[Non-traumatic myositis ossificans in a child. Review of the literature apropos of a case mimicking malignant tumor].

A ten year nine month-old girl was admitted to hospital for a painful inflammatory tumour of the right popliteal area. There was a calcification on X-ray and computerised angiography showed a tumour. MRI showed a heterogenous irregular mass. This looked like a malignant tumour. At surgical biopsy: it was a circonscripta myositis ossificans. This benign tumour of soft tissues, rare in children (25 cases in the literature), had a spontaneous favourable evolution. Differential diagnosis with malignant tumour is well known, but is still difficult. Biopsy is necessary in doubtful cases. We had to remove the mass because of acute pain.