Soft Tissue Chondroma Carrie Y. Inwards Mayo Clinic Rochester, MN

History A 35-year-old male presented with a mass involving his "distal ring finger" that had been there since he was a teenager. Slide 1 Click to view with ImageScope Click to view with a Web-Based Viewer Figure 1 - Low power view of a cellular hyaline cartilaginous neoplasm with a nodular growth pattern. The nodules are closely associated with spicules of bone. Figure 2 - The tumor nodules tend to pull away from the bone. Loose fibrous connective tissue also surrounds some of the bone. Figure 3 - Low power view of a cellular hyaline cartilaginous neoplasm with a nodular growth pattern. The nodules are closely associated with spicules of bone. Figure 4 - The tumor nodules tend to pull away from the bone. Loose fibrous connective tissue also surrounds some of the bone. Figure 5 - Calcification diffusely involving some of the cartilage nodules. Figure 6 - Some of the chondrocytes contain abundant eosinophilic cytoplasm. Figure 7 - Multinucleated giant cell at the periphery of one of the nodules. Figure 8 - The chondrocytes show mild to moderate cytologic atypia. Figure 9 - Focal myxoid change in the matrix Radiographic Findings Radiographs showed a nodular mass in the soft tissues adjacent to the base of the second proximal phalanx with matrix mineralization. The mass was near the bone but the epicenter of the mass was in the soft tissues with a concave deformity of the adjacent cortex, typical of a chronic extrinsic-type of erosion secondary to an adjacent soft tissue mass. The imaging findings are consistent with a soft tissue chondroma. A tiny metallic foreign body in the adjacent soft tissues was likely an incidental finding. Pathologic Findings The mass was submitted as multiple pieces of rubbery, gray-brown tissue aggregating 2.3 x 2.0 x 0.3 cm. Histologically, the tumor was composed of hyaline cartilage with a nodular growth pattern. It was hypercellular and contained scattered areas of myxoid change within the stroma. The chodrocytes showed mild to moderate cytologic atypia. Throughout the lesion nodules of tumor were closely associated with thick, irregular trabeculae of bone. Dark blue granular calcification filled some of the cartilage nodules. Diagnosis Soft tissue chondroma Discussion Clinical Aspects Soft tissue chondroma is a rare benign cartilage lesion that has also been called extraskeletal chondroma or chondroma of soft parts. It occurs most commonly in the soft tissues of the hands and feet. The majority are located in the hands and wrists, especially in the fingers. The tumor is typically associated with a tendon, tendon sheath or joint capsule. They can be seen in patients of any age, but most are diagnosed in the fourth to sixth decades of life. Patients typically present with a slowly growing and painless mass. They are solitary lesions and relatively small, rarely exceeding 3 cm in diameter. Radiographic Findings There is some overlap between the histologic features of chondrosarcoma and soft tissue chondroma of the distal extremities. Therefore, one of the most helpful pieces of information the radiologist can give a pathologist who is dealing with this differential is whether the lesion is arising primary in soft tissue or bone. Radiographically, soft tissue chondroma is a well-demarcated extraskeletal tumor. Occasionally it erodes the underlying bone giving rise to histologic and radiographic findings that may be mistaken as features of malignancy. Radiographic evidence of calcification described as punctate, ring-like, dystrophic, dense, or curvilinear has been reported in 30% – 70% of cases. MR signal intensity can vary depending on the degree of calcification. Microscopic Findings Most soft tissue chondromas contain variable amounts of mature hyaline cartilage with a lobular growth pattern. They display increased cellularity and cytologic atypia when compared to benign intraosseous cartilage tumors. The tumor cells oftentimes display a clustering pattern similar to synovial chondromatosis. In addition, a variety of microscopic changes commonly occur in soft tissue chondroma that can lead to confusion and misdiagnosis. These include myxoid degeneration, ossification, ischemic necrosis, cystic change, a granuloma-like proliferation of epithelioid cells and multinucleated giant cells around the periphery of cartilaginous nodules, and focal or diffuse calcification. The calcification can be heavy and chunky or granular and lace-like. Chondroblastoma-like chondroma of soft tissue is the term that has been used for soft tissue chondromas that contain hypercellular areas