Tc-99m MDP uptake in retroperitoneal fibrosis

A 60-year-old man with a history of surgical resection of leiomyosarcoma of the right kidney had a bone scan to evaluate possible metastatic osseous disease. The bone scan showed significantly increased Tc-99m MDP activity in the right abdomen, corresponding to a heterogeneous mass in the right retroperitoneal region on the subsequent abdominal CT scan. These findings were initially interpreted as recurrent malignancy. However, the surgical pathology examination demonstrated that the lesion was retroperitoneal fibrosis, which was not previously known to have increased MDP uptake.