Endoscopic transnasal surgery offers a minimally invasive alternative to transcranial approaches for accessing midline skull base lesions involving the petrous apex and petroclival region. However, lateral access, particularly behind the petrous internal carotid artery (ICA), remains limited. The contralateral transmaxillary (CTM) approach provides a more direct surgical trajectory, more parallel to the petrous ICA. Yet, lateral access through this approach can be restricted by anatomic barriers, including the pterygoid process and lateral buttress of the maxillary sinus. We aimed to evaluate the contralateral transmaxillary-transpterygoid (CTMP) approach, with and without the lateral buttress removal (CTMP-LBR), to determine whether these modifications could enhance surgical access to the petroclival region. Ten sides from 5 formalin-fixed, latex-injected cadaveric specimens were dissected to compare CTM, CTMP, and CTMP-LBR approaches. Petrous bone drilling was directed posterolaterally behind the petrous ICA toward the region medial to the cochlea. In addition, 30 sides from computed tomography angiography scans were analyzed to obtain radiographic measurements for each approach. Compared with CTM, both CTMP and CTMP-LBR significantly increased access for retrocarotid petrous bone drilling (P < .001) and yielded a wider surgical angle relative to midline (P < .001), in both cadaveric and radiographic analyses. In dissections, 20% of sides required CTM only, 50% benefited from CTMP, and 30% required CTMP-LBR to achieve adequate lateral access. Radiographic analysis revealed that CTMP required a median of 4 mm of pterygoid drilling, whereas CTMP-LBR required 9 mm and enabled a trajectory parallel to the petrous ICA with only 11 mm of soft tissue displacement. Patients with smaller angles between the petrous ICA and the horizontal plane were significantly more likely to benefit from CTMP over CTM (P = .005). Modification of the CTM approach with pterygoid drilling and optional LBR improves retrocarotid access. Preoperative evaluation of the petrous ICA angle may help optimize patient-specific planning in endoscopic petroclival surgery.

The far-lateral approach remains essential for accessing ventral and ventrolateral lesions of the craniovertebral junction. However, traditional exposures may involve extensive condylar drilling and muscle dissection, which can compromise craniocervical junction stability. This study aimed to define and quantitatively evaluate a stability-preserving mini far-lateral corridor that provides adequate surgical exposure while minimizing bony and soft-tissue disruption. A systematic literature review was conducted following Preferred Reporting Items for Systematic Reviews and Meta-Analyses 2020 guidelines to characterize technical advancements of the far-lateral approach. Additional cadaveric dissections were performed on 6 fresh-frozen adult specimens using a Z-shaped incision, single-plane craniocaudal muscle dissection, limited suboccipital craniectomy, and one-third occipital condyle drilling. Neuronavigation-based morphometric measurements were used to quantify petroclival exposure. A comparative statistical analysis was conducted against the classical (Spektor, 2000) and minimally invasive (Zhang, 2011) series. The mean petroclival exposure area was 376.86 ± 45.54 mm2, larger than the values reported by Spektor et al (338.00 ± 86.00 mm2; t(17) = 7.22; P = 1.49 × 10-6) and Zhang et al (208.50 ± 28.40 mm2; t(16) = 20.31; P = 7.61 × 10-13). The approach offered a direct posterolateral trajectory to the bulbomedullary junction and lower cranial nerves while maintaining occipitocervical integrity. The mini far-lateral approach provides comparable petroclival exposure, compared with both the classical and keyhole variants, by combining surgical effectiveness with the preservation of stability. These results support its adoption as the standard method for ventral and ventrolateral craniovertebral lesions, with wider condylectomy or fusion reserved for specific trajectory-driven indications.

