Myositis ossificans mimics an osteoid osteoma: a pitfall for Tc-99m MDP planar and SPECT scintigraphy.

摘要

Myositis ossificans is a form of heterotopic bone formation that is caused most commonly by a traumatic injury. In the active phase, it shows intense uptake on a Tc-99m MDP bone scan, and its extraosseous location is usually evident from planar images alone. However, if it is small and very close to adjacent bone, it can mimic a bone lesion, even when imaged with SPECT. We present a 13-year-old girl, who had a Tc-99m MDP bone scan to assess a 2-week history of left hip pain and inability to ambulate. Planar images showed a small focus of very intense uptake in the left greater trochanter, confirmed by SPECT. As the patient also complained of nocturnal hip pain, a diagnosis of osteoid osteoma was suggested. Further imaging with computed tomography (CT) and magnetic resonance imaging (MRI), however, showed a focus of heterotopic bone formation in the obturator intemus muscle and tendon, as well as bone marrow edema in the greater trochanter, compatible with myositis ossificans.