Mature retroperitoneal cystic teratoma in an adult alpaca: a case report

Abstract

Background: Retroperitoneal mature cystic teratomas are rare in both human and veterinary medicine. These tumors arise from pluripotent germ cells and can contain tissues from all three germ layers. While the majority of teratomas are benign, their location in the retroperitoneum can lead to significant mass effects and clinical complications.

Case presentation: A four-year-old female alpaca was presented with a history of abdominal distension. Clinical signs included tenesmus with lifted tail, reduced fecal output and hypothermia. Initial ultrasound revealed severe accumulation of anechoic fluid in the abdomen and complete homogeneous soft tissue opacification of the abdomen was visible in radiography, with mass effect on all other abdominal organs. A CT scan confirmed a considerable cystic lesion in the caudal abdomen. Histopathological analysis of the cystic structure revealed mature connective tissue, both striated and smooth muscle, as well as gland-like formations. Immunohistochemical staining identified markers from multiple tissue types. Based on these findings, a diagnosis of mature retroperitoneal cystic teratoma was established.

Conclusions: To our knowledge, this is the first reported case of a mature retroperitoneal cystic teratoma in an adult alpaca. The rare nature of this condition in both humans and animals makes it a noteworthy addition to veterinary literature. This case emphasizes the importance of considering such conditions in the differential diagnosis of abdominal masses in livestock.

Keywords: Alpaca (vicugna pacos); Cystic teratoma; Histopathology; Radiology; Retroperitoneum.

Fig. 1

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

Fig. 2

Gross pathology of the excised cyst: a large, well-demarcated structure with a smooth, glistening, and vascularized outer surface. Insert (upper right): Cross-sectional view revealing broad, band-like internal structures and clear yellow fluid within the lumen of the cyst. All abdominal organs are markedly displaced cranially (left in the picture)

Fig. 3

Histological and immunohistochemical characterization of the cyst. (A) Overview of the cyst wall, H&E, Bar 5 mm. (B) Band-like structure composed of centrally located striated muscle fibers surrounded by collagenous connective tissue and vasculature, H&E, Bar 1 mm. (C) The ectodermal component includes nerve fibers (*), the predominant mesodermal component comprises clusters of adipocytes (**), mature collagen-rich connective tissue (→), and bundles of both striated (skeletal) (▲) and smooth muscle fibers (×), H&E, Bar 250 μm. (D) Neuroectodermal nerve fibers exhibit positive staining for neuron-specific enolase (NSE), Bar 100 μm. (E) Smooth muscle cells stain positively for smooth muscle actin (SMA), Bar 250 μm. (F). Endodermal component: small numbers of cuboidal to columnar epithelial cells arranged in tubules, along with clusters of mucous gland-like cells, H&E, Bar 100 μm. (G) Cuboidal to columnar epithelial cells and mucous glands demonstrate cytokeratin positivity, Bar 100 μm