Trichoepithelioma is a rare cutaneous tumor that originates from hair follicle matrix or inner root sheet. It is a benign, well demarcated subcutaneous tumor composed of multiple horn cysts¹. The occurrence of the tumour is documented in dogs although its clinical features are not well described. It is generally suspected grossly on the basis of ulcerative and large plaque-like appearance with rough edges². Though it is regarded as a benign tumor, it grows rapidly in the dermis and subcutaneous tissue and can also metastasise into regional lymph nodes and lungs. The affected skin appears “glassy” complicated often with ulcers. Its predilection sites are the dorsal trunk and the neck, thoracic region and tail¹. In the current investigation, pathology of anencapsulatedtumor mass located in the let lateral digit of right forelimb diagnosed as trichoepithelioma is described.

A four year old female Golden Retriever was presented to Department of Veterinary Clinical Complex, Veterinary College, Hassan with a history of growing mass on the let lateral digit of right forelimb. On physical examination, the mass was found to be soft in consistency. On radiography, by AP (Anterioposterior) and ML (mediolateral) view, it revealed soft tissue swelling at 5^th digit involving all the 3 phalanges. The periosteal reaction was noticed in 1^st to 3^rd phalanx of 5^th digit. The mass was surgically excised and representative tissue samplesfrom the mass were collected and fixed in 10% NBF (Neutral Buffered formalin) for histopathological examination. The sample was processed by routine paraffin embedding technique, sectioned at approximately five micron thickness and stained with routine Haematoxylin and Eosin method³.

In the present case, an encapsulated tumor mass located in let lateral digit of right forelimb was recorded in a 4- year- old female Golden Retriever. This tumour is considered to be an infrequent one among general dog population and known to occur between 1 and 15 years of age. Its predilection sites are the dorsal trunk and the neck, thoracic region and tail¹. In dogs, most affected are the animals of late middle age. Although there is no defined sex predilection, a breed predisposition exists in Basset Hounds, Bull Mastiffs, Irish Setters, Poodles, English Spaniels, and Golden Retrievers with male/female showing higher susceptibility⁴.

The mass weighed 115gram and with highest diameter of 6 cm and was located within the dermis deeply extending into the subcutaneous tissue mass.(Fig 1) The cut surface was hard with multiple greyish white foci.

On histopathological examination, the mass showed several cysts of variable size with trichogenetic differentiation. Cysts wall were lined by thickened basal lamina cells. The cells were arranged in a palisade arrangement near the periphery along with shadow cells in the cystic lumen⁵ (Fig 2). Few areas of necrosis and inflammation were also observed.

Trichoepithelioma is histologically similar to basal cell carcinoma, and although benign, there is a risk of malignant transformation. Many different methods have been proposed for trichoepithelioma management, low incidence and lack of enough evidences make it a controversial domain in human medicine. Surgical excision is considered as the treatment of choice^1,5. Metastasis is not common, possible sites are the regional lymph nodes and the lungs.

In the present case, follow up was taken upto six months post-surgery and there was no history of any recurrence.

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