Essentials of Orthopedic Surgery, third edition / 04-Tumors of the Musculoskeletal System

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may be variable cellularity, but the chondrocytes tend to remain small and uniform. Nuclear atypia is minimal, and occasional binucleate forms are not inconsistent with the diagnosis of a benign lesion. As a rule, the chondrocytes are situated in individual lacunae. Correlating with the gross findings, foci of calcification, and endochondral ossification can be observed. Features such as marked nuclear atypia, mitotic activity, myxoid degeneration of matrix, and multiple cells in individual lacunae should raise a strong suspicion of chondrosarcoma.

Chondroblastoma, Osteoblastoma, and

Osteoid Osteoma

Chondroblastoma and osteoblastoma are characterized by immature but benign chondroid and osteoid production, respectively. Both may undergo malignant transformation in rare cases, and osteoblastoma can metastasize. Osteoid osteomas are small (less than 1 cm), painful, bone-forming tumors that are always benign. Chondroblastomas typically occur in the epiphysis of a skeletally immature child. Although osteoblastomas may be found in any bone, the spine and skull account for 50% of all reported cases. The differential diagnosis of chondroblastoma includes GCT, aneurysmal bone cyst, and clear cell chondrosarcoma. Osteoblastoma must be differentiated from osteosarcoma and osteoid osteoma. Clinical correlation of age, site, and histologic findings often points to the correct diagnosis.

Chondroblastomas and osteoblastomas are aggressive benign lesions with a high recurrence rate following simple curettage. Local control can be obtained by primary resection; however, routine resection cannot be recommended for tumors adjacent to a joint. Cryosurgery has avoided the need for resection and extensive reconstruction in select patients.

Osteoid Osteoma

Clinical Characteristics and Physical Examination

This lesion has classic symptoms and CT scan appearance in 80% of patients (Fig. 4-16). Osteoid osteomas are extremely painful (equivalent to a severe toothache) and well localized. Pain is often worse at night. The pain is relieved by salicylates; narcotics often are not helpful. The response to salicylates is dramatic, occurring in 20 to 30 minutes with a minimal dose of one or two tablets of regular-strength aspirin. This pain pattern may exist for 6 to 9 months before the appropriate diagnosis is considered. Occasionally, the pain precedes the appearance of radiographic abnormalities and therefore leads to multiple incorrect diagnoses, including neuroses. The most common anatomic sites are the femur and tibia, although any bone, including the skull, spine, and small bones of the hands

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FIGURE 4-16. Osteoid osteoma. CT scan demonstrating an intracortical (nidus) osteoid osteomas of the proximal humerus. Osteoid osteomas are small (less than 1 cm), characteristically painful, and usually found in young patients.

and feet, may be involved. When the lesion is located near a joint, symptoms may mimic those of monoarticular arthritis. Osteoid osteomas of the spine often present as a painful scoliosis mimicking a vertebral osteomyelitis, spinal cord tumor, or abdominal disease. There is an interfacing network of irregular partially calcified bony trabeculae that resembles that seen in osteoblastoma.

Radiographic Appearance and Evaluation

The tumor can be found in any portion of a bone. The position relative to the cortex, periosteum, and spongiosa determines the radiographic appearance. The most common site is intracortical. Plain radiographs may show the nidus (lesion), which is radiolucent but often obscured by a large amount of dense, white, reactive bone that is stimulated in response to the tumor. When the lesion is intramedullary, there is less sclerotic response. Detection and localization of the lesion are difficult. Bone scintigraphy is the most useful staging study and demonstrates markedly increased uptake of contrast medium.

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Treatment

Surgical removal of the nidus is required; the sclerotic, reactive bone need not be removed. Pain is dramatically resolved if the nidus has been excised. Incomplete removal routinely results in a clinical recurrence. Recently, nonsurgical removal by CT-guided radiofrequency ablation has been recommended.

