A large thigh mass: a blood clot or a rare skeletal muscle metastasis from renal cell carcinoma

BACKGROUND: Renal cell carcinoma (RCC) is a tumor known for its unusual presentations and high rate of metastasis. Metastasis to lung, liver, bone and brain are common, but to skeletal muscle(SM) is very rare. Because only 11% of the RCC metastases to SM present after 10 years of initial presentation, there is no general consensus for its annual surveillance. METHODS: We report a case of a 58 year old male with a history of RCC, initially diagnosed 11 years ago, who presented with a large SM mass. A large mass measuring more than 25 cm was located in left posterior thigh and was present for more than a year. It initially was diagnosed as a large blood clot and was treated with warfarin for more than 6 months. Clinical work up including FDG-PET/CT and MRI raised the possibility of a tumor, but a negative biopsy made the diagnosis uncertain. Because of high suspicion for a tumor, patient underwent a complete resection of the mass. RESULTS: The resected mass measuring 28 × 18 × 7 cm was detailed as the largest skeletal muscle metastasis from RCC ever reported. CONCLUSION: This case emphasizes the importance of maintaining a high suspicion for metastasis even in less common metastatic sites mainly in patients with a history of RCC. It also highlights the importance of annual surveillance for metastasis in patients with RCC even after 10 years of initial presentation using FDG-PET/CT.