Category: anatomy

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The Mastoid Foramen and Mastoid Emissary Vein Canal as Surgical Landmarks for Mastoid Pneumatization During Retrosigmoid Approach

Operative Neurosurgery 31:74–84, 2026

This study investigates the anatomical, radiological, and intraoperative relationships between the mastoid foramen (MF), mastoid emissary vein canal (MEVC), and mastoid air cell (MAC) pneumatization to improve planning and safety of the retrosigmoid approach (RSA). It reports measurements from cadaveric specimens, high-resolution CT of 100 patients, and surgical outcomes from 54 RSA procedures, linking MF/MEVC positions with pneumatization grades.

Key findings show the MF and MEVC are reliably posterior to MACs in most cases, with higher pneumatization grades correlated with shorter MF‑MAC and mMEVC‑MAC distances. Preoperative radiological assessment of these landmarks guided burr hole placement and border‑sealing techniques, reducing intraoperative MAC openings and postoperative complications.

Goal Assess whether the mastoid foramen (MF) and mastoid emissary vein canal (MEVC) can predict mastoid pneumatization and guide safer retrosigmoid approach (RSA) craniectomy planning.

Methods Combined anatomic dissection/drilling (2 dry temporal bones; 2 formalin-fixed heads), radiology (100 high‑resolution CTs; Han grade 1–4), and surgical review (54 RSA cases with complication tracking).

Classification & measures MF labeled “posterior” vs “anterior” to the most posterior mastoid air cell (MAC); MEVC labeled type 1 (posterior to MACs) vs type 2 (within MACs); quantified MF‑MAC distance and minimal MEVC‑MAC (mMEVC‑MAC) distance.

Key anatomy pattern MF was posterior to MACs in 99.4% of CT sides; MEVC was posterior to MACs in 88.0% (i.e., type 2 “within MACs” in the remainder).

Pneumatization relationships Higher Han pneumatization grades were associated with shorter MF‑MAC and mMEVC‑MAC distances (both P < .001), and these two distances were strongly correlated (r = 0.741, P < .001).

Age association Mastoid pneumatization grade decreased with age (inverse correlation, P < .001).

Surgical risk signal Intraoperative MAC opening occurred in 5.6% (3/54), and all had Han grade 4 pneumatization with type 2 MEVC (“within” MACs).

Clinical outcome No major intraoperative complications were reported; only one CSF wound leak (1.9%) occurred postoperatively and resolved with lumbar drainage.

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Perimesencephalic hemorrhage: a proposed explanation of its cause and clinical manifestations

J Neurosurg 144:740–746, 2026

This neurosurgical forum article analyzes perimesencephalic hemorrhage (PMH), proposing that small dural arterial variants—particularly the artery of Wollschlaeger and Wollschlaeger (AWW) arising from the superior cerebellar artery—can undergo distraction-avulsion and explain PMH’s characteristic cisternal distribution and benign clinical course. The authors present a surgical case with intraoperative identification of an SCA-derived dural branch and perform detailed anatomical correlation.

The paper contrasts venous and arterial hypotheses, reviews perimesencephalic cisternal anatomy and tentorial blood supply, and argues that spontaneous tearing of a tethered intradural dural branch best accounts for imaging, pathophysiology, and low recurrence of PMH, while acknowledging limits of confirmatory testing.

PMH profile Nonaneurysmal perimesencephalic hemorrhage (PMH) is ~10%–15% of spontaneous cisternal SAH, with CT blood confined around the midbrain and typically a benign course with complete recovery and rare recurrence.

Unknown etiology Despite decades of imaging/anatomical work, the cause often remains unidentified on initial and follow-up angiography, leading to the concept of “SAH of unknown cause,” especially when bleeding is perimesencephalic-only.

Index case A 54-year-old woman with SAH had angiography showing a dural arteriovenous fistula (DAVF) fed by the meningohypophyseal trunk and draining via the superior petrosal vein; surgery disconnected the fistula with good outcome.

Unexpected anatomy Intraoperatively, a dural branch from the superior cerebellar artery (SCA) was found bridging the ambient cistern to the undersurface of the tentorium (the artery of Wollschlaeger and Wollschlaeger, AWW) and was sacrificed; it had not been seen on preop angiography and was not the hemorrhage source in that case.

Key anatomical concept The perimesencephalic cistern system (interpeduncular, ambient, quadrigeminal) surrounds the midbrain at the tentorial incisura; vessels can traverse cisternal spaces and arachnoid septations, influencing where blood can collect.

Tentorial dural supply variants The medial tentorium can be supplied by the marginal tentorial artery from the meningohypophyseal trunk, plus intradural-origin dural branches from the PCA (artery of Davidoff and Schechter, ADS) and from the SCA (AWW) that course within the ambient cistern before entering tentorium.

