A case of unilateral moyamoya disease suffered from intracerebral hemorrhage due to the rupture of cerebral aneurysm, which appeared seven years later

BACKGROUND Whether unilateral moyamoya disease (MMD), confirmed by steno-occlusive lesion at the terminal portion of internal carotid artery with formation of moyamoya vessels unilaterally and normal or equivocal findings contralaterally, is an early form of definite (bilateral) MMD remains controversial. It is well-known that adult patients with MMD tend to suffer from cerebral hemorrhage, occasionally due to the rupture of aneurysm arising from moyamoya vessel. CASE DESCRIPTION A 61-year-old woman was diagnosed as unilateral MMD incidentally and followed by magnetic resonance imaging annually. Seven years after the diagnosis, cerebral aneurysm appeared on the moyamoya vessel. Before further examination, the aneurysm ruptured and resulted in massive cerebral hemorrhage. CONCLUSION Even in the unilateral MMD, cerebral hemorrhage may occur due to the rupture of cerebral aneurysm. Careful follow-up is recommended and early treatment is required once cerebral aneurysm is detected.