Two patients presented with massive subependymal hemorrhage caused by vascular anomalies occult to angiography, computed tomography (CT) scanning, and magnetic resonance (MR) imaging. A 47 -year-old male initially presented with a headache and became comatose 3 weeks later. CT and MR imaging demonstrated a massive hematoma in the right caudate head projecting into the lateral ven tricle. A 60-year-old male sustained heaviness of his left extremities 8 days prior to admission and his condition

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... adually deteriorated. Neuroimaging revealed a right thalamic hematoma adjacent to the lateral ventricle. Cerebral angiography, CT, and MR imaging failed to detect any vascular anomaly. The hematomas increased in size gradually and were surgically explored. The histological diagnosis was arteriovenous malformation for the first case and cavernous angioma for the second case that had ruptured repeatedly. These cases were unique in the unusual location in the subependyma, and diag nostic neuroimaging modalities could not disclose the vascular anomalies, and the hematomas enlarged progressively to become critically symptomatic. Surgical intervention is mandatory for mass reduction and correct diagnosis of such lesions, with favorable outcome as long as the surgery is not delayed until too late.