The combined transpetrosal approach provides effective exposure to the petroclival region and ventral brainstem, although its technical demands necessitate advanced neurosurgical expertise. Proficiency in skull base drilling and meticulous separation of the dual dural layers is crucial. Recently, three-dimensional printing has gained attention as a tool for surgical training. To evaluate its potential in transpetrosal approach education, we developed a three-dimensional head model that reproduces the soft brain tissue, cranial nerves, vasculature, and tumors. A petrotentorial meningioma case was selected, and a corresponding three-dimensional model was generated using computed tomography and magnetic resonance imaging data. The skull base was printed using a three-dimensional printer. Liquid rubber-coated kitchen paper simulated the dura mater, wool yarn represented blood vessels, and rubber bands were used for cranial nerves. Ultra-soft polyurethane resin was employed to replicate the brain, brainstem, cerebellum, and tumor. Neurosurgeons practiced the combined transpetrosal approach on the model and completed a questionnaire evaluating anatomical accuracy and operative usability. Thirteen neurosurgeons participated. No statistically significant differences were found between those with experience in ≥5 combined transpetrosal approach and those with less experience. All participants gave favorable evaluations regarding the model's anatomical accuracy and its value for preoperative planning and surgical training. The model supported essential transpetrosal approach steps, including skull base drilling, dual-layer dural dissection, and tentorial incision, allowing for thorough practice of the combined approach. It offers a practical, realistic training platform that closely resembles actual surgical conditions.

Maximizing Access to the Petroclival Region: An Anatomic Comparison of the Transcranial Preauricular Subtemporal Infratemporal Fossa and Endoscopic Contralateral Transmaxillary Approaches with Clinical Case Series

Lesions of the cerebellopontine angle (CPA) and petroclival region represent a challenging surgical target due to the complex anatomy of the involved neurovascular structures. In this scenario, cranial nerve (CN) VI is particularly exposed to potential injuries due to its deep-seated location and absence of a bony foramen that serves as a reference of its most distal cisternal point, especially when it is encased or displaced by large lesions. This study aimed to provide reliable operative guidance for preventing injuries to CN VI during the retrosigmoid approach to address CPA and petrotentorial lesions. Four formalin-fixed, latex-injected anatomical specimens were dissected to highlight and investigate the relevant anatomy of the CPA and petroclival region during the retrosigmoid approach. Additionally, 50 sides of noninjected formalin-fixed specimens were dissected for morphometric evaluation. Correlations between the petrotentorial junction (PTJ), porus acusticus (PA), and trigeminal impression (TI) with the entry point of CN VI into Dorello's canal were evaluated. An illustrative clinical case and a 3D anatomical model generated through the photogrammetry scanning technique were described. In the sagittal plane, CN VI entrance into Dorello's canal was found in a trajectory parallel to the PTJ, passing through the inferior aspect of the PA and 21.5 ± 1.3 mm anteriorly. In the coronal plane, the entry point of CN VI into Dorello's canal was estimated at 6.2 ± 1.2 mm from the anterior edge of the TI in a trajectory perpendicular to the PTJ in 47 (81%) specimens. The obtained results demonstrated two surgical strategies to locate Dorello's canal within the retrosigmoid route: 1) approximately 20 mm anterior along the inferior edge of the PA parallel to the PTJ; and 2) approximately 6 mm inferior to the anterior edge of the TI, perpendicular to the PTJ. The defined operative strategies provide reliable anatomical guidance to locate the entrance of CN VI into Dorello's canal within the retrosigmoid route, potentially reducing the risk of abducens nerve palsy and improving patient outcomes.

Inframeatal intradural retrosigmoid petrosectomy (IIRP): Multicenter experience and anatomical review of an effective approach to the petroclival region.

Meningiomas are histologically and genetically heterogeneous tumors with varying anatomical distributions. While distinct genetic mutations have been associated with specific tumor locations, the spatial distribution of histological subtypes and their relationship to radiogenomic profiles remains poorly defined. Moreover, the predictive value of spatial information for histopathological classification and tumor grading has not yet been systematically explored. This study aimed to systematically analyze the anatomical predilection of histological meningioma subtypes and their concordance with known mutation-specific spatial patterns, and the predictive potential of voxel-based spatial features. We retrospectively analyzed 737 patients undergoing surgical resection of intracranial meningiomas. Preoperative magnetic resonance images were normalized to a common stereotactic space, and tumors were semi-automatically segmented. Voxel-based lesion-symptom mapping (VLSM) was performed to identify subtype-specific spatial clustering. Spatial distributions were compared with mutation maps from current literature using receiver operating characteristic analysis (AUC-ROC). Additionally, multinomial logistic regression models were applied to evaluate whether tumor localization could predict histological subtype and World Health Organization (WHO) grading. Histological subtypes showed distinct spatial preferences. Meningothelial meningiomas clustered in the anterior and middle skull base; fibrous and transitional types predominated in the convexity, falx, and tentorium; secretory tumors localized to the sphenoid wing and petroclival region; and atypical meningiomas were common in the anterior falx and frontal convexity. Psammomatous meningiomas displayed a broader distribution with involvement of the petrous bone and foramen magnum. AUC analysis revealed strong concordance between histological subtypes and mutation maps, confirming known histogenomic associations (e.g. KLF4/TRAF7 with secretory; NF2 with fibrous and transitional; SMO with meningothelial). No associations to any mutation map were observed for angiomatous, microcystic and metaplastic meningiomas. Predictive modeling based solely on spatial features achieved moderate accuracy for subtype classification and higher accuracy for WHO grade prediction. Meningioma subtypes show distinct, statistically robust anatomical predilections that align with known genetic mutation maps. Predictive modeling highlights that spatial features themselves hold diagnostic and prognostic value, linking anatomical localization to tumor biology and aggressiveness. The study introduces anatomically precise voxel-based templates that may improve radiogenomic classification and non-invasive genotype prediction.

