Low-grade fibromyxoid sarcoma (LGFMS) is a rare soft-tissue neoplasm with metastatic potential and needs to be recognized as such, because it can be mistaken for other types of sarcoma due to its unremarkable appearance. This 49-year-old man presented with an approximately 5-cm mass on the anteromedial aspect of his left thigh that slowly increased over 10 years. Clinical symptoms were limited to local discomfort and intermittent distal numbness. Due to the location, imaging findings, and lack of serious symptoms, the initial differential diagnosis favored a schwannoma. An initial biopsy revealed histopathological findings consistent with a perineurioma, although with atypical features. The patient elected to have the mass excised, and the tumor, which arose from a branch of the saphenous nerve, could be separated well from the surrounding soft tissue. Histopathological investigation of the mass displayed characteristic features of a fibromyxoid sarcoma, which was confirmed by subsequent fluorescence in situ hybridization analysis. Due to concerns about infiltration beyond the margins, radical reexcision was advocated and performed, resulting in definite clear surgical margins. At follow-up, the patient had regained full strength with no residual neurological symptoms or any new deficits. He has since been healthy and disease free for a total of 4 years in follow-up. This case documents, to the authors' knowledge, the first observation of an LGFMS associated with a peripheral nerve. It also supports the use of fluorescence in situ hybridization analysis as an essential diagnostic method in establishing the diagnosis of LGFMS.
Low-grade fibromyxoid sarcoma around the knee involving the proximal end of the tibia and patella: A rare case report
