Osteosarcoma in a California Mountain Kingsnake (Lampropeltis zonata)

Kenneth S. Latimer,¹ Gregory A. Rich,² and Christopher R. Gregory¹

¹College of Veterinary Medicine, The University of Georgia, Athens, GA 30602-7388 (USA); ²West Esplanade Veterinary Clinic and Bird Hospital, 3640 West Esplanade, Metairie, LA 700002 (USA).

Abstract. The clinical and histologic features of an osteosarcoma in a California mountain kingsnake (Lampropeltis zonata) are reported.

Case Report

An adult California mountain kingsnake (Lampropeltis zonata) of undetermined gender was presented for examination of a firm, progressively enlarging, circumscribed mass located in the caudal 1/3 of the spine anterior to the cloaca (Fig. 1). The mass extended from side to side and extended ventrally obscuring palpation of the spinal column.

Figure 1

Survey radiographs were taken (Fig. 2). The mass was slightly elliptical with a starburst appearance. The mass involved two vertebrae and the proximal portions of eight ribs. Areas of increased and decreased density were apparent within the mass. The differential diagnosis included a healing fracture, neoplasia, or granulomatous lesion, possibly secondary to infection.

Figure 2

Due to the poor prognosis, the snake was euthanized. On cut surface, the mass was gritty and appeared pale (Fig. 3). Some of the material from the lesion had a caseous appearance. Decalcified sections of the mass were prepared for histologic examination.

Figure 3

Microscopically, the mass was composed of a population of pleomorphic spindle cells arranged in interlacing bundles and sheets (Fig. 4). Individual cells had round to elongate, plump, vesicular nuclei and basophilic cytoplasm with attenuated cell margins. Some cells displayed osteocyte differentiation and were surrounded by osteoid (Fig. 4). The mitotic index was 5 mitoses / ten 45x fields of view. Foci of necrosis were present within the mass and occasionally had a mild infiltrate of heterophils. Vimentin immunohistochemical staining was positive, indicating mesenchymal origin of the neoplastic cells. Giemsa and acid-fast staining were negative for bacteria, including mycobacteria. PAS staining was negative for fungus. Masson's trichrome stain indicated a lack of collagen production by the neoplastic cells. The histologic diagnosis was osteosarcoma.

Figure 4

Discussion

Neoplasms originating in bone or cartilage appear to be rare in reptiles, especially snakes. A six-year retrospective study of histologic lesions in reptiles revealed only a single chondrosarcoma in a snake of undetermined species (Gregory et al. , 1995). An osteochondrosarcoma (compound osteosarcoma) also has been reported in the cervical area of a Bengal (yellow tree) monitor (Varanus bengalensis) (Frye, 1991). From a comparative standpoint, osteosarcomas are rare in reptiles but appear to have a poor prognosis, as is the case in mammals.

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