Peripheral nerve sheath tumours (PNSTs) are a group of primary neurogenic tumours that arise from nerve sheaths outside of the central nervous system. The vast majority are benign, however, malignant transformation is seen particularly in large tumours and those associated with neurofibromatosis type 1 (NF1).
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Pathology
Markers
Many peripheral nerve sheath tumours may express somatostatin receptors 6
Classification
Their imaging appearances, demographics, treatment and prognosis vary greatly and these are therefore discussed separately.
Peripheral nerve sheath tumours may be classified as follows:
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benign
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malignant
Radiographic features
Imaging of a solitary peripheral nerve sheath tumour, 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 tumour, and evidence of rapid growth. As such these are discussed separately in each of the aforementioned tumours. A number of features are, however, shared by localised neurogenic tumours of peripheral nerves.
MRI
As a group, localised peripheral nerve sheath tumours 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 tumours, e.g. myxoid liposarcoma, myxofibrosarcoma, fibromyxoid sarcoma