Competing sources considered Two structures fit many PMH constraints: the basal vein of Rosenthal (BVR) (venous, tethered to vein of Galen) and the ADS/AWW (arterial dural branches tethered to the medial tentorial edge).

Proposed mechanism for PMH Spontaneous distraction-avulsion of the AWW from its fragile tentorial attachment during everyday Valsalva/exertion could cause focal cisternal bleeding that self-limits as pressure equalizes in the confined cistern; this is proposed to explain PMH distribution, negative angiography, generally mild course, low hydrocephalus/vasospasm, and rare rebleed.

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Three-dimensional microsurgical anatomy of the basal aspect of the cerebrum: a fiber dissection study

J Neurosurg 144:690–702, 2026

This study presents a three-dimensional microsurgical fiber-dissection analysis of the basal aspect of the human cerebrum, detailing the spatial organization of commissural, projection, and association fibers and their relationships with subcortical nuclei, ventricles, and cortical landmarks. Using 10 formalin-fixed brains with layer-by-layer dissection and stereoscopic photography, the authors map tracts such as the ILF, UF, SS, cingulum, fornix, and connections around the amygdala and nucleus accumbens.

The findings emphasize surgical implications by clarifying trajectories and landmarks relevant to approaches like STIO and SCTT, illustrating a clinical case of hippocampal glioma resection with optic-radiation preservation, and proposing that 3D anatomical insight enhances safe, precise planning for medial temporal and basal lesions.

Objective Limited surgical exposure of the cerebral base makes basal fiber-tract injury a key risk; detailed 3D tract anatomy is needed to plan safer resections and support brain-function research.

Aim Mapped the topography of basal white-matter tracts and subcortical gray matter (including hippocampus, amygdala, and nucleus accumbens) and their relationships to cortex, ventricles, and nuclei.

Methods Performed Klingler-style layer-by-layer fiber dissection on 10 formalin-fixed human brains under ×6–×40 magnification, documenting each stage with stereoscopic 3D photography.

Key anatomy (basal tracts) Sequential basal dissection exposed U fibers, inferior cingulum (lower part), Li-Am fasciculus, SRF, and ILF; removing Li-Am/ILF revealed the temporal horn with the hippocampus medially.

Sagittal stratum layering The lateral wall of the atrium is layered (medial→lateral): ependyma, tapetum, IC-SL, optic radiations, posterior AC extension, IFOF, MdLF, posterior SLF/AF, U fibers, cortex—together forming the sagittal stratum.

ILF clarification The ILF was identified as a long association tract connecting the base of the temporal pole to the occipital base, located above the fusiform gyrus and beneath the sagittal stratum; “merging fibers” in lateral occipital base were distinguished from the temporal portion of the AF.

Amygdala connectivity The amygdala links to septal nuclei/hypothalamus/thalamus via the stria terminalis, projects to cortical regions via the uncinate fasciculus, and connects via additional pathways including amygdalofugal routes and the anterior commissure.

Surgical application (STIO case) A right hippocampal WHO grade 2 glioma was resected via a supratentorial-infraoccipital (STIO) approach; the fusiform gyrus was incised anterior to the basal turning point of the optic radiation to reach the lateral ventricle, and postoperative DTI confirmed optic-radiation preservation.

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Suprasellar Versus Third Ventricular Cysts: Anatomic and Surgical Considerations

Operative Neurosurgery 30:468–471, 2026

This surgical case instruction contrasts suprasellar arachnoid cysts (SACs) and third ventricular cysts (3VCs), emphasizing their distinct imaging features, clinical presentations, and risks of obstructive hydrocephalus. It summarizes patient examples, MRI findings, and outcomes after endoscopic cyst fenestration, demonstrating restoration of cerebrospinal fluid flow and symptom resolution.

The article details stepwise endoscopic techniques—cyst plane development, wall reduction, excision, and membrane management—highlighting anatomical cues that guide whether endoscopic third ventriculostomy is necessary. Practical tips on preserving hypothalamic structures, restoring aqueduct patency, and minimizing reaccumulation are provided for neurosurgical practice.

Prevalence Intracranial arachnoid cysts occur in ~2.6% of children and ~1.4% of adults; suprasellar arachnoid cysts (SACs) comprise ~9%–21% of pediatric arachnoid cysts and can be confused with rarer third ventricular cysts (3VCs).

Presentation SACs and 3VCs often enlarge and cause obstructive hydrocephalus with symptoms of increased intracranial pressure, prompting urgent treatment to restore CSF circulation.

Imaging differences (SAC) SACs elevate the third ventricular floor, displace mammillary bodies superiorly/posteriorly, and elongate/stretch the midbrain and aqueduct, with aqueduct occlusion from distortion and the posterior cyst wall.

Imaging differences (3VC) 3VCs displace the third ventricular floor and mammillary bodies inferiorly with midbrain compaction; the aqueduct is obstructed by midbrain distortion and the inferoposterior cyst wall.

