Introduction
This topic covers three benign bone-forming tumours that are common exam questions: osteoma, osteochondroma and osteoid osteoma (with osteoblastoma as its larger relative). For each you should know the typical site and age, the clinical picture, the characteristic X-ray and CT findings, and the treatment. These lesions are often found incidentally or present with local symptoms, and plain radiography followed by CT or MRI is usually enough to reach a diagnosis.
Osteoma
An osteoma is a benign, slow-growing tumour made of mature compact or cancellous bone. It is rare in the long bones and is typically seen in the skull and paranasal sinuses, especially the frontal and ethmoid sinuses.
- Often asymptomatic and found by chance on imaging
- Large or sinus lesions may cause headache, sinus obstruction or recurrent sinusitis; orbital involvement may cause proptosis or diplopia
- Multiple osteomas of the skull and jaw are a feature of Gardner syndrome (familial adenomatous polyposis), so ask about bowel polyps and family history
- Radiology: a well-defined, very dense, sclerotic mass with a smooth outline, sometimes with a narrow pedicle; CT shows the extent and the bony density clearly. On an AP skull X-ray three types are seen: compact (radiopaque, homogeneous shadows), spongy (covered with cortex, with well-formed bone beams and bone marrow spaces visible) and mixed (a combination of spongy and compact)
- Treatment: observation if asymptomatic; surgical excision for symptoms, cosmetic reasons, or when another lesion must be excluded