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A vascular lesion cannot be established by angiography in approximately 15% of patients with a spontaneous subarachnoid hemorrhage.1 Within this subset of patients with a negative cerebral angiogram, 50 to 75% of the initial CTs depict a so-called perimesencephalic pattern.1-3 Typically, there is a propensity of blood to layer around the brain stem, with minimal extension into the fissures and no intraventricular entry.2,3 This pattern has been recognized as a benign variant of nonaneurysmal subarachnoid hemorrhage because none of the patients have rebled or developed cerebral infarction, and long-term outcome is excellent. The cause of perimesencephalic nonaneurysmal hemorrhage has been a mystery. Surgical explorations in a few patients have been unsuccessful in localizing a vascular lesion, and none of the patients has come to autopsy.4,5 We recently had the opportunity to study a patient with a perimesencephalic nonaneurysmal hemorrhage with detailed MR imaging and could demonstrate the presence of a pontine vascular anomaly that most likely represents a capillary telangiectasia.
Case report. A 45-year-old man developed an occipital headache and neck pain while shoveling gravel. The headache came on within 15 seconds and was not associated with loss of consciousness or transient neurologic …
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