Malignant Peripheral Nerve Sheath Tumor (MPNST)

MPNSTs represent 5–10% of all soft-tissue sarcomas. They correspond to malignant forms of neurofibromas and schwannomas.

Known main risk factors include previous radiation exposure (either therapeutic or environmental), preexisting neurofibromas, and neurofibromatosis type 1 (Von Recklinghausen disease), which is the most important risk factor, accounting for around 50% of patients with MPNST.

 

 

The main clinical symptoms of MPNST are increasing size of tumors, local or radicular pain, paraparesis, and paresthesia and/or weakness of extremities.

The most frequent gene alterations include inactivation of the NF1 tumor suppressor gene (17q11.2) and the p53 gene (17q13), both in sporadic cases and in those related to patients with neurofibromatosis type 1. The de novo mutations represent about 50% of patients.
 

 

Although there is a significant overlap between the imaging features of large benign and malignant peripheral nerve sheath tumors, MPNST should be suspected if there is heterogeneous signal on MR, or if there are focal areas of necrosis contrast enhancement, ill-defined borders, rapid growth on interval imaging, invasion of surrounding soft tissues, and destruction of surrounding bone structures.

Increased FDG uptake on PET-CT with SUV > 1.8 (sensitivity of 100%, specificity of 83%) can help to distinguish benign from malignant peripheral nerve sheath tumors. 

No distinctive features are seen on advanced MR imaging techniques. Imaging behavior on serial studies is the best indicator. 

 

 

Benign peripheral nerve sheath tumor (BPNST): Well-defined margins and no bone destruction. Several histologic features distinguish BPNST from MPNST, such as the presence of a tumor capsule, lack of necrosis, low mitotic activity, and diffuse S100 expression, which are typical for BPNST.

Neurofibroma: Similar findings to BPNST. No bone destruction.

Soft-tissue sarcoma: Usually does not follow the path of a peripheral nerve or plexus

  

 

Surgery and adjuvant radiotherapy

Prognosis is usually poor, especially in large tumors, those invading the spinal canal (as with this patient), those related to NF1, and those with high-grade features in histology.