Endoscopic anatomy of the velum interpositum: A sequential descriptive anatomical study

BACKGROUND: The velum interpositum and structures lying within and over it undergo morbid anatomical changes with hydrocephalus that have not been mentioned in the literature. OBJECTIVES: The aim of this article is to describe the diverse endoscopic anatomical findings for this surgically important region. MATERIALS AND METHODS: One thousand five hundred and twenty cranial endoscopic procedures performed from September 1993 till March 2011 have been retrospectively reviewed. Anatomical `situm and covering layers have been reported in 40 cases. RESULTS: The changes of the velum interpositum have four patterns. These are 1-Distraction mounting to disruption of layers, 2-Reverse in the normal curvature, 3-Reverse of the triangular shape with change in size, and 4-Cystic dilatation causing hydrocephalus. CONCLUSION: The velum interpositum and roof of the third ventricle are sites of changes associated with hydrocephalus that show specific patterns described in a sequential anatomical study.