Blood, Brain, and Bypass: Moyamoya Syndrome Unmasked During Hematologic Optimization in an Adult With Sickle Cell Disease.

Moyamoya syndrome is a rare, progressive cerebrovascular disorder characterized by stenosis or occlusion of the terminal internal carotid arteries with the formation of fragile collateral vessels. While classically described in pediatric patients and idiopathic Moyamoya disease, secondary Moyamoya syndrome has been reported in association with sickle cell disease (SCD). Adult presentations remain uncommon and are frequently underrecognized. We report a unique case of a 36-year-old man with sickle cell anemia who developed acute neurological deterioration following hematologic optimization with packed red blood cell transfusion and therapeutic phlebotomy during a vaso-occlusive crisis. Cerebral angiography revealed complete occlusion of the left internal carotid artery at its terminus, consistent with Moyamoya syndrome. The patient subsequently underwent surgical revascularization with encephaloduroarteriosynangiosis with subsequent neurological stabilization. This case illustrates how advanced but previously compensated large-vessel cerebrovascular disease in adults with SCD may become clinically manifest during physiologic perturbation, underscoring the importance of early vascular imaging and multidisciplinary management when neurologic symptoms evolve during hematologic therapy.