A 3.2-year-old male pet Guinea pig (Cavia porcellus) was presented with a rapidly growing mass in the right cervical region behind the ear. Following a complete clinical evaluation, the unusual mass was surgically removed. Based on the histopathological features, the tumour mass was diagnosed as a subcutaneous liposarcoma. The Guinea pig was recovered well and no post-operative complications were observed over one year follow-up period.
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.
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.
The authors are thankful to the Scientist, Dr. S.B.Senapati, Institute of Life Science for carrying out the histopathology section.