Malignant peripheral nerve sheath tumours in magnetic resonance imaging: primary and recurrent tumour appearance, post-treatment changes, and metastases

Purpose
To analyse the appearance of primary and recurrent malignant peripheral nerve sheath tumours (MPNSTs) in magnetic resonance imaging (MRI) with a focus on configuration, and to assess the occurrence of loco-regional post-treatment changes and metastases during post-treatment follow-up.

Material and methods
Twenty patients with histologically proven MPNST underwent post-treatment 1.5 T MRI. Primary and recurrent MPNSTs were examined for configuration, contrast enhancement, extent, and signal intensity in MRI. Loco-regional post-treatment changes and information on metastases were extracted from the follow-up.

Results
MPNSTs occurred most often in the extremities (p = 0.006). Twenty per cent (n = 4) of the patients developed recurrences, with a total of 24 lesions. Recurrent MPNSTs were significantly smaller than primary MPNSTs (p = 0.003). Primary MPNSTs mostly occurred unifocally as multilobulated or ovoid and heterogeneous lesions with mostly well-defined borders. Recurrent MPNSTs purely occurred multifocally as mostly nodular (p < 0.001), multilobulated, or ovoid lesions. 80%, 65% and 30% of the patients showed post-treatment subcutaneous oedema (p = 0.002 to 0.03), muscle oedema (p = 0.02), and seroma, respectively. Twenty-five per cent (n = 5) of patients presented metastases during follow-up. The relative risk in patients with recurrences to develop lung or lymph node metastases is eightfold (p = 0.056).

Conclusions
While primary MPNSTs mostly appear unifocally as multilobulated or ovoid lesions, recurrent MPNSTs purely occur multifocally as mostly nodular lesions. Subcutaneous and muscle oedema are very common locoregional post-treatment changes. Patients with recurrences have a higher risk for lung and lymph node metastases.