Case Report: Oviductal adenocarcinoma in an Argentine black and white tegu (Salvator merianae): clinical, imaging, surgical, and histopathological findings

1 Introduction

Neoplasia in reptiles has been increasingly recognized in recent decades, likely reflecting improvements in husbandry, increased longevity in captivity, and advances in diagnostic techniques. Among reptiles, squamates, including lizards and snakes, appear to be particularly affected by a diverse range of neoplastic disorders involving multiple organ systems (Solanes-Vilanova et al., 2025). However, compared to mammals, the overall prevalence, biological behavior, and pathogenesis of neoplasms in reptiles remain poorly characterized, and the available literature is still relatively limited (Catão-Dias and Nichols, 1999; Willig et al., 2024). Reports of neoplasia in the Argentine black and white tegu (Salvator merianae) remain scarce, reflecting the limited number of published cases and the underrepresentation of this species in reptile oncology literature. Several neoplastic conditions have been described in Salvator merianae (formerly Tupinambis merianae), including oral squamous cell carcinoma, periocular iridophoroma, melanophoroma, tracheal chondrosarcoma, multicentric lymphoma, muscular fibrosarcoma, osteosarcoma, and ovarian hemangiosarcoma (Kubiak et al., 2020; Saldanha et al., 2021; Freitas et al., 2024; Solanes-Vilanova et al., 2025; Catoi et al., 2026; Kim et al., 2026). Broader retrospective investigations of captive lizards and reptiles have documented a diverse range of neoplastic disorders and suggest that neoplasia in reptiles may occur more frequently than previously recognized (Kubiak et al., 2020; Solanes-Vilanova et al., 2025). Relevant reproductive studies conducted in S. merianae have also characterized ovarian follicular development, ovulation, anovulatory cycles, and follicular regression (García Valdez et al., 2011). Despite the increasing documentation of neoplastic and reproductive disorders in this species, published descriptions of oviductal adenocarcinoma in S. merianae appear to be lacking. Of particular relevance to the present case, Solanes-Vilanova et al. (2025) reported a highly invasive ovarian hemangiosarcoma in a 18-year-old female S. merianae, demonstrating that malignant neoplasia of the female reproductive system can occur in this species. To the authors’ knowledge, this report is the first description of the clinical, imaging, surgical, gross pathological, and histopathological findings of oviductal adenocarcinoma in S. merianae.

2 Case report

An adult female Argentine black and white tegu (Salvator merianae) of unknown exact age, estimated to be approximately 18 years old, weighing 2.8 kg, was presented to the hospital from a zoological collection with a history of anorexia and progressive distension of the coelomic cavity for more than 6 months. The animal was housed in a zoological collection in an enclosure with an adult male of the same species. No detailed reproductive history was available, including information regarding previous reproductive activity, egg laying, reproductive seasonality, previous episodes of follicular stasis or dystocia, or previous contraceptive or hormonal treatments. On physical examination, the animal was in poor body condition (2/5), mildly dehydrated, and exhibited pale mucous membranes. The coelomic cavity was markedly distended. Palpation revealed a firm, oval mass located in the cranial medial coelomic region, adjacent to the liver, measuring approximately 5 cm in diameter. Blood samples were collected for analysis. The microhematocrit was 25.7%, slightly below the reported reference interval for S. merianae (Chamut and Arce, 2018). Blood-smear examination revealed increased erythrocyte polychromasia, supporting an erythroid regenerative response and the interpretation of mild regenerative anemia. Serum biochemistry values were within the reference interval.

Radiographic and ultrasonographic examinations were initially performed. The animal was not sedated for any of the procedures. Radiographs were obtained in lateral and dorsoventral projections using exposure settings of 44 kV and 4 mAs. The dorsoventral radiograph (Figure 1) demonstrated marked, diffuse coelomic distension characterized by a large, homogeneous soft-tissue opacity occupying most of the mid and caudal coelomic cavity. This resulted in poor visualization and displacement of the normal coelomic organs, including the gastrointestinal structures.

