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Malignant peripheral nerve sheath tumour

Dr Jeremy Jones and Dr Yuranga Weerakkody et al.

A malignant peripheral nerve sheath tumour (MPNST) is malignant form of a neurofibroma or a schwannoma.

Epidemiology

They are estimated to account for 5-10% of all soft-tissue sarcomas. They typically present in adults. There is no recognised gender predilection and clinical presentation varies dependant on location.

Pathology

They can either arise de-novo or de-differentiate from an exising neurofibroma or schwannoma.

Location

Tumours commonly occur close to a plexus of nerve trunk (e.g sacral plexus / brachial plexus)

Associations

neurofibromatosis type I - in 25-70% of cases
previous irradiation

Radiographic features

Imaging criteria are generally considered unreliable in differentiating from a more benign neurofibroma or schwannoma ⁴. However general rules favouring a MPNST include

the larger the lesion, the more likely for it to be malignant
irregular borders (although most MPNST's can have well defined margins)
rapid growth on interval imaging

MRI

T1 : usually iso intense to muscle ⁴; heterogenous signal on T1 (if present) may useful in differentiating from a neurofibroma ³
T2 : can have low signal due to high collagen content ⁴