Objective: To identify if morphology of the entering and exiting nerve involved by a nerve sheath tumour in the brachial plexus can help differentiate between benign (B) and malignant (M) peripheral nerve sheath tumours (PNSTs).
Materials and methods: Retrospective review of 85 patients with histologically confirmed primary PNSTs of the brachial plexus over a 12.5-year period. Clinical data and all available MRI studies were independently evaluated by 2 consultant musculoskeletal radiologists blinded to the final histopathological diagnosis assessing for maximal lesion dimension, visibility and morphology of the entering and exiting nerve, and other well-documented features of PNSTs.
Results: The study included 47 males and 38 females with mean age 46.7 years (range, 8-81 years). There were 73 BPNSTs and 12 MPNSTs. The entering nerve was not identified in 5 (7%), was normal in 17 (23%), was tapered in 38 (52%) and showed lobular enlargement in 13 (18%) BPNSTs compared with 0 (0%), 0 (0%), 2 (17%) and 10 (83%) MPNSTs respectively. The exiting nerve was not identified in 5 (7%), was normal in 20 (27%), was tapered in 42 (58%) and showed lobular enlargement in 6 (8%) BPNSTs compared with 4 (33%), 0 (0%), 2 (17%) and 6 (50%) MPNSTs respectively. Increasing tumour size, entering and exiting nerve morphology and suspected MRI diagnosis were statistically significant differentiators between BPNST and MPNST (p < 0.001). IOC for nerve status was poor to fair but improved to good if normal/tapered appearance were considered together with improved specificity of 81-91% for BPNST and sensitivity of 75-83%.
Conclusions: Morphology of the adjacent nerve is a useful additional MRI feature for distinguishing BPNST from MPNST of the brachial plexus.
Keywords: Magnetic resonance imaging; Malignant peripheral nerve sheath tumour; NF-1; Neurofibroma; Neurofibromatosis; Schwannoma.