Orbitozygomatic-transsylvian approach to the insula: microsurgical anatomy and endoscopic correlation using the fiber-separation technique.

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.