Porth's Essentials of Pathophysiology, 4e

Disorders of the Skeletal System: Trauma, Infections, Neoplasms, and Childhood Disorders 1095

C h a p t e r 4 3

Benign BoneTumors Benign bone tumors usually are limited to the confines of the bone, have well-demarcated edges, and are surrounded by a thin rim of sclerotic bone. The most common benign tumors are of either fibrous or cartilaginous tissue origin. Benign fibrous tumors of the bone are common in grow- ing bones. They are usually asymptomatic, resolve in 2 to 3 years, and do not require treatment. 8 Common carti- laginous tumors include chondromas and osteochondro- mas. Giant cell tumors, which contain mononuclear and osteoclast-type giant cells, are often classified as “interme- diate” in nature between malignant and benign. Chondromas are benign tumors of hyaline cartilage that usually occur in bones of endochondral origin. 18,19 They can arise within the medullary cavity, where they are known as endochondromas , or on the surface of bone, where they are called subperiosteal or juxtacor- tical chondromas . They are usually solitary lesions of and are most commonly found in short tubular bones of hands and feet. Most endochondromas are asymp- tomatic and detected incidentally. Occasionally they are painful and cause fractures. Treatment is usually sim- ple observation, with surgical intervention reserved for cases in which pain or danger of fracture is present. An osteochondroma, also known as an exostosis, is a benign cartilage-capped tumor that is attached to the underlying bone by a bony stalk. It is the most com- mon benign bone tumor, about 85% of which occur as solitary tumors. 19 The remaining tumors are seen as part of a multiple hereditary exostosis syndrome, which is inherited as an autosomal dominant disorder. Solitary exostoses are usually first diagnosed in late adolescence or early adulthood, but multiple exostoses become apparent in childhood. Exostoses develop only in bones of endochondral origin, arising from the metaphysis near the growth plate of tubular bones, especially about the knee. Clinically, osteochondromas present as slow- growing masses, which can be painful if they impinge on a nerve or if the stalk is fractured. In many cases they are discovered incidentally. In multiple hereditary exostosis, the underlying bone may be bowed and short- ened, reflecting an associated disturbance in epiphyseal growth. Osteochondromas usually stop growing at the time of growth plate closure. Malignant changes are rare, and excision of the tumor is done only when necessary. A giant cell tumor, or osteoclastoma, is an aggressive tumor that often behaves like a malignant tumor, metas- tasizing through the bloodstream and recurring locally after excision. 19,42,43 The tumor is a mixture of mononu- clear and multinucleated osteoclast-type giant cells. The mononuclear cells in the tumor express RANKL, and the giant osteoclast-like cells are believed to form via the RANK/RANKL signaling pathway (see Chapter 42). Giant cell tumors usually arise in people in their thir- ties or forties. 19 The majority of tumors arise around the knee (distal femur and proximal tibia), but virtually any bone can be involved. The tumor begins in the metaphy- seal region, grows into the epiphysis, and may extend into the joint surface. Pathologic fractures are com- mon because the tumor destroys the bone substance.

Clinically, pain may occur at the tumor site, with gradually increasing swelling. X-ray films show destruc- tion of the bone with expansion of the cortex. The bio- logic unpredictability of these tumors complicates their management. Conservative surgery such as curettage is associated with a 40% to 60% recurrence rate; up to 4% metastasize to the lungs. 19 Malignant BoneTumors In contrast to benign tumors, primary malignant tumors tend to be ill defined, lack sharp borders, and extend beyond the confines of the bone. Primary malignant bone tumors occur in all age groups and may arise in any part of the skeleton. However, certain types of tumors tend to target certain age groups and anatomic sites (Fig. 43-10). For example, most osteosarcomas occur in adolescents and are particularly common around the knee joint. Also, people with certain conditions such as Paget dis- ease are at increased risk for development of bone cancer.

Osteosarcoma

Chondrosarcoma

Ewing sarcoma

Giant cell tumor

FIGURE 43-10. Common sites of primary malignant bone tumors (chondrosarcoma, osteosarcoma, and Ewing sarcoma) and giant cell tumor, a locally aggressive benign tumor.