Retrospective analysis of missed or improperly diagnosed malignant lesions often uncovers significant clues in both the clinical history and physical examination.

A complete physical examination must be undertaken with special attention paid to nodules, adenopathy, masses, skin changes, and local tenderness.

Although most malignant musculoskeletal tumors metastasize to the lung, some soft tissue sarcomas go to the draining lymph nodes. A careful physical examination of both regional and systemic lymph nodes is required.

Malignant neoplasms of the soft tissues are ~ 3-4 times more common than malignant tumors of the bone, but both are rare with soft tissue sarcoma comprising < 2% of all malignancies.

This is used for soft tissue sarcoma.

The 3 most important prognostic factors are as follows.

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  Grade (most important in staging)

  
  
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  Size (> 5 cm) portends worse prognosis

  
  
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  Relationship of tumor to fascia (deep to fascia portends worse prognosis)

In soft tissue sarcomas, almost all metastases occur to the lungs. A chest CT is obtained to stage the tumor. Bone scan is usually not necessary.

The 5-year survival rate of high-grade soft tissue sarcoma is 50%; of all stages combined, it is 70%.

The basic work-up of an adult patient with possible metastatic disease is a bone scan; CT scans of the chest, abdomen, and pelvis; and a biopsy of the most accessible lesion. Lesions in the foot are unlikely to be metastatic but if so are usually lung or renal carcinoma.

Synovial chondromatosis

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  Synovial chondromatosis is a benign condition that involves the synovial lining of joints, bursae, or tendon sheaths and is characterized by the development of multiple osteochondral loose bodies that are the result of metaplasia of the synovium. When it arises in the soft tissues from tendon sheaths, it is called soft tissue chondroma.

  
  
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  It is rare in the ankle and can present as tarsal tunnel syndrome. Symptoms include swelling, pain, locking, stiffness, limited joint motion, crepitus, or giving way.

  
  
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  On physical examination, an effusion may be present. There may be tenderness of the joint or pain on range of motion. The range of motion may be limited. A palpable tender mass may be present.

  
  
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  Until the loose bodies are ossified or calcified, they may be radiographically invisible. Damage to the joint from multiple loose bodies may lead to early degenerative arthritis.

  
  
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  The histologic appearance of this process shows well-defined cartilage nests embedded in a layer of synovium.

  
  
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  Treatment includes arthroscopic or open debridement of loose bodies ± a synovectomy.

  
  
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  Synovial chondromatosis is reported to be a benign, self-limited disease process, although chondrosarcoma of synovium has been described.

Giant cell tumor

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  It is a benign, yet locally aggressive tumor that typically occurs in the 2nd and 3rd decades of life. Giant cell tumor of the foot is rare.

  
  
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  It is usually a metaphyseal-epiphyseal, juxtaarticular lesion found most commonly about the knee (50%), shoulder, and distal radius, although it has been reported in virtually all the foot bones.

  
  
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  It originates in the metaphysis and extends into the epiphysis following physeal closure.

  
  
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  Radiographs reveal a lytic, eccentric, expansile appearance. It typically thins out the cortex, has no internal matrix, and may have a sclerotic rim centrally.

  
  
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  It can metastasize, although < 2% metastasize to the lungs.

  
  
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  Treatment typically involves biopsy to confirm the diagnosis with intralesional curettage and mechanical burring possibly with adjuvants, such as phenol, cryosurgery, or hydrogen peroxide and subsequent packing of the resultant defect with bone graft or bone cement.

  
  
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  When a metatarsal is involved, resection may be more expeditious than reconstruction, depending on the degree of destruction and which metatarsal is involved.

Aneurysmal bone cyst

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  An aneurysmal bone cyst (ABC) is a solitary, expansile osteolytic lesion with a thin wall, containing blood-filled cystic cavities. Approximately 30% are secondary to preexisting bone tumors.

  
  
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  ABCs occur in patients between 10-30 years of age; peak incidence is 16 years of age; 75% are < 20 years of age.

  
  
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  Radiographs often have a blown out appearance with thin septations. CT and MR characteristically demonstrate multiple fluid-fluid levels within cystic spaces. ABC appears on both T1 and T2 MR images with a low-signal rim encircling the cystic lesion.

  
  
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  Histology reveals cystic spaces filled with blood. Typically, the fibrous septa have immature woven bone trabeculae.

  
  
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  ABCs are active lesions that destroy bone and therefore are almost always treated. Treatment consists of curettage and bone graft or, rarely, resection. Local recurrence with curettage and bone grafting can be as high as 25%.

  
  
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  If a recurrence is detected, a thorough examination of the original radiographs and pathology specimens should be performed to ensure that the primary lesion, if any, is discovered, because this may alter the treatment plan. One unfortunate scenario is to biopsy an ABC, which then recurs and presumably evolves into a telangiectatic osteosarcoma. Once the precise diagnosis is known, local recurrences may be retreated by appropriate methods.

