Surgical Anatomy of the Third Ventricle Floor: Implications for Endoscopic Third Ventriculostomy

Neuroendoscopy has made a breakthrough in the field of neurosurgery. Since its first application at the start of the 20^th century, it has evolved enormously and become more specialized. Endoscopic Third Ventriculostomy (ETV) is a type of ventriculoscopies where the floor of the third ventricle is opened to divert the CSF from the third ventricle to the subarachnoid space. Nowadays, ETV is the gold-standard treatment for selected cases of hydrocephalus. Its success depends on, among others, the anatomy of the floor of third ventricle. From anterior to posterior, structures related to the floor of the third ventricle are the preoptic area, optic chiasm, tuber cinereum, mammillary bodies, posterior perforated substance, and tegmentum of the midbrain. The infundibulum of the pituitary gland is attached to the tuber cinereum. Inferiorly, the floor is related to the basilar artery complex. A condensation of arachnoid (known as Liliequist membrane) is sometimes present below the floor. Knowledge of the floor anatomy and its relations is crucial for successful ETV. Many anatomical variations have been described in the floor, such as thickened, thinned, partially effaced/erased, or herniated floor. Neurosurgeons have to be acquainted with the normal anatomy of the ventricles, in general, and that of the third ventricle and its variants, in particular, to ensure a successful procedure. Pre- and postsurgical MRI are important to assess and manage ETV cases. This article presents an up-to-date review of the anatomical variations in the floor of the third ventricle and their implications for the outcome of ETV.