Treatment rationale A shunt without cyst fenestration can lead to asymmetric hydrocephalus and/or continued cyst enlargement due to cyst-related occlusion of the foramina of Monro; neuroendoscopy enables cyst fenestration with low morbidity risk at experienced centers.

Endoscopic steps A stepwise intraventricular endoscopic approach includes: developing the cyst/ventricle plane; reducing cyst wall size (coagulation); excising roof/lateral/medial walls (with caution laterally in SACs due to hypothalamic fusion); removing/reducing floating membranes (especially posteriorly) to open access to the aqueduct.

Inferior wall strategy In SACs, inferior membrane fenestration may be unnecessary because the prepontine cistern is already exposed/communicates with the third ventricle; in 3VCs, the inferior aspect is the third ventricular floor, and endoscopic third ventriculostomy (ETV) is an option.

ETV decision point If posterior membrane resection fully restores aqueduct patency, ETV may not be necessary; reducing expansile membranes is pursued to lower risk of reaccumulation from scarring.

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Lumbar Multifidus Intramuscular Fat Concentrations are Associated With Recovery Following Decompressive Surgery for Lumbar Spinal Stenosis

Spine 2026;51:25–33

This longitudinal cohort study investigates whether preoperative intramuscular fat (IMF) in lumbar paraspinal muscles predicts five-year recovery and surgical success after decompressive surgery for lumbar spinal stenosis causing intermittent neurogenic claudication. Using automated MRI segmentation and quantitative IMF thresholds, outcomes included global perceived effect, Zurich Claudication Questionnaire-based surgical success, pain VAS, and disability scores.

Key findings show lower preoperative multifidus IMF (but not erector spinae IMF) was associated with higher rates of perceived recovery, surgical success, and reduced long-term disability over five years. No consistent relationship was found between IMF and leg or back pain trajectories; results were adjusted for age, BMI, sex, smoking, reoperation, and surgical technique.

Lumbar multifidus intramuscular fat (IMF): Lower preoperative IMF in the lumbar multifidus muscle is associated with higher rates of perceived recovery and surgical success after decompression surgery for lumbar spinal stenosis (LSS) over a five-year period.

Erector spinae IMF: Preoperative IMF levels in the erector spinae muscle are not significantly associated with recovery or surgical success following LSS surgery.

Disability outcomes: Patients with nonsevere IMF in the right lumbar multifidus experience less postoperative disability for up to five years compared to those with severe IMF.

Pain outcomes: No significant association exists between preoperative paraspinal IMF (either muscle) and the clinical course of leg or back pain intensity after surgery.

IMF quantification method: Automated MRI-based quantification and categorization of IMF (<50% = nonsevere, ≥50% = severe) using computer vision models enables objective assessment of paraspinal muscle health.

Prognostic value: Assessing lumbar multifidus IMF preoperatively can improve prediction of which patients are at risk for poor recovery and help tailor individual interventions.

Study limitations: Missing data (up to 32% at five years), dichotomized IMF classification, and limited field-of-view for some muscles may affect precision; more detailed and larger studies are needed.

Clinical implication: Routine IMF assessment may enhance clinical decision-making and rehabilitation strategies for patients undergoing lumbar decompressive surgery.

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Skull Base Anatomy Presented in 360° Photogrammetry 3-Dimensional Models

Operative Neurosurgery 30:124–136, 2026

This article presents the creation of seven photorealistic 360° photogrammetric 3D models of the central skull base derived from stepwise dissections of a formalin-fixed, vessel-injected cadaveric head. The workflow—dissection stages, smartphone-based image capture, cloud photogrammetry, refinement in Blender, and VR/MR upload—enables immersive visualization of cranial nerves, ICA/vertebral segments, and regional anatomy.

The models offer progressive exocranial-to-endocranial perspectives for education and preoperative planning, highlighting cavernous sinus, infratemporal and pterygopalatine fossae, petrous bone, and foraminal relationships. Limitations include a single-specimen dataset, color variations from fixation, and resolution constraints in deep cavities; nevertheless, the freely accessible VR models complement traditional dissection and anatomical atlases.

360° Photogrammetric 3D Models: Realistic, photogrammetry-based 3D models of the central skull base were created from cadaveric dissections, offering immersive 360° visualization of complex neuroanatomical structures for enhanced spatial understanding.

Stepwise Dissection and Scanning: Seven progressive anatomical models were generated by systematically dissecting and scanning a formalin-fixed, vessel-injected head specimen, documenting both exocranial and endocranial perspectives.

Key Structures Visualized: The models detail the courses of cranial nerves, major vessels (including all internal carotid artery segments), skull base foramina, infratemporal and pterygopalatine fossae, paranasal sinuses, and deep neck spaces.

