Is Quasi-moyamoya Disease a Uniform Disease Entity? A Three-Dimensional Constructive Interference in Steady State Imaging Study

Background Quasi-moyamoya disease (MMD) or moyamoya syndrome is based on various underlying diseases and radiologically simulates MMD, but its disease entity is still unclear. Recent studies have proven specific shrinkage of the involved arteries in MMD. Using 3-dimensional constructive interference in steady state (3D-CISS), therefore, this study aimed to analyze the outer diameter of the involved arteries in quasi-MMD. Methods This study included 9 patients with quasi-MMD (unilateral type, n = 2; bilateral type, n = 7). Using 3D-CISS, the outer diameter was quantified in the internal carotid artery distal to the posterior communicating artery (C1), the horizontal portion of the middle and anterior cerebral arteries (M1 and A1, respectively), and the basilar artery. Control values were obtained from 17 healthy subjects. Results In 7 of 9 patients, the outer diameters of C1, M1, and A1 were significantly smaller than those of the controls. On the other hand, the values were normal in other 2 patients. There was no significant difference in the underlying disorders between the 2 groups. All 3 pediatric patients are categorized into the arterial shrinkage group, but 2 of 6 adult patients were not. Conclusions These findings strongly suggest that quasi-MMD is not a uniform disease entity and includes at least 2 pathophysiologically different groups: the arterial shrinkage group and the nonarterial shrinkage group. A certain subgroup of MMD patients may be misdiagnosed as quasi-MMD because of the patients' comorbid disorders and mixed up with the patients who present angiographic findings similar to MMD in spite of the lack of arterial shrinkage.