[Early Development of a Symptomatic Expanding Porencephalic Cyst in the Hematoma Cavity after Subcortical Hematoma Removal in an Adult:A Case Report].

A 69-year-old woman presented on an emergency basis, with headache and left hemiparesis. Initial head CT at the time of admission revealed a large subcortical hematoma with perihematomal edema extending from the right parietal to the occipital lobe. A small part of the hematoma extended toward the trigone of the right lateral ventricle. CT angiography revealed no vascular abnormalities. Emergency craniotomy was erformed, and the patient's initial postoperative course was unremarkable. However, the patient's neurological symptoms worsened 10 days postoperatively, and CT revealed a new low-density cystic lesion with perifocal edema at the site of hematoma removal, in addition to severe cerebral compression. We performed a reoperation, and intraoperatively we observed hematoma fluid mixed with cerebrospinal fluid without any abnormal blood vessels or neoplastic lesions in the hematoma cavity. We identified the choroid plexus deep within the surgical field, and slight leakage of cerebrospinal fluid was detected from the ventricular aspect, indicating the formation of a small passage between the hematoma cavity and the ventricle. After the second operation, her postoperative course was uneventful without recurrent cyst formation. An early symptomatic expanding porencephalic cyst in the hematoma cavity after removal of an intracerebral hematoma is rare, and only a few cases have been reported in the literature. Based on literature review and considering the likely mechanism of cyst development, we speculated that progressive cyst expansion could be attributed to a check valve mechanism between the ventricle and the cavity from which the hematoma was removed, as observed in the present case.