Technical Workflow: High-resolution images were captured using a smartphone multi-camera system, processed via cloud-based photogrammetry, refined in 3D software, and made accessible through web, VR, and MR platforms.

Educational Value: The interactive models allow customizable, layered exploration of anatomy, overcoming limitations of traditional 2D images and static atlases, and are freely accessible for educational and preoperative planning purposes.

Limitations: The study used a single specimen, which may not represent anatomical variants; image quality in deep/narrow regions could be further improved with advanced imaging and fixation techniques.

Broad Accessibility: Smartphone-based and cloud photogrammetry methods make high-resolution anatomical modeling more accessible and less resource-intensive, facilitating widespread dissemination.

Conclusions: 360° photorealistic 3D models significantly enhance comprehension of skull base anatomy and are a valuable adjunct to traditional teaching, with potential to improve neurosurgical training and patient outcomes.

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Afferent and efferent fiber systems of the human amygdala: anatomical, pathophysiological, and clinical significance

J Neurosurg 143:1202–1216, 2025

This paper presents a comprehensive neuroanatomical and radiological analysis of the human amygdala, detailing its nuclei, major afferent and efferent fiber systems, and spatial relationships using white matter fiber dissection and diffusion tensor tractography. The authors synthesize structural descriptions with functional roles in emotion, memory, olfaction, and seizure propagation, emphasizing clinical relevance for neuroclinicians.

The study maps key pathways—the ansa peduncularis, ventral and dorsal amygdalofugal routes, stria terminalis, medial forebrain bundle, olfactory striae, and stria medullaris thalami—correlating anatomy with neurosurgical applications such as deep brain stimulation and lesion resection. Anatomical findings are supported by illustrative dissections, tractography, and a clinical cavernoma case demonstrating surgical implications.

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Microsurgical anatomy of the fiber tracts and vascular structures lateral to the internal capsule

J Neurosurg 143:1068–1076, 2025

This microsurgical study maps white matter fiber tracts and vascular anatomy from the brain’s lateral surface to the internal capsule using perfused cadaveric specimens and Klingler fiber dissection. Key tracts (AF, SLF II/III, FAT, MdLF, UF, IFOF) and vascular elements (MCA segments, LSAs, LSVs, venous drainage groups) are described with measurements and surgical landmarks.

Findings emphasize trajectories relevant to Kocher’s point, the spatial relationships of LSAs/LSVs to the putamen and internal capsule, and implications for minimizing functional and vascular injury during neurosurgical approaches and revascularization procedures.

• Anatomical Focus: The study investigates the microanatomy of white matter fiber tracts and vascular structures lateral to the internal capsule, using fiber dissection and vessel perfusion techniques on human cadaveric brains.

• Key Structures: Major fiber tracts identified include the arcuate fasciculus (AF), superior longitudinal fasciculus (SLF), frontal aslant tract (FAT), middle longitudinal fasciculus (MdLF), uncinate fasciculus (UF), and inferior fronto-occipital fasciculus (IFOF); the main vascular structures are branches of the middle cerebral artery (MCA) and lenticulostriate arteries (LSAs), each accompanied by lenticulostriate veins (LSVs).

• Vascular Territories: Superficial arteries supply only the gray matter of the lateral brain surface, while deeper white matter and basal ganglia receive blood from LSAs originating from the M1 segment of the MCA; there is no direct communication between insular arteries and LSAs, with the external capsule marking their vascular boundary.

• Surgical Implications: Kocher’s point, a standard neurosurgical entry site, traverses the posterior middle frontal gyrus, SLF III, external capsule, and basal ganglia, avoiding major arteries, veins, and critical fiber tracts such as the AF and internal capsule, thus minimizing functional risk.

• Clinical Relevance: Understanding the course of LSAs and LSVs is crucial for safe neurosurgical procedures in the basal ganglia and insular region, as injury to these vessels can cause severe neurological deficits; the study provides anatomical evidence supporting the safety of the Kocher’s point approach.

• Functional Anatomy: The AF is essential for language by connecting Broca’s and Wernicke’s areas; the internal capsule is critical for motor and sensory information transfer between cortex and brainstem/spinal cord.

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Validation of Härtel Surface Anatomical Landmarks for Locating the Foramen Ovale: A Computed Tomography Scan Analysis and Revised Technique Description

Operative Neurosurgery 29:399–407, 2025

CT-based validation of Hartel’s anatomical landmarks shows the foramen ovale is closer to the tragus and more medial than previously described. Revised needle trajectories, targeting 2–2.5 cm anterior to the tragus and between the inner canthus and midpupillary lines, may improve safety and accuracy in trigeminal procedures.

• Hartel surface anatomical landmarks for foramen ovale (FO) localization were assessed using CT scans in 99 adults (198 foramina).

