Unilateral traumatic posterior fossa subdural effusion in an infant.

Supratentorial subdural effusion is common after infection and trauma, but rarely occurs in the posterior fossa, and is even less commonly unilateral. The authors report a rare case of unilateral traumatic posterior fossa subdural effusion with secondary hydrocephalus. A 6-month-old female infant presented with lethargy, poor appetite, and persistent vomiting after head trauma 2 weeks previously. A non-enhanced brain CT scan revealed a right posterior fossa subdural fluid collection that displaced the fourth ventricle and brainstem and dilated lateral ventricles. While monitoring the intracranial pressure, the baby was treated with temporary external subdural drainage, followed by a permanent subdural peritoneal shunt. The treatment and likely physiopathology of this unique case are discussed.