Extraosseous uptake of 99mTechnetium phosphate in an extremity

Abstract

F OCAL OR diffuse extraskeletal uptake of 99mTechnetium (Tc)-labeled phosphate complexes may occur in a multitude of disorders. Frequently, the findings are incidental to evaluation of the osseous system by bone imaging. However, it is important that these causes of soft-tissue localization of bone-seeking radiopharmaceuticals be kept in mind when bone imaging studies are reviewed so that mistakes in interpretation are not made. In this article we discuss a case with increased 99mTc uptake on both soft and bone tissues of the right arm and hand. A year ago, a 67-year-old woman with total oophorectomy for ovarian cancer was receiving chemotherapy. She had no medical complaints. A bone scan was performed using 20 mCi (740 MBq) of 99mTc-MDP. Increased intense skeletal and mild soft-tissue activity in the right hand, wrist, and arm were noted (Fig 1). The conventional radiograph of this extremity was normal. Four days later, a repeat three-phase bone scan of both upper extremities showed no abnormalities (Fig 2). There are many possibilities to consider when this is observed. The mechanisms of 99rnTcdiphosphonate uptake in nonosseous tissues are thought to closely resemble those of bone uptake. Soft-tissue activity may be secondary to any process that evokes increased blood flow or soft-tissue calcification. However, the first and most obvious cause is surface contamination by urine or radionuclide during injection? However, in this case, the increased skeletal and soft-tissue activity in the right upper extremity was because of intra-arterial injection of the radioisotope.