Incidental finding of a peripheral nerve sheath sarcoma

Sadie Dunne, Ultrasound, Benenden Hospital, Kent

A 30 year old female presented with six month history of calf pain with foot drop and a recent intense calf pain and swelling. No history of trauma. Initial referral for MRI scan of her foot and ankle reported suggested myopathic changes in several muscles. No follow-up treatment given. Patient experienced difficulty walking and developed localised severe calf pain and was referred by her GP for an ultrasound of her leg veins to exclude DVT.

On ultrasound examination there was no evidence of a DVT, however, in the popliteal fossa a well-defined, heterogeneous, intramuscular mass was visualised extending down the posterior calf with abnormal vascularity measuring 20 cm in length with a diameter of 6 x 6 cm. Images were reviewed immediately by a radiologist and referred for urgent MRI calf.

MRI reported a well-defined elongated intermuscular soft tissue mass lesion in the calf closely related to the neurovascular bundle, suspicious for a tumour of neurogenic origin, possibly a malignant peripheral nerve sheath tumour or given its close relationship to neurovascular bundle possibly a leiomyosarcoma. The previous signal changes on the MRI foot could be due to denervation/compression of the posterior tibial nerve.
Patient was referred to the specialist sarcoma team and underwent amputation and is undergoing chemotherapy. She has been hospitalized with sepsis twice since surgery.

Malignant peripheral nerve sheath tumours (MPNST), also known as neurofibrosarcomas, can occur anywhere throughout the body, mainly in adults.
MPNST is a rare malignant mesenchymal lesion that accounts for 5% to 10% of all soft tissue sarcomas. They are extremely aggressive with high local recurrence rate and poor survival. Early diagnosis of sarcoma increases the chance of successful treatment. Resection surgery with a margin is the main therapy for MPNST, radiation and systemic chemotherapy are also widely used despite their uncertain effect.

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