B. Stephens Richards
SOLITARY OSTEOCHONDROMA
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.1 More than 50% of solitary osteochondromas occur in the metaphyseal area of the knee (distal femur and proximal tibia) and shoulder (proximal humerus) (Fig. 219-1).
The tumor often resembles a cauliflower. The surface usually is lobular, with multiple bluish-gray cartilaginous caps covering the irregular bony mass. The cartilaginous cap is usually 1 to 3 mm thick, but in the younger patient it may be noticeably thicker.
In the majority of patients, the osteochondroma becomes evident 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.
TREATMENT
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. 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 that have been preformed in cartilage. The median age at the time of diagnosis is approximately 3 years. Hereditary multiple exostoses has a penetrance of 50% by age 3 years. By 12 years of age, nearly all affected individuals have evidence of exostoses, as penetrance of the disorder has been found to reach 96% to 100%.2,3
Numerous genetic studies have found anomalies on chromosomes 8, 11, and 19, making this a genetically heterogenous disorder.4-6 Specifically, the three loci include 8q24.1 (EXT1), 11p11–12 (EXT2), and 19p (EXT3). These genes are deleted in exostoses-derived tumors, supporting the hypothesis that they encode tumor suppressors.
The gross pathologic and microscopic features of hereditary multiple exostoses are similar to those described for solitary osteochondromas. Numerous sites can be involved. On presentation, 5 or 6 exostoses typically may be found, involving both the upper and lower extremities.
FIGURE 219-1. A: Solitary osteochondroma involving the distal left femur. B: Clinical photograph in the operating room showing the resected specimen.
TREATMENT
The only treatment for hereditary multiple exostoses is surgery. However, the mere presence of an osteochondroma is not an indication for surgery. Reasonable indications include (1) pain from external trauma or irritation of surrounding soft tissues; (2) growth disturbance leading to angular deformity or limb length discrepancy; (3) joint motion compromised by juxta-articular lesions; (4) soft tissue (tendon, nerve, or vessel) impingement or tethering; (5) spinal cord compression; (6) false aneurysm produced by an osteochondroma; (7) painful bursa formation; (8) obvious cosmetic deformity; and (9) a rapid increase in the size of a lesion. Life expectancy is average unless malignant degeneration of an osteochondroma has occurred and metastases have developed.
Transformation of a lesion in hereditary multiple exostoses to chondrosarcoma during childhood is exceedingly rare.7 In general, transformation in adulthood remains uncommon, with current reports indicating the risk to be 0.9% to 5%.2,6,8,9 The most frequent sign of sarcomatous change is a painful, enlarging mass, usually one of long duration.10
NONOSSIFYING FIBROMA AND FIBROUS CORTICAL DEFECT
Fibrous defects in bone are common lesions in childhood. They are found in the metaphyseal regions of the long bones, particularly the femur and the tibia. These lesions contain fibrous tissue, thus leading to the terms fibrous cortical defect and nonossifying fibroma. These fibrous lesions appear to be developmental defects due to a localized disturbance of bone growth and may not be representative of true neoplasms. Most are asymptomatic, picked up as an incidental finding during radiographs taken for other reasons, and eventually resolve during remodeling at the metaphyseal (growing) end of the bone.
On radiographs, these lesions are sharply delineated, radiolucent, multiloculated, eccentric, and outlined by a sclerotic border (Fig. 219-2).11 These findings are usually so characteristic that further radiologic studies are unnecessary.
TREATMENT
Fibrous cortical defects do not require treatment because they usually regress over time. Larger, nonossifying fibromas can be monitored without surgical intervention, and if fractures do occur, they can be successfully managed nonoperatively.12 Occasionally, discomfort or repeated fractures may require intralesional excision by curettage down to normal bone, with the defect filled with bone graft.
SIMPLE BONE CYSTS (SOLITARY BONE CYST, UNICAMERAL BONE CYST)
Simple bone cysts represent approximately 3% of all biopsied primary bone tumors and nearly always occur during the first 2 decades of life, most often between 4 and 10 years of age.13 The majority of cysts occur in the metaphyseal region of the proximal humerus or femur, with approximately 50% of cases involving the humerus and 18% to 27% affecting the femur. Its cause remains uncertain.
Cysts can be asymptomatic and may be discovered incidentally when radiographs are obtained for other reasons. More often, though, the cysts are diagnosed because of pain. The pain may be mild and reflective of a microscopic pathologic fracture. More abrupt discomfort occurs when a pathologic fracture occurs following relatively minor trauma, such as a fall. These fractures occur in up to 90% of patients and heal readily, though the cysts do not.
FIGURE 219-2. A large nonossifying fibroma is located in the metaphyseal region of the distal right tibia.
There are several characteristic radiographic features of simple bone cysts. The cyst is metaphyseal and usually extends to, but not across, the growth plate (physis). Typically, the cyst is symmetrically expansile and radio-lucent, with a thin cortical rim surrounding it. Magnetic resonance imaging (MRI) may detect fluid levels, soft-tissue changes, and septations not seen on plain film.
