Malignant Peripheral Nerve Sheath Tumour of the Forearm Presenting as Foreign Body

Abstract

Malignant peripheral nerve sheath tumour (MPNST) is a rare form of soft tissue sarcoma that arises from peripheral nerves, accounting for less than 5% of cases. MPNST most commonly affects trunk and extremities, and It is commonly associated with neurofibromatosis type 1 (NF1) (40%-50%). We present a case of MPNST in a 52-year-old man with history of well-controlled epilepsy. He presented with a painful and erythematous mass in his left forearm, which was initially diagnosed as an abscess secondary to retained foreign bodies. Despite incision and drainage, he experienced recurrence of this mass two months later. Subsequent debridement, biopsy and histology revealed a high-grade MPNST. This prompted a referral to the regional sarcoma unit. Unfortunately, repeat scans demonstrated rapid progression of disease into the anterior forearm compartment and bony invasion. Despite radiotherapy, the tumour metastasised to his lungs. After undergoing palliative chemotherapy, unfortunately, the patient survived only 14 months from the initial presentation. Our study affirms that all resected tissues should be sent for histological confirmation of the suspected diagnosis. When intraoperative findings do not correlate with the initial presentation, the clinician should have a high index of suspicion for potential malignancy. Finally, it is essential that all patients with soft tissue sarcoma should be referred to the specialist regional soft tissue sarcoma service, to be managed by a specialist sarcoma multidisciplinary team according to guidelines.

Keywords: foreign bodies; histology; malignant peripheral nerve sheath tumour; mpnst; soft tissue sarcoma.

Figure 1. X-rays of the elbow on initial presentation with 'foreign bodies' present

Figure 2. Initial MRI, white arrow points to the reported collection around 'foreign bodies'

Figure 3. Repeat MRI scan with significant progression of the malignant peripheral nerve sheath tumour (MPNST) evident