Abstract
BACKGROUND: Chronic encapsulated expanding hematoma (CEEH) is a rare form of intracerebral hemorrhage with a slow progression, characterized by repeated bleeding within a fibrous capsule. Herein, the authors report the first case of fetal-onset CEEH associated with an arteriovenous malformation (AVM). OBSERVATIONS: A large intracranial mass and ventriculomegaly were detected at 32 weeks of gestation. At 35 weeks, the infant was delivered via emergency cesarean section because of progressive head enlargement and fetal anemia. Postnatal imaging revealed a large intracerebral mass with signs of rebleeding. The patient began having seizures on day 4. MRI demonstrated heterogeneous signal changes and a new intraventricular hematoma. At 67 days, the mass was surgically resected. Intraoperative observation revealed the mass to be a hematoma surrounded by a thick capsule containing fresh and organized blood, indicating repeated hemorrhages. A vascular cluster was observed along the medial capsule wall. Histopathology confirmed AVM-associated CEEH. The postoperative course was uneventful, and there was no recurrence at the 3-year follow-up. LESSONS: This case underscores the importance of early recognition and close monitoring in suspected perinatal CEEH. When rebleeding is suspected, prompt evaluation and resection of both the hematoma and underlying AVM are critical to achieving optimal outcomes. https://thejns.org/doi/10.3171/CASE25633.