BACKGROUND AND OBJECTIVES:Anatomic variability and poor mastoid pneumatization increase the risk of facial nerve injury during mastoidectomy by reducing the reliability of conventional anatomic landmarks. Currently, no standardized numerical guidelines define safe drilling depth relative to the facial canal. The objective of this study was to analyze the mastoid segment of the facial nerve on noncontrast head computed tomography (NCCT) to quantify facial nerve depth at 3 reproducible mastoid reference points and to define a practical, imaging-based safe-drilling zone for mastoidectomy. METHODS:We retrospectively reviewed 100 adult NCCT examinations (200 sides; 65 women, 35 men) acquired with bone windows, submillimetric slice thickness (≤0.6 mm), and multiplanar reformations aligned to the orbitomeatal line (Reid's baseline). Bilateral measurements captured the perpendicular cortex-facial canal distance at 3 anatomic landmarks: (1) incus level, (2) midpoint between the incus and the stylomastoid foramen, and (3) stylomastoid level. Distances (mm) were summarized using 2.5th to 97.5th percentiles. RESULTS:Across 200 sides, cortex-facial canal distances were 15.81 to 24.22 mm at the incus level, 11.53 to 20.22 mm at the midpoint, and 10.34 to 19.77 mm at the stylomastoid level (2.5th-97.5th percentiles). For intraoperative usability and safety, we rounded the 2.5th percentiles down to define safe-drilling limits of 15 mm (incus), 11 mm (midpoint), and 10 mm (stylomastoid). CONCLUSION:NCCT-based percentile mapping yielded reproducible thresholds for drill depth relative to the facial canal. Limiting depth to ≤15 mm at the incus, ≤11 mm at the midpoint, and ≤10 mm at the stylomastoid level provides an anatomically grounded reference that may support operative depth awareness and safer mastoid drilling, particularly when conventional landmarks are unreliable.

BACKGROUND AND OBJECTIVES:Contemporary skull base surgeons must understand transcranial and endoscopic endonasal approaches to the petrous apex (PA). We provide an anatomic overview and comparison of main approaches to the PA through illustrative anatomic dissections. METHODS:On 10 sides of 5 specimens, transcranial approaches to the PA including the anterior petrosal, transcochlear, and retrosigmoid with suprameatal extension were performed. For endoscopic endonasal approaches, the transclival approach was performed in the midline of 5 specimens and its contralateral transmaxillary extension was performed on 10 sides. RESULTS:The anterior petrosal approach offers an anterolateral view of the PA bounded by petrous ridge posteromedially, internal auditory canal posterolaterally, greater superficial petrosal nerve anterolaterally, and lateral boundary of cranial nerve V, the Gasserian ganglion, and V3 anteromedially; it exposes the middle fossa and, once the PA is removed, the superomedial cerebellopontine angle. The transcochlear approach affords a lateral view of the PA defined medially and inferiorly by inferior petrosal sinus, posteriorly by posterior fossa dura, anteriorly by the petrous internal carotid artery, and superiorly by the superior petrosal sinus and middle fossa dura. Through a retrosigmoid approach, the PA is bounded by the superior petrosal sinus superiorly, the sagittal plane of cranial nerve VI medially, and the axial and sagittal plane of the internal auditory canal porus inferiorly and laterally, respectively. It affords a panoramic view of the posterior fossa and access to Meckel's cave after PA drilling. Endoscopic endonasal approaches target the anteromedial PA, and it is demarcated by a triangle consisting of cranial nerve VI posterolaterally, the paraclival segment of the internal carotid artery anteriorly, and the petroclival synchondrosis inferiorly and medially. The addition of the contralateral transmaxillary approach enhances lateral access up to the internal auditory canal. CONCLUSION:We provide a comprehensive overview of the main approaches to the PA through illustrative anatomic dissections and representative cases.

[This corrects the article DOI: 10.3389/fonc.2026.1731276.].