Ultrasonographic examination was performed using a LOGIQ P9 Vet ultrasound system equipped with a 6S transducer operating set at 5 MHz. The examination revealed a markedly distended coelomic cavity occupied by free fluid and a heterogeneous, mixed echogenic structure. The content was predominantly moderately to highly echogenic with an irregular texture, interspersed with small hypoechoic to anechoic areas, suggestive of fluid within a soft tissue matrix. Normal coelomic organs were poorly visualized and displaced, consistent with a significant space-occupying lesion. Free fluid was identified within the mid-caudal coelomic cavity, and approximately 40 mL of dark red fluid was drained. Following drainage of approximately 40 mL of coelomic fluid, a repeat dorsoventral radiograph was obtained immediately after drainage. The repeat examination demonstrated reduced coelomic distension and improved visualization of the coelomic structures. Cytological evaluation of this fluid revealed predominantly erythrocytes with a small number of inflammatory cells. A cystic component of the palpable mass was aspirated, yielding approximately 20 mL of greenish fluid. Cytology of this sample was acellular, with the presence of lipid droplets. The animal received meloxicam (0.4 mg/kg, IM, q24h) for 5 consecutive days.

During this period, increased activity and partial return of appetite were observed. Before surgery, computed tomography (CT) of the coelomic cavity, including pre- and delayed post-contrast acquisitions, identified two well-defined cystic lesions. CT examinations were performed using a Revolution™ ACT 16-slice CT scanner (GE Medical Systems) at 120 kVp and 70 mA, with a rotation time of 1.2 s and a spiral pitch factor of 0.5625. Images were reconstructed using lung, bone, and soft-tissue algorithms, with a slice thickness of 1.25 mm and 0.625-mm spacing between reconstructed images. Pre-contrast images were acquired, followed by intravenous administration of iohexol (300 mg I/mL; 3 mL/kg) via the ventral tail vein. Subsequent post-contrast acquisitions were obtained immediately after contrast administration and at 2.5 and 5 min. CT identified two well-defined cystic lesions within the coelomic cavity. The larger lesion occupied the left side of the coelomic cavity, extended to the left body wall, and contained an intralesional soft-tissue attenuating component. A smaller cystic lesion containing homogeneous fluid was present on the right side of the coelomic cavity. Marked mass effect resulted in ventral displacement of the coelomic viscera and rightward displacement of the gas-filled colon. Comparison between the pre- and delayed post-contrast images demonstrated no appreciable enhancement of the cyst walls or the intralesional soft-tissue component, whereas normal enhancement of the adjacent coelomic viscera was evident (Figure 2). During CT staging, the lungs, liver, kidneys, and other visible coelomic organs were systematically evaluated for evidence of metastatic disease. No CT-detectable lesions suggestive of metastasis were identified.

After the CT examination, an exploratory coeliotomy was performed to excise the mass. Premedication consisted of midazolam (2 mg/kg, IM) and morphine (2 mg/kg, IM). Anesthesia was induced 20 minutes later with IV propofol (10mg/kg) and maintained with 2% isoflurane vaporized in oxygen flow of 1 L/min following endotracheal intubation. The animal was positioned in dorsal recumbency, and a paraventral coeliotomy of approximately 5 cm was performed under aseptic conditions. The cystic mass was carefully exteriorized and was found to be anatomically associated with the reproductive tract. Ovariosalpingectomy was subsequently performed. At exploratory coeliotomy, the two cystic lesions identified separately on CT were found to represent distinct cystic components of the same reproductive-tract lesion. Both components were removed en bloc during ovariosalpingectomy. Representative samples from both cystic components and the solid/nodular neoplastic regions were submitted for histopathological examination. The surgical site was closed routinely.

