Changes in third ventricular size with neuroendoscopic third ventriculostomy: a blinded study.

The objective was to study the relation between changes in cerebral ventricular size and clinical outcome after neuroendoscopic third ventriculostomy (NTV) in both primary (no previous surgery) and secondary (previous CSF diversion for hydrocephalus) NTV. Changes in ventricular size were related to the need for further surgery for CSF diversion. A blinded retrospective study of the pre-NTV and post-NTV sizes of the ventricles in an unselected series of patients undergoing this procedure was done. A decrease in third ventricular size was seen in significantly more patients in the primary group than in the secondary group. Median change in third ventricle width for those who did not require further CSF diversion was significantly greater than those with no clinical benefit (p=0.01). Positive predictive power for successful outcome was highest for measures of the third ventricle; 73% and 68% for third ventricle width and height respectively, 88% for anterior to posterior commissure distance. In conclusion, third ventricular size reduces after NTV. The use of such a change as an arbiter of success in this procedure is questionable as clinically successful cases can have no change in ventricular size. It is considered that clinical outcome is the most important guide to success or failure as reduction in ventricular size is by no means guaranteed. Radiological outcomes alone may be misleading and reliance on them should be avoided.