BACKGROUND:Choosing between two-burr-hole craniostomy and bone-flap elevation for subdural hematoma (SDH) drainage is usually straightforward; however, in subacute cases there is often uncertainty about whether burr holes will achieve adequate evacuation. A hematoma density threshold in Hounsfield units (HU) on non-contrast computed tomography (CT) may offer an objective guide. METHODS:We retrospectively analyzed 281 surgically treated SDHs. Mean hematoma density was measured on standardized NCCT using a polygonal region of interest at the axial slice of maximal thickness. The primary outcome ("bone-flap need") included initial bone-flap elevation, intraoperative conversion, or immediate postoperative evacuation <80%. Threshold derivation was restricted to subacute cases (n = 114). As a secondary analysis, chronic-with-rebleeding cases underwent receiver operating characteristic evaluation without threshold derivation (n = 93). Diagnostic performance was assessed using receiver operating characteristic curves with bootstrap estimation of the area under the ROC curve and 95% confidence interval. Threshold selection used Youden's index, and operating characteristics were also reported at a fixed reference of 40 HU. RESULTS:In subacute cases, mean density discriminated the primary outcome (area under the ROC curve 0.846; 95% confidence interval 0.758-0.914). A threshold near 40 HU provided sensitivity 85% and specificity 79%. Burr-hole success decreased progressively with increasing density: 96% (63/66) for HU < 40, 57% (12/21) for HU 40-45, and 46% (5/11) for HU > 45. In chronic cases with rebleeding, no evaluated variable demonstrated clinically meaningful discrimination. CONCLUSIONS:A threshold near 40 HU may serve as an adjunct to guide burr-hole versus bone-flap selection in subacute SDH. Prospective multicenter validation is needed.

Background: CNS tumors present significant diagnostic challenges due to their heterogeneity. Successive editions of the World Health Organization (WHO) classification have progressively incorporated molecular markers as essential criteria. Nonetheless, in low- and middle-income countries, limited access to molecular testing hampers the full application of these classifications. To assess this situation, we decided to evaluate the impact of successive WHO classifications on glioma diagnostic accuracy in a high-volume neurosurgical center in Latin America. We conducted a retrospective analysis of patients that underwent elective tumor surgery between January 1st, 2010 and December 31st, 2024 and whose pathology report was consistent with a glioma. Demographic, anatomical, histological, and molecular data were collected. Tumors were classified according to WHO CNS Tumor Classification criteria of 2007, 2016, and 2021. Statistical analyses were performed using STATA v15.A total of 443 patients were included. Under WHO 2007 criteria, glioblastoma was the most common tumor type, with virtually all tumors classified histologically. With WHO 2016 implementation, the proportion of tumors labeled as “not otherwise specified” (NOS) and cases with incomplete tumor characterization increased. Application of WHO 2021 further highlighted diagnostic limitations, with 24% of tumors categorized as high- or low-grade glioma NOS, instead of a particular tumor type/entity. This work sheds light on the fact that the progressive complexity of glioma classification with the addition of new molecular and genetic factors may have as a counterpart an increase in the number of cases with inadequate tumor characterization due to the lack of accessibility to key molecular studies in diagnosis.

Few studies have compared different topical hemostatic agents in live models or brain tissue, and their doses are not standardized. Little is known about the combined use of these different elements in terms of efficacy and safety, especially in neurosurgery. The objective of this study was to evaluate the efficacy of different topic hemostatic agents used in daily neurosurgical practice in an experimental animal model study. A group of 42 Wistar rats was used. A stereotaxic frame was fixed, and coordinates were determined to locate the bregma. A 3 mm hole was drilled with a bone-profile burr on each side of the midline. A stylet was inserted into the brain to create the defect and induce bleeding. The rats were randomly divided into seven groups, with each group assigned a hemostatic agent. Hemostasis time and control time on the opposite side were measured. Hemostasis was achieved after an average of 1 82 s in the group treated with Beriplast, making it the hemostatic agent that stopped the bleeding the fastest. The control time was an average of 40, 14 s. Compared with the negative control, all the agents resulted in significantly better hemostasis (P < 0.05). A reduction in postoperative bleeding positively impacts annual morbidity and mortality rates, hospitalization time, and hospital bed turnover. Understanding the efficacy and safety of different hemostatic agents will enable surgeons to optimize intraoperative hemostasis, thereby achieving better postoperative outcomes and increased patient safety.

BACKGROUND AND OBJECTIVES: Härtel triangle provides surface landmarks for locating the foramen ovale (FO) when performing trigeminal nerve percutaneous procedures. Although widely adopted in clinical practice, there is no report that these landmarks have ever been formally validated through modern imaging techniques. Here we aim to validate Härtel anatomical landmarks using computed tomography scans and propose technical considerations for percutaneous trigeminal procedures. METHODS: Retrospective analysis of 198 FO from 99 adult head computed tomography scans. Measurements included distances from FO to external auditory canal (EAC), FO to midline, eye's midpupillary (MP) line to midline, and eye's inner canthus (IC) line to midline. Statistical analysis was performed, and results were compared with Härtel description. RESULTS: The mean distance from EAC to FO was 23.26 mm (SD: 3.00 mm). Distance from midline to FO was 25.43 mm overall (SD: 1.87 mm). Distance from midline to MP line was measured at 31.96 mm (SD: 1.89 mm). The mean distance from midline to IC line was 14.68 mm (SD: 1.73 mm). CONCLUSION: Härtel landmarks can be adjusted for greater accuracy when performing percutaneous trigeminal nerve procedures. The FO is located closer to the EAC and more medially situated than previously assumed. Revised technique suggests aiming the needle trajectory approximately 2 to 2.5 cm anterior to the tragus and targeting a point between the IC and MP lines rather than directly along the MP line. Excessive medial and posterior needle displacement should be avoided to prevent inadvertent vascular injury. These adjustments could enhance procedural accuracy and safety, improving patient outcomes.