Aneurysmal Bone Cysts

Aneurysmal bone cysts (ABC) are benign tumors of childhood, occurring typically before skeletal maturity. They never become malignant. ABC often involve the metaphyseal regions of the long bones or the vertebrae. Radiographically, ABC are eccentric, lytic, and expansile, characterized by cortical destruction and periosteal elevation (Fig. 4-17). They can grow rapidly and appear extremely aggressive, and distinguishing them from a primary malignancy may be difficult. Differential diagnosis includes GCT and telangiectatic osteosarcoma. ABC contain some osteoid; however, careful examination reveals this to be reactive and not neoplastic. Approximately one-third arise in conjunction with another bony neoplasm.

Unicameral (Simple) Bone Cysts

Unicameral bone cysts (UBC) are benign lesions that occur during growth. They involve the metaphysis and/or the diaphysis of a long bone. They are not believed to be true neoplasms.

The most common sites are the proximal humerus (67%) and proximal femur (15%). UBC are usually asymptomatic until a fracture occurs. Radiographically, UBC are radiolucent and slightly expansile, with welldefined margins (Fig. 4-18). UBC are rarely confused with other benign or malignant tumors. Plain radiograph is the primary imaging study utilized for diagnosis when these tumors arise in common locations. Other preoperative staging studies usually are not required. Bone scintigraphy is

FIGURE 4-17. Aneurysmal bone cyst (ABC). (A) Plain radiograph demonstrates an ABC and fibrous dysplasia of the proximal third of the femur. ABCs are expansile and lytic lesions arising in skeletally immature patients with cortical thinning, as seen both medially and laterally in this patient. Approximately one-third of all ABCs arise in conjunction with another bony neoplasm, as seen here. The hip is a common site of fibrous dysplasia. (B) CT scan of the same patient demonstrates marked cortical thinning and periosteal elevation. CT scans are very good in determining bony changes. (C) CT scan shows marked involvement of the distal portion of the right ilium and entire ischium and acetabulum. This ABC shows a classic eccentric, lytic, expansile lesion with periosteal elevation and cortical thinning. This patient was treated with curettage and bone grafting. ABCs often occur in the skeletal flat bones.

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A

B

C

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FIGURE 4-18. Unicameral bone cyst (UBC). AP radiograph demonstrates a UBC in the proximal humerus of a skeletally immature patient. This lesion has a welldefined border and a narrow transition area that is often associated with a reactive sclerosis. The lateral cortex is thin but appears intact; this is the most common site for UBCs to arise.

the most useful study when the diagnosis is in doubt. The bone scan typically shows a photon-deficient area corresponding to detail on the plain radiograph. A small area of increased uptake of contrast reflects a typical hairline crack that initiates pain and radiographic investigation.

Treatment

The traditional treatment has been curettage. Recently, aspiration, flushing, and injection with methylprednisolone acetate have successfully treated UBC.

UBCs are treated by aspiration, high-pressure Renografin injection, and intracavitary methylprednisolone. Pathologic fractures should be allowed to heal before injection is performed. If the diagnosis is in doubt, a Craig needle procedure or small incisional biopsy should be performed. There may be radiographic recurrence; this can be successfully treated with repeat injections. UBCs should not be left untreated in the hope that they

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will spontaneously regress. Less than 1% of UBC do so; the remainders often become large before the appropriate treatment is undertaken, making definitive treatment more difficult. Alternatively, UBC are treated by curettage and bone grafting.

Eosinophilic Granuloma (Histiocytosis X)

Langerhans’ cell histiocytosis is a more descriptive and recently accepted term to describe the disease commonly referred to as histiocytosis X. Eosinophilic granuloma (EG) is a solitary destructive lesion arising presumably from the reticuloendothelial system during the first decade of life. There is slight male predominance. Any bone may be involved, but the most common sites are the long bones and commonly the periacetabular region. The skull, mandible, ribs, and vertebrae are frequent sites. Multiple bony involvement is common; between 10% and 20% of patients develop multiple lesions. Plain radiographs characteristically show a lytic, punchedout lesion with some evidence of cortical destruction. Approximately 50% of patients have periosteal elevation. The differential diagnosis includes osteomyelitis, Ewing’s sarcoma, and lymphoma. The diaphysis and the metaphysis are equally affected. Primary epiphyseal involvement or extension is rare.

