Abstract
Myositis ossificans (MO) is a benign soft-tissue lesion characterized by the heterotopic formation of the bone in skeletal muscles, usually due to trauma. MO is occasionally difficult to diagnose because of its clinical and radiological similarities with malignancy. We report a case of traumatic MO (TMO) in the masseter and brachial muscles of a 37-year-old man who presented with painless swelling in the left cheek and severe trismus. Due to the absence of a traumatic history at the first consultation and identification of a tumorous lesion in the left masseter muscle by magnetic resonance imaging (MRI), the lesion was suspected to be a malignant tumor. Subsequently, 18F-fluorodeoxyglucose positron-emission tomography/computed tomography (FDG-PET/CT) showed multiple regions of high FDG uptake across the whole body, suggestive of multiple metastases or other systemic diseases. However, intramuscular calcifications were also observed in the left masseter and brachial muscles, overlapping the areas with high FDG uptake. Moreover, multiple fractures were seen in the rib and lumbar spine, also overlapping the areas with high FDG uptake. Based on these imaging findings, along with a history of jet-ski trauma, TMO was suspected. The left cheek mass was surgically excised and histologically diagnosed as TMO. In this case report, FDG-PET/CT could detect multiple TMOs across the whole body. To the best of our knowledge, cases of multiple TMOs located far apart in different muscles are rare, and this may be the first report.
Highlights
Myositis ossificans (MO) is a self-limiting, benign ossifying lesion, which classically presents with a “do not touch” lesion [1]. It is characterized by heterotopic ossification within muscles and soft tissues, and is most commonly observed in the
The pathogenesis of MO has not been fully elucidated, but it is considered that heterotopic ossification is induced by pluripotent mesenchymal stem cells; these cells are derived from vascular endothelial cells via endothelial-mesenchymal transition and are capable of producing cartilage and bone [3]
MO without ossification or calcification can be misdiagnosed as malignancy or infection
Summary
Myositis ossificans (MO) is a self-limiting, benign ossifying lesion, which classically presents with a “do not touch” lesion [1]. On the fat-saturated T2-weighted image, the left masseter showed a reticular or mass-like low and peripheral high signal intensities (Fig. 1b). A dynamic study after gadolinium contrast-enhancement revealed an increased enhancement in the central mass-like area (Fig. 1c), time-intensity curves showed the same rapid uptake, followed by a gradual increment pattern in the various regions of interest placed in the left masseter muscle. The apparent diffusion coefficients from diffusion-weighted imaging were relatively low in the central mass-like region and intermediate-to-high in the periphery These MRI findings were suggestive of an inflammatory process; combined with the clinical findings, the possibility of a malignant tumor could not be discarded. Based on these findings and the recent traumatic episode, TMOs of the masseter and brachial muscles with multiple fractures and subcutaneous inflammation throughout the limbs were strongly suspected. Re-occurrence was not detected over a follow-up period of 2 years
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