Moyamoya disease masquerading as CNS vasculitis: Diagnostic challenges and imaging insights.

Background: Moyamoya disease (MMD) is a rare, progressive cerebrovascular disorder that can mimic central nervous system (CNS) vasculitis on imaging, particularly when advanced imaging techniques, such as vessel wall imaging, are used; thereby creating significant diagnostic uncertainty. Case Presentation: A 38-year-old woman presented with a one-week history of headache and binocular diplopia. Neuroimaging demonstrated a subacute right occipitoparietal infarct. Magnetic resonance angiography showed multifocal stenoses with extensive collateral vessels. High-resolution vessel wall imaging demonstrated circumferential enhancement, initially raising concern for CNS vasculitis; however, cerebrospinal fluid analysis was non-inflammatory, and autoimmune and infectious panels were negative. Digital subtraction angiography confirmed bilateral terminal internal carotid artery stenosis with lenticulostriate collaterals, consistent with MMD. The presence of a positive family history of MMD further supported the diagnosis. She improved clinically, was discharged on aspirin, and remained asymptomatic at neurosurgery follow-up. Discussion: This case highlights the diagnostic challenges in differentiating MMD from CNS vasculitis. The presence of circumferential vessel wall enhancement, which is not specific and may overlap with inflammatory vasculopathies, illustrates how reliance on vessel wall imaging alone can be misleading. This case emphasizes the importance of integrating clinical, laboratory, radiological, and familial data to distinguish non-inflammatory arteriopathies from true vasculitis accurately. Similar diagnostic dilemmas have been reported in the literature, emphasizing the need for careful evaluation to avoid unnecessary immunosuppressive treatment. Conclusion: Differentiating MMD from CNS vasculitis requires careful integration of clinical, radiological, and familial data to prevent misdiagnosis and unnecessary immunosuppression. A structured, multimodal diagnostic approach is essential, particularly when imaging findings are atypical or potentially misleading. Early recognition and appropriate management can lead to favorable outcomes, as illustrated by our patient, who showed complete recovery and remained symptom-free on medical therapy.