Giuliana Rosato, Elisabeth Kolp, Carina Oschlies, Brice Donati, Karl Klisch
Background
Teratomas are rare germ cell tumors containing tissues derived from at least two or all three embryonic germ layers—ectoderm, mesoderm, and endoderm. While these tumors typically occur in the gonads, extragonadal manifestations, including those in the retroperitoneum, are exceedingly rare in both humans and animals. Previous reports in New World camelids have documented only renal and intracranial teratomas. This study reports the first known case of a mature retroperitoneal cystic teratoma in an adult alpaca.
Methods
A four-year-old female alpaca presented with abdominal distension, tenesmus, reduced fecal output, and hypothermia. Diagnostic imaging—including ultrasonography, radiography, and computed tomography (CT)—revealed a large cystic lesion in the caudal abdomen causing significant organ displacement. Following euthanasia, necropsy and histopathological analysis were performed. Immunohistochemical staining for markers such as neuron-specific enolase (NSE), smooth muscle actin (SMA), cytokeratin, glial fibrillary acidic protein (GFAP), and S100 was used to identify tissue origins.
Results
A 40 cm cystic mass containing approximately 15 L of clear yellow fluid was discovered in the abdominal and pelvic cavities, displacing all abdominal organs. Histological evaluation demonstrated differentiated tissues from all three germ layers: ectodermal nervous tissue, mesodermal muscle and connective tissue, and endodermal glandular structures. Immunohistochemistry confirmed tissue diversity consistent with a mature teratoma. Differential diagnoses such as ectopic pregnancy and hydronephrosis were excluded through histological and immunohistochemical analysis.
Limitations
As a single case report, findings cannot be generalized across alpacas or other species. The absence of longitudinal follow-up limited assessment of tumor behavior or recurrence potential. Additionally, data on possible embryologic origin or genetic predisposition were not available.
Conclusions
This report documents the first identified case of a mature retroperitoneal cystic teratoma in an adult alpaca. The tumor’s benign histological features and well-differentiated composition align with mature teratoma characteristics. The case underscores the diagnostic value of combining imaging, histopathology, and immunohistochemistry in evaluating abdominal masses in livestock and broadens the differential diagnosis for such presentations in camelids.
Left paramedian sagittal slice at the level of the left kidney (A), transverse slice at the level of the right kidney (B), and dorsal slice at the level of both kidneys (C). A large, homogeneously fluid-attenuating, thin-walled cystic structure is visible, occupying most of the abdominal cavity. Sporadic thin, soft tissue–attenuating inclusions are present within the cystic lesion, representing the described band-like structures (yellow asterisk) radiating from the center to the periphery. There is crowding of most of the gastrointestinal tract within the left cranial abdomen (yellow arrows). The kidneys are dorsally compressed, the left kidney maintaining a more normal architecture compared to the right kidney, where reduced contrast accumulation and filling defects are observed (black asterisk). In the right craniodorsal abdomen, multiple mineral-attenuating inclusions are visible within the liver (white asterisk), consistent with chronic verminous granulomatous hepatopathy
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