Squamous cell carcinoma (SCC) is the most common type of eyelid tumor in the cat. The prevalence of SCC is higher for white cats, especially for older, outdoor cats with prolonged sun exposure. Local invasion of eyelid tissues by this tumor can be extensive, and metastasis, which is spread of the tumor to distant body sites, occurs in advanced stages of the disease. Multiple local treatment options are available when SCC is diagnosed in the early stages of disease. 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 for several months before either decreasing in size or returning to the more active form.
Lymphosarcoma and mast cell tumors (mastocytomas) are the next most common tumors that affect the feline eyelid. Medical therapy is available for both tumor types and may induce regression of the tumor.
Other forms of malignant tumors that occur in the eyelids of cats include basal cell carcinoma, fibrosarcoma, neurofibrosarcoma and melanoma.
The most important aspect of treating eyelid tumors is 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 plan for treating the cat.
Fungal granuloma. A systemic fungal infection called histoplasmosis may cause the development of small nodules along the eyelid margin. They can appear very similar to eyelid tumors.
Fungal blepharitis. Ringworm can causes inflammation of the eyelids, but usually causes hairless and crusty lesions rather than the development of nodules or masses.
Bacterial blepharitis. Inflammation of the eyelids is often caused by Staphylococcus and Streptococcus spp. of bacteria. These bacteria infect the meibomian glands located along the eyelid margin. Abscesses in these glands may form nodules along the eyelid margin. Chronic infections can have a similar appearance to chalazia of the eyelids.
Parasitic blepharitis. Mites such as demodex, notedric, and sarcoptic mange can involve the eyelids in cats. In young cats, the infection is commonly isolated to the face and eyelids. Typically these mites cause crusty, hairless lesions on the eyelids rather than nodule formation.
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.
Eosinophilic blepharitis. This is a rare form of inflammation of the eyelid in which small nodules form that are filled with eosinophils, which are a type of white blood cell. The cause of this condition is unknown in the cat.