Congenital external carotid-internal carotid artery anastomosis associated with moyamoya disease diagnosed by magnetic resonance angiography.

We herein report a case of congenital right external carotid artery-internal carotid artery (EC-ICA) anastomosis associated with moyamoya disease. The patient was a 12-year-old girl with known moyamoya disease who had previously undergone intracranial indirect revascularization at another institution. She presented with sudden weakness of both upper limbs and the left lower limb. Cranial magnetic resonance imaging (MRI) showed no acute ischemic lesions. Cranial magnetic resonance angiography (MRA) demonstrated moyamoya vessels. Cervical MRA revealed a hypoplastic proximal right internal carotid artery (ICA), which was smaller than the main trunk of the external carotid artery (ECA). The ECA and ICA anastomosed at the C2/3 cervical disc level, forming an arterial ring in the cervical carotid region. Because the patient's neurological symptoms resolved spontaneously, conservative management was selected. Congenital EC-ICA anastomosis is extremely rare, and only 9 cases have been reported in the English-language literature. An association has been suggested between congenital EC-ICA anastomosis and a nonbifurcating cervical carotid artery. Moyamoya disease is a rare but important cerebrovascular occlusive disease and has been reported in association with several cerebrovascular arterial variations, particularly persistent trigeminal artery and fenestrations of the vertebrobasilar system. To our knowledge, this is the first report describing the coexistence of congenital EC-ICA anastomosis and moyamoya disease.