• The FO is typically closer to the external auditory canal (mean 23.26 mm) and more medial (mean 25.43 mm from midline) than Hartel’s original description.

• FO is usually located between the eye’s inner canthus (IC) and midpupillary (MP) lines, not directly along the MP line as previously thought.

• Recommended needle trajectory: 2–2.5 cm anterior to tragus and targeting a point between the IC and MP lines, avoiding excessive medial/posterior displacement.

• A posteromedial “Danger Zone” exists within 20 mm of the midline and EAC, where vascular injury risk increases.

• Imaging guidance (fluoroscopy, CT) remains essential for safe and accurate needle navigation.

• These adjustments may improve procedural accuracy, safety, and patient outcomes for percutaneous trigeminal procedures.

• Further clinical and cadaveric validation is needed for these technique modifications.

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Anatomy of the superior hypogastric plexus and its relevance to anterior lumbar interbody fusion

J Neurosurg Spine 43:19–25, 2025

This cadaveric study details the anatomy of the superior hypogastric plexus (SHP) at L5–S1, its variations, and implications for anterior lumbar interbody fusion (ALIF). The authors recommend left-sided SHP retraction to minimize nerve injury and retrograde ejaculation; if unfeasible, midline splitting and lateral mobilization are advised.

• The study examined the anatomy of the superior hypogastric plexus (SHP) at the L5–S1 level and its relevance to anterior lumbar interbody fusion (ALIF) surgery.

• Injury to the SHP during ALIF can cause retrograde ejaculation (RE) in males and sexual dysfunction in females.

• The SHP typically overlays the midline at L5–S1 with a slight leftward shift and is covered by connective tissue beneath the peritoneum.

• Three morphological types of SHP were found: single cord, plexiform, and fiber; the plexus divides into hypogastric nerves below the aortic bifurcation.

• Retraction of the SHP to the left side is generally more feasible (up to 15.3 mm) than to the right (up to 5.3 mm); left-sided retraction is recommended.

• If left retraction is not possible, splitting the SHP at the midline and retracting both components laterally is advised.

• Careful SHP mobilization and avoidance of electrocautery are crucial to reduce risk of RE and sexual dysfunction in ALIF patients.

• The findings highlight the importance of detailed SHP anatomy knowledge for safer ALIF, especially with minimally invasive approaches.

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Application of Topographical Anatomy of the Trochlear Nerve in Transtentorial Approaches: An Anatomic Study

Operative Neurosurgery 28:705–711, 2025

his study examines the topographical anatomy of the trochlear nerve in relation to the free edge of the tentorium (FET) for safer transtentorial surgical approaches. It identifies safe zones for FET transection, minimizing injury risk to the trochlear nerve, crucial for surgeries involving the cavernous sinus.

• Study Focus: The study investigates the relationship between the trochlear nerve (CN IV), oculomotor nerve (CN III), and the free edge of tentorium (FET) to identify a safe zone for surgical maneuvers.

• Methods: Ten embalmed specimens were analyzed using digital microcalipers to measure morphometric details such as the distance between CN IV and CN III.

• Key Findings: CN IV pierces the deep layer of the FET and continues within it before entering the cavernous sinus. A nerve-free portion of FET averages 1.93 mm, with significant variability among specimens.

• Surgical Implications: Transection of the FET poses the lowest risk of CN IV injury if performed less than 2 mm or more than 10 mm posterior to the oculomotor porus (OP).

• Anatomical Observations: The FET is composed of deep and superficial layers, with the deep layer continuous with the petrous bone dura.

• Clinical Relevance: Knowledge of the topographical anatomy of CN III and CN IV is crucial for safe surgical approaches, especially in cases involving tumors or aneurysms.

• Limitations: The study’s experimental nature and limited sample size may not fully capture the anatomical variance encountered in vivo.

• Conclusion: The study provides essential anatomical guidance for reducing the risk of nerve injury during transtentorial surgical approaches.

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Impact of Sigmoid Sinus Anatomy on Assessing the Feasibility of the Retrofacial Access to the Entire Jugular Fossa Before Surgery

Operative Neurosurgery 28:677–686, 2025

The study evaluates the feasibility of the neuronavigated microsurgical transmastoid extended infralabyrinthine extradural retrofacial approach (mTEIER-A) in accessing the jugular fossa, emphasizing the significance of the sigmoid sinus position and horizontal angle of attack, while the sinus size has limited impact.

• The study examines the feasibility of the neuronavigated microsurgical transmastoid extended infralabyrinthine extradural retrofacial approach (mTEIER-A) for accessing the jugular fossa (JF), considering the position and size of the sigmoid sinus (SS) and the horizontal angle of attack.

• SS position medial to a reference line (P1) and horizontal angles greater than 12.5° enhance retrofacial access to the lateral aspect of the JF. The size of the SS has a limited impact.

