Background/Objectives: This study aimed to describe the sequential microsurgical relationships surrounding the lateral mesencephalic sulcus (LMS) through fiber dissection and characterize regional anatomical variation using MRI morphometry in an independent adult cohort. Methods: Eight formalin-fixed adult specimens underwent stepwise fiber dissection. T2-weighted MRI examinations from 100 adults were retrospectively analyzed. Measurements included the inferior colliculus–straight sinus angle (ICSSA), corpus callosum–pontomesencephalic junction distance (CCPJD), LMS–midline angle (LMS-MA), LMS–midline distance (LMS-MD), and LMS–cerebellar surface distance (LMS-CSD). The splenium–mesencephalon relationship (SMR) was categorized descriptively. Comparisons and age correlations were evaluated using Holm-adjusted p values. Results: Dissection documented sequential relationships between the LMS, lemniscal pathways, superior cerebellar peduncle, and deep tegmental structures. The MRI cohort included 50 women and 50 men aged 23–88 years. Mean ICSSA was 29.6 ± 5.3° and CCPJD was 24.17 ± 3.85 mm. Right and left values were 21.9 ± 3.9° and 22.2 ± 4.0° for LMS-MA, 9.77 ± 0.81 and 9.91 ± 0.84 mm for LMS-MD, and 6.12 ± 1.87 and 6.28 ± 1.68 mm for LMS-CSD. No right–left differences remained significant after correction. Males had greater left LMS-MD and right LMS-CSD (adjusted p = 0.002 and 0.004, respectively). Age correlated negatively with CCPJD (ρ = −0.389; adjusted p < 0.001) and positively with right and left LMS-CSD (ρ = 0.268 and 0.379; adjusted p = 0.042 and <0.001, respectively). SMR Types A, B, and C occurred in 70%, 29%, and 1%, respectively. Conclusions: Fiber dissection and MRI morphometry provide complementary descriptive anatomical reference data. The MRI parameters characterize regional variation; their correspondence with deep microsurgical boundaries and clinical applicability remain to be established.

Background Insular surgery remains technically demanding because of the region’s deep location and intimate relationships with the middle cerebral artery complex and surrounding white matter pathways. Safe resection requires precise understanding of vascular landmarks and subcortical functional boundaries. Methods Eight formalin-fixed adult cadaveric heads (16 hemispheres) underwent bilateral two-piece orbitozygomatic (OZ) transsylvian (TS) dissections. Endoscopic assistance (0° and 30°) was used selectively to enhance visualization of deep and anatomically concealed regions. Following cortical exposure, approach-oriented subinsular fiber separation and dedicated hemispheric Klingler fiber dissections were performed to define operative surgical boundaries and characterize the three-dimensional organization of the peri-insular white matter. Results The OZ–TS corridor provided wide anterior and anteroinferior exposure of the insula, allowing early identification of the M2 trunks, M3 opercular branches, and lenticulostriate arteries, thereby clarifying the medial vascular limit. Endoscopic assistance provided complementary visualization of the limen insulae, anterior perforated substance, and deep perforators while maintaining the established operative corridor. Layered subinsular dissection consistently revealed the extreme capsule, claustrum, external capsule with its uncinate fasciculus and inferior fronto-occipital fasciculus (IFOF), followed by the putamen and internal capsule. The IFOF formed a critical medial boundary in anterior resections, whereas the posterior limb of the internal capsule and optic radiation defined posteromedial and posterior functional limits. Conclusion Endoscope-assisted OZ–TS exposure combined with a structured fiber-separation strategy provides an integrated anatomical perspective of the insular region. Early identification of vascular landmarks and systematic progression along intrinsic white matter planes facilitate anatomical definition of subcortical surgical boundaries.

Objective: To delineate the anatomical spectrum, frequency, and neurosurgical relevance of anterior inferior cerebellar artery (AICA) variations through combined radiological and microsurgical cadaveric analysis, and to explore potential associations between AICA anomalies and posterior circulation aneurysms. Material and Methods: Computed tomography angiography (CTA) scans of 400 patients (212 males, 188 females; mean age 55.9 years) were retrospectively reviewed for AICA anomalies, aneurysms, and other vascular variations. Cadaveric dissections of two formalin-fixed adult heads (four sides) were performed through retrosigmoid and far-lateral approaches under microscope magnification, with attention to cranial nerve relationships and labyrinthine artery origin. Results: AICA variations were identified in 26 patients (6.5%), totaling 27 variant arteries. The most common anomaly was AICA-PICA common trunk (2.5%), followed by early bifurcation (1.5%) and duplication (1.0%). Hypoplasia (0.75%), double origin (0.5%), aplasia (0.25%), and fenestration (0.25%) were less frequent. Posterior circulation aneurysms were present in 17 patients (4.25%); 11.5% of patients with AICA variations harbored aneurysms versus 3.7% without variations, suggesting a potential anatomical predisposition to aneurysm formation. Cadaveric dissection confirmed AICA origin from the basilar artery, looping around the CN VII–VIII complex, and consistent relationship with the labyrinthine artery and flocculus. Conclusion: AICA variations occur in ~6.5% of individuals, most commonly as an AICA-PICA common trunk or early bifurcation, and show a higher association with posterior circulation aneurysms. Accurate preoperative identification and understanding of microsurgical anatomy are essential, as these variants increase surgical complexity and potential complications in skull base and vascular procedures.

Aim: The temporo–parieto–occipital junction (TPOJ) represents a critical convergence zone of the dorsal and ventral language pathways. Preservation of these tracts is essential during surgery for lesions involving this region. The aim of this study is to define the microsurgical anatomy of the dorsal and ventral language pathways at the TPOJ using the fiber dissection technique and to propose a surgical strategy based on the principles of fiber separation.Materials and Methods: Three formalin-fixed adult human cadaveric brains (six hemispheres) and two silicone-injected adult human cadaveric heads (four sides) were prepared using the Klingler fiber dissection technique. Stepwise microscopic dissections were performed from the cortical surface toward the deep white matter. The spatial relationships of the superior longitudinal fasciculus (SLF II–III), arcuate fasciculus (AF), inferior fronto-occipital fasciculus (IFOF), middle longitudinal fasciculus (MdLF), and extreme capsule (ExtC) were analyzed. Special attention was given to the depth, orientation, and natural separation planes between the dorsal and ventral language pathways.Results: The dorsal language system, mainly composed of SLF II–III and the arcuate fasciculus, was identified in all dissections as a superficial-to-intermediate layer beneath the U-fibers. The ventral language pathways, including the IFOF, MdLF, and extreme capsule system, were observed in deeper and more medial planes throughout the dissections. Between the dorsal and ventral systems, a distinct separation corridor was consistently identified, particularly along the interface between the arcuate fasciculus and the IFOF, across different cadaveric specimens. This corridor corresponded to a potential surgical plane for fiber separation techniques.Conclusions: At the TPOJ, the dorsal and ventral language pathways demonstrate a layered anatomical organization with distinct separation planes. Recognition of these natural separations may contribute to the development of fiber-preserving microsurgical strategies.