Microsurgical Anatomy of the Posterior Commissure and Habenular Commissure in the Human Cadaveric Brain

Background/Objectives: The posterior commissure (PC) and habenular commissure (HC) are fine-caliber midline fiber bundles located within the epithalamic roof of the third ventricle. Their small size and deep anatomical position render them vulnerable during fiber dissection, and it is difficult to delineate reliably with conventional diffusion MRI. To define a reproducible microsurgical strategy for three-dimensional exposure of the PC and HC, and to evaluate their tractographic representation using high-resolution diffusion template data. Methods: Four formalin-fixed adult cadaveric brains were prepared using a modified Klingler technique and underwent systematic microsurgical fiber dissection focused on preservation of the epithalamic roof and midline commissures. Diffusion MRI data from the Human Connectome Project (HCP-1065) were reconstructed in MNI space using q-space diffeomorphic reconstruction in DSI Studio to attempt deterministic tractographic reconstruction of the PC and HC. Results: In all specimens, the PC was identified as a compact transverse bundle superior to the rostral cerebral aqueduct within the inferior pineal lamina. The HC appeared as a thinner band superior to the pineal recess, interconnecting the bilateral habenular nuclei and separated from the PC by the hypothalamic sulcus. A midline-prioritized dissection sequence facilitated preservation of commissural continuity. Deterministic tractography reproduced adjacent peduncular trajectories but failed to consistently reconstruct discrete HC or PC streamlines. Conclusions: Cadaveric fiber dissection remains the most reliable method for studying the fine commissural anatomy of the epithalamus. A midline-first, roof-preserving strategy enhances visualization of the PC and HC and may have implications for posterior third ventricular surgery and stereotactic targeting.