Ectopic ossification associated with osteoid osteoma in the acetabulum. A case report.

Ectopic bone formation was associated with osteoid osteoma in the anterior rim of the acetabulum. A factor, which has been speculated to be secreted from the nidus and is responsible for increased osteoblastic activity, also seemed to have the capacity to stimulate young mesenchymal cells to differentiate into an osteogenic pathway. A case of a 35-year-old woman with osteoid osteoma, which caused ectopic ossification adjacent to the nidus, is presented.