An Adult Case of Symptomatic Porencephalic Cyst Following Removal Massive Subcortical Hematoma.

The hematoma cavity typically remains collapsed after intracranial hematoma evacuation, but here we report an adult case in which the cavity expanded into a cystic form, developing into a porencephalic cyst, after the removal. A 73-year-old woman was admitted to our hospital presenting with a disturbance of consciousness. A CT scan showed a subcortical hemorrhage with a blend sign and brain herniation, prompting emergent hematoma evacuation. Although there was an improvement in her symptoms after the operation, her consciousness deteriorated on the 14th day post-operation. A CT scan revealed a porencephalic cyst. Reoperation was performed, and no further recurrence of the cyst was noted. Reports of hematoma cavities expanding into a cystic form after hematoma removal are rare, and the mechanisms of such cyst expansion are not well understood. In this case, we hypothesize two pathways: 1) Residual hematoma components moving through the ventricular wall due to osmotic pressure differences between the hypertonic fluid and cerebrospinal fluid (CSF), and 2) Protein-rich plasma components leaking out of cells due to blood-brain barrier (BBB) disruption caused by cerebral hemorrhage. We also consider the possibility of a check valve mechanism.