• Precise preoperative planning is crucial to minimize the need for more invasive approaches, potentially reducing morbidity.

• The study was conducted on cadaveric specimens and highlights the importance of further clinical studies to validate findings.

• Creating an anterofacial space carries risks, including potential damage to the facial nerve (FN) and external auditory canal, which mTEIER-A aims to avoid.

• Statistical analysis confirms the significance of SS position and α-angle for retrofacial access, while SS size has a minor role.

• The study suggests that mTEIER-A is a viable approach for addressing intraosseous JFPs, emphasizing the need for careful preoperative imaging assessment.

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Microsurgical anatomy and the inner architecture of the retrocommissural portion of the hippocampal formation demonstrated through fiber microdissection

J Neurosurg 142:1085–1098, 2025

The study explores the complex anatomy of the retrocommissural portion of the hippocampal formation (RHF) using fiber microdissection. It clarifies nomenclature, describes the RHF’s structures and spatial relations, and provides insights for surgical approaches in the mediobasal temporal region.

• Objective: The study aims to clarify the complex nomenclature and 3D spatial relations of the retrocommissural portion of the hippocampal formation (RHF) for surgical purposes.

• Methods: Fiber microdissection was performed on 20 formalin-fixed human brains to study the RHF’s topography and internal structure.

• Results: The RHF is divided into head, body, and tail sections, each with distinct intra- and extraventricular configurations.

• Components: The RHF includes the hippocampus (Ammon’s horn and dentate gyrus), subiculum, and related white matter fibers.

• Surgical Challenges: The RHF’s complex architecture and location present challenges for surgical approaches, necessitating a detailed anatomical understanding.

• Terminology: The study addresses inconsistencies in terminology, emphasizing the importance of clear definitions for surgical planning.

• Conclusion: Detailed anatomical knowledge of the RHF enhances surgical strategies for lesions in the mediobasal temporal region.

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The oculomotor cistern and pituitary adenomas: anatomical and clinical study

J Neurosurg 142:766–776, 2025

• Study Focus: The research investigates the oculomotor cistern (OMC) and its involvement with pituitary adenomas (PitNETs), aiming to provide a histomorphological description and analyze its clinical impact.

• Methods: Ten hemisellae from formalin-fixed specimens were studied, and clinical data from patients undergoing endoscopic transsphenoidal surgery for PitNETs between 2014 and 2021 were analyzed.

• Results: OMC involvement was graded as not compressed, compressed, and invaded. Significant associations were found between OMC involvement and PitNET dimensions, Knosp grade, and preoperative oculomotor palsy.

• OMC Shape and Measurements: The OMC is elliptical with an average area of 3.1 mm² and a length of 5.5 mm. No points of weakness were identified in the histomorphological study.

• Clinical Findings: OMC compression and invasion were recorded in 43.1% and 9.3% of patients, respectively. Preoperative CN III palsy was documented in compressed (11.3%) and invasive (26.1%) OMCs.

• Surgical Implications: Endoscopic transsphenoidal surgery is effective in treating PitNETs with OMC involvement, though the choice between transcranial and endoscopic approaches remains debated.

• Histological Observations: The study confirmed the OMC’s extension ends before the anterior clinoid process (ACP), with potential points of weakness at the CS roof and MWCS.

• Conclusion: OMC involvement is significant in PitNETs, affecting patient outcomes. Detailed preoperative evaluation and postoperative follow-up are crucial for managing these cases.

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Lateral compartment of the cavernous sinus from the endoscopic endonasal approach: anatomical considerations and surgical relevance to adenoma surgery

• Objective: The study investigates the lateral compartment of the cavernous sinus (CS) and its surgical relevance in adenoma surgery using the endoscopic endonasal approach.

• Methods: Dissection was performed on 22 colored silicone-injected specimens to identify anatomical landmarks and techniques for mobilizing the internal carotid artery (ICA).

• Findings: The lateral compartment is divided into two subcompartments, with the upper housing the lateral parasellar ligament (LPL) and inferolateral trunk (ILT), and the lower containing sympathetic nerve branches.

• LPL and ILT: The LPL was identified in 86% of hemispheres, with varying configurations, and the ILT was found in 93%, primarily originating from the horizontal ICA segment.

• Techniques: Transection of the LPL, ILT, and COM facilitates medial ICA mobilization, enhancing access to the lateral compartment.

• Conclusions: The study underscores the anatomical intricacies of the lateral compartment and the potential benefits of the lateral transcavernous approach.

• Limitations: The study’s findings are based on cadaveric dissections, which may not fully replicate live surgical conditions.

