Extraosseous 99mTc Methylene Diphosphonate Uptake in Perianal Dystrophic Calcification: Incremental Value of Single-photon Emission CT/CT.

A 57-year-old woman underwent 3-phase 99mTc methylene diphosphonate bone scintigraphy for persistent right hip pain after cannulated screw fixation of a femoral neck fracture. The flow and pool phases were unremarkable, with delayed uptake around the right femoral neck screws. Incidentally, intense focal tracer uptake was seen in the right perianal region. Single photon emission CT/CT localized this activity to coarse subcutaneous perianal calcifications, corresponding clinically to chronic pruritic, discharging, chalky perianal plaques. The appearance favoured dystrophic calcinosis cutis/postinfective sequelae rather than skeletal disease. This case highlights single-photon emission CT/CT for recognizing extraosseous methylene diphosphonate uptake and preventing misinterpretation as contamination, nodal disease, or osseous pathology.