Fig. 1

Imaging of the initial paraspinal tumor and additional intramuscular lesions and histopathology of the index tumor. MRI demonstrated a T2-inhomogeneous tumor within the paraspinal musculature (a), showing central necrosis and strong contrast enhancement (coronal T1-weighted imaging in b). Additional tumor foci in the left psoas muscle (c) and left triceps muscle (d), each smaller than the index lesion, but with similar T2 signal intensity (asterisk in d indicates humeral head). Histopathology of the paraspinal tumor showed dense spindle-shaped tumor cells and a prominent intratumoral capillary network (hemangiopericytoma-like pattern) (hematoxylin-eosin stain, × 400, in e). In immunohistochemical analysis, tumor cells stained strongly positive for WT1 (f), but largely negative for SMA and desmin (not shown), while intratumoral vessels stained positive for CD34 (g). Tumor cells displayed only low Ki-67 labeling index of 1–2% (h)