Objective: To investigate the clinicopathological features, immunophenotype, molecular genetic characteristics, and prognosis of clear cell meningioma (CCM). Methods: Seventeen cases with diagnosed of CCM from four hospitals [Xuanwu Hospital (6 cases), Sanbo Brain Hospital (3 cases), Beijing Children's Hospital (4 cases) Affiliated with Capital Medical University; Provincial Hospital Affiliated to Shandong First Medical University (4 cases)], from August 2017 to April 2025, were analyzed. All specimens of CCM cases were H&E stained, followed by immunohistochemistry (IHC), next-generation sequencing (NGS), and DNA methylation profiling. Clinical follow-up and prognostic analysis were performed. Results: The cohort included six males and eleven females, with a median age of 11 (6, 44) years; 10 were pediatric patients, 7 were adult patients. None had neurofibromatosis type 2. Tumor locations included spinal canal (n=5), cerebellopontine angle (n=4), middle/posterior fossa (n=4), petroclival region (n=3), and jugular foramen (n=1). Histologically, tumors showed sheets of polygonal cells with clear glycogen-rich cytoplasm, round/oval nuclei with inconspicuous nucleoli, prominent perivascular and interstitial hyalinized collagen proliferation, and scattered lymphoplasmacytic infiltrates. No other meningioma subtypes were identified (17/17). IHC showed variable expression of EMA, vimentin, SSTR2, and PR, with universal loss of SMARCE1 nuclear expression. The median Ki-67 index was 6%. NGS revealed no NF2 alterations (0/10), while SMARCE1 mutations were detected in 9/10 of cases, including: 2 sites with splice-site mutations, 2 sites with nonsense mutations and 3 sites with frameshift mutations. DNA methylation unsupervised clustering demonstrated distinct profiles separating CCMs (8/33) from other meningiomas (25/33). Among 14 patients with follow-up (median 32 months, range 2-145 months), recurrence occurred in 6 cases and death in 1 case; all recurrence/death cases were pediatric patients. CCM patients had significantly higher recurrence/progression risk compared with WHO grades 1 and 2 meningiomas (HR=3.863, 95%CI: 1.435-10.401,P=0.02), with earlier recurrence. High Ki-67 index (≥10%) was associated with increased risk of recurrence (P<0.01). Conclusions: CCMs exhibit unique age distribution, anatomical predilection, histopathological changes, immunophenotype (SMARCE1 loss), and molecular profile (SMARCE1 mutations, distinct methylation signature). They demonstrate aggressive behavior, particularly in pediatric patients and cases with high proliferative activity, warranting close clinical surveillance and consideration of adjuvant therapy.

Access to complex lesions in the sphenocavernous and petroclival regions are challenging due to their deep location and proximity to critical neurovascular structures. This study aims to re-evaluate the microsurgical anatomy of the anterolateral, lateral, and posterior surgical corridors in three dimensions and present this anatomy using educational models. Pretemporal transcavernous, anterior petrosal, translabyrinthine, and far lateral approaches were performed on five cadavers. Each step was photographed, the images were processed using photogrammetry to create three-dimensional models, and 3D models were tested in an augmented reality and virtual reality environment. In addition, to correlate each anatomical corridor with its corresponding surgical application, an illustrative surgical video case was prepared for each approach. Three-dimensional models were successfully created for each surgical approach in the study. The models detailed the spatial relationships of the surgical corridors in the petroclival and sphenocavernous regions and made them viewable from different angles. Tests conducted using augmented reality applications confirmed that the models could be used interactively. This holistic approach may be used to facilitate the selection of the appropriate corridor or combined approach based on the orientation of the lesion and its neurovascular relationships. Three-dimensional cadaveric models can be used as powerful support tools forn education and planning by enhancing spatial awareness for complex skull base surgeries.

