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.