The vast majority of eyelid tumors in the dog are benign. Malignant tumors tend to grow more rapidly than benign tumors and local invasion of surrounding tissues can be more extensive.
Canine eyelid tumors most often originate from the glands located within the eyelid margin. Sebaceous gland (meibomian) adenoma, squamous papilloma and benign melanocytoma represent the most commonly diagnosed eyelid tumors in the dog. Other less common benign tumors include the fibroma and histiocytoma. Complete surgical removal is usually curative for these tumors.
Malignant tumors that occur in the eyelid of dogs include the basal cell carcinoma, mast cell tumor, lymphosarcoma, malignant melanoma, squamous cell carcinoma, sebaceous adenocarcinoma (rare) and fibrosarcoma (rare).
The most important aspects of treating eyelid tumors are to determine the specific tumor type and the degree of local invasiveness and/or spread to other parts of the body. These two factors are essential to determine the most appropriate therapy for each animal.
A few other eyelid conditions can mimic the symptoms similar to those observed with eyelid tumors. It is important to exclude these conditions before establishing a conclusive diagnosis. Hordeolum (stye). Styes represent bacterial infections or inflammation of the eyelid margin glands. They can appear as either a single abscess or multiple abscesses with swelling along the eyelid margins.
Chalazion. A chalazion is the retention and accumulation of material within one of the glands of the eyelid. Chalazia typically appear as smooth white, yellow or tan nodules along the inside rim of the eyelid margins. They may remain quiet and non-painful with little to no change in appearance, they may eventually decrease in size, or they may induce inflammation and increase in size.
Allergic blepharitis (inflammation of the eyelids). Ocular exposure to a contact allergen can result in a rapid onset of symptoms that include eyelid (conjunctival) swelling and redness. The eyelid condition may also be associated with a generalized allergic reaction of the body. This is most often seen after insect bites, drug reactions and as a post-vaccination reaction.
Autoimmune skin diseases. Certain autoimmune skin diseases can manifest as eyelid inflammation, swelling and ulceration. These include pemphigus foliaceus, pemphigus vulgaris, and pemphigus erythematosus. These diseases commonly affect the skin of the face, lips, nose pads, ears and eyelids.
Bacterial blepharitis. Inflammation of the eyelids is often caused by Staphylococcus and Streptococcus spp. of bacteria infecting the meibomian glands located within the eyelid margin. Abscesses form nodules along the eyelid margin. The infections can be long-standing and recurrent in nature. In puppies, this condition can be quite severe and cause considerable facial and eyelid swelling.
Parasitic blepharitis. Both demodectic and sarcoptic mange can involve the eyelids in dogs. In young dogs, the infection is commonly isolated to the face and eyelids. Typically these mites cause crusty, hairless lesions on the eyelids rather than nodule formation.
Mycotic (fungal) blepharitis. Ringworm can cause inflammation of the eyelids, but usually cause hairless and crusty lesions rather than the development of nodules or masses.
Cuterebra larvae. The Cuterebra fly may lay its eggs along the eyelid margin. After the eggs hatch, a large larval worm begins to grow under the skin and a slow growing mass may develop around it. The mass always has a small hole in the surface of the skin through which the larva breathes.
Granulomatous inflammation. Certain immune-mediated inflammations of the eyelids of dogs may form nodules that appear very similar to eyelid tumors. These include two rather unusual diseases: nodular granulomatous episcleritis and periadnexal multinodular granulomatous dermatitis. Both of these conditions may be accompanied by nodules in other locations, such as within the eye or skin.