Gradually Progressive Symptoms of Normal Pressure Hydrocephalus Caused by an Arachnoid Cyst in the Fourth Ventricle: a Case Report

Abstract

Arachnoid cysts in the fourth ventricle are extremely rare, with only 13 cases having been described in the literature. Especially, only 1 case of a patient older than 70 years has been reported. Arachnoid cysts in the fourth ventricle may cause obstructive hydrocephalus. Here, we report the case of a 72-year-old man who presented with an arachnoid cyst in the fourth ventricle that caused gradually progressive symptoms of normal pressure hydrocephalus. A 72-year-old man complaining of persistent dizziness and gait difficulty was admitted to our hospital due to a gradual worsening of his symptoms and apparent cognitive impairment. Computed tomography scan of the head showed symmetrically dilated third, fourth, and lateral ventricles. Though we performed a ventriculoperitoneal shunt operation, his trunk ataxia persisted. We finally diagnosed an arachnoid cyst in the fourth ventricle by direct ventricular infusion of enhanced material. We performed direct surgical fenestration of the cyst and achieved a good outcome. Arachnoid cysts of the fourth ventricle are exceedingly rare, but it is important to recognize them because they cause normal pressure hydrocephalus symptoms and cerebellar or brainstem deficit. We propose detailed neurologic and radiologic examinations of patients with normal pressure hydrocephalus symptoms to avoid unnecessary shunt.