Eyelid, Conjunctival and Peri-ocular Tumors

 These notes are provided to help you understand the diagnosis or possible diagnosis of cancer in your pet. For general information on cancer in pets ask for our handout "What is Cancer". Your veterinarian may suggest certain tests to help confirm or eliminate diagnosis, and to help assess treatment options and likely outcomes. Because individual situations and responses vary, and because cancers often behave unpredictably, science can only give us a guide. However, information and understanding about tumors and their treatment in animals is improving all the time.

We understand that this can be a very worrying time. If you have any questions please do not hesitate to ask us.

What are these tumors?

A "tumor" is a lump. Most, but not all, are cancerous. A large number of different types of tumor, with a bewildering array of names, but often of confusingly similar appearance, can occur in association with the tissues around the eye.

Tumors that occur on the haired eyelids are similar to those arising elsewhere in the skin. They include cysts, overgrowths (hyperplasias), benign (non-spreading) and occasionally malignant (spreading) cancers. Tumors may originate from the sebaceous (Meibomian) glands, sweat glands (glands of Moll) and from cells such as those which produce melanin pigment, mast cells and the covering epithelium. Many Meibomian tumors rupture to cause nodules of inflammation called chalazions.

The conjunctiva is the lining tissue that covers the globe of the eye (the eyeball) and lines the eyelids and the third eyelid. Some tumors that occur on the third eyelid and conjunctiva are similar to those elsewhere, for example those arising from the covering epithelium (particularly squamous cell carcinomas), melanin producing cells (melanomas), blood vessels and lymphoid tissue (lymphosarcomas or lymphomas). Tumors specific for this site include cysts and malignant tumors of the glands and an inflammatory condition called 'nodular granulomatous episcleritis' (nodular fasciitis).

Tumors of the adjacent orbital tissues (peri-ocular tumors) include those originating in the tear (lachrymal) glands and connective tissue, including that of the brain envelope (meninges).

What do we know about the cause?

The reason why a particular pet may develop this, or any cancer, is not straightforward. Cancer is often the culmination of a series of circumstances that come together for the unfortunate individual.

"Squamous cell carcinoma and blood vessel tumors are related to exposure to sunlight."

Squamous cell carcinoma and blood vessel tumors are related to exposure to sunlight. Papillomas (warts) in this site are rarely of viral origin. As some develop over other tumors, they may be the result of trauma.

"There is a genetic predisposition in some breeds of dog for Meibomian gland tumors."

We do not know precisely what causes the other tumors, but there is a genetic predisposition in some breeds of dog for Meibomian gland tumors. Chalazion is the result of rupture of an inflamed or cancerous Meibomian gland. Dermoids or choristomas and some conjunctival inclusion cysts are errors in development, with epithelium or skin tissue that has become trapped in the wrong site. Most conjunctival inclusion cysts are the result of mechanical implantation of surface epithelium (skin) because of surgical incision or accidental penetrating injuries.

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