Atypical skull base meningiomas are characterized by aggressive growth and neurovascular invasion, which complicate resection and predispose to high recurrence rates. Lesions encasing major vessels and cranial nerves or refractory to surgery and radiation therapy are associated with significant morbidity, while systemic therapies remain largely ineffective despite ongoing trials. Their management, therefore, necessitates advanced microsurgical strategies. We describe a radiation-induced WHO grade II atypical meningioma extensively involving the cavernous sinus, supra-/parasellar, and petroclival regions in a patient with 6 prior surgeries, 2 Gamma Knife treatments, and multiple systemic therapies, presenting with ophthalmoplegia and right-eye blindness, treated using a three-stage surgical approach.The video can be found here: https://stream.cadmore.media/r10.3171/2025.10.FOCVID25163

Background: Accurate middle cranial fossa (MCF) morphometry is crucial for the safe application of middle fossa approaches such as the Dolenc and Kawase approaches, which expand exposure to the cavernous sinus and petroclival region. These parameters vary widely among individuals and populations, making population-specific data important. We therefore collected MCF measurements in Mexican adults using both CT scans and dry skulls to establish normative values and assess the accuracy of CT scans.Methods: Two cohorts (97/107 subjects each) were analyzed: head CT scans (in vivo) and dry skulls (ex vivo) of adult Mexicans. Key distances (Foramen ovale (FO) - Foramen spinosum (FS), FO - arcuate eminence (AE), FS - AE) and innominate pillar thickness were measured bilaterally (each in duplicate). CT versus skull differences were tested (α = 0.05) using side-to-side symmetry analysis, and the 5th/95th percentiles were used as anatomical limits.Results: CT and osteology showed close concordance for FO-FS, supporting CT-based extradural orientation for the middle fossa approach. In contrast, FO-AE and FS-AE were larger on dry skulls by a few millimeters, indicating that routine CT slightly underestimates the drillable petroclival window relevant to Kawase. The innominate pillar was consistently present and appeared slightly thicker on CT (partial-volume effect), remaining a practical landmark to localize CN V3 (mandibular division of the trigeminal nerve) between FO and FS. Left-right asymmetry was not evident on CT; osteology showed only small AE-related leftward tendencies. Percentile guardrails (P5, P50, P95) provide pragmatic bounds for preoperative planning.Conclusions: This study provides the first MCF morphometric norms for Mexican adults to support safer, individualized Dolenc, Kawase, and middle fossa approach planning. CT-based measurements are largely reliable for surgical planning, although they slightly underestimate the Kawase approach reference points.

Abstract Primary intracranial squamous cell carcinoma (SCC) is a rare disease entity that is usually derived from the malignant transformation of an epidermoid cyst. Even less common is the primary intracranial SCC that arises de novo, with only 11 patients reported in literature. Most patients are managed with surgery and radiotherapy. We report a 37-year-old female who presented with a 3-year history of ear fullness and decreased hearing on the right, initially diagnosed and managed as chronic sinusitis. Three years from the onset of otologic symptoms, she also experienced right hemifacial numbness and paresthesia. A cranial magnetic resonance imaging (MRI) with contrast revealed a right middle cranial fossa mass, along the right petroclival region, for which a meningioma was initially considered. She underwent right pterional craniotomy and excision of tumor. Histopathology results showed a non-keratinizing squamous cell carcinoma of the undifferentiated type. Two months after the surgery, she developed new neurologic symptoms of right peripheral facial palsy and gait imbalance. Neuroimaging confirmed tumor recurrence. An MRI of the nasopharynx, transnasal flexible endoscopy, and a whole-body positron emission tomography and computed tomography (PET/CT) scan did not show evidence of a tumor elsewhere. She underwent chemotherapy with cisplatin, etoposide, and cyclophosphamide (CCE protocol) for four cycles followed by radiation therapy, with a significant decrease in the size of the tumor and improvement of her craniopathies. The patient remains stable three months from completion of treatment. This case illustrates a rare case of primary intracranial SCC arising de novo and the success of multi-modality treatment. Due to the rarity of this disease entity and with limited literature available, the standard treatment modality is yet to be identified. More studies are needed to optimize the management of this rare and aggressive tumor.

