comparison with the endoscopic endonasal approach (EEA) and the microscopic transcranial approach (TCA). The CS was exposed, accessed, and explored, first using the ETOA, followed by the EEA and TCA. A dedicated endoscopic system aided by neuronavigation guidance was used for the procedures. During the ETOA, neurovascular structures inside the CS were approached through different surgical triangles. Results: After completing the ETOA with interdural dissection, the lateral wall of the CS was fully exposed. The lateral and posterior compartments of the CS, of which accessibility is greatly limited under the EEA, were effectively approached and explored under the ETOA. The anteromedial triangle was the largest window via which most of the lateral compartment was freely approached. The internal carotid artery and abducens nerve were also observed through the anteromedial triangle and just behind V1. During the ETOA, the approaching view through the supratrochlear and infratrochlear triangles was more directed towards the posterior compartment. After validation of the feasibility and safety based on the cadaveric study, ETOA was successfully performed in a patient with a pituitary adenoma with extensive CS invasion. Conclusions: Based on the cadaveric study, we demonstrated that the lateral CS wall was reliably accessed under the ETOA. The lateral and posterior compartments of the CS were effectively explored via surgical triangles under the ETOA. ETOA provides a unique and valuable surgical route to the CS with a promising synergy when used with EEA and TCA. Our experience with a clinical case convinces us of the efficacy of the ETOA during surgical management of skull base tumors with CS-invasion.

Intracranial Extraskeletal Myxoid Chondrosarcoma in Fourth Ventricle.

We present an extremely rare case of intracranial extraskeletal myxoid chondrosarcoma. A 36-year-old male presented with dizziness persisting for 2 weeks. MRI of the patient showed well-enhanced mass of fourth ventricle. The tumor was totally removed under telovelar approach. Pathology results confirmed an intracranial extraskeletal myxoid chondrosarcoma. Adjuvant radiotherapy was initiated one month after the surgery, and MRI followed 3 months after initial operation and showed no evidence of tumor recurrence.

Importance of Sufficient Petrosectomy in an Anterior Petrosal Approach: Relightening of the Kawase Pyramid.

BACKGROUND: In 1985, Kawase published an anterior petrosal approach to expose the posterior cranial fossa and to minimize retraction of the temporal lobe. However, some neurosurgeons still have difficulty with removing tumors through an anterior petrosal approach because a complete understanding of the Kawase pyramid has not been achieved. We hypothesized that if anterior petrosectomy were performed with three-dimensional understanding of the Kawase pyramid, it would have a positive effect on extent of tumor resection. METHODS: We performed a retrospective study of patients who underwent surgical treatment for meningioma through an anterior petrosal approach. Patients were divided into total resection and subtotal resection groups, and statistical differences between the groups were analyzed. To identify factors predictive of complete tumor removal, univariable and multivariable logistic regression analyses were performed. RESULTS: Width and height of the drilled internal auditory canal of the total resection group were significantly larger than those of the subtotal resection group (P = 0.001, P = 0.033). The operative angle of the total resection group was significantly larger than that of the subtotal resection group (P < 0.001). Regression analyses showed only drilled internal auditory canal width to be predictive of complete tumor removal, increasing the likelihood of complete tumor removal by 2.778-fold with an increase in drilled internal auditory canal width by 1 mm (P = 0.023). CONCLUSIONS: Insufficient petrosectomy during an anterior petrosal approach adversely affects the extent of tumor resection. Furthering three-dimensional understanding of the Kawase pyramid could aid in complete tumor resection and better outcomes without causing damage to the surrounding organs.

Endoscopic Transorbital Approach to Mesial Temporal Lobe for Intra-Axial Lesions: Cadaveric Study and Case Series (SevEN-008).

