Pathology Case of the Month - Sandhill Crane

Gross Findings: This adult male sandhill crane was in emaciated body condition and good postmortem condition. On the cranial aspect of the right leg, overlying and distal to the hock, was a 45 x 45 x 35 mm firm, ovoid mass with a mildly roughened black and tan surface (Fig. 1A). On cut section, the mass was gelatinous, contained both firm and soft areas, and was mottled light pink to gray (Fig. 1B). The base of the mass extended to the joint space (Fig. 1B). There were no significant internal abnormalities.

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Histopathological Findings: The mass is composed of islands of well-differentiated chondrocytes separated by fibrovascular connective tissue containing mixed inflammatory cells. There is mild cellular pleomorphism and no mitotic figures are seen (Fig. 2A). Islands of chondrocytes are multifocally hypereosinophilic (necrotic) and surrounded by granulomatous inflammation (Fig. 2B). There is multifocal hyperkeratosis and focal ulceration of the overlying skin.

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Morphologic Diagnosis/es:

1. Mass, hock: Chondroma

Disease: Chondroma (benign neoplasm of cartilage origin)

Etiology: The etiology of chondromas in cranes is unknown, although both traumatic and viral etiologies have been suggested. In domestic chickens, avian leukosis/sarcoma virus can be a cause of chondrosarcomas.

Host range: In birds, chondromas have been reported in both sandhill and whooping cranes (Grus americana), as well as few other captive and free-ranging avian species. Both adult and immature cranes can be affected. Chondromas also occur in mammals, including dogs, cats, cattle, and sheep. 

Clinical signs: In cranes, chondromas are most often reported on the pelvic limbs or plantar surface of the foot. In one case, regression of the remaining mass occurred two years after partial biopsy.

Pathology: Chondromas can arise within the medullary cavity of bone (enchondromas) or can protrude outwards from cartilage (ecchondromas). Grossly, chondromas appear as slow-growing firm to hard spherical masses with a fibrous capsule. On cut section, the surface may have a lobular and/or gelatinous appearance. Microscopically, chondromas are composed of lobules of well-differentiated hyaline cartilage within a fibrous matrix. Differentiation between chondroma and low-grade chondrosarcoma (malignant tumor of cartilage) can be difficult histologically; chondrosarcomas are more likely to be locally invasive.

Wildlife population impacts: Chondromas are rare and typically diagnosed as an incidental finding, although bacterial infection could result if overlying skin is ulcerated. No population impacts are reported.

References:

• Behera D, Kumar D, Samal A, Panda SK. 2013. Chondroma in an Indian ring neck parrot (Psittacula krameri manillensis): a case report. Vet. World 6(4):223-225.
• Craig LE, Dittmer KE, Thompson KG. 2016. Chapter 2 - Bones and Joints. In: Jubb, Kennedy & Palmer's Pathology of Domestic Animals: Volume 1 (Sixth Edition), Maxie GM, editor. W.B. Saunders, p. 116.
• Dittmer KE, French AF, Thompson DJ, Buckle KN, Thompson KG.  2012. Primary bone tumors in birds: a review and description of two new cases. Avian Diseases, 56(2), 422–426.
• Forrester DJ and Spalding MG. 2003. Parasites and diseases of wild birds in Florida. University Press of Florida, Gainesville, Florida. pp. 1132
• Hatai H, Tokorozaki K, Haraguchi Y, Matsui T, Ozawa M. 2020. Chondrosarcoma with undifferentiated neoplastic cell proliferation around the distal tibiotarsus bone in a wild Hooded Crane (Grus monacha). J Vet Med Sci. Aug 19;82(8):1093-1096.
• Miller JL, Spalding MG, Folk MJ. 2010. Leg problems and power line interactions in the Florida resident flock of whooping cranes. In: Proceedings of the Eleventh North American Crane Workshop, Sep 23-27, 2008, Wisconsin Dells, Wisconsin. Hartup BK., editor. North American Crane Working Group, Baraboo, Wisconsin, pp. 156–165.