Myxoid Type of Malignant Fibrous Histiocytoma (myxofibrosarcoma) - A Case Report of an Unexpected Histopathology of Intermuscular Mass

Malignant fibrous histiocytoma is a rare and highly aggressive neoplasm believed to originate from primitive mesenchymal cells; arising from soft tissue or bone, usually in the extremities (large muscles of thigh) or retroperitoneum. It is now referred to as undifferentiated pleomorphic sarcoma (UPS). This neoplasm is the most common soft tissue sarcoma of late adult life and has a slight male predominance. The mostcommon is storiform/pleomorphic that forms 50-60% of all such tumours while myxoid type is the second most common at 25%. A 57-year-old male presented to us with a swelling over the antero-lateral aspect of upper and middle third of left thigh measuring about 20 x 15 centimeters. He was thoroughly investigated and swelling was excised in toto. Soft swelling excised and on histopathology found to be an intermuscular myxoid type of malignant fibrous histiocytoma (high grade myxofibrosarcoma). Excisions of intermuscular lesions is not an uncommon story but most are confirmed to be benign myxomas or nerve sheath cell tumor. However, the entity of malignant fibrous histiocytoma should be kept in mind. Patients will usually present late with advanced local disease or metastasis, usually to lungs and lymph nodes. Treatment is surgical with wide local excision and neoadjuvant/adjuvant radiotherapy has been advocated as well. This case report is being presented as the tumor is rare and also an important consideration in the differential diagnosis of myxomas, intermuscular lipomas, peripheral nerve sheath tumor, hemangioma, hematoma and desmoid tumor. Another important feature is that the tumor can be diagnosed with certainty only after excision with histopathological examination.