Good results have been achieved with the use of steroids to treat localized bony EG. The natural history of EG of bone is to spontaneously heal. Curettage or intralesional steroid is recommended for documented lesions, especially in a weight-bearing bone.

Tumors of the Joint

Specific Diagnoses

Pigmented Villonodular Synovitis (Aggressive Synovitis)

Pigmented villonodular synovitis (PVNS) is a rare primary disease of the synovium characterized by exuberant proliferation with the formation of villi and nodules. It presents with localized pain, joint swelling, a thickened synovium, and an effusion that on aspiration shows either a brownish or a serosanguineous discoloration. PVNS commonly occurs between the second and the fifth decades of life. The knee is most commonly involved (75%–90%), followed by the hip and ankle joints (Fig. 4-19). Treatment is often delayed because PVNS is not considered in the differential diagnosis.

Clinical suspicion is the key to early diagnosis. PVNS should be considered in the differential diagnosis of a monoarticular arthritis of the knee or hip joint. Simple aspiration is often suggestive, and synovial biopsy is definitive. Plain radiographs demonstrate juxtacortical erosions of both sides of an affected joint and may show marked joint or bone destruction if the

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FIGURE 4-19. Pigmented villonodular synovitis. Magnetic resonance imaging (MRI) demonstrates pigmented villonodular synovitis (PVNS) of the knee. PVNS is the most common neoplastic lesion of the synovium. Note the fullness and effusion within the joint.

disease has been present for a long time. Arthrography and arthroscopy are helpful in establishing the correct diagnosis. Arthrography shows diffuse nodular masses, whereas arthroscopy shows a brownish, discolored synovium with large, flattened nodules and villous proliferation. Rarely, PVNS may present as a primary bony or soft tissue tumor because of marked proliferation of the synovium with destruction of the adjacent joint or a soft tissue mass. The histologic findings in this situation may incorrectly suggest a MFH.

PVNS is treated by surgical excision. Localized lesions require simple excision, whereas extensive involvement requires a synovectomy. If the anterior or posterior compartments of the knee may be extensively involved, a staged approach is required. The anterior joint is treated through a standard midline incision and arthrotomy. The posterior knee is best approached by a popliteal incision with complete exposure of the posterior capsule. The author’s preference is to begin by performing an anterior synovectomy, which should enable the patient to regain knee motion, and then to perform a posterior synovectomy. Recurrent disease should be treated by surgical excision. If there is extensive bony destruction, arthrodesis or prosthetic

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replacement, combined with an extraarticular joint resection, is required. Low-dose radiation treatment may be beneficial in improving local control, particularly in high-risk patients.

Microscopic Characteristics

The typical lesion consists of heterogeneous population of cells. The villi are lined by several layers of plump synovial cells. Beneath the synovium are sheets of histiocytes, xanthoma cells, hemosiderin-laden macrophages, and multinucleated giant cells, all in variable proportions. Occasionally, slitlike spaces are present within the more cellular areas.

Ganglia

Ganglia are among the most common soft tissue lesions. The wrist is the most common location; other sites include the metatarsophalangeal joints and the ankle and knee joints. When the lesions are located in unusual sites, the diagnosis is often less obvious. Ganglia represent benign myxoid degeneration. It must be emphasized that all masses are not ganglia and should be critically evaluated. All too often, a sarcoma of the hand or ankle is assumed to be a ganglion. Excision is undertaken, and the correct diagnosis is made only after extensive soft tissue contamination has occurred. This unfortunate circumstance leads to many lost limbs. Treatment of ganglia is simple excision or aspiration.

Soft Tissue Sarcomas

Soft tissue sarcomas (STS) are malignant tumors arising from or within the soft tissues of the extremities or the shoulder and/or the pelvic girdle. These heterogeneous groups of tumors arise specifically from the supporting extraskeletal mesenchymal tissues of the body, that is, muscle, fascia, connective tissues, fibrous tissues, and fat. They are rare lesions, constituting less than 1% of all cancers. There are wide morphologic differences among these tumors, probably resulting from the different cells of origin; however, all STS, similar to bone sarcomas, share certain biologic and behavioral characteristics.