Disclosure: C. Rizk: None. G. Sydney: None. P. Gopal: None. S. Omay: None. P. Balasubramanian: None.Background: Ectopic salivary tissue within the sella is rare and mostly asymptomatic. Preoperative diagnosis is often challenging as they mimic pituitary neoplasms and the diagnosis is typically made after resection or biopsy. We present a case of ectopic intrasellar salivary gland tissue confirmed on histopathology in a patient who was presumed to have a meningioma on her initial imaging performed for the evaluation of headache. Case Presentation: A 61-year-old female presented with 4 month history of severe bifrontal headache and bilateral upper extremity weakness. Brain MRI was performed revealing a 2.8 x 2.6 x 1.9 cm mass along the left petroclival region extending into the sella, and into the left cavernous sinus with deviation of the pituitary stalk. The MR imaging characteristics were consistent with meningioma. Endocrine biochemical evaluation was unremarkable. Given the discordance between the patient’s clinical presentation and imaging characteristics and the short duration of her symptoms, endoscopic endonasal biopsy of the sellar lesion was performed for a definitive diagnosis. Histopathology was consistent with benign seromucinous salivary gland tissue with chronic inflammatory infiltrate. To rule out metastatic disease, DOTATATE PET scan was done which showed tracer uptake within the sella and the left cavernous sinus but no other abnormality. The patient was managed conservatively with improvement in her symptoms, and the lesion has remained stable on serial MRI imaging over the last one year. Conclusion: Ectopic salivary gland tissue in the sellar region is a rare finding and is typically asymptomatic. When symptoms do occur, they are often attributed to leakage of glandular secretions leading to localized inflammation. In uncommon instances, larger lesions may cause endocrine disturbances, including hyperprolactinemia or growth hormone deficiency. Definitive diagnosis generally relies on histopathological evaluation, and the overall prognosis is excellent.Presentation: Sunday, July 13, 2025

The jugular tubercle (JT) is a bony prominence located between the basilar and condylar parts of the occipital bone, superior to the hypoglossal canal. This study compares the volume of the JT removed, the overall area of exposure and the surgical corridor among the far lateral approach (FLA), far medial approach (FMA), and contralateral transmaxillary (CTM) corridor. Using image guidance, 10 cadaveric specimens were dissected: The JT was drilled through FMA and CTM in 10 sides, whereas FLA was performed on the opposite 10 sides. The surgical corridor and overall area of exposure were measured. A subanalysis was conducted to compare the angle of the surgical trajectory between FMA and CTM. Computed tomography scan volumetric measurements were used to compare the approaches. Five illustrative cases are presented. The angle of the surgical trajectory to the JT was significantly greater for CTM (33.8° ± 7.1°) compared with FMA (14.3° ± 2.6°, P < .001). The area of exposure was significantly larger with FLA (410.7 ± 78.1 mm2) and CTM (436.8 ± 44.8 mm2) compared with FMA (270.7 ± 21.9 mm2, P < .001). In addition, CTM (212.2 ± 32.2 mm2) provided a significantly wider surgical corridor than FMA (82.7 ± 12.4 mm2, P < .001) and showed a trend toward greater exposure compared with FLA (P = .05). The mean percentage of JT resected was 56.7% for FLA, 40.4% for FMA, and 94% for CTM (P < .05). Open and endoscopic approaches are complementary for addressing lesions in the inferior clival and petroclival regions. The CTM approach represents a feasible extension of the standard endoscopic endonasal approach, increasing the surgical corridor angle and providing greater lateral exposure than the FMA. In addition, CTM enables a substantially greater volume of JT resection compared with both FLA and FMA.