BACKGROUND: Endoscopic transorbital approach (ETOA) has been proposed as a minimally invasive technique for the treatment of skull base lesions located around mesial temporal lobe (MTL), mostly extra-axial pathology. OBJECTIVE: To explore the feasibility of ETOA in accessing intraparenchymal MTL with cadaveric specimens and describe our initial clinical experience of ETOA for intra-axial lesions in MTL. METHODS: Anatomic dissections were performed in 4 adult cadaveric heads using a 0° endoscope. First, a stepwise anatomical investigation of ETOA to intraparenchymal MTL was explored. Then, ETOA was applied clinically for 7 patients with intra-axial lesions in MTL, predominantly high-grade gliomas (HGGs) and low-grade gliomas (LGGs). RESULTS: The extradural stage of ETOA entailed a superior eyelid incision followed by orbital retraction, drilling of orbital roof, greater and lesser wing of sphenoid bone, and cutting of the meningo-orbital band. For the intradural stage, the brain tissue medial to the occipito-temporal gyrus was aspirated until the temporal horn was opened. The structures of MTL could be aspirated selectively in a subpial manner without injury to the neurovascular structures of the ambient and sylvian cisterns, and the lateral neocortex. After cadaveric validation, ETOA was successfully performed for 4 patients with HGGs and 3 patients with LGGs. Gross total resection was achieved in 6 patients (85.7%) without significant surgical morbidities including visual field deficits. CONCLUSION: ETOA provides a logical line of access for intra-axial lesions in MTL. The safe and natural surgical trajectory of ETOA can spare brain retraction, neurovascular injury, and disruption of the lateral neocortex.

Triggered Electrooculography for Identification of Oculomotor and Abducens Nerves during Skull Base Surgery.

OBJECTIVE: Electrooculography (EOG) records eyeball movements as changes in the potential difference between the negatively charged retina and the positively charged cornea. We aimed to investigate whether reliable EOG waveforms can be evoked by electrical stimulation of the oculomotor and abducens nerves during skull base surgery. METHODS: We retrospectively reviewed the records of 18 patients who had undergone a skull base tumor surgery using EOG (11 craniotomies and seven endonasal endoscopic surgeries). Stimulation was performed at 5 Hz with a stimulus duration of 200 µs and an intensity of 0.1-5 mA using a concentric bipolar probe. Recording electrodes were placed on the upper (active) and lower (reference) eyelids, and on the outer corners of both eyes; the active electrode was placed on the contralateral side. RESULTS: Reproducibly triggered EOG waveforms were observed in all cases. Electrical stimulation of cranial nerves (CNs) III and VI elicited positive waveforms and negative waveforms, respectively, in the horizontal recording. The median latencies were 3.1 and 0.5 ms for craniotomies and endonasal endoscopic surgeries, respectively (p=0.007). Additionally, the median amplitudes were 33.7 and 46.4 µV for craniotomies and endonasal endoscopic surgeries, respectively (p=0.40). CONCLUSION: This study showed reliably triggered EOG waveforms with stimulation of CNs III and VI during skull base surgery. The latency was different according to the point of stimulation and thus predictable. As EOG is noninvasive and relatively easy to perform, it can be used to identify the ocular motor nerves during surgeries as an alternative of electromyography.

Endoscopic transorbital approach to the insular region: cadaveric feasibility study and clinical application (SevEN-005).

OBJECTIVE: The insula is a complex anatomical structure. Accessing tumors in the insula remains a challenge due to its anatomical complexity and the high chance of morbidity. The goal of this study was to evaluate the feasibility of an endoscopic transorbital approach (ETOA) to the insular region based on a cadaveric study. METHODS: One cadaveric head was used to study the anatomy of the insula and surrounding vessels. Then, anatomical dissection was performed in 4 human cadaveric heads using a dedicated endoscopic system with the aid of neuronavigation guidance. To assess the extent of resection, CT scanning was performed before and after dissection. The insular region was directly exposed by a classic transcranial approach to check the extent of resection from the side with a classic transcranial approach. RESULTS: The entire procedure consisted of two phases: an extradural orbital phase and an intradural sylvian phase. After eyelid incision, the sphenoid bone and orbital roof were extensively drilled out with exposure of the frontal and temporal dural layers. After making a dural window, the anterior ramus of the sylvian fissure was opened and dissected. The M2 segment of the middle cerebral artery (MCA) was identified and traced posterolaterally. A small corticectomy was performed on the posterior orbital gyrus. Through the window between the lateral lenticulostriate arteries and M2, the cortex and medulla of the insula were resected in an anteroposterior direction without violation of the M2 segment of the MCA or its major branches. When confirmed by pterional craniotomy, the sylvian fissure and the MCA were found to be anatomically preserved. After validation of the feasibility and safety based on a cadaveric study, the ETOA was successfully performed in a patient with a high-grade glioma (WHO grade III) in the right insula. CONCLUSIONS: The transorbital route can be considered a potential option to access tumors located in the insula. Using an ETOA, the MCA and its major branches were identified and preserved while removal was performed along the long axis of the insula. In particular, lesions in the anterior part of the insula are most benefited by this approach. Because this approach was implemented in only one patient, additional discussion and further verification is required.