On gross examination, the mass measured approximately 15×5 cm. The external surface was smooth to mildly nodular and exhibited heterogeneous coloration, with darker and paler areas. Upon sectioning, the tissue was thin and fragile, and approximately 30 mL of dark red fluid was released from its interior. The cut surface revealed a heterogeneous, partially cavitated structure with multiple cystic spaces containing fluid (Figure 3). Within the cavity, an organized blood clot was present, consistent with previous or chronic hemorrhage. The internal architecture was irregular, with areas of soft, friable tissue interspersed with fluid-filled regions. Multifocal regions of necrosis and hemorrhage were suspected based on the tissue’s variable coloration and texture. On sectioning, multiple round, firm, white to yellow-white nodules were identified within the wall of the mass, ranging from approximately 0.5 to 2.0 cm in diameter (Figure 3). Representative samples were collected from different areas of the mass, including the cystic wall and solid/nodular neoplastic regions. The examined tissue was extensively replaced by neoplastic tissue, and no recognizable residual normal oviductal epithelium was identified. Following excision, the mass was fixed in 10% neutral buffered formalin. A total of four tissue blocks were routinely processed, embedded in paraffin, sectioned at 3 µm, and stained with hematoxylin and eosin. Six histological sections were examined.

Microscopically, the mass was an unencapsulated, infiltrative epithelial neoplasm that extensively replaced the submitted oviductal wall and extended through its full thickness (Figure 4). Neoplastic cells were arranged in variably sized tubules and acini, nests, cords, and papillary projections supported by a delicate fibrovascular stroma. Individual neoplastic cells were polygonal, with variably distinct cell borders and moderate amounts of eosinophilic cytoplasm. Nuclei were round to elongate and occasionally irregular, with vesicular chromatin and generally one prominent nucleolus. Mitotic activity varied throughout the neoplasm, ranging from 1 to 10 mitotic figures per high-power field, assessed using a 40× objective with a field number of 20, corresponding to a field diameter of 0.50 mm and a field area of 0.196 mm². Extensive multifocal to coalescing areas of intralesional necrosis and hemorrhage were present, occasionally associated with cholesterol clefts (Figure 4). Neoplastic cells were identified within the lumina of multiple blood vessels, consistent with multifocal vascular invasion (Figure 5). The examined sections did not show recognizable residual normal oviductal epithelium or normal oviductal wall architecture; therefore, direct histological continuity between normal oviductal epithelium and the neoplasm could not be demonstrated. Nevertheless, the anatomical association of the mass with the reproductive tract observed during surgery, together with its infiltrative epithelial morphology and tubular, acinar, and papillary differentiation, supported an oviductal origin.

After surgery, the animal received meloxicam (0.4 mg/kg, IM, q24h) for 5 consecutive days and marbofloxacin (10 mg/kg, PO, q48h) for 10 consecutive days. Given the prolonged surgical procedure, extensive tissue manipulation, and presence of necrotic neoplastic tissue, postoperative antimicrobial therapy was initiated. Marbofloxacin was selected considering the expected bacterial spectrum and its longer dosing interval, which reduced the need for repeated handling and associated stress in this aggressive animal. The animal subsequently regained its appetite, gained weight, and became more active. At three months postoperatively, the animal remained clinically stable. Follow-up ultrasonography included evaluation of the surgical region and the visible coelomic organs, including the liver, heart, kidney, and gastrointestinal tract, while radiography was used to assess the coelomic cavity and pulmonary fields. No radiographically or ultrasonographically detectable evidence of local recurrence or metastatic disease was identified.

