Bilateral Proatlantal Arteries in Moyamoya Disease: Case Report and Implications

Introduction Fetal carotid‐vertebrobasilar anastomoses normally regress during embryonic development. The persistent proatlantal artery type 1, also known as the persistent proatlantal intersegmental artery (PPIA), arises from the cervical portion of the internal carotid artery (ICA), courses posteriorly and superiorly along the first cervical vertebra, and joins the vertebral artery at the C1‐C2 level to supply the vertebrobasilar circulation. We present a case of bilateral PPIA diagnosed concurrently with bilateral Moyamoya disease (MMD) and the possible clinical implications of this concurrence. Methods This is a retrospective review of a single case report regarding a 28‐year‐old female treated at our institution who presented acutely with intraventricular hemorrhage. Data including demographic, radiographic, procedural, and latest follow‐up were collected. Collection of data was approved by our Institutional Review Board. Results A 28‐year‐old female with past medical history notable for Trisomy 21 presented with acute, severe headache followed by unresponsiveness. Prior to admission, there was no clinical suspicion of MMD. Non‐contrast computed tomography (CT) revealed bilateral intraventricular hemorrhage, a small left periatrial intraparenchymal hemorrhage, and developing hydrocephalus. An external ventricular drain was placed, and the patient was stabilized with improvement in neurologic status. CT angiography showed bilateral stenosis of the distal internal carotid, proximal middle cerebral, and proximal anterior cerebral arteries concerning for MMD. Cerebral angiography demonstrated bilateral PPIA serving as dominant contributors to the posterior circulation with extensive distal collateralization from both anterior and posterior circulations (Figure 1). A tortuous left posterior choroidal artery was identified, though no definite aneurysm or vascular anomaly was observed. The angiogram findings confirmed the suspicion of MMD in the setting of bilateral persistent fetal carotid‐vertebrobasilar anastomoses. The patient was successfully weaned from the EVD and was discharged home on day 19. Discussion regarding revascularization options is ongoing. Conclusion This is the first ever reported case of bilateral PPIA in the setting of MMD. This finding is significant given the unique alteration in hemodynamics and the consequences it may have in either limiting or accelerating the progression of MMD. The persistent anastomoses may improve the development of distal collaterals between the posterior circulation and anterior circulation due to the lack of flow via the posterior communicating arteries. In contrast, the bilateral PPIAs may accelerate the progression of MMD by further limiting flow through the stenotic ICA. Recognition of PPIA has implications for diagnostic interpretation and risk stratification for future interventions.