TREATMENT
A common misconception in the treatment of simple bone cysts in children is that once the pathologic fracture heals, the cyst also has an excellent chance of spontaneously healing. However, most investigators examining this phenomenon have found that the likelihood of spontaneous healing of the cyst following pathologic fracture is very low, probably less than 5%.14 In mature individuals, if the cyst has a sufficiently thick cortex and is located in the upper extremity, periodic observation may be all that is needed.
The treatment approach is more aggressive for all simple bone cysts in younger children. Plans should be made for definitive treatment of the cyst in order to prevent future fractures and possible associated complications (e.g., shortening due to growth arrest and deformity).15 The diagnosis is usually confirmed at surgery, when straw-colored fluid is aspirated through a large-bore needle introduced into the cystic cavity. Treatment modalities include injection of corticosteroids into the cyst, injection of autologous bone marrow, multiple drilling and drainage of the cavity, and curettage of the membranous wall followed by bone grafting. A relatively high recurrence rate has been historically associated with treatment of simple bone cysts.16 Older forms of treatment, such as subtotal resection with or without bone grafting and total resection have been associated with increased cyst recurrence and are rarely, if ever, used today.
ANEURYSMAL BONE CYST
An aneurysmal bone cyst is a solitary, expansile, radiolucent lesion generally located in the metaphyseal region of the long bones. Seen much less often than simple bone cysts, they represent 1% of all biopsied primary bone tumors.17 Nearly 70% of affected patients are between 5 and 20 years of age with approximately half occurring in the second decade of life.18
The most common sites are the femur, tibia, spine, humerus, pelvis, and fibula, with approximately half of reported cases occurring in the long bones of the extremities.19 Although they usually involve the metaphyseal region, aneurysmal cysts may on occasion cross the growth plate into the epiphysis or may extend into the diaphysis.
The clinical presentation includes localized pain of several weeks’ or months’ duration, tenderness, and, if the aneurysmal bone cyst occurs in an extremity, swelling.
The classic radiographic feature of aneurysmal bone cysts is a ballooned-out lesion outlined by a thin shell of subperiosteal new bone formation. In about 80% of cases, the cyst involves the metaphyseal region of the long bones and, unlike simple bone cysts, is eccentric in its location.
TREATMENT
Although spontaneous healing of aneurysmal bone cysts has been reported,30 it is uncommon. Thus, expectant management should be considered only when the diagnosis has been made with confidence and the lesion is in a location and at a stage that do not entail any risk of fracture or further destruction. More often, when the diagnosis of aneurysmal bone cyst is made, active treatment is recommended.
Curettage followed by bone grafting of aneurysmal cysts has been the standard treatment for many years.31 Unfortunately, this tumor has a high incidence of local recurrence (14% to 59%) after curettage.26,32Adjunctive therapy, such as cementation, cryotherapy, or embolization, should be considered along with curettage.33
OSTEOID OSTEOMA
Osteoid osteomas are solitary, benign, painful lesions of the bone, of unknown etiology. They have a nidus, 1.5 to 2.0 cm in size, which is surrounded by an area of reactive, dense bone. Osteoid osteomas are relatively common, benign bone lesions, exceeded in incidence only by osteochondromas and nonossifying fibromas.41 Osteoid osteomas account for approximately 10% to 11% of benign bone tumors and 2% to 3% of all primary biopsied bone neoplasms. They are characteristically seen in children and adolescents.
Patients with osteoid osteoma typically present with a history of dull, aching pain in the region overlying the affected long bone. The pain may have been present for several months before presentation, tends to be worse at night, and is relieved significantly by nonsteroidal anti-inflammatory drugs (NSAIDs). The most commonly involved sites are the femur and tibia.
On radiographs, most of the tumors are intra-cortical, with the nidus appearing as a radiolucent lesion. This nidus rarely exceeds 1 cm in diameter but may be as large as 2 cm. The dense surrounding reactive sclerotic bone may extend for several centimeters away from the nidus. Cross-sectional imaging with CT will best demonstrate the well-circumscribed area representing the nidus.
Over the long term, these lesions are described as self-limiting and may mature spontaneously. The nidus may gradually calcify, then ossify, and finally blend into the sclerotic surrounding bone. However, very few patients are willing to continue with conservative management long term because of the intensity of the pain and the favorable outcomes that are achieved with surgery.
TREATMENT
Nonsteroidal anti-inflammatory drugs (NSAIDs) are effective in relieving symptoms of pain associated with osteoid osteoma. If the symptoms are moderate and controlled by this treatment program, observation alone is sufficient.41Most families recognize persistent pain and elect to undergo surgical excision. More recently, less-invasive maneuvers utilizing pinpoint CT-guided localization, followed by radiofrequency ablation, have become popular. Relief from the pain is usually immediate, dramatic, and permanent unless the nidus has been incompletely excised. See for discussion of fibrous dysplasia and histiocytosis x.
MALIGNANT TUMORS
Osteosarcoma is discussed in Chapter 453, Ewing sarcoma in Chapter 454, and histiocytic disorders in Chapter 463.