This definition appears very rarely
, Posterior fossa tumors and cysts with hydrocephalusEndoscopic third ventriculostomy has been attempted with good success rates ranging up to > 90% in patients with posterior fossa tumors and brain stem gliomas with hydrocephalus. ,,, ETV has been of proven value in patients with posterior fossa tumors, who have persistent hydrocephalus after tumor resection.  No technical difficulties were encountered in patients with brain stem tumors in one series.  However, routine performance of ETV prior to posterior fossa tumor surgery or in postoperative hydrocephalus may not be necessary.  Dandy-Walker complex malformations, retrocerebellar cysts, mega cisterna magna, and hydrocephalus secondary to fourth ventricular outlet obstruction.