The extradural anterior petrosal approach (EAPA) is a surgical technique utilized to access pathologies in the petroclival region and the anterolateral aspect of the brainstem, allowing enhanced visualization and maneuverability. Despite its advantages, the EAPA is associated with significant potential complications that remain a topic of debate within the neurosurgical community. This meta-analysis aims to evaluate the incidence of approach-related complications following EAPA. A systematic literature review was conducted across several databases, including PubMed, Scopus, and Embase. The primary outcome was cerebrospinal fluid (CSF) leak, while secondary outcomes included facial palsy, hearing loss, temporal lobe injury, postoperative seizures, and dry eye. Statistical analysis was performed using RStudio 2024.04.1 + 748. Heterogeneity was assessed using I² statistics. Sensitivity analysis was performed with the leave-one-out test. The risk of bias was assessed using ROBINS-I for non-randomized studies. Publication bias was assessed using a funnel plot and Furuya-Kanamori's Doi plot. Exclusion criteria were cases of intradural anterior petrosal approaches and articles where the data concerning approach-related complications could not be extracted. Our systematic search yielded 1098 articles, of which five met the inclusion criteria, encompassing 404 patients. The overall CSF leak rate was estimated at 3.15% (95% CI: 0.07-8.92), with a lower reoperation rate for CSF leaks at 0.40%. Other complications included temporal lobe injury (1.12%), postoperative seizures (2.42%), approach-related facial palsy (2.23%), and approach-related hearing loss (1.04%). Notably, the incidence of postoperative dry eye was reduced from 6.04 to 2.36% following refinements in surgical practices. The EAPA is a safe procedure with a low complication rate when performed in specialized centers. Outcomes depend on meticulous technique, experienced teams, comprehensive preoperative assessment, and neurophysiological monitoring. This meta-analysis is the first to focus on approach-related complications of EAPA, providing valuable insights to enhance surgical safety and patient care.

Lower petroclival meningiomas (PCMs) and jugular tubercle meningiomas are among the most challenging tumors in neurosurgery, with the optimal approach still debated. Traditional posterior and lateral open approaches are still commonly employed but are invasive and carry significant risks due to brain retraction and neurovascular manipulation. The extended endonasal transclival approach has emerged as a less invasive alternative for midline lesions, offering direct access with early tumor devascularization and reduced manipulation of critical structures. However, limitations include lateral tumor extension, challenging skull base reconstruction, and nasal morbidity, especially when using a nasoseptal flap, which may negatively affect quality of life. To minimize both intracranial and nasal morbidities, we propose a right mononostril contralateral endonasal approach using the chopstick technique with angled scopes and instruments, combined with sphenoid sinus cranialization and rostral mucosal suturing for reconstruction. A 33-year-old man presented with progressive headaches. Neuroimaging revealed a 29 × 39-mm PCM centered in the lower petroclival junction. Preoperative embolization was followed by tumor resection using a right mononostril endoscopic endonasal approach. Closure involved cranialization of the sphenoid sinus with rostral mucosa suturing. Postoperatively, lumbar punctures for cerebrospinal fluid depletion were conducted. No cerebrospinal fluid leakage or new neurological deficits were observed. The mononostril endoscopic endonasal chopstick technique provides direct access to the petroclival region, enabling total resection of selected low-lying PCMs or jugular tubercle meningiomas. This minimally invasive technique, combined with rostral mucosal closure, may reduce surgical morbidity and improve postoperative quality of life.

To investigate the impact of endoscopic techniques on the exposure of the petroclival region and the protection of the abducens nerve in the retrosigmoid approach by comparing the exposure range of the petroclival region and the length of the abducens nerve exposed in the retrosigmoid approach using endoscopic and microscopic techniques. Twelve skull specimens, which had been perfused with colored latex, were used for microanatomical dissection of the retrosigmoid approach to the petroclival region in the endoscopic anatomy laboratory with the aid of a 0-degree endoscope and a ZEISS microscope. The anatomic structures exposed in the petroclival region under endoscopy and microscope were observed and compared. The area of the petroclival region exposed and the length of the abducens nerve exposed were measured and analyzed. The area of the petroclival region exposed by the endoscope (1244.98±83.80mm²) was larger than that exposed by the microscope (631.02±58.32mm², P<0.001). The subarachnoid segment of the abducens nerve was completely visualized under the endoscope with an average length of 16.62±0.95mm, while only partially exposed under the microscope with an average length of 10.23±0.50mm (P<0.001). In the retrosigmoid approach for exposing the petroclival region, the endoscopic technique can expose a larger area of the petroclival region, which is beneficial for the exposure of the petroclival region. The endoscopic technique can expose a longer segment of the abducens nerve, which is more conducive to the protection of the abducens nerve.

