Stereotactic third ventriculostomy: assessment of patency with MR imaging.

Ventricular CSF signal-intensity characteristics indicative of flowing CSF on MR images (CSF flow void) were analyzed in 20 patients who underwent a CT-based stereotactic third ventriculostomy for presumed internal obstructive hydrocephalus between October 1985 and June 1988. The status of all ventriculostomies was assessed postoperatively by radionuclide ventriculography. Postoperative MR and ventriculographic findings were correlated with the patients' subsequent clinical course. A CSF flow void in the anterior and inferior third ventricle, which seems to indicate vigorous pulsatile CSF flow through a functioning ventriculostomy, was present in all 19 patients who were clinically improved after ventriculostomy. In all 19 of these patients the radionuclide ventriculogram demonstrated normal CSF dynamics. One of the 20 patients did not improve postoperatively. The ventriculogram in this patient revealed delayed ventricular clearing and impaired CSF resorption, and the postoperative MR image did not demonstrate an anterior/inferior third ventricular CSF flow void. Eight of these patients were evaluated preoperatively by MR; one of these eight was the single nonimproved individual. None of the eight preoperative MR studies demonstrated a CSF flow void in the anterior/inferior third ventricle; however, this finding was present in seven of seven postoperative MR studies in clinically improved patients. We conclude that the presence of a CSF flow void in the anterior/inferior third ventricle on a postoperative MR examination is sufficient to document patency of a third ventriculostomy. The absence of this finding may be due to a nonpatent ventriculostomy or perhaps an extraventricular CSF obstruction. The more invasive ventriculogram may be reserved for this situation to distinguish between these latter two possibilities.