Imaging description

Radiography is often negative or it shows a non-specific soft tissue mass. As with other soft tissue tumors MRI is the diagnostic modality of choice for imaging malignant peripheral nerve sheath tumors (MPNSTs). The location of the mass in relationship to a deep large nerve trunk is helpful in diagnosing a neurogenic tumor. The tumor may appear fusiform in shape and may also be noted to enter and exit a nerve (Figure 81.1). The signal intensity of a MPNST on both T1- and T2-weighted images is non-specific. MPNSTs show low signal intensity similar to muscle on T1-weighted images and heterogeneous increase in signal intensity on T2-weighted images. On gadolinium-enhanced images MPNSTs can show central necrosis (Figure 81.2). Malignant and benign peripheral nerve sheath tumors cannot be reliably distinguished on the basis of imaging criteria alone; however certain findings should raise the suspicion that the tumor is malignant. MPNSTs tend to be larger tumors, typically more than 5 cm. They may exhibit ill-defined margins due to infiltration of adjacent soft tissues and are often associated with soft tissue edema. An infiltrative tumor border on CT or MR suggests malignancy, but may be present also in benign plexiform neurofibromas. Conversely a malignant neoplasm may have a smooth, non-infiltrating margin. Bone erosions may occur with both benign and malignant neoplasm, but are more irregular with malignant lesions.