Malignant peripheral nerve sheath tumour

Malignant peripheral nerve sheath tumours (MPNSTs) are forms of peripheral nerve sheath tumours and comprise of malignant forms of neurofibromas and schwannomas. Approximately half of such tumours are seen in individuals with neurofibromatosis type I (NF1), in such cases arising from pre-existing neurofibromas. 

Malignant peripheral nerve sheath tumours are estimated to account for 5-10% of all soft-tissue sarcomas. They typically present in young and middle-aged adults 8. There is no recognised gender predilection. When seen in the setting of NF1, they tend to occur in younger patients 8. They are also encountered with greater frequency in individuals who have previously received radiotherapy 8

Clinical presentation varies dependant on location. 

MPNSTs can either arise de-novo or de-differentiate from an existing neurofibroma (most often plexiform neurofibromas in NF1) or rarely other neurogenic tumours (e.g schwannoma, ganglioneuroblastoma, ganglioneuroma, pheochromocytoma) 8

Location

MPNSTs usually arise from a large nerve, and thus usually occur close to a plexus (e.g. sacral plexus/brachial plexus). Cranial nerves are rarely involved, and on the rare occasions they are, then the MPNST has usually arisen from an underlying schwannoma rather than a neurofibroma 8.

Genetics

Most MPNSTs demonstrate inactivation of a number of genes: NF1, CDKN2A and PRC2 8

Macroscopic appearance

The macroscopic appearance depends both on location and on whether or not the MPNST has arisen from an underlying pre-existing tumour. They are often large (>5cm) at diagnosis, and may demonstrate local infiltration into surrounding tissues 8

Microscopic appearance

The microscopic appearance of MPNSTs is heterogeneous, varying in cellularity and growth pattern, generally including tightly packed spindle cells arranged in either a herringbone or interwoven fasciculated pattern 8

Immunophenotype

Immunohistochemistry reflects their neurogenic origin, with the following immunoreactivity 8

  • S100: positive in 50-70% - low in high-grade MPNSTs
  • p53 protein: positive in 75%
  • EGFR: positive in ~35%
Variants

A number of histological variants are recognised 8:

  • epithelioid MPNST
  • MPNST with divergent differentiation (aka malignant triton tumour)
  • MPNST with perineural differentiation (aka malignant perineurioma)

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 MPNSTs can have well-defined margins)
  • rapid growth on interval imaging
MRI
  • T1
    • usually isointense to muscle 4
    • heterogeneous signal on T1 (if present) may useful in differentiating from a neurofibroma 3
  • T2
    • can have low signal due to high collagen content 4
Scintigraphy

Gallium67 scintigraphy may show higher uptake than that of a neurofibroma 6-7.

It is an aggressive tumour that carries a poor prognosis, with 20-25% of patients developing metastases 8. Poor prognostic factors include 8

  • NF1
  • large size
  • location on the trunk
  • high-grade histological features
Share article

Article information

rID: 11066
Synonyms or Alternate Spellings:
  • Neurofibrosarcoma
  • MPNST
  • Malignant schwannoma
  • Neurofibrosarcomas
  • Malignant schwannomas
  • MPNST's

Support Radiopaedia and see fewer ads

Cases and figures

  • Drag
    Axial
    Case 1
    Drag here to reorder.
  • Drag
    Case 2
    Drag here to reorder.
  • Drag
    Case 3
    Drag here to reorder.
  • Drag
    Case 4: left V1 involving supra-orbital and frontal branches
    Drag here to reorder.
  • Drag
    Case 5: malignant schwannoma
    Drag here to reorder.
  • Updating… Please wait.
    Loadinganimation

    Alert accept

    Error Unable to process the form. Check for errors and try again.

    Alert accept Thank you for updating your details.