Unicameral bone cyst (simple bone cyst)

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  A unicameral bone cyst (UBC) is a benign radiolucent cavity found within a bone that is filled with straw-colored fluid. It is unifocal and affects patients who are skeletally immature, most frequently in children between 5-15 years of age. The male:female ratio is 2:1.

  
  
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  The rarity of the lesion in adults supports a hypothesis of spontaneous resolution. They enlarge during skeletal growth and become inactive after skeletal maturity.

  
  
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  Proximal humerus (50%) and proximal femur (40%) account for 90% of UBCs. Less common locations include the pelvis, talus, and calcaneus.

  
  
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  Historically, location played a prognostic role. If the cyst is immediately adjacent to the physis, it is active. If it is distant from the physis, it is latent. Recurrence is high for active cysts (50%) and low for latent cysts (10%).

  
  
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  Radiographs typically reveal a central lytic metaphyseal lesion with a sclerotic rim and little to no bone expansion. MR/CT are not routinely necessary.

  
  
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  Most UBCs are asymptomatic and incidentally discovered. Lesions usually remain asymptomatic unless complicated by fracture. In contrast to ABCs, UBCs are often not treated, such as in the absence of symptoms or mechanical compromise of the involved bone.

  
  
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  Treatment should be considered for lesions that have resulted in fracture or marked weakening of bone. Spontaneous healing of a UBC may occur occasionally following fracture. Factors, such as age and lesion location, may strongly influence surgical decisions.

Enchondroma

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  Enchondromas are benign cartilaginous tumors of bone that present in patients of all ages. The majority are asymptomatic unless associated with a pathologic fracture. Characteristically, they are found in the intramedullary canal of the central metaphysis. Enchondromas result from failure of normal endochondral ossification below the physis.

  
  
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  Common sites of involvement include the small tubular bones of the hands or feet (40-65%). With respect to the feet, it most frequently involves the diaphysis of the proximal phalanx followed by the middle phalanx and the metatarsals; it commonly spares the distal phalanx.

  
  
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  Histologically, it is composed of hyaline cartilage. Radiographs reveal “speckled” or “popcorn” calcifications in this central radiolucent lesion with well-defined margins, endosteal erosion, and no aggressive features.

  
  
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  The risk of malignant transformation is low: < 2% of asymptomatic solitary enchondromas transform to chondrosarcoma. In contrast, enchondromatosis, i.e., Ollier disease, has a 10-30% risk of malignant transformation. Multiple enchondromas plus soft tissue hemangiomas, known as Maffucci disease, are associated with an increased risk of astrocytoma and gastrointestinal cancer as well as a higher risk of malignant transformation to chondrosarcoma than in Ollier disease. It can be difficult to distinguish an enchondroma from a low-grade chondrosarcoma.

  
  
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  Asymptomatic solitary enchondromas may be followed nonoperatively with serial radiographs. If an enchondroma becomes symptomatic or begins to enlarge, it may require biopsy to rule out malignancy; curettage and bone grafting is usually adequate for borderline lesions. Pathologic fractures are commonly allowed to heal with closed treatment followed by curettage and bone grafting to prevent refracture.

Osteochondroma

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  Osteochondroma is the most common benign bone tumor. It is a developmental dysplasia of the peripheral growth plate, which forms a cartilage-capped projection of bone found near the metaphysis of long bones, pointing away from the joint. It grows via endochondral ossification of the proliferating cartilage cells and often presents as a firm, nontender, immobile mass arising near the end of a long bone.

  
  
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  It frequently occurs in the distal tibia and metatarsals. Specific to the foot and ankle, they may cause angular deformities &/or limit the range of motion of the ankle via syndesmotic impingement.

  
  
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  On radiographic analysis, it is classically continuous with the medullary canal of the underlying metaphyseal bone, growing away from the epiphysis. A cartilaginous cap of 2.0-2.5 cm or greater and growth after skeletal maturation may indicate malignant transformation.

  
  
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  They may be solitary or multiple, as seen in hereditary multiple exostoses (HMEs), an autosomal dominant condition associated with mutations in EXT1 &/or EXT2 genes.

  
  
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  Malignant degeneration is the most significant of potential complications. Less than 1% of solitary osteochondromas undergo malignant transformation to a low-grade, secondary chondrosarcoma. In patients with HME, the incidence is higher.

  
  
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  No intervention is warranted if asymptomatic. Marginal excision of the exostosis, cartilaginous cap, and overlying perichondrium can be done if the lesion is symptomatic. If the osteochondroma continues to grow after skeletal maturity, chondrosarcoma must be ruled out with an MR to measure the thickness of the cartilage cap and to look for an associated soft tissue mass.

Osteoid osteoma

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  Osteoid osteoma is a benign vascular osseous tumor, which occurs primarily in adolescents. The typical presentation is dull pain, often with increased severity at night, classically relieved by prostaglandin E2 inhibitors, such as aspirin or nonsteroidal antiinflammatory drugs (NSAIDs).

