The Leptomeningeal Ivy Sign on Fluid-Attenuated Inversion Recovery Images in Moyamoya Disease: Positron Emission Tomography Study

Background: The ivy sign is sometimes seen on fluid-attenuated inversion recovery (FLAIR) images in moyamoya disease (MMD). In recent studies using single-photon emission computed tomography, ivy sign proliferation correlated with decreases in cerebrovascular reserve. However, a decreased vascular reserve is not concrete. The purpose of this study was to evaluate the correlation between ivy sign proliferation and the findings of 15O gas positron emission tomography (PET). Methods: In 19 MMD patients (12 women, age 31-69 years) with ischemic symptoms, FLAIR magnetic resonance imaging and 15O gas PET were performed. We classified the middle cerebral artery (MCA) territory into 2 regions in each hemisphere, and the degree of the ivy sign (ivy sign score) in each region was classified into 3 grades (0-2), where grade 0 indicated an absence of the ivy sign, grade 1 indicated that the ivy sign was seen on less than half of the cortical surface in each region, and grade 2 indicated that the ivy sign was seen on more than half of the cortical surface. We examined the relationship among the ivy sign score, the severity of ischemic symptoms and PET parameters in 76 MCA regions of 19 patients. Results: Ivy sign scores of the regions were 0 (n = 19), 1 (n = 40), and 2 (n = 17). Total ivy sign score of a hemisphere increased as clinical symptoms became more severe. Cerebral blood flow (CBF) values were lower, cerebral blood volume (CBV) values were higher, and CBF/CBV values were lower than those of controls as symptoms became severe (p < 0.05). CBF and CBF/CBV values decreased and CBV values increased as the ivy sign score increased, and were significantly higher and lower, respectively, than control values (p < 0.05). No significant differences in cerebral metabolic rate of oxygen and oxygen extraction fraction were found between the 3 ivy sign scores. A positive correlation was found between ivy sign score and increases in CBV (p < 0.01), and a more obvious negative correlation was found between ivy sign score and decreases in CBF/CBV (p < 0.001). Conclusions: We evaluated the correlation between ivy sign proliferation and the findings of 15O gas PET. We suggested that ivy sign proliferation was associated with both dilated pial vasculature and the slow flow of developed leptomeningeal collaterals in patients with MMD.