Fig. 1

a, b: Axial T2- and T1-weighted image shows a mixed slight hyperintense signal mass lesion in the left frontal lobe with severe brain edema. c: Increased signal of same lesion is noted on FLAIR image. d: Postcontrast T1-weighted image shows heterogeneous enhancement of ill-defined and dural-based lesion. e. Histological section of typical field showing perivascular infiltration of small lymphocytes, plasma cells, macrophages and histiocytes. Lymphocytes transmigrating to small vessel walls and intravascular IP tissue was noted (Hematoxylin and eosin staining, original magnification × 200). f. Histological section of some areas shows numerous thin-walled blood vessels, areas of congestion and hemorrhage (Hematoxylin and eosin staining, original magnification × 100). g, h, i: Axial T2-weighted image, FLAIR image and T1-weighted image six months after surgical section showed that there was no recurrence