  
  
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  Most commonly, it is found in the proximal femur (femoral neck = 30% incidence). Other locations include the posterior spine (often causing painful scoliosis) and the talus, navicular, or calcaneus.

  
  
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  The pathognomonic radiographic finding is a nidus typically measuring < 1.5 cm in diameter. The nidus is best localized with CT scans with cuts set to 1.0-2.0 mm.

  
  
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  They spontaneously resolve with time, and treatment options include medical management with NSAIDs, en bloc excision or curettage, or percutaneous radiofrequency coagulation under CT guidance.

Osteoblastoma

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  Osteoblastoma is a benign osseous tumor typically occurring in the 2nd and 3rd decades.

  
  
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  Osteoblastoma presents as a dull, deep pain; however, unlike osteoid osteoma, it is not nocturnal, does not improve with NSAIDs, and is progressive in nature. The size of the nidus is > 1.5 cm (vs. osteoid osteoma, which is < 1.5 cm).

  
  
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  The talar neck is the 3rd most common location after the posterior spine and long bones. They can also occur in the metatarsals.

  
  
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  Treatment typically involves excision and curettage; if it is aggressive in nature, wide excision is favored. Recurrence rate following curettage and bone graft is 10-20%.

Chondroblastoma

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  Chondroblastoma is considered a benign, aggressive tumor, typically occurring in the 2nd decade.

  
  
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  In the foot and ankle, the talus and calcaneus are the most frequent locations.

  
  
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  Radiographically, it is lytic; histologically, it has chicken-wire calcification and stains with S100 antibody.

  
  
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  About 2% metastasize to the lungs. Treatment is curettage and bone graft.

Subungual Exostosis

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  Radiographically, subungual exostosis resembles an osteochondroma. It typically develops on the distal phalanx, most commonly on the medial aspect of the great toe in young children. It is often associated with a history of trauma.

  
  
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  Surgical excision is indicated if elevation of the nail leads to deformity &/or pain. The nail bed can usually be preserved.

Acral metastases

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  The incidence of skeletal metastasis to primary bone tumor is 25:1. Frequently, the metastatic bone lesion is found before the primary tumor, and it is occasionally mistaken for a primary bone lesion.

  
  
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  In general, bones distal to the knee and elbow are very rare sites for metastases. The majority of acral metastases (those distal to the knee or elbow) are from lung and renal carcinoma. Lung is more common than renal.

  
  
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  Many of the metastatic bone lesions are multiple, compared with primary bone tumors, which tend to be single lesions. Treatment should always involve consultation with an oncologist.

Osteosarcoma

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  Osteosarcoma is the 2nd most common primary bone malignancy after myeloma. 75% occur in patients between 10-25 years old. It is associated with mutations of the TP53 and retinoblastoma tumor suppressor genes.

  
  
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  Osteosarcoma is usually a metaphyseal tumor. In the foot and ankle, it is most commonly found in the distal tibia with reports of lesions in the metatarsals and tarsals. In a retrospective review of 52 patients with osteosarcoma of the foot by Choong et al (1999), the most common site was the calcaneus.

  
  
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  Prior to current treatment regimens, long-term survival was 20%. With present treatment protocols, the mainstay being neoadjuvant chemotherapy and surgical resection, long-term survival is 60-70%.

  
  
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  Specific to the foot and ankle, wide surgical resection in the face of close proximity of neurovascular structures can be difficult. Small tumors may be possible to resect with preservation of the foot. Larger tumors may require below-knee amputation.

Chondrosarcoma

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  Chondrosarcoma is a malignant cartilage tumor typically found in patients between 40-70 years of age.

  
  
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  In the foot and ankle, this tumor is most often a malignant transformation in patients with Ollier disease or multiple hereditary exostoses.

  
  
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  Treatment involves wide excision, as radiotherapy and chemotherapy are ineffective.

Ewing sarcoma and peripheral primitive neuroectodermal tumors

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  Ewing sarcoma is a rare, malignant neoplasm in the small blue round cell family of tumors that is most common in children and adolescents. The peak incidence is between 10-20 years of age. While any bone of the axial or appendicular skeleton can be affected, it has rarely been reported in the bones of hands and feet.

  
  
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  The characteristic radiologic findings includes an onion skin &/or moth-eaten appearance of the lesion. Histologically, it consists of sheets of round blue cells separated by bands of stroma. Metastases are common to lungs and other bones.

  
  
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  Treatment consists of surgery and chemotherapy. Survival is highly dependent on the initial presentation of the disease. About 80% of patients present with localized disease, whereas 20% present with metastatic disease, most often to the lungs, bone, and bone marrow. The overall survival rate in patients with Ewing sarcoma is 60%; however, for patients with localized disease, it approaches 70%. If metastatic, the long-term survival rate is < 25%.