Costal Osteoma: Report of a Case in an Unusual Site.

BACKGROUND Osteoma is a benign bone tumor that typically arises in facial bones and less frequently in the long bones. It rarely occurs in the appendiceal skeleton. Pathologic findings are similar to those for parosteal osteosarcoma, periostitis ossificans, and osteoid osteoma. Diagnosing osteoma at an unusual site is always problematic. Here, we present a case of costal osteoma that was found incidentally on screening and produced mild symptoms in the patient. CASE REPORT A 53-year-old man was examined because of a rib mass in the eighth rib on his left side, which had been present for 2 years. A computed tomography scan revealed that the intensely dense mass arose from the external surface of the eighth rib. Microscopic examination showed that the lesion consisted of mature lamellar bone with several Haversian systems, typical of an osteoma. No atypical spindle cells or necrosis were identified. The diagnosis was osteoma. CONCLUSIONS Because the anatomy of the ribs poses a challenge when performing needle biopsy, diagnosing bony lesions solely based on that technique is difficult. The diagnosis of costal osteoma should be made carefully, based on clinical, radiological, and pathological findings. To the best of our knowledge, ours is the first case report about a costal osteoma. It is useful for chest surgeons, pathologists, and radiologists as an example of a rare presentation of this tumor.