Painless osteoid osteoma of the rib in an adult. A case report and a review of the literature

BACKGROUND: An asymptomatic rib lesion was discovered by means of a bone scan obtained during the clinical evaluation of an adult man with biopsy proven prostate adenocarcinoma. Clinically and radiologically considered to be a metastatic focus, on resection it proved to be an osteoid osteoma (OO). METHODS: A review of the English medical literature on OO was conducted with emphasis on the occurrence in older patients, costal location, and the absence of pain. RESULTS: OO in patients older than age 50 years is rare (1% - 2% of cases). Only 18 cases of painless OO were found. Of these, 8 (44%) occurred in the phalanges, and 3 (17%) in the cranial-facial bones, both uncommon sites for OO; only 7 (39%) arose in the long bones, the most common site for conventional OO. A disproportionate number of these patients (44%) were younger than age five years, a rarity for OO. Fourteen reported examples of costal OO were found, all of which were associated with pain. The possible mechanisms involved in the production of pain, including analysis of the effect of its site of origin and the presence of nerve fibers, is reviewed. CONCLUSIONS: Costal OO is distinguished from osteoblastoma and from what has been described as painless fibro-osseous lesion of the rib. The infrequency of metastases as a cause of solitary rib lesion is emphasized.