of cells resembling the mononuclear cells of chondroblastoma. Genetics Abnormalities of chromosomal region 12q14-15 and extra copies of chromosome 5 have been prominent in the few cases that have been characterized cytogenetically. HMGA2 expression has also been documented in a few cases of soft tissue chondroma. Differential Diagnosis Chondrosarcoma: Hypercellularity, cytologic atypia, and myxoid change are all histologic features of both soft tissue chondroma and chondrosarcoma of bone. In addition, biopsies of soft tissue chondroma containing areas of cortical erosion or metaplastic bone could be misinterpreted as chondrosarcoma invading cortical bone. All of these features were seen in this case, emphasizing the need for radiographic and clinical correlation. Histologic and/or radiographic evidence of destructive permeation of bone are the most important criteria for diagnosing chondrosarcoma of the hands and feet. Therefore, care should be taken when assessing a cartilage tumor for invasion. When soft tissue chondromas erode cortical bone, nodules of the tumor are situated adjacent to the bone. This differs from the destructive permeation of chondrosarcoma where fragments of pre-existing bone are totally engulfed by tumor pouring through bone. It is also important to remember that among bone tumors of the hands and feet, enchondroma is the most common tumor and chondrosarcoma is quite rare, representing less than 10% in the Mayo files. Bizarre parosteal osteochondromatous proliferation (Nora's lesion): The calcified cartilage of Nora's lesion and soft tissue chondroma are histologically similar. However, in Nora's lesion the cartilage matures into reactive new bone surrounded by a fibrovascular stroma. Radiographically, Nora's lesion also differs from soft tissue chondroma since it shows a broad based attachment to the underlying bone. Periosteal chondroma: Radiographic information is probably the most helpful tool in separating soft tissue chondroma composed entirely of cartilaginous nodules from periosteal chondroma. Radiographically, periosteal chondroma typically is juxtacortical, attaches to the bone from beneath the periosteum, and has saucer-like erosion. Tenosynovial chondromatosis: Tenosynovial chondromatosis is an extraarticular counterpart of synovial chondromatosis. Histologically, it shows the same features as soft tissue chondromas composed predominately of mature hyaline cartilaginous nodules. However, grossly they differ since soft tissue chondroma is a solitary lesion and tenosynovial chondromatosis is composed of multiple nodules. Distinguishing the two lesions is important since tenosynovial chondromatosis reportedly has a higher rate of local recurrence. Tenosynovial giant cell tumors: Chondroblastoma-like soft tissue chondroma may be confused with tenosynovial giant cell tumor due to a resemblance between the mononuclear cells of both lesions and the presence of multinucleated giant cells. However, metaplastic cartilage is rarely seen in tenosynovial giant cell tumor. Unlike most soft tissue chondromas, they usually contain scattered lymphocytes and foamy histiocytes admixed with the mononuclear cells. Synovial chondrosarcoma: Synovial chondrosarcoma is probably the rarest of chondrosarcomas. Approximately 30 cases have been reported in the English literature. They usually occur with signs of pre-existing or concurrent synovial chondromatosis. There is only one reported case of acral synovial chondrosarcoma in the literature. It occurred de novo and involved the metacarpophalangeal joint of the thumb in a 69-year-old male. Microscopically, synovial chondrosarcoma shows prominent nuclear atypia, spindling at the periphery of chondroid lobues, necrosis, and myxoid change Treatment Local excision is the treatment of choice for soft tissue chondromas. With complete removal of the lesion, recurrence is rare. Summary This case emphasizes the importance of correlating the clinical, radiographic and histologic features when dealing with cartilage tumors. Benign extraskeletal cartilage tumors and chondrosarcoma of bone can have similar histologic features. In addition to soft tissue chondromas, synovial chondromatosis can be mistaken for chondrosarcoma, particularly when it occurs at uncommon sites such as the vertebral column and temporomandibular joint. Selected References Bertoni F, Unni KK, Beabout JW, Sim FH. Chondrosarcomas of the synovium. Cancer 67:155-162, 1991. Buddingh EP, Naumann S, Nelson M, Neff JR, Birch N, Bridge JA. Cytogenetic findings in benign cartilaginous neoplasms. 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