Abstract
This report outlines the findings of teratoma in two desert grassland whiptails (Cnemidophorus uniparens), a southwestern lizard species of the family Teiidae. Case 1 was a wild-born female C. uniparens from New Mexico received into quarantine at the North Carolina Zoological Park at approximately two years old. It had no history of medical problems while in captivity. One year after capture, it became lethargic, anorexic, and appeared distended. One month previously, it had successfully laid eggs. On physical examination, it became slightly dyspneic. No eggs were palpated. Dorsoventral radiographs showed fluid density in the caudal coelomic cavity, lungs slightly compressed cranially, and no evidence of calcified eggs. The lizard became progressively debilitated after a bout of normal feeding behavior and defecation and was later found dead in its cage. At gross necropsy, the primary abnormality was a large (1.5×2.0 cm) dark colored cystic structure in the coelomic cavity. Histologic examination showed the walls of the cyst structure contained fronds of pseudostratified to columnar epithelium with occasional subadjacent follicular structures. The majority of the section contained irregular masses composed of well-differentiated, keratinizing, stratified, squamous epithelium overlaying haphazardly arranged blood-filled spaces, cartilage, clumps of glandular epithelium, adipose tissue, and neuroglial cells.
Case two was a captive-born female lizard with no direct relationship to the first case. At two years old it developed coelomic distention and appeared gravid for a long period of time. Activity and feeding remained normal. Physical examination revealed palpable round masses in the caudal coelomic cavity which were presumed to be eggs. The animal was placed back in its enclosure for monitoring and was found dead three days later. At gross necropsy, a 2-cm-diameter mass was identified, and the colon was impacted with feces. Histopathologic examination of the mass showed a disorganized arrangement of well-differentiated tissues representing skin, digestive tract, fat, bone, respiratory tract, cartilage, and smooth muscle surrounded by a thin fibrous capsule.
Cnemidophorus uniparens is a parthenogenic species. Most parthenogenic species are polyploid (2–4n), are of female gender, and often have both male and female sexual behaviors. Individuals are considered to be clones of each other, although family lines may be far removed. Although the two animals in this report were not directly related, they technically have the same genetic makeup.2 Parthenogenic reproduction for C. uniparens involves a premeiotic endoreduplication followed by two meiotic divisions preserving the triploid chromosomal number.3
Teratoma is a rare neoplasm of domestic animals.5 Ovarian teratoma has been reported in the green iguana (Iguana iguana)1 and ovarian teratoadenocarcinoma also in the green iguana4. It is a tumor of the germ cells, is comprised of one or more of the primary germ layers (ectoderm, mesoderm, endoderm), occurs in both males and females, and can be gonadal or extragonadal.6 Teratomas are believed to be parthenogenic tumors that have developed from a single germ cell after the first meiotic division.6 In humans they are characterized as benign or cystic (dermoid cyst), immature or malignant, or specialized. Usually, teratomas in animals are well-differentiated and benign and are composed of a combination of recognizable tissues of germ cell origin.7
No chromosomal analysis was conducted on the teratoma tissues; therefore, it is unknown at what stage of division the neoplasia occurred or the chromosomal number present in the tumors of these lizards. It is assumed that the formation of teratoma in this species would be similar to formation in mammals, but it is unknown if a parthenogenic neoplasia in a parthenogenic lizard species is different than that found in mammals. An etiology of teratogenesis was not identified.
Literature Cited
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