EXTRAOSSEOUS TC-99M MDP UPTAKE - A PATHO-PHYSIOLOGICAL APPROACH

Scintigraphy with technetium-99m methylene diphosphonate (MDP) delinea tes a wide spectrum of nonosseous disorders. Neoplastic, hormonal, inf lammatory, ischemic, traumatic, excretory, and artifactual entities de monstrate abnormal soft-tissue uptake of Tc-99m MDP. Mechanisms leadin g to increased extraosseous Tc-99m MDP uptake include extracellular fl uid expansion, enhanced regional vascularity and permeability, and ele vated tissue calcium concentration. The composition of the calcium dep osition and the presence of other metallic ions (eg, iron and magnesiu m) are important. Soft-tissue Tc-99m MDP uptake is seen in benign (tum oral calcinosis, myositis ossificans) and malignant (sarcomas, adenoca rcinomas, metastases) neoplastic entities. Hormonal disturbances in ca lcium metabolism, especially in hyperparathyroidism, can lead to metas tatic calcification, visualized with Tc-99m MDP scintigraphy. Tissue d amage from inflammation, infection, or physical trauma results in loca lized hyperemia, edema, or calcium (and hemosiderin) deposition based on their pathophysiologic characteristics. Urinary tract obstruction, anomalies, or dysfunction are demonstrated by Tc-99m MDP imaging. Comm on artifacts are related to faulty radiopharmaceutical preparation, Tc -99m MDP administration, and imaging technique. Recognition of these m odes of extraskeletal Tc-99m MDP uptake can enhance the diagnostic val ue of bone scintigraphy.