Introduction

Guinea pigs (GP) have recently gained popularity as pets (Flecknell, 2002). Most studies addressing neoplasms in this species have reported spontaneous or induced tumors in animals reared under laboratory conditions (Ediger and Kovatch, 1976). Spontaneous tumors are quite rare in guinea pig and they usually occur over the age of three years (Kitchen et al., 1975). Spontaneous tumors reported in this species include bronchogenic papillary adenomas, trichofolliculomas, carcinomas of the skin, ovary teratomas and tumors of the mammary gland (Jelinek, 2003; Greenacre, 2004). Occurrence of cutaneous tumors in increasing order is as follows- trichofolliculomas, lipomas, trichoepitheliomas and mammary gland carcinomas (Kanfer and Reavill, 2013). World Health Organization (WHO) classification of soft tissue tumors recognizes three categories of liposarcomas in animals- well differentiated liposarcoma (which includes the adipocytic, sclerosing and inflammatory subtypes), myxoid liposarcoma, and pleomorphic liposarcoma (Goldschmidt and Hendrick, 2002; Baez et al., 2004). In myxoid liposarcomas, metastatic rate can reach 60% and in pleomorphic liposarcomas between 30% and 50%. (Dei Tos, 2014). The present study describes spontaneously occurring rare cutaneous neoplasm in the right neck region of a pet guinea pig.

Case History and Clinical Examination

 A 1.6 kg, 3.2-year-old male pet guinea pig (Cavia porcellus) was presented to Teaching Veterinary Clinical Complex (TVCC), College of Veterinary Science and Animal Husbandry with complaint of a solid growing mass in the right cervical region behind the ear accompanied by hair loss over the area and ulceration (Fig.1).

Fig.1: Solid growing mass in the right cervical region behind the ear

The owner reported that the mass had grown from less than 1 cm to over 6 cm within four months. On physical examination, the Guinea pig was found to be sound, alert, responsive and in good body condition. Cardiac and respiratory auscultation revealed regular heart rhythms and breathing pattern. The tumor mass was found to be isolated from body wall without disrupting adjacent structure. On the basis of history, clinical and physical examination it was tentatively diagnosed as a tumour mass and decided for surgical correction.

Treatment

The Guinea pig was sedated with 0.2 mg/kg body weight (BW) of butorphanol IM and 0.2 mg/kg BW of midazolam IM. A 24-gauge intravenous catheter was placed in the left cephalic vein and lactated Ringer’s solution with 2.5% dextrose was given at a rate of 5 mL/kg BW per hour. Thermal support was provided with a forced warm-water blanket. Anesthetic monitoring included heart rate and rhythm using a stethoscope and blood oxygen saturation and pulse rate were monitored and maintained within physiological parameters with a pulse oximeter placed on the paw. The rectal temperature was monitored with a digital thermometer. The anesthetized Guinea pig was placed in dorsal recumbency. The entire area was clipped and aseptically prepared using a routine scrub protocol. A circular incision was made around the tumour mass and was separated by blunt dissection. The tumor mass was removed taking care of surgical haemostasis and the skin was closed with 5-0 PDS in an intradermal pattern. Post-operatively Amoxycillin and clavulanic acid @ 20 mg/kg BW, q12h, PO for 5 days, Tramadol @ 4 mg/kg BW, q12h for 4 days were given. Recovery from surgery and anesthesia was uneventful. The excised mass was fixed in 10% neutral buffered formalin for histopathological study.

Result and Discussion

Grossly the excised tumor mass was of soft texture, single, rounded structure of 6x4x3 cm³ with epithelial excoriation. Histopathology revealed tumourous tissue consisted of large quantity of vacuolated amorphous intercellular substance. Neoplastic cells showed polymorphic changes with cytoplasmic processes (Fig.2).

In many of these cells the nucleus was displaced to the periphery and compressed by a single lipid droplet. Other cells contained a large lipid droplet and one to multiple more centrally located round nuclei. The amorphous intercellular substance contained acid glycoproteins. Infiltration of tumourous tissue into the surrounding tissues was well apparent. The myxoid variant is an uncommon variant of liposarcoma and is described as multilobular and non encapsulated with poorly defined mass margins (Messick and Radin, 1989; Kwon et al., 2007). This subtype is usually composed of a mixture of lipocytes with a single large and clear cytoplasmic lipid vacuole compressing the nuclei; lipoblasts appear as scattered spindle and stellate cells interspersed in a myxoid background with small number of collagen fibrils (Messick and Radin, 1989)^. Surgical removal is considered as the gold standard in treatment of subcutaneous liposarcomas (Sara et al.,2013). In the present study surgical correction was found successful and the animal was found comfortable in feeding and wandering. There was no report of any reoccurrence and spread of the neoplasm in the same animal after eleven months of surgery.

Acknowledgement

The authors are thankful to the Scientist, Dr. S.B.Senapati, Institute of Life Science for carrying out the histopathology section.

References

1. Baez JL, Hendrick MJ, Shofer FS, Goldkamp C and Sorenmo KU. 2004. Liposarcomas in dogs: 56 cases (1989–2000). J Am Vet Med Assoc. 224: 887–891.
2. Dei Tos AP. 2014. Liposarcomas: diagnostic pitfalls and new insights. Histopathology. 64: 38–52.
3. Ediger RD and Kovatch RM. 1976. Spontaneous tumors in the Dunkin- Hartley guinea pig. Journal of National Cancer Institute. 56: 293–294.
4. Flecknell P. 2002. Guinea pigs. In: Mannual of Exotic Pets, Eds A Meredith, S. Redrobe. BSAVA Publication, UK. 4:70–88.
5. Goldschmidt MH and Hendrick MJ. 2002. Tumors of the skin and soft tissues. In: Meuten DJ, ed. Tumors in Domestic Animals. Ames, IA: Iowa State University Press. 4: 119–198.
6. Greenacre CB. 2004. Spontaneous tumors of small mammals. Vet Clinics of North America Exotic Animal Practice. 7: 627–651.
7. Jelinek F. 2003. Spontaneous tumours in Guinea pigs. Acta Vet. Brno. 72: 221-228.
8. Kanfer S and Reavill DR. 2013. Cutaneous neoplasia in Ferrets, Rabbits, and Guinea Pigs. Vet Clinical Exotic Animal. 16: 579-598.
9. Kitchen DN, Carlton WW and Bickford AA. 1975. A report of fourteen spontaneous tumors of the guinea pig. Laboratory Animal Science Journal. 25: 92–102.
10. Kwon HJ, Park MS, Kim DY, Cho DY, Yoon BI, Shin NS and Kim DY. 2007. Round cell variant of myxoid liposarcoma in a Japanese Macaque (Macaca fuscata). Vet Pathology. 44: 229–232.
11. Messick JB and Radin MJ. 1989. Cytologic, histologic, and ultrastructural characteristics of a canine myxoid liposarcoma. Veterinary Pathololgy. 26: 520–522.
12. Sara G, David E, Jordan F and Smith DA. 2013. Diagnosis and successful surgical treatment of an unusual inguinal liposarcoma in a pet ferret (Mustela putorius furo).Canadian Veterinary Journal. 54: 739–742.