BACKGROUND AND OBJECTIVES:The coexistence of complete carotico-clinoid bridge (CCB), an ossification between the anterior (ACP) and the middle clinoid (MCP), and an interclinoidal osseous bridge (ICB), between the ACP and the posterior clinoid (PCP), represents an uncommonly reported anatomic variant. If not adequately recognized, osseous bridges may complicate open or endoscopic surgery, along with the pneumatization of the ACP, especially when performing anterior or middle clinoidectomies. METHODS:According to Preferred Reporting Items for Systematic Reviews and Meta-Analyses for Scoping Reviews guidelines, a systematic scoping review was conducted up to June 5, 2023. PubMed, Scopus, Web of Science databases, and additional citations were searched. Two hundred high-resolution noncontrast computed tomography (CT) scans (400 sides) and 41 dry skulls (82 sides) were analyzed to identify the different morphology of sellar bridges, focusing on the coexistence of complete CCF and ICB. Two embalmed latex-injected heads with coexisting CCF and ICB were dissected step-by-step to show the anatomic relationship with the surrounding structures from an endoscopic and microscopic perspective. RESULTS:A total of 19 articles were included. The review identified a complete CCF and ICB rate ranging from 4.92% to 6.3%. The analysis of 200 CT scans revealed a rate of coexistence in 4% of the cases, all encountered in White women. Two different types of interclinoid bridges were identified based on the degree of bone mineralization. Both endoscopic and macroscopic step-by-step dissections highlighted variability in morphology and consistency of the sellar bridges and the close relationship with the cavernous sinus neurovascular structures. CONCLUSION:The coexistence of CCF and ICB is an anatomic variation found in 4% of cases. Preoperative knowledge of the degree of mineralization and its relationship with surrounding structures is essential to performing safe surgery and minimizing cranial nerve and vascular injuries. Preoperative high-resolution CT scans can adequately identify these anatomic variations.

Posterior circulation aneurysms represent one of the least common sites affected by intracranial aneurysms, accounting for less than 1% of cases.(1,2) Although advancements in endovascular techniques have enabled the exclusion of most of these aneurysms, surgical treatment is still required for complex lesions characterized by wide neck,3 signs of dissection, giant morphology, or those involving perforators or adjacent branches.4 Several surgical approaches have been described including the pterional, orbitozygomatic, pretemporal, or subtemporal route.(2,4,5) However, in certain cases, a high basilar bifurcation and the presence of dominant pretemporal veins may compromise the surgical feasibility by posing an obstacle to access and increasing the risk of venous complications, particularly in the dominant hemisphere. To facilitate the splitting of Sylvian fissure, some authors have proposed an extradural dissection of the cavernous sinus, followed by a dural incision to allow sphenoparietal sinus transposition and preserve the pretemporal veins.(6-8) In this video, a 46-year-old man developed sudden horizontal diplopia and incomplete ptosis in the left eye with thalamomesencephalic ischemia due to perforating arteries occlusion. Angiography confirmed an unruptured wide-neck aneurysm at the P1/P2 segment, along with significant pretemporal venous drainage on the left side. The patient consented to the procedure and the publication of the images; Institutional Review Board approval was not required. A combined extradural-intradural pretemporal transzygomatic approach with sphenoparietal sinus transposition and aneurysm clipping was performed. Postoperative computed tomography angiography confirmed complete aneurysm exclusion. The patient's left sided ptosis resolved completely within two months.

