Introduction: Knowledge of neuroanatomical structures that form the floor of third ventricle is important in the context of third ventriculostomy.

Methods: From Jan 2009 to December 2011 we performed 228 endoscopic third ventriculostomies for different pathologies like non communicating hydrocephalus (Aqueductal stenosis or IV ventricular outlet obstruction) n=186, communicating hydrocephalus (post meningitic, post tuberculous) n=28, posterior third ventricular tumors n=12 and third ventricular parasitic cysts n=2

Results: Anatomical variations were noted in 48 patients. Thick membrane (anterior to mamillary bodies at the site of perforation) n=12, double membrane n=18, high basilar bifurcation precluding third ventriculostomy n=3, large venous structure in the prepontine cistern precluding ventriculostomy n=1, lack of adequate space in prepontine cistern for the fogarty's catheter to be introduced n=2, prominant infundibular recess n=4, widely separated mamillary bodies n=2, redundant membrane in the floor of third ventricle making it difficult to perforate since the membrane gets stretched deep into the prepontine space n=4 and a very prominent massa intermedia n=2 patients. Extensive adhesions in the prepontine cistern were noted 16 of the 28 patients who underwent the procedure for post tuberculous meningitic hydrocephalus. In two of these patients the floor was pasty making it impossible to identify any structure.

Conclusions: Significant differences in the floor of third ventricle were noted in 21% of patients in our series. In 18 patients the procedure could not be completed and had to be abandoned. Thickened membrane n=2, High basilar bifurcation n=3,large venous structure in prepontine cistern n=1,lack of adequate space in prepontine cistern n=2,redundant membrane n=3, inability to identify the structures in floor of third ventricle (post meningitic) n=7 were the reasons for abandoning the procedure.

Patient Care: This study makes us aware of the anatomical discrepancies in floor of third ventricle and hence better planning of procedure

Learning Objectives: By the conclusion of this session participants will be able to have a knowledge of anatomical variations in floor of third ventricle which helps in better planning and management of patients undergoing third ventriculostomy for varied reasons.

References: 1.Clin Anat. 2009 Nov;22(8):916-24. Anatomy of the floor of the third ventricle in relation to endoscopic ventriculostomy. Aydin S et al SourceDepartment of Neurosurgery, School of Medicine, Uludag University, Bursa, Turkey. 2.Neurosurgery: June 2011 - Volume 68 - Issue - pp ons347-ons354 doi: 10.1227/NEU.0b013e318211449a Surgical Anatomy and Technique Quantitative Ventricular Neuroendoscopy Performed on the Third Ventriculostomy: Anatomic Study Becerra Romero et al