Fig. 2

MRI appearance, pathological features, and hemorrhage risk across different mutational subgroups of CCMs. The typical MRI manifestations and gross pathological appearance of hematoxylin and eosin (H&E), Masson’s trichrome, and immunohistochemistry staining for COL1A1 and CD31 of among different mutational subgroups. PIK3CA mutations typically manifest as circular hematomas on MRI, classified as Zabramski type (I). Pathologically, these lesions are characterized by sinusoidal collagen structures enclosing the hematoma fluid. High-magnification images reveal newly formed microvessels within the collagen, filled with red blood cells both inside and outside the vessels, with some exhibiting rupture, potentially serving as the source of the hematoma fluid. In contrast, patients with MAP3K3-PIK3CA mutations exhibit a characteristic popcorn-like appearance on MRI, corresponding to Zabramski type (II). Pathologically, these lesions display typical CCM changes, including more extensive and irregularly dilated vessels surrounded by a thin collagen layer, along with erythrocyte accumulation within the vessels. Scale Bars 1000 μm. The dashed box (Scale Bar 50 μm) indicates the original image magnified twenty times.