Very advanced grade 3 central incisural herniation. Imaging features of the most advanced state are presented in this figure. Notice that in this most advanced state of central incisural herniation the mammillary bodies have reached the belly of the pons completely effacing the interpeduncular fossa. The tuber cinereum typically buckles over the dorsum sella (a second characteristic sign of central incisural herniation), which creates a pocket of CSF within the lower third ventricle. The suprasellar space is effaced as the optic chiasm position reaches the entrance to the sella. The long axis of the chiasm/visual tracts is oriented at a significantly negative angle relative to the tuberculum-venous confluence line. The iter and the splenium have crossed the incisural line well into the posterior fossa. The obex position is low and the cerebellar tonsils are also herniated beyond normal range.