3 Discussion

Neoplasia affecting the reproductive tract of reptiles is rarely reported, particularly in S. merianae, making this case a noteworthy addition to the limited literature on squamate oncology. The clinical presentation—progressive coelomic distension, anorexia, and poor body condition—was nonspecific but consistent with previously described intra-coelomic neoplasms in reptiles, which often remain clinically silent until advanced stages (Garner et al., 2004; Sykes, 2010). The ability of reptiles to accommodate large intra-coelomic masses contributes to delayed diagnosis and highlights the importance of thorough physical examination and imaging. Diagnostic imaging was essential in identifying the presence and extent of the lesion. Radiography demonstrated significant coelomic distension and organ displacement, while ultrasonography and computed tomography provided further characterization, revealing a heterogeneous mass with cystic and fluid components. These findings are consistent with descriptions of malignant epithelial tumors in reptiles and other vertebrates, where necrosis, hemorrhage, and cystic degeneration are common (Sykes, 2010). Cytological analysis of coelomic and cystic fluids was non-diagnostic, a limitation frequently reported in reptile oncology due to low cellular exfoliation in body cavity effusions. In female reptiles, differential diagnoses for progressive coelomic distension include follicular stasis, egg retention, oviductal disease, salpingitis, coelomic effusion, abscessation, granulomatous inflammation, hematoma, hepatic enlargement, gastrointestinal disease, and neoplasia. In the present case, imaging and cytology were insufficient for definitive diagnosis, and histopathology was required to confirm oviductal adenocarcinoma (Sykes, 2010). Immunohistochemistry was not performed, which represents a limitation of the present report. Immunohistochemical characterization could have provided additional support for the epithelial phenotype of the neoplasm and assisted in further characterization of its differentiation. Nevertheless, the anatomical origin of the mass together with the infiltrative tubular and papillary epithelial morphology and associated malignant features supported the diagnosis of oviductal adenocarcinoma. Although recognizable residual normal oviductal epithelium was not present in the examined sections, precluding demonstration of direct continuity between normal epithelium and the neoplasm, the surgical association of the mass with the reproductive tract and the characteristic infiltrative tubular and papillary epithelial morphology supported an oviductal origin. The etiology of reproductive neoplasms in reptiles remains poorly understood. Oviductal adenocarcinoma has been reported infrequently in reptiles, including several snake species. In a series of five captive snakes with oviductal adenocarcinoma, the tumors were characterized histologically by papillary and infiltrative growth, frequently extending transmurally through the oviductal wall, with neoplastic epithelial cells arranged in acini, nests, cords, and ducts supported by fibrovascular stroma (Pereira and Viner, 2008). Hemorrhage and necrosis were also prominent features. These findings closely resemble the histopathological characteristics observed in the present case. In the previously reported snake cases, however, histological evidence of metastatic spread was identified, including vascular tumor emboli and metastases to several visceral organs. In the present case, vascular invasion was identified histologically, supporting malignant biological potential, but no radiographically or ultrasonographically detectable metastatic disease was identified during the three-month postoperative follow-up. Nevertheless, the relatively short follow-up period and the presence of vascular invasion preclude definitive conclusions regarding long-term biological behavior and support a guarded prognosis (Hernandez-Divers and Garner, 2003). Proposed contributing factors include chronic inflammation, hormonal influences, environmental conditions, and increased lifespan under captive management (Garner et al., 2004; Sykes, 2010; Willig et al., 2024). In captive settings, improved husbandry and veterinary care may contribute to increased detection of neoplastic conditions that would otherwise go unrecognized in wild populations. Surgical excision remains the primary treatment for localized neoplasms in reptiles. In this case, the animal showed a favorable postoperative outcome, with recovery of appetite, weight gain, and return to the zoological collection. This suggests that, despite the large size and invasive nature of the mass, surgical intervention can be effective in improving short-term clinical status. Nevertheless, the risk of recurrence or metastasis should be assessed. In general, adenocarcinomas are considered to have potentially aggressive biological behavior, and prognosis should be regarded as guarded (Sykes, 2010; Willig et al., 2024). The presence of intravascular neoplastic cells suggests vascular invasion and may indicate an increased risk of metastatic spread. Although no radiographically or ultrasonographically detectable recurrence or metastatic disease was identified at 3 months postoperatively, longer follow-up is required before concluding prognosis.

4 Conclusion

This case documents an oviductal adenocarcinoma in an adult female Salvator merianae and illustrates the diagnostic challenge of reproductive tract neoplasia in reptiles. Although imaging was essential to identify and characterize the coelomic mass, definitive diagnosis required histopathological examination. Surgical excision resulted in short-term clinical improvement, but the presence of vascular invasion supports a guarded prognosis and the need for long-term follow-up.

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Footnotes

Edited by: Ferran Solanes Vilanova, Peticare Kowloon East Animal Hospital (Exotic), Hong Kong SAR, China

Reviewed by: Frine Eleonora Scaglione, University of Turin, Italy

Maciej Janeczek, Wroclaw University of Environmental and Life Sciences, Poland