The clinical, radiographic, and surgical management of most STS is identical, regardless of histogenesis. The surgical grading system developed by the Musculoskeletal Tumor Society applies to both bone sarcomas and soft tissue sarcomas.

Clinical Findings and Physical Examination

Soft tissue sarcomas are a disease of adulthood, occurring in persons between 30 and 60 years of age. The sole exception is rhabdomyosarcoma,

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which occurs in young children. Approximately one-half of STS are found in the extremities; the remainders arise in the head/neck and trunk. The lower extremity is the most common anatomic site; 40% of all STS occur in this location. The anterior thigh (quadriceps) is the most common compartment, followed by the adductors and hamstrings.

Most STS present as a painless mass. Systemic signs such as fever, weight loss, or anemia are rare. There are no useful laboratory screening examinations. Clinical suspicion is therefore crucial to diagnosis. Any adult presenting with an extremity mass must be presumed to have a sarcoma until proved otherwise and should be further evaluated. History of coincident trauma often can be especially misleading. Unfortunately, a presumptive diagnosis of lipoma, ganglion, hematoma, or muscle tear is often made, thereby delaying definitive evaluation and treatment. Local examination reveals a well-localized, nontender mass that may be movable. The lesion may be firm or, rarely, cystic (Fig. 4-20).

Biologic Behavior and Natural History

The pattern of growth, metastasis, and recurrence of STS is similar to that of spindle cell sarcomas arising in bone. The major distinctions are

FIGURE 4-20. Soft tissue sarcoma. Clinical photograph demonstrates a large soft tissue sarcoma of the posterior leg (soleus muscle). This patient underwent an open biopsy (not recommended) before referral for definitive diagnosis. Resection of this tumor will require complete excision of the biopsy tract and scar in addition to en bloc removal of the tumor. Malignant fibrous histiocytoma (MFH) is the most common type of soft tissue sarcoma.

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the tendency of STS to remain intracompartmental and a significant incidence of lymphatic involvement in a few of the less common entities, such as the epithelioid, synovial, and alveolar soft-part sarcomas. The prognosis of an STS is most closely related to its histologic grade and the presence or absence of metastases. Historically, high-grade STS have an overall survival rate of 40% to 60%. In half of all cases, wide local excision is followed by local recurrence within 12 to 24 months, followed by pulmonary metastases resulting from hematogenous dissemination to the lungs. Visceral and lymphatic involvement are rare. Pulmonary and local recurrence are the most common sites of relapse. Aggressive surgical resection of local recurrences should be considered. If distant metastases have not occurred, a 5-year salvage rate of 50% to 80% can be achieved.

Decision-Making Process

In order to accurately assess the diagnosis, stage, and grade of a suspected soft tissue tumor, rigid protocol should be followed to facilitate the deci- sion-making process as to what staging studies are required and when a biopsy should be performed. Figure 4-21 entitled Evaluation of Patient with a Soft-Tissue Mass succinctly describes the steps any clinician should follow for patients presenting with any type of soft tissue tumor.

Pathology and Staging

STS are classified on the basis of histologic cell of origin. Individual grading is often difficult; in general, however, the extent of pleomorphism, atypia, mitosis, and necrosis correlates with the degree of malignancy. Notable exceptions are synovial sarcomas, which tend to behave like high-grade lesions even in the absence of these findings. The exact histogenesis of some soft tissue sarcomas often cannot be accurately defined, although grading can still be adequately performed. The surgical stage is determined by grade, location, and the presence or absence of pulmonary or lymphatic metastases, similar to other malignancies. Staging studies must be done before treatment.

Radiographic Evaluation

Magnetic Resonance Imaging

Because of better visual contrast and the ability to image in coronal and sagittal planes, MRI has surpassed CT as the most useful study for evaluating STS of the extremities. CT remains valuable for retroperitoneal tumors and for assessment of lung metastases. Either imaging method can delin-