The abducens nerve (AN), our sixth cranial nerve, is responsible for the innervation of the lateral rectus muscle of the eye. The abducens nerve is a vulnerable structure at the skull base with its long intracranial course and complex topographic relationships. The AN anatomy in the petroclival region, where the nerve passes from the posterior to the middle cranial fossa, is of great interest for neurosurgical procedures. Despite detailed studies of its anatomy from the past 150 years, there is a need for more recent data on macroscopical and microscopical aspects of the AN in well defined populations. We investigated macroscopical variations and the number of nerve fibers of the AN in the petroclival region in German body donors. In our histological samples (n = 24) we counted 4688 (+/-1,041) nerve fibers per AN. There was no correlation between sex, age and body side regarding the number of nerve fibers. In our macroscopic examination (n = 76 skull base sides), we found six duplications (four left-sided, two right-sided; 7.9%) and one triplication (right-sided; 1.3%) of the AN in the petroclival region. The AN triplication was further examined: Three nerve bundles pierce the dura mater separately and united before passing under the petrosphenoidal ligament (of Gruber). Variations of the AN in the petroclival region are not a rare phenomenon but occur very frequently. Consequently, we have developed a new classification system for AN variations. This knowledge might help neurosurgeons, as it prepares them to be aware of such variations and adapt their surgical approaches accordingly.

Meningiomas of the petroclival region (MPR) are among the most challenging skull base tumors to manage surgically. Historically, their treatment carried high risks and significant mortality due to the complex anatomy and proximity to critical neurovascular structures. Advances in microsurgical techniques and neuroimaging have significantly improved surgical outcomes. The retrosigmoid approach is a well-established technique for accessing the posterior cranial fossa, further enhanced by specific working corridors and accessory techniques. To illustrate the versatility of the retrosigmoid approach in managing MPR, emphasizing accessory techniques and tailored working corridors to optimize outcomes. Between January 2015 and August 2024, 32 patients with MPR underwent surgical resection using the retrosigmoid approach in the semi-sitting position. Surgical videos were analyzed to identify working corridors and accessory techniques. Preoperative clinical status, extent of resection, and postoperative outcomes were evaluated. The study included 32 patients (mean age: 56.2 years; 46.9% female). Accessory techniques were used in 28.1% of cases, including suprameatal tubercle drilling (12.5%), tentorial sectioning (9.4%), and petrous apex drilling (6.2%). Working corridors were adapted based on tumor location: the lateral cerebellar corridor alone was used in 37.5%, supracerebellar alone in 12.5%, and both combined in 50%. New or progressive cranial nerve deficits occurred in 18.75% of patients. No major complications, such as cerebrospinal fluid leakage or infections, were reported. This study demonstrates how accessory techniques and tailored working corridors enhance the retrosigmoid approach's versatility, establishing it as a safe and effective option for MPR resection. Not applicable.

Resection of deep cerebral lesions presents significant challenges for neurosurgeons. However, advancements in neuroendoscopic techniques have led to the adoption of endoscopic surgery via the supracerebellar infratentorial approach for addressing deep cerebral lesions located in the petroclival region, cerebellopontine angle, and pineal region. The aim of this study was to explore the curative effects and analyse the characteristics of the neuroendoscopic far-lateral supracerebellar infratentorial approach for treating these lesions. Sixteen cases of deep cerebral lesions treated with this method were reviewed, and the surgical outcomes and patients’ postoperative conditions were assessed to evaluate the approach’s effectiveness. Among the 16 patients, ten were diagnosed with petroclival region meningiomas, two with epidermoid cysts in the cerebellopontine angle, two with germ cell tumours in the pineal region, one with a trigeminal schwannoma, and one with a thalamic haematoma. Notably, only two patients (12.5%) experienced postoperative complications, and during follow-up, three patients (18.6%) exhibited no symptom improvement. These findings indicate that the neuroendoscopic far-lateral supracerebellar infratentorial approach enhances lesion exposure, improves the surgeon’s view of the surgical field, minimizes the risk of intraoperative injury, and reduces the risk of postoperative complications, demonstrating significant potential for the clinical treatment of skull base lesions due to its effectiveness and safety.