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Radiological and anatomical evaluation of the internal venous system in the context of access to the third ventricle ‑ proposal of a new classification

Acta Neurochirurgica (2025) 167:23

The internal venous system of the brain is a crucial anatomical landmark during accesses to the third ventricle through the foramen of Monro. Many classifications based on radiological assessment of the system have been developed, but they tend to be descriptive and do not highlight favorable anatomical variants. The aim of our study was to create a system based on morphometric measurements to facilitate preoperative decision-making regarding access to third ventricle tumors.

Methods We conducted an analysis of 119 MRI scans with SWI sequence using BrainLab software to create a model of the ventricular system, which allowed us to perform radiological measurements. We then validated these findings anatomically using 32 human brain specimens. The analyzed structures included the foramen of Monro (FM), the anterior septal vein (ASV), the thalamostriate vein (TSV), the venous angle (VA), the internal cerebral vein (ICV), and the distance between the FM and VA.

Results Based on the radiological analysis, we identified 9 internal venous systems, accounting for variations in each analyzed structure. The statistical analysis revealed no differences in the frequency of subtypes between radiological and anatomical studies (p = 0.097), nor in the occurrence of false venous angles (p = 0.520). We identified venous configurations that, in our assessment, are unfavorable in the context of accessing the third ventricle.

Conclusion The resulting classification accounts for significant clinical anatomical variations and, for the first time, provides specific morphometric values for each anatomical subtype. Consequently, it serves as a reproducible reference framework for preoperative planning of access to the third ventricle.

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Are the Umbilicus and Iliac Crests Truly at the Level of L4 to L5? A Computed Tomography-Based Study of Surface Anatomy of the Anterior Lumbar Spine

International Journal of Spine Surgery, Vol. 18, No. 6, 2024, pp. 660–666

This study aimed to determine whether the iliac crests are truly at the level of L4 to L5, accounting for patient demographic and anthropometric characteristics.

Methods: We measured the umbilicus and iliac crests relative to the lumbar spine using computed tomography of patients without spinal pathology, accounting for the influences of patient height, weight, body mass index (BMI), sex, race, and ethnicity.

Results: A total of 834 patients (391 men and 443 women) were reviewed. The location of the umbilicus relative to the lumbar spine demonstrated a unimodal distribution pattern clustered at L4, while the iliac crests were most frequently located from L4 to L5. Iliac crests were located above the L4 to L5 disc space 26.5% of the time. Iliac crests were located at the L4 to L5 disc space 29.8% of the time. No correlations were observed between the umbilicus and iliac crests with patient height, weight, or BMI. There was no difference in the location of the umbilicus with respect to patient sex, race, and ethnicity. The locations of the iliac crests were cephalad in women compared with men and in Hispanics compared with African American, Caucasian, and Asian patients.

Conclusions: The iliac crests were located above the level of the L4 to L5 disc space approximately 26% of the time. The umbilicus is most frequently at the level of the L4 vertebral body. Patient height, weight, and BMI do not influence the location of the umbilicus or the iliac crests relative to the lumbar spine. Patient sex and ethnicity influence the location of the iliac crests but not the umbilicus relative to the lumbar spine.

Clinical Relevance: Modern neurosurgical techniques require clearance of the iliac crests during anterior and anterolateral approaches. Understanding the level of the iliac crests is crucial in planning for transpsoas fusion approaches.

Level of Evidence: 2

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3-Dimensional Printed Model of the Temporal Bone for Neurosurgical Training

Operative Neurosurgery 27:749–755, 2024

The development of neurosurgical skills stands out as a paramount objective for neurosurgery residents during their formative years. Mastery of intricate and complex procedures is a time-intensive process marked by a gradually ascending learning curve. Consequently, the study and simulation on surgical models assume significant importance. One of the most intricate neuroanatomical regions includes the petrous and mastoid portions of the temporal bone. These regions host critical, highly functional, and vital neurovascular structures, including the facial nerve, cochlea, semicircular canals, internal carotid artery, and middle ear. This fully open-source 3-dimensional (3D) model of the temporal bone, created for educational purposes, should be easily and economically reproducible using a 3D printer, offering all residents the opportunity to understand the spatial location, three-dimensional anatomical structures, and fundamental intricacies of mastoidectomy.

METHODS: A 3D model of the temporal bone was fabricated using a computed tomography (CT) scan derived from an actual human body. The CT scan of the model was meticulously juxtaposed with the reference sample CT scan. Neurosurgical residents were recruited as participants for this study. Each participant was tasked with executing a mastoidectomy on 2 separate occasions, with a 2-week interval between attempts. Throughout these sessions, various parameters, including the time taken for task completion, the volume of bone removal, and any potential complications, were systematically registered.

RESULTS: The mean volume of bone removed increased by 34.5%, and the mean task time and the mean number of complications decreased by 10.3% and 25%, respectively, during the training.

CONCLUSION: Engaging in training with cost-effective anatomical models constitutes a valuable tool for refining technical skills during residency. We posit that this type of model training should be incorporated as part of the trainee’s curriculum during the residency program because of the myriad advantages evidenced by the findings of this study.