The intraosseous subarcuate loop is an anatomic variant of the anterior inferior cerebellar artery (AICA), in which the artery gives off the subarcuate artery at the apex of the loop, entrapped in the subarcuate fossa (SF) of the temporal bone. First reported by Tanriover and Rhoton, 1 few others 2-5 have addressed this additional challenge during cerebellopontine angle surgery, occurring in 0.6%–4%. 3,6 We present a case of the safe mobilization of the intraosseous variant of the AICA and resection of a trigeminal schwannoma through a retrosigmoid approach with reverse anterior petrosectomy. Illustration of the same anatomic variation in a specimen is also provided. A 42-year-old male patient presented with intermittent right trigeminal neuropathy. MRI identified an extra-axial dumbbell-shaped heterogeneously contrast-enhancing lesion extending from the right Meckel cave into the cerebellopontine angle. The 3D-CISS sequence demonstrated a possible vascular loop of the right AICA within the SF. Physical examination was negative. Documented and verified informed consent was obtained. A right retrosigmoid craniotomy with reverse anterior petrosectomy was performed. The subarcuate artery was coagulated and divided, and the intraosseous loop of the AICA was safely mobilized, with the steps demonstrated on a specimen. The extra-axial mass was exposed, and gross total resection was achieved. The Doppler signal in AICA was appropriate at the end of the operation. The patient recovered well with mild ipsilateral trigeminal sensory loss and no new neurological deficits. Intraosseous AICA loop in the SF is a relatively common anatomic variation. Identification and safe mobilization are essential to avoid intraoperative lesion of AICA.

Distal anterior cerebral artery (ACA) aneurysms constitute 4%–5% of all intracranial aneurysms.1, 2, 3 Rarely, these aneurysms can be complex and less amenable to conventional clipping or endovascular techniques, requiring alternative treatment strategies.4,5 Surgical modalities utilized in these situations may involve trapping and flow replacement techniques to exclude the aneurysm while maintaining normal perfusion to the affected territories.4, 5, 6, 7 In this Video 1, we describe the modified trapping technique for cases where 2 branches arise from the aneurysm and cannot be sacrificed. This technique involves the transposition of 1 of the branches and its reimplantation distally to the lesion. The aneurysm is then clipped, trapping the segment from which the disconnected branch originated, while preserving anterograde blood flow to both non-occluded and reimplanted branches. Compared with complete trapping in similar situations, this technique prevents the formation of a dead-end in the parent artery that could lead to thrombosis,8 poses no risk to uninvolved arteries, and requires only one anastomosis. This technique was applied in a 54-year-old female patient who presented at our institution with an incidental fusiform distal ACA aneurysm diagnosed after head trauma. Imaging demonstrated that the aneurysm originated from a bihemispheric ACA with 2 pericallosal arteries arising from it. The patient tolerated the procedure well, and postoperative imaging showed complete aneurysm occlusion and patency of both the non-occluded and reimplanted pericallosal arteries. The patient consented to the procedure and the publication of her images. Institutional review board approval was deemed unnecessary.

BACKGROUND AND OBJECTIVES: The intraosseous subarcuate loop (SL) is a unique variant of the anterior inferior cerebellar artery (AICA), where a loop of the artery is trapped in the petrous bone's subarcuate fossa (SF). Recognizing this variant is crucial for planning cerebellopontine angle (CPA) surgeries; however, data regarding its frequency and management vary in the published literature. A cohort from a single center was studied using MRI to assess its prevalence, and the findings were compared with the existing literature. In addition, an intraoperative guide for mobilizing the intraosseous AICA's SL was provided through a detailed step-by-step cadaveric dissection. METHODS: Two hundred fifty-eight patients who had undergone MRI scans of the CPA (516 sides) were retrospectively reviewed. MRIs displaying vascular loops visible in the axial view were analyzed using multiplanar reconstruction, and the intraosseous loop frequency was evaluated. A scoping review was undertaken to provide an overview of previously published data on its prevalence. One embalmed and latex-injected specimen with intraosseous AICA's SL was dissected through a retrosigmoid approach, and 1 surgical case was detailed, describing the procedure to release it. RESULTS: Intraosseous AICA's SL mobilization involves the identification of its entry and exit points within the petrous bone, dural incision to expose the SF, SF drilling, subarcuate artery division, and detaching the vascular loop. Preservation of a dural cuff is crucial to prevent vascular injury. We analyzed 258 brain MRIs (mean age 55 years, 42% male). The intraosseous AICA's SL was present in 4 of 516 evaluated CPAs (0.8%). The prevalence of the vascular anomaly in the reviewed literature using different radiological modalities ranged from 0.2% to 1.6%. CONCLUSION: The intraosseous AICA's SL is an uncommon anatomic variation detectable by MRI, posing an added risk in CPA surgery. Identifying and properly mobilizing it is crucial for safe vascular preservation.

