A rare association of moyamoya disease with the accessory middle cerebral artery was seen in two patients. The terminal portions of bilateral internal carotid arteries and their vicinities were markedly stenotic and so-called moyamoya vessels developed at the base of the brain. The left accessory middle cerebral artery originating near the anterior communicating artery supplied the left anterior frontal lobe in both patients. Although the accessory middle cerebral artery coursed in the vicinity of the markedly stenotic terminal portion of the left internal carotid artery, the artery was not stenotic. This finding implies that the steno-occlusive changes in the cerebral vasculature in moyamoya disease have topological predilection to the distal internal carotid arteries.

Moyamoya disease is characterised by angiographic features of steno-occlusive changes of the terminal portions of bilateral intracranial internal carotid arteries as well as dilated perforating arteries at the base of the brain known as “moyamoya” vessels. The clinical manifestation of moyamoya disease is typically brain ischaemia in the paediatric population and brain haemorrhage in adults.1 The accessory middle cerebral artery is a variation of middle cerebral artery branching and its incidence has been reported to be 0.3–4.0%.2-4 The accessory middle cerebral artery originates from either the proximal or distal horizontal portion of the anterior cerebral artery coursing parallel to the horizontal portion of the middle cerebral artery …