Management of Equine Adnexal Squamous Cell Carcinoma

Introduction
Adnexal neoplasia presents a significant challenge to the ambulatory equine practitioner. Clinical decision making regarding space occupying lesions in the vicinity of the globe must take into account preservation of eyelid function, risks of corneal exposure if tear production or eyelid cover is compromised and the fact that the palpebral conjunctiva is confluent with the conjunctiva of the nictitans and the anterior scleral surface of the globe. Cases are often presented at an advanced stage, limiting surgical options. It is not uncommon for adnexal neoplasia to spread locally onto the surface of the globe, compromising vision. Tumours may also spread into the sinus or retrobulbar region and occasionally may invade the brain.

The most common neoplasm of the equine eye and ocular adnexa is squamous cell carcinoma (SCC). This neoplasia can occur on the surface of the cornea, on the conjunctiva, on the nictitans or on the eyelid. The appearance of SCC is variable; early lesions involving skin may be simple hyperaemic areas with small erosions or crusts. More advanced lesions range in appearance from papillomatous growths to cobblestone like plaques to erosive masses. Some corneal lesions have a smooth, fleshy appearance while others have a proliferative or ulcerative character. Biopsy is required for confirmation as other tumours and inflammatory conditions can resemble SCC lesions. Histopathology of the sample will document the differentiation characteristics of the neoplasm as well as determine the degree of tissue invasion in the sample. Squamous cell carcinoma has a low rate of metastasis to distant sites but is frequently locally invasive (Giuliano 2011). [...]