[A case presenting with hydrocephalus and posterior fossa subdural effusion].

We report a case of hydrocephalus due to posterior cranial fossa subdural effusion. The patient was a 4-year-old boy, presenting headache and nausea, with a medical history of viral meningitis 2 months before. Cerebrospinal fluid provided no evidence of infection, and symptoms caused by increased intracranial pressure gradually deteriorated, although glycerol infusion was effective temporarily. Computed tomography revealed marked ventriculomegaly with subdural effusion in the right posterior cranial fossa. The subarachnoid space in the posterior fossa was very tight, and the cerebellum and brain stem were compressed anteriorly. Magnetic resonance imaging demonstrated stenosis of the aqueduct and foramens of Luschka and Magendie. The cerebeller tonsil was dislocated inferiorly, indicating impending herniation, so an emergency operation was performed. Ventriculoperitoneal shunt was undertaken after implantation of an Ommaya reservoir for the posterior fossa subdural effusion. The patient's postoperative course was uneventful, and the symptoms were improved. Although hydrocephalus and subdural effusion following viral meningitis is rare, neuroimaging studies such as CT and MRI should be examined when a young child suffers from symptoms of increased intracranial pressure.