JPC SYSTEMIC PATHOLOGY
Signalment (JPC #2594133): 5-year-old female Chesapeake Bay retriever
HISTORY: This dog had an 8-month history of progressively worsening lameness of the right rear leg. Radiographic examination revealed lysis of the right tibial tarsal (tarsus) bone.
HISTOPATHOLOGIC DESCRIPTION: Bone, tibial tarsal (per contributor): Filling the marrow cavity, effacing over 75% of normal bone and infiltrating the surrounding connective tissue is an unencapsulated, moderately cellular neoplasm composed of haphazardly arranged plump neoplastic spindle cells surrounded by irregular islands and thick trabeculae of abundant, variably basophilic, chondromatous matrix. Neoplastic cells are individualized or congregated in lacunae within the matrix and have a moderate amount of finely granular eosinophilic to basophilic cytoplasm. Nuclei are oval, have 1-2 magenta nucleoli and finely stippled chromatin. The mitotic count averages less than one per 10 HPF. Multifocally there are irregular trabeculae of reactive woven bone and foci of osteolysis characterized by scalloped margins and few multinucleated osteoclasts within Howship's lacunae. Loose, well-vascularized mesenchymal tissue is interspersed between islands of cartilage. There is mild hemorrhage and low numbers of hemosiderophages.
MORPHOLOGIC DIAGNOSIS: Bone, tibial tarsal (per contributor): Chondrosarcoma, Chesapeake Bay retriever, canine.
- Chondrosarcomas are malignant mesenchymal tumors in which the neoplastic cells produce variable quantities of cartilaginous or fibrillar matrix, but not osteoid; although bone may be present in chondrosarcomas, it forms by endochondral ossification of tumor cartilage, rather than being produced directly by malignant mesenchymal cells.
- Reported most frequently in the dog; accounts for 10% of the primary tumors of the bone and is second to the osteosarcoma in incidence; most commonly affects medium to large breed, middle to older aged dogs, particularly boxers, German shepherds, and golden retrievers; rare in giant and small breeds, most commonly affected sites involve the flat bones more often than long bones (ribs, turbinates, and pelvis)
- Rare tumor in other species
- Primary chondrosarcomas arise from either within bone (central or medullary) or from the periosteal surface (peripheral), the former being the most common
- Secondary chondrosarcomas develop by malignant transformation of cartilage in an osteochondroma or osteochondromatosis (rare)
- Metastasis most commonly to the lungs
TYPICAL CLINICAL FINDINGS:
- Multilobular (“popcorn”) appearance radiographically
- Cytology (FNA): Moderately abundant, amorphous “lakes” of homogeneous eosinophilic matrix compatible with cartilage; chondrocytes may be detected within cartilaginous lacunae
TYPICAL GROSS FINDINGS:
- Firm or hard, resembling hyaline cartilage
- Multiple small, contiguous nodules of translucent blue, white, or pink tissue
- Areas of necrosis and hemorrhage
- Some tumors (especially in the nasal cavity) contain soft mucoid areas, chalky white foci, areas of mineralization or ossification
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Large pleomorphic round to fusiform cells with basophilic cytoplasm which occasionally contain fine pink granules; large hyperchromatic, plump nuclei (single or multiple) and a prominent nucleoli; produce variable quantities of disorganized hyaline cartilage
- Mitoses are rare in well differentiated chondrosarcomas; the presence of even one mitotic figure strongly supports a diagnosis of malignancy
- No osteoid production
- Chondroma: Differentiation difficult; lack cellular pleomorphism and lack invasive growth and metastasis
- Osteosarcoma: Osteosarcomas with cartilaginous dysplasia, and chondrosarcomas with mineralization produce osteoid and bone
- Although rare in sheep, chondrosarcomas are the most common bone tumor which affect the following sites: Cartilage of the sternocostal complex > scapula > tuber coxae
- Chickens and other avian species: Osteosarcromas more common than chondrosarcomas
- Cats: Primary intraocular chondrosarcomas have been reported (often post-traumatic)
- Beck AP, Jones ML. Chondrosarcoma of the scapula of an 8-month-old Holstein steer. J Vet Diagn Invest. 2012;24(4):791-793.
- Beckwith-Cohen B, Teixeira LB, Dubielzig RR. Presumed primary intraocular chondrosarcoma in cats. J Vet Diagn Invest. 2014;26(5):664-668).
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- Ramirez GA, Altimira J, Vilafranca M. Cartilagenous tumors of the larynx and trachea in the dog: Literature review and 10 additional cases (1995-2014). Vet Pathol. 2015;52(6):1019-26.
- Thompson K. Bones and joints. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 1. 6th ed. Philadelphia, PA: Saunders Elsevier; 2016: 118-120.
- Thompson KG, Dittmer KE. Tumors of Bone. In: Meuten, DJ, ed. Tumors in Domestic Animals. 5th ed. Ames, IA; John Wiley & Sons, Inc; 2017: 394-400.