Intramuscular Myxoma of the Shoulder in Neurofibromatosis Type 1.

Background/Aim: Neurofibromatosis type 1 (NF1) is an autosomal dominant tumor predisposition syndrome. Characteristic tumors associated with NF1 can be traced to derivatives of the neural crest. Tumors of the sheath cells of peripheral nerves (neurofibromas) are particularly common in NF1. NF1 patients have an increased risk of developing malignant peripheral nerve sheath tumors (MPNSTs). These lesions primarily occur along the trunk and extremities. This report aims to expand the diagnostic spectrum of soft tissue tumors in NF1. Case Report: A male patient with NF1 diagnosed in early childhood and a history of repeated surgical treatment for a facial plexiform neurofibroma (PNF) developed a rapidly growing, firm, protruding mass near the right shoulder joint over several months. Clinical examination and magnetic resonance imaging suggested a PNF; however, the biological nature of the lesion could not be determined conclusively. The tumor was surgically excised, and the postoperative course was uneventful. Histopathological examination revealed an intramuscular myxoma of the periarticular shoulder region. No recurrence was observed during two years of follow-up. Conclusion: Myxomas are not among the characteristic tumors of NF1. It appears that the development of a sporadic myxoma in NF1 is very rare. In this case, the findings and symptoms resembled those of a nodular PNF. Only surgical removal and histological examination could reveal the true biology of the lesion in this case.