Fig. 13

Malignant peripheral nerve sheath tumour with atypical features. This patient presented with a painful swelling on the lateral side of the right leg. The initial diagnosis after biopsy was a benign cystic lesion. Coronal T1-WI (a) showing a lesion with a signal intensity almost isointense to the surrounding muscle (arrow). Axial fat-suppressed PD WI (b) shows almost homogeneous hyperintense signal (arrow) in the lesion with a thin hypointense rim. Axial T1-WI (c) after IV administration of gadolinium shows absence of enhancement (arrow). EMG was not performed in this case, as the diagnosis of a malignant PNST was confirmed histologically and the nerve would certainly be sacrificed during surgery. The sometimes misleading cystic appearance of soft tissue tumours is discussed in more detail in the text