OBJECTIVE:Several pathologies either invade or arise within the orbit. These include meningiomas, schwannomas, and cavernous hemangiomas among others. Although several studies describing various approaches to the orbit are available, no study describes all cranio-orbital and orbitocranial approaches with clear, surgically oriented anatomical descriptions. As such, this study aimed to provide a comprehensive guide to the microsurgical and endoscopic approaches to and through the orbit.METHODS:Six formalin-fixed, latex-injected cadaveric head specimens were dissected in the surgical anatomy laboratory at the authors' institution. In each specimen, the following approaches were modularly performed: endoscopic transorbital approaches (ETOAs), including a lateral transorbital approach and a superior eyelid crease approach; endoscopic endonasal approaches (EEAs), including those to the medial orbit and optic canal; and transcranial approaches, including a supraorbital approach, a fronto-orbital approach, and a 3-piece orbito-zygomatic approach. Each pertinent step was 3D photograph-documented with macroscopic and endoscopic techniques as previously described.RESULTS:Endoscopic endonasal approaches to the orbit afforded excellent access to the medial orbit and medial optic canal. Regarding ETOAs, the lateral transorbital approach afforded excellent access to the floor of the middle fossa and, once the lateral orbital rim was removed, the cavernous sinus could be dissected and the petrous apex drilled. The superior eyelid approach provides excellent access to the anterior cranial fossa just superior to the orbit, as well as the dura of the lesser wing of the sphenoid. Craniotomy-based approaches provided excellent access to the anterior and middle cranial fossa and the cavernous sinus, except the supraorbital approach had limited access to the middle fossa.CONCLUSIONS:This study outlines the essential surgical steps for major cranio-orbital and orbitocranial approaches. Endoscopic endonasal approaches offer direct medial access, potentially providing bilateral exposure to optic canals. ETOAs serve as both orbital access and as a corridor to surrounding regions. Cranio-orbital approaches follow a lateral-to-medial, superior-to-inferior trajectory, progressively allowing removal of protective bony structures for proportional orbit access.

Introduction: The contemporary skull base surgeon must understand both transcranial and expanded endonasal approaches (EEAs) to the petrous apex. We provide a comprehensive anatomical overview and comparison of the main approaches to the petrous apex through illustrative anatomical dissections.

BACKGROUND: Although tractography-guided surgery is used by many surgeons, there is controversy in the published literature as it relates to its clinical utility. Here we adopted a survey-based approach with the goal of attaining a broader view of how tractography influence preoperative planning in a sampling of practicing neurosurgeons.METHODS: Three cases were prepared where the presence of a tumor distorted the optic radiation (case 1), arcuate fasciculus (case 2), and corticospinal tract (case 3). This survey was administered at the Medtronic Cranial Consortium attended by 20 practicing neurosurgeons. To avoid commercial bias, we used both the Brainlab and Medtronic platform to compute tractography. Each partic-ipant is asked to vote on a surgical trajectory before and after seeing the tractography images, as well as whether tractography added value in validating their surgical approach.RESULTS: In the 3 cases surveyed, 16%e44% of the surgeons changed the surgical corridor selected after seeing the tractography images. The most common finding associated with a change in surgical corridor involved intersection of the surgical corridor with visualized tracts. Consistently, >80% of the surgeons surveyed felt that tractography added value in their surgical planning.CONCLUSIONS: The clinical utility of tractography in preoperative planning varies as a function of surgeon and the tumor anatomy, with >80% of the participating surgeons believing that tractography added value in preoperative surgical planning.

BACKGROUND:The transorbital approaches (TOAs) have acquired growing notoriety, thanks to their ability to offer alternative corridors to the skull base. However, the limited access and the unfamiliarity with this surgical perspective make recognition of key landmarks difficult, especially for less experienced surgeons. The study wants to offer a detailed description of the anatomy to comprehend the potential and limitations of TOAs.METHODS:Measurements of the orbit region and the surrounding areas were performed on two hundred high-resolution CT scans and thirty-nine dry skulls. Five specimens were dissected to illustrate the TOA, and one was used to perform the extradural clinoidectomy. Three clinical cases highlighted the surgical applications.RESULTS:A step-by-step description of the key steps of the TOA was proposed and a comparison with the transcranial anterior clinoidectomy was discussed. The mean work distance was 6.1 ± 0.4 cm, and the lateral working angle increased 20 ± 5.4° after removing the lateral orbital rim.CONCLUSIONS:TOAs are indicated in selected cases when tumor involves the lateral portion of the cavernous sinus or the middle skull base, obtaining a direct decompression of the optic nerve and avoiding excessive manipulation of the neurovascular structures. Comprehension of surgical anatomy of the orbit and its surrounding structures is essential to safely perform these approaches.