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| IMAGE QUIZ ARCHIVE | ||||||
| Image Quiz | ||
| A Neoplasm of the Arm (continued) | ||
| Answer: Secondary chondrosarcoma (malignant change in an enchondroma) of the proximal aspect of the right humerus with an impending fracture. | ||
 Fig. 1 |
Posteroanterior plain radiograph of the right arm and shoulder joint, demonstrating a proximal humeral lesion with intralesional lysis, endosteal scalloping, and pathological fracture. For larger view, click on image |
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 Fig. 2-A |
Oblique coronal intermediate T2-weighted magnetic resonance image showing the intramedullary extent of the lesion with heterogeneous signal intensity and evidence of fracture. For larger view, click on image |
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 Fig. 2-B |
Axial gradient echo (TR-1500) image showing the extent of the tumor and extraosseous extension. For larger view, click on image |
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 Fig. 3 |
Radionuclide bone scan demonstrating the intensity of abnormal uptake involving the proximal aspect of the right humerus. For larger view, click on image |
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 Fig. 4 |
Low-power photomicrograph of the biopsy specimen, demonstrating the zone of benign chondrocytes (inset at top right, long arrow) and malignant transformation with Grade-II chondrosarcoma (inset at bottom left, short arrow) (hematoxylin and eosin, ×400). For larger view, click on image |
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| Discussion | ||
| Enchondromas are a common intramedullary benign neoplasm composed of mature cartilage. They account for between 12% and 25% of all benign bone tumors. The small bones of the hand are more frequently involved than the bones of the feet, with an approximate ratio of 7:1. The femur is the most frequently involved long tubular bone, followed by the proximal aspect of the humerus1. | ||
| On a plain radiograph, enchondroma appears as a localized lesion with varying amounts of punctate or stippled calcification. Magnetic resonance imaging demonstrates noncalcified chondroid lesions within the marrow cavity as a low-signal-intensive area on T1-weighted images and as a high-signal-intensive area on T2-weighted images. Low-grade chondrosarcomas and enchondromas both occur in long tubular bones and may sometimes pose a diagnostic problem2. Typically, enchondromas do not erode the host bone, whereas chondrosarcomas, or growing lesions, can cause substantial erosive changes. The hallmarks of chondrosarcoma include radiographic factors, such as intralesional lysis, endosteal scalloping, cortical thinning, erosion, or expansion, and the condition may be associated with pain. The intralesional lysis that is typical of chondrosarcoma is a lytic area usually within the medullary canal, which typically demonstrates a "moth-eaten" margin with a zone of transition that measures several millimeters and shows no reactive sclerosis. Endosteal scalloping is another radiographic "red flag" for the presumptive diagnosis of chondrosarcoma. It is important to note, however, that not all scalloping is associated with the diagnosis of malignant disease. Occasionally, otherwise quiescent enchondromas will demonstrate some scalloping of the endosteal surface of the adjacent cortex. These scallops are usually less than 1 cm in length and are not typically associated with cortical expansion. In the presence of chondrosarcoma, however, the scallops into the adjacent cortex are usually each greater than 1 cm in length and are often associated with cortical expansion in the zone with an attempt to maintain some cortical continuity over the expanding lesion. | ||
| Histologically, enchondroma is associated with low cellularity. The chondrocytes have small dark pyknotic nuclei, the matrix is hyaline, and the lesion is well demarcated with islands of cartilage bordered by bony trabeculae and with no evidence of invasion of haversian canals of the cortex. Any deviation from this pattern suggests the possibility of malignant disease1. | ||
| *The authors did not receive grants or outside funding in support of their research or preparation of this manuscript. One or more of the authors received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity (Dr. Hosalkar's position of Tumor Fellow is funded by a grant from Howmedica Osteonics). In addition, a commercial entity paid or directed, or agreed to pay or direct, benefits to a research fund, foundation, educational institution, or other charitable or nonprofit organization with which the authors are affiliated or associated (Dr. Lackman is a consultant for Stryker Howmedica Osteonics). | ||
| References | ||
| 1. Dorfman HD, Czerniak B. Benign cartilage lesions. In: Dorfman HD, Czerniak B, editors. Bone tumors. Philadelphia: Mosby; 1998. p 253-352. 2. Mirra JM, Gold R, Downs J, Eckardt JJ. A new histologic approach to the differentiation of enchondroma and chondrosarcoma of the bones. A clinicopathologic analysis of 51 cases. Clin Orthop. 1985;201:214-37. |
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