The evaluation of third ventriculostomy function in hydrocephalic patients is challenging. The utility of the constant flow infusion test in predicting response to shunt insertion in normal-pressure hydrocephalus, as well as in identifying shunt malfunction, has been previously demonstrated. The object of this study was to evaluate its usefulness in determining whether a revision CSF diversion procedure was indicated in patients presenting with recurring symptoms and persisting ventriculomegaly after endoscopic third ventriculostomy (ETV).
The authors conducted a prospective study of all patients who, after undergoing ETV at their institution, presented postoperatively with recurring symptoms and persisting ventriculomegaly.
Forty-six patients (mean age 40.7 years, including 11 patients younger than 18 years) underwent 56 constant flow ventricular infusion tests (VITs) at a mean of 24.7 months post-ETV. Thirty-three patients with resistance to CSF outflow (Rout) less than 13 mm Hg/ml/min underwent follow-up (median 17 months) and experienced resolution of symptoms. In 10 episodes Rout was greater than 13 mm Hg/ml/min; the patients in these cases underwent revisional CSF diversion. Two patients demonstrated high and frequent B (slow) waves despite a low Rout; these patients also underwent successful revisions. Patients who improved after surgery had increased B wave activity in the plateau phase of the VIT (p = 0.01). Thirty-four patients underwent MR imaging at the same time; 4 had high Rout despite evidence of flow across the stoma. These 4 patients underwent surgery and experienced resolution of symptoms. Of 9 patients without flow, Rout was less than 13 mm Hg/ml/min in 4; these patients were successfully treated conservatively.
The VIT is a useful and safe adjunct to clinical and MR imaging evaluation when ETV failure is suspected.
Abbreviations used in this paper: AMP = amplitude of the ICP waveform; ETV = endoscopic third ventriculostomy; ICP = intracranial pressure; LOVA = long-standing overt ventriculomegaly of adulthood; NPH = normal-pressure hydrocephalus; RAP = moving correlation coefficient between mean ICP and changes in AMP; Rout = resistance to CSF outflow; VAD = ventricular access device; VIT = ventricular infusion test; VP = ventriculoperitoneal.
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