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Microsurgical anatomy and approaches to thalamic gliomas. Part 1

J Neurosurg 141:1457–1471, 2024

The selection of appropriate microsurgical approaches to treat thalamic pathologies is currently largely subjective. The objective of this study was to provide a structured cartography map for surgical navigation to treat gliomas involving different surfaces of the thalamus.

METHODS Fifteen formalin-fixed, silicone-injected cadavers (30 sides) were dissected, and 10 adult brain specimens (20 sides) were used to illustrate thalamic microsurgical anatomy using the Klingler fiber dissection technique. Exposures and trajectories for the six most common microsurgical approaches were depicted using MR data from healthy subjects converted into surface-rendered 3D virtual brain models. Additionally, thalamic surfaces exposed with all six approaches were color mapped on the virtual 3D model and compared side-by-side in 360° views with previously reported microsurgical approaches. These 3D models were then used in conjunction with topographic data to guide cadaveric dissection steps.

RESULTS There are two general surgical routes to thalamic lesions: the subarachnoid transcisternal and transcortical routes. The transcisternal route consists of the following three approaches: 1) anterior interhemispheric transcallosal approach, which exposes the anterior and superior thalamus; 2) posterior interhemispheric transcallosal approach, which exposes the posterosuperior thalamus; and 3) supracerebellar infratentorial approach, which exposes the posteromedial cisternal thalamus and can be extended laterally to approach the posterolateral thalamus by cutting the tentorium. The three transcortical approaches are the 1) superior parietal lobule approach, which exposes the posterosuperior thalamus and is particularly advantageous in the setting of hydrocephalus; 2) transtemporal gyrus approach, which exposes the inferolateral thalamus; and 3) transsylvian transinsular approach, which exposes the lateral thalamus (slightly more superiorly and posteriorly) and is advantageous for pathologies extending laterally into the peduncle, lenticular nucleus, or insula.

CONCLUSIONS Microsurgical approaches to thalamic gliomas continue to be challenging. Nonetheless, safe and effective cisternal, ventricular, and cortical corridors can be developed with thoughtful planning, anatomical understanding, and knowledge of the advantages, risks, and limitations of each approach. In some cases, it is wise to combine these approaches with staged procedures, as the authors demonstrate in Part 2. In Part 1 of this two-part series, they discuss thalamic microsurgical anatomy and illustrate the trajectory and exposures of all six approaches to guide decision-making. Part 2 discusses their thalamic glioma microsurgical case series, which utilizes these microsurgical approaches.

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Revisiting the microsurgical anatomy of the sagittal stratum and surgical implications: fiber microdissection and tractography study

J Neurosurg 141:1433–1446, 2024

The term “sagittal stratum” was coined by Heinrich Sachs in 1892 to define a parasagittally oriented white matter layer at the temporo-occipital cortex. Although this term has been widely used for more than 100 years, the description, classification, borders, and involved fibers of the structure vary among authors and remain imprecise. Through fiber microdissection and tractography, the authors aimed to define the sagittal stratum and resolve the uncertainty by revealing the relationship of this structure to other cerebral white matter pathways and the orientation of fibers in it.

METHODS Twenty postmortem human cerebral hemispheres were prepared according to Klingler’s method. Fiber dissections were performed under a surgical microscope and with microsurgical techniques. The results of dissection at each step were photographed with 2D and 3D imaging techniques, and 3D photogrammetry techniques were used to create a 360° model. Diffusion tensor imaging and 7T high-resolution MRI were used to confirm the findings.

RESULTS This study revisited the 3D organization of white matter tracts in the sagittal stratum through fiber microdissection and tractography. The microneuroanatomical structure of the sagittal stratum and its special organization with fibers from all three fiber systems are demonstrated. The authors’ findings revealed that the sagittal stratum has two layers consisting of four different fiber tracts. Its external layer consists of a long association fiber and a commissural fiber, while its internal layer consists of intertwined projection fibers, including temporo-parieto-occipitopontine fibers and the posterior thalamic peduncle. Detailed microdissection also showed the location of the posterior thalamic peduncle in the most medial site of all posterior hemispheric projection fibers.

CONCLUSIONS The structure of the sagittal stratum is distinctive in that it contains all three main fiber systems: association, commissural, and projection. Because of its expansive location in the temporal and occipital lobes, it can be damaged by most neurosurgical pathologies and procedures. The authors emphasize the significance of preserving the sagittal stratum during surgical interventions while also challenging the notion of a “silent” brain, suggesting that the current inability to fully comprehend cerebral function contributes to this misconception. Detailed knowledge of the complex white matter anatomy of the sagittal stratum can guide neurosurgeons in surgical planning and the selection of appropriate surgical approaches with intraoperative orientation for safe surgery and less comorbidity.

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