Anatomy of the floor of the third ventricle in relation to endoscopic ventriculostomy.

Neuroanatomical structures that form the floor of the third ventricle (FTV) and neighboring tissues are important in the context of third ventriculostomy (TV) procedures. Thorough knowledge of the anatomical and histological organization of the region would be useful in understanding and preventing surgical complications. Taking the third ventricle region as a model, we aimed to simulate TV and make measurements of 23 cadaver brains, as well as perform histological examinations of the third ventricular floor on five cadaver brains. During the endoscopic TV, we examined the degree to which the structures surrounding the FTV were affected by surgical simulation. To make a clinical comparison, the distance between the center of the FTV and the basilar apex was measured on cranial magnetic resonance images (MRIs) of 15 subjects with normal ventricular systems and 15 subjects with moderately enlarged ventricles. Histological examination revealed that the ependymal cells and arachnoid membrane formed the inner and outer surfaces of the third ventricle floor, respectively, whereas the stroma was made up of glial cells exclusively. This region was gliotic and avascular. When cadaver brains with normal and hydrocephalic ventricles were compared, there were significant differences in the distance between the center of the floor and the basilar apex (P < 0.001). On the basis of our study, the optimal site for TV fenestration and balloon inflation is just anterior to the mamillary bodies to avoid injury to neighboring structures.