The Empty Sylvian Fissure Sign: A Novel Non-contrast CT Finding in Moyamoya Disease

Background and objective In Moyamoya disease, occlusion occurs at the terminus of the bilateral internal carotid artery, resulting in poor visualization of the distal middle cerebral artery (MCA) on imaging. This study aimed to investigate whether the absence of the MCA on non-contrast CT images constitutes a characteristic feature of Moyamoya disease. Methods Patients who were documented as having "Moyamoya disease" or "suspected Moyamoya disease" for insurance purposes in medical records were selected. Retrospective analysis of their datasets was conducted. Non-contrast head CT images were reviewed to ascertain the presence or absence of the MCA at four specified locations (right proximal, left proximal, right distal, and left distal) within the Sylvian fissure. Results Of the 151 patients identified, 23 cases of Moyamoya disease and 35 cases without Moyamoya disease were investigated. The Moyamoya disease cohort exhibited a significantly higher number of absent MCA observations within the four locations (2.65 vs. 0.83, p<0.001). With a threshold of ≥3 locations devoid of the MCA, the sensitivity and specificity of this finding for Moyamoya disease detection were 61% and 94%, respectively. Conclusions This study represents the first exploration of non-contrast head CT findings indicative of Moyamoya disease. Although cerebral angiography or MRI is indispensable for definitive diagnosis, a subset of patients may not undergo these detailed examinations. Focusing on the "empty Sylvian fissure sign" on non-contrast head CT images, frequently encountered in acute medical settings, may help detect patients with Moyamoya disease and support further evaluation.