Efficacy of endoscopic third ventriculostomy in fourth ventricular outlet obstruction

OBJECTIVE: Fourth ventricular outlet obstruction (FVOO), an uncommon cause of obstructive hydrocephalus, is most commonly associated with prior intraventricular hemorrhage or intraventricular infection in children. There have been few reports of FVOO in an adult population. METHODS: Twenty-two patients with FVOO treated with endoscopic third ventriculostomy (ETV) were analyzed retrospectively. RESULTS: Of the 22 patients, 10 were younger than 2 years, 6 were between 2 and 18 years, and 6 were older than 18 years of age. Predisposing factors included tubercular meningitis (1 patient), ventriculitis (2 patients), and intraventricular hemorrhage (3 patients). Twelve patients (mostly >2 years of age) had no prior significant history. The third ventricular floor and the adhesions in the basal cisterns were individually graded (I-IV). An inflamed floor was encountered in 3 patients. ETV was successfully performed in 20 patients. Fourth ventricular exploration was carried out in 5 patients, with outlet membrane fenestration in 2 patients. The follow-up period was 1 to 8 years (mean, 4.2 years). The ETV failed in 7 patients, requiring shunt insertion. The overall success rate was 65%; 91% success was achieved in patients who were more than 2 years of age, whereas the procedure failed in all patients younger than 6 months of age. The cerebrospinal fluid yielded a positive bacterial culture (1 patient), antitubercular antibody (1 patient), anticysticercal antibody (1 patient), and cryptococcosis (1 patient). With a successful procedure, lateral ventricular size was reduced in all patients, whereas fourth ventricular size decreased in 12 patients. The extent of adhesions in the basal cisterns directly correlated with failure. None of the patients demonstrated isolated fourth ventricle on follow-up magnetic resonance imaging. In 4 of the 7 patients with failure, endoscopic exploration was performed, and a patent stoma was observed in all of these patients. CONCLUSION: ETV is a viable option for treatment of patients with FVOO. The high failure rate in infants younger than 6 months of age suggests that ventriculoperitoneal shunting is a favorable option in this age group, rather than ETV. Isolated fourth ventricle is uncommon after ETV in hydrocephalus attributable to FVOO.