RESUMEN
BACKGROUND: The presentation of moyamoya disease (MMD) as an aneurysmal subarachnoid hemorrhage (SAH) is relatively frequent and in the absence of aneurysms is extremely rare. CASE DESCRIPTION: A 53-year-old male patient suddenly developed severe headache associated with dysarthria and an altered state of consciousness. At the time of admission, he was found drowsy with global aphasia, stiff neck, right hemiparesis and right Babinski's sign. A non-contrast brain computed tomography was performed and a small bleeding in the subarachnoid space over the left frontal and parietal cortex was observed. Four-vessel cerebral angiography showed bilateral stenosis of the internal carotid arteries, with multiple tortuous vessels branching from the anterior and middle cerebral arteries. These abnormal vessels were anastomosing with branches from the posterior cerebral and middle meningeal arteries. With this information, a diagnosis of MMD was made. A three-dimensional reconstruction from digital angiography ruled out aneurysms or vascular malformations. After 4 weeks, another angiography was performed and remained the same as previous one. CONCLUSION: Clinical and radiological characteristics of this case are consistent with previous reports, supporting the theory that non-aneurysmal SAH in MMD is caused by rupture of fragile moyamoya vessels.