A three years-old intact female guinea pig (Cavia porcellus) with 980gr in body weight was presented with abdominal distension, lethargy and weight loss. On physical exam it was detected a hard consistency abdominal mass. There was no signs of pain or discomfort on this palpation. Conscious abdominal radiographs were taken, and an abdominal soft tissue opacity was detected.  Differential diagnosis considered were renal or ovarian neoplasia.

An exploratory laparotomy was performed, and a 6cm diameter mass involving the right ovary was detected. The kidneys had regular and similar shape with no aspect of disease. An ovariectomy was performed, surgically removing this mass together with the left ovary.

Histological examination of the mass showed lack of normal ovarian, Fallopian tube or uterine structures, which precluded the identification of the origin of the tumor. However, a grade II soft-tissue sarcoma was diagnosed, and differential diagnosis includes fibrosarcoma or leiomyosarcoma. Immunohistochemistry analysis was considered essential for definitive diagnosis, being currently in progress, since it will contribute to the identification of the origin of the tumor. Multiple ovarian cysts were identified in the left ovary.

Bearing in mind the histological nature of the tumor, it is considered therefore that a complete ovariohysterectomy should be performed instead of an ovariectomy, as it be curative. It is also recommended that ovariohysterectomy becomes the standard procedure in future similar cases.

1. Quesenberry KE, Donnelly TM, Mans C: Biology, husbandry, and clinical techniques of guinea pigs and chinchillas. In: Quesenberry KE, Carpenter JW (eds). Ferrets, Rabbits, and Rodents: Clinical Medicine and Surgery, 3rd ed. St. Louis, MO: Elsevier Saunders; 2012: 280-283.

2. Schuetzenhofer G, Goericke-Pesch S, Wehrend A: Effects of deslorelin implants on ovarian cysts in guinea pigs. Scweiz Arch Tierheilkd 2011; 153(9):416-417.

3. Laik-Schandelmaier C, Klopfleisch R, Schöniger S, et al. Spontaneously arising tumours and tumour-like lesions of the cervix and uterus in 83 pet guinea pigs (Cavia porcellus) 2017; J Comp Pathol 156(4):339-351.

4. Pollock C, Arbona N. Guinea pig reproduction basics. Nov 12, 2017. LafeberVet Web site. Available at https://lafeber.com/vet/guinea-pig-reproduction-basics/

5. Lukášová R, Bártová1 E, Škorič M: Leiomyosarcoma of the ovary in a young female guinea pig – a case report. ACTA VET. BRNO 2017; 86: 269-272