Adding a chapter to the literature: A rare encounter of unilateral Moyamoya disease with ipsilateral persistent trigeminal artery.

Background: The coexistence of persistent trigeminal artery (PTA) and Moyamoya disease (MMD) has been reported. If their pathogenesis is related and if PTA is protective or harmful in MMD remains unknown as these are rare cerebrovascular anomalies. Case presentation: A 35-year-old woman with sudden global aphasia whose CT head and CT angiography of head and neck showed a hypodensity in the left posterior middle cerebral artery (MCA), a possible left proximal internal carotid artery occlusion, and a left PTA with hypoplasia of vertebral and basilar arteries. Digital subtraction angiography showed chronic MMD in the left MCA with extensive pial collateralization from anterior cerebral artery (ACA). The patient was initiated on single antiplatelet therapy and later she underwent direct bypass surgical intervention and rehabilitation. Discussion: Our case report brings attention to the infrequent coexistence of ipsilateral MMD and PTA suggesting a potential congenital pathogenesis based on embryologic development and hemodynamics. Also, we propose a protective role of PTA in MMD in case of large anterior vessel occlusion. This case contributes to the scarce literature on the intriguing relationship between MMD and PTA.