Giant High-Grade Myxofibrosarcoma of the Right Thigh Treated by Hip Disarticulation: A Case Report with Imaging–Pathology Correlation

Background Myxofibrosarcoma (MFS) is a soft-tissue sarcoma of fibroblastic origin that typically presents as a slowly enlarging, painless mass. High-grade tumors are locally aggressive, and their diagnosis can be delayed by misleading clinical findings and by under-grading on initial biopsy. Case presentation: A 61-year-old man developed a small fatty-type swelling in the muscular region of the right lower limb in February 2024. It was initially diagnosed as a benign fatty cyst and excised in April 2024. The mass recurred and enlarged, and histology of the excised specimen listed liposarcoma, leiomyosarcoma and rhabdomyosarcoma as differential diagnoses. The patient was referred for chemotherapy, which he received only intermittently (seven cycles of MAID/ifosfamide-based chemotherapy in total). Over the following two years the tumor grew to approximately 31 × 25 × 26 cm. CT showed a cystic-solid necrotic mass eroding the femoral cortex and displacing the femoral vessels, with pelvic and inguinal lymphadenopathy and a small right upper-lobe pulmonary nodule. Pre-operative assessment showed rapid atrial fibrillation with a preserved ejection fraction (58%). Because of neurovascular encasement and bone destruction, limb salvage was not feasible, and a radical right hip disarticulation was performed in July 2026. Histopathology confirmed high-grade MFS with approximately 80% viable tumor after chemotherapy, and R0 margins were achieved. The patient received no adjuvant therapy and was in good condition at the time of writing. Conclusion Deep-seated MFS can remain clinically silent until it reaches massive dimensions. Core biopsy of myxoid-rich tumors may under-grade or misclassify the lesion, radiological stability may mask substantial viable tumor after chemotherapy, and radical amputation remains a valid option when neurovascular encasement and bone destruction preclude limb salvage.