Symptomatic Porencephalic Cyst in the Chronic Postoperative Phase Following Evacuation of Cerebellar Hemorrhage: A Case Report.

Porencephalic cysts are typically observed in fetal or pediatric patients and are rarely reported in adults. While some cases have been reported in the acute or subacute phase following intracerebral hemorrhage, delayed formation during the chronic phase is exceedingly uncommon, particularly in the posterior fossa. We report the case of a 53-year-old woman who developed progressive ataxia and dysarthria eight months after surgical evacuation of a cerebellar hemorrhage. Imaging revealed a 55-mm CSF-filled cyst in the left cerebellum. She underwent cyst wall fenestration and opening of the cisterna magna, which resulted in gradual cyst shrinkage and symptom resolution. No recurrence was observed at the five-month follow-up. Only four cases of porencephalic cyst formation following hematoma evacuation have been reported, all in the supratentorial region and during the acute or subacute phase. This case is the first to describe delayed symptomatic cyst formation in the cerebellum. The clinical course suggests a check-valve mechanism as the underlying pathophysiology. This case highlights the importance of considering delayed porencephalic cyst formation in the differential diagnosis of new neurological symptoms during the chronic postoperative phase. It underscores the value of long-term imaging surveillance after parenchymal brain injury.