INTRODUCTION

Neoplastic and non-neoplastic bone forming lesions are found within both the soft tissues (especially muscles and joints) and bones. Aspiration biopsy of heavily ossified lesions generally results in extremely hypocellular or acellular aspirates and in these cases, small core biopsy may also be unsuccessful.

Heterotopic bone may be found as a metaplastic product in both neoplastic and non-neoplastic lesions. Aspiration samples of heterotopic ossification usually yield hypocellular smears or at most reactive fibroblasts scattered in a bloody background. Morphologically dissimilar but potentially etiologically related are aspirates of dystrophic calcification. Both lesions can reach massive size and are frequently found in periarticular areas particularly around the hip. Other lesions with non-neoplastic ectopic ossification include myositis ossificans and fibrodysplasia ossificans progressive.

MYOSITIS OSSIFICANS

Clinical features

Myositis ossificans is a benign bone forming proliferation of a reactive or reparative nature. It most commonly occurs in striated muscle but similar lesions are reported to occur in the subcutaneous tissues and tendons. Myositis ossificans is related to nodular and proliferative fasciitis but differs morphologically in that bone formation occurs with various degrees of maturation. Some authors subdivide myositis ossificans into traumatic and non-traumatic forms but this appears to have little if any clinical value. Many examples follow a traumatic incident and are often associated with pain and tenderness. Over a period of 2 to 3 weeks, the soft tissue swelling becomes increasingly localized and mass-like. With further time, the lesion becomes rock hard as true ossification develops. The masses average between 3 and 6 cm in greatest dimension.