Abdominal pseudocysts are common complications of ventriculoperitoneal shunt (VPS). We report the case of a 37-year-old woman treated by VPS for congenital obstructive hydrocephalus, who presented shunt dysfunction related to a voluminous abdominal cyst initially diagnosed as cerebrospinal fluid pseudocyst. The cyst was drained and the VPS was removed after endoscopic third ventriculocisternostomy (ETV). A few months later, a large new abdominal cyst appeared and was operated on. Diagnosis was rectified as massive ovarian mucinous cystadenoma. In any intra-abdominal cyst, differential diagnoses need considering to avoid mis-diagnosis in shunted patients, especially if the cyst is very large. The etiology of the hydrocephalus should also be investigated in case of shunt dysfunction. Even in case of longstanding shunt, ETV can be an alternative to shunt revision surgery in obstructive hydrocephalus, enabling VPS withdrawal and treatment of the hydrocephalus.