Unilateral increased radioactivity in the lower extremities on routine 99mTc-pyrophosphate bone imaging.

Unilateral increased activity in the lower extremities was noted in 5 patients who underwent routine 99mTc-pyrophosphate bone imaging for metastatic evaluation. In three patients a large pelvic mass or retroperitoneal hematoma was noted on the affected side. Clinical evidence of lymphatic obstruction was apparent in two cases with pelvic mass. In the fourth case, venous disease (thrombophlebitis) was noted and the fifth case showed osteomyelitis. The possible mechanism for this phenomenon may include obstruction of the lymphatic or venous circulation and inflammation. Other causes of soft tissue uptake of 99mTc-PYP are reviewed. The above mentioned conditions must be excluded when asymmetrical activity of 99mTc-PYP is seen on routine bone imaging.