Peripheral nerve sheath tumors (PNSTs) are a group of primary neurogenic tumors that arise from nerve sheaths outside of the central nervous system. The vast majority are benign, however, malignant transformation is seen particularly in large tumors and those associated with neurofibromatosis type 1 (NF1).
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Pathology
Markers
Many peripheral nerve sheath tumors may express somatostatin receptors 6.
Classification
Their imaging appearances, demographics, treatment, and prognosis vary greatly, and these are discussed separately.
The WHO classification of tumors of soft tissues recognizes a variety of peripheral nerve sheath tumors:
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benign
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malignant
Radiographic features
Imaging of a solitary peripheral nerve sheath tumor, in most cases, cannot reliably distinguish between the different histological subtypes, and a presumptive diagnosis must take into account the patient demographics, including pre-existing conditions (such as neurofibromatosis type 1 or neurofibromatosis type 2), the location and size of the tumor, and evidence of rapid growth. As such these are discussed separately in each of the aforementioned tumors. A number of features are, however, shared by localized neurogenic tumors of peripheral nerves.
MRI
As a group, localized peripheral nerve sheath tumors demonstrate the following features:
fusiform-shaped mass with tapered ends, with nerve seen leading into and out of the mass
denervation changes in muscles supplied by the involved nerve
Differential diagnosis
Considerations include 7,8:
benign and malignant myxoid tumors, e.g. myxoid liposarcoma, myxofibrosarcoma, fibromyxoid sarcoma
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