Osteochondroma, a cartilage-capped bony projection protruding from the surface of a bone, is the most common benign bone tumor. It reportedly accounts for 36% to 41% of all bone tumors. More than 50% of solitary osteochondromas occur in the metaphyseal area of the knee (distal femur and proximal tibia) and shoulder (proximal humerus).
Its cause is related to a localized herniation of a portion of the growth plate, which results in the formation of a cartilage-capped eccentric small bone. Unlike the more extensive hereditary (autosomal-dominant) multiple exostoses, solitary osteochondromas do not appear to be genetically transmitted.
Osteochondromas may be sessile (broad based) or pedunculated (narrow based). The surface usually is lobular, with multiple bluish-gray cartilaginous caps covering the irregular bony mass. The cartilaginous cap usually is 1 to 3 mm thick, but in the younger patient, it may be noticeably thicker. The thickness of the cartilaginous cap may be much greater if the tumor has undergone sarcomatous change.
In the majority of patients, the osteochondroma becomes evident when the patient is between the ages of 10 and 20 years, with a slight male preponderance. An osteochondroma may be discovered as an incidental radiographic finding, or it may be detected by the patient who feels a protruding bump. Other factors that often draw attention to the osteochondroma include localized pain, growth disturbance, limited joint motion, or abnormal cosmetic appearance.
On the radiograph, the cortex and cancellous bone of the osteochondroma blend with the cortex and cancellous bone of the normal bone. This is the main radiographic finding, and any deviation from this feature should raise suspicion of a more serious lesion. Steady growth of the cartilaginous cap is acceptable during childhood and early adolescence, but growth should cease when skeletal maturity is reached. If the cartilaginous cap continues to grow after skeletal maturity, malignant transformation should be considered and the appropriate follow-up studies undertaken.
Because a solitary osteochondroma is a benign tumor, it does not need to be surgically excised if it is asymptomatic. Excision usually is reserved for those lesions that cause pain or symptomatic impingement on neurovascular structures or that interfere with joint function. Pain usually becomes an issue when an osteochondroma is repeatedly bumped on its prominence. Sometimes the osteochondroma is considered cosmetically unacceptable, and the adolescent will ask to have it removed, preferring a scar to a bump. Malignant degeneration of a peripheral solitary osteochondroma can lead to chondrosarcoma in adulthood. However, malignant degeneration of solitary osteochondromas is a rare occurrence, found in fewer than 0.25% of lesions. The prognosis following excision of a chondrosarcoma is excellent.
HEREDITARY MULTIPLE EXOSTOSES
Hereditary multiple exostoses, or multiple osteochondromatosis, is considered an autosomal-dominant condition affecting numerous areas of the skeleton. Its overall prevalence approaches 1 in 50,000 persons. The median age ...