Magnetic resonance imaging helps in the early diagnosis of myositis ossificans in children

Two cases on myositis ossificans circumscripta (MOC) in the arm are reporte d. Plain X-ray films and magnetic resonance imaging (MRI) were performed in both cases. In the first, an intramuscular tumor-like mass without calcifi cations was found on MRT with soft-tissue edema extension. In the second, M RI disclosed additional bone-marrow edema. The diagnosis of MOC was confirm ed by biopsy in one case and by follow-up in the other. MOC is a benign sof t-tissue lesion that is rare in children, with an acute course and usually spontaneously favorable evolution. The differential diagnosis from an infec tion or a malignant tumor remains difficult. The best imaging modalities ar e conventional radiography and MRI. The MRI patterns of MOC are typical but not pathognomonic; typical MRI findings in conjunction with clinical sympt oms during the early phase of MOC permit the postponement of a biopsy or ag gressive surgical procedures. Surgery is indicated for cases not showing ty pical MOC calcifications at a later stage.