Incidental primary renal extraosseous osteosarcoma: A case report

Primary renal extraosseous osteosarcoma is a rare, aggressive tumor with nonspecific features, often diagnosed via histopathology and immunohistochemistry.

A 56-year-old man with no symptoms was incidentally found to have a calcified left renal mass on contrast-enhanced CT during routine health screening. Imaging showed a 4 × 5 × 5 cm heterogeneous lesion at the renal hilum, abutting the left psoas muscle. Laparoscopic radical nephrectomy was performed without complications. Histopathology revealed osteoid and chondroid matrix, and immunohistochemistry was positive for Vimentin and SATB2, confirming osteoblastic osteosarcoma. The patient recovered well but developed multiple bone metastases at six months.

Given the tumor's location and histologic features, differential diagnoses such as sarcomatoid carcinoma and retroperitoneal liposarcoma were excluded through extensive sampling. Surgical resection remains the mainstay of treatment, while the role of adjuvant therapy remains uncertain due to limited data.

Primary renal osteosarcoma is a diagnosis of exclusion confirmed by histopathology and immunohistochemistry. This case emphasizes the importance of routine imaging in early detection, even for rare malignancies.