Flattened sheet-like fornix forming a 'Cobra Hood' deformity: A previously unreported variant of fornix anatomy and its implication for surgical approaches to the third ventricle

Background: The fornix is the main efferent tract from the hippocampus and is an important component of the memory pathways. Variations in the anatomy of the fornix are not commonly encountered. Materials and Methods: The anatomy of the fornix was studied in 30 cadavers of normal adult healthy males who had died in road accidents. The full extent of the hippocampus was prosected up to the tail under the magnoscope. Results: In 10 of the 30 brains, the crura and the body of fornix were bilaterally broad and flat like a sheet, rather than the usual compact bundle, forming a cobra-like hood over the roof of the third ventricle. The maximum width was approximately 16 mm on the right side (mean: 11.7 mm) and 11 mm on the left (mean: 8.5mm). Conclusion: Knowledge of this variation will be useful during the transcallosal approach to third ventricle tumors, especially while going subchoroidal, because an unexpected lateral span of the fornix in the surgical corridor can result in inadvertent injury to it, leading to memory defects.