Q-I My son has been diagnosed with osteochondroma of the lower sacroiliac joint. We have received no treatment or advice from the hospital and are uncertain of how we should approach the treatment of this condition. Can you help? Name of asker?......
A-An osteochondroma (or exostosis) is a tumour composed of bone and cartilage. It is the most common of the benign bone tumours and usually develops early in childhood, though it is often not discovered until adulthood. The tumour tends to arise on the ends of the long bones, most commonly the thigh, shin and upper arm. The tumour attaches to the skeleton by a stalk and is capped by cartilage.
Little is known of how these benign tumours develop, though they may grow as a result of radiation therapy or trauma. They most commonly appear during the period of rapid skeletal growth, and may be the result of displaced fragments of bone (in much the same way that irritating fragments in an oyster shell result in a pearl). Their growth usually mirrors the patient's growth so, often, when bone growth ceases, osteochondromas stop growing as well. Ninety percent of patients have only a single growth. Because of this, it is thought that osteochondromas may be developmental malformations rather than a true tumour.
Osteochondromas in themselves don't usually cause pain so, often, they are diagnosed only because the patient notices a small lump. However, larger lesions may cause pain by irritating the surrounding tissues and, occasionally, those that grow on a stalk from the bone may rupture.
Very occasionally, a benign osteochondroma can turn into a malignant growth called a chondrosarcoma, although this is more likely with multiple osteochondromas than with a single tumour. Magnetic resonance imaging can determine the difference between a benign tumour and a malignant one. The thicker the cap, the greater the likelihood the tumour could become cancerous (Eur Radiol, 2000; 10: 832-40). Likewise, when an adult has an osteochondroma that seems to enlarge or becomes painful, it should probably be removed as malignant transformation is possible.
Usually, however, no treatment is required. If an osteochondroma is large enough to cause symptoms because of pressure on the surrounding tissues, or if it is considered unsightly, the growth can be removed. After removal, recurrence is rare as long as the surgeon has removed the entire cartilage cap.
Evidence suggests that unless there are pressing reasons to operate, it is best to leave the removal of the tumour until the child has reached skeletal maturity. Otherwise, there is a greater risk of recurrence of even larger lesions which may cause bone deformities (J Bone Joint Surg Am, 2000; 82: 1269-78).