Myositis ossificans circumscripta: a benign lesion with a malignant differential diagnosis.

Localized areas of active myositis ossificans, occurring without a clear history of antecedent trauma, have been referred to as a "pseudo-malignant osseous tumor of soft tissue." This lesion may be mistaken both roentgenographically and pathologically for a malignancy. The roentgenographic signs which favor a diagnosis of non-neoplastic heterotopic bone formation include a lucent zone between the lesion and the adjacent bone, an intact underlying cortex, diaphyseal location, dense calcification in the periphery, and loss of volume on serial films.