Meibomian Gland Adenoma in Dogs

What is a meibomian gland adenoma?

An adenoma is a benign tumor that starts in the epithelial tissue that lines a gland or glandular organ. “Benign” means that the tumor does not invade nearby tissues or spread to other parts of the body.

A meibomian gland adenoma is a tumor that arises from the epithelial tissue of the eyelid. These tumors start out quite small, as a bulge from one of the small ducts at the edge of the eyelid, and can expand into a full-thickness, nodular (bumpy) mass.

The meibomian glands help to form the tear film that keeps the eye moist and lubricated. A meibomian gland adenoma can grow to the point that it rubs against the cornea, causing pain and irritation.

These tumors can affect any breed but are most often found in middle-aged and older dogs, with an average age of 8 years. They are not uncommon in dogs in this age group. A meibomian gland adenoma is different from a stye. A stye is a painful swelling at the edge of the eyelid that forms when a meibomian gland becomes blocked. The swelling may become infected, causing pain and redness.

What are the signs of a meibomian gland adenoma?

Signs of a meibomian gland adenoma may include:

• A small bump or “pimple” arising from one of the tiny openings at the edge of the eyelid
• A bump on the inner surface of the eyelid that looks like a small, flattened head of cauliflower
• A bump at the edge of the eyelid that looks like a head of cauliflower, usually darker than surrounding tissue

What causes meibomian gland adenomas?

The exact cause of meibomian gland adenomas is unknown. These tumors are not caused by an infection, so they are not contagious to other animals. However, eyelid swellings can be caused by infection or other conditions, so any eyelid mass should be assessed by your veterinarian. Although some types of eyelid tumors can be triggered by exposure to sunlight, meibomian gland adenomas are not associated with sunlight exposure.

Are meibomian gland adenomas painful?

They can become painful if they grow to the point that they rub against the cornea. This may cause irritation similar to having a piece of grit or an eyelash in the eye.

Can my dog go blind from a meibomian gland adenoma?

A meibomian gland adenoma does not directly cause blindness. However, constant rubbing against the cornea may eventually cause an ulcer. If left untreated, the ulcer could cause permanent scarring and affect vision.

Are meibomian gland adenomas cancerous?

A meibomian gland adenoma is benign, not malignant. This means that it does not usually invade nearby tissues or metastasize (spread) to other parts of the body. However, other types of eyelid tumors, such as squamous cell carcinoma, can be malignant. For this reason, all eyelid masses should be assessed by your veterinarian.

How are meibomian gland adenomas diagnosed?

This type of tumor is generally suspected based on its appearance, but eyelid swelling can have several different causes. Your veterinarian will develop a diagnostic plan to determine what treatment is required. Preliminary testing may include cytology, which involves examining cells collected from the mass.

How are meibomian gland adenomas treated?

If a meibomian gland adenoma is rubbing against the eye or causing discomfort, surgical treatment may be recommended. In some cases, your veterinarian may recommend cryosurgery, which uses extreme cold to kill the tumor cells.  

More commonly, the mass is removed surgically under general anesthesia. This involves removing a V-shaped wedge of tissue that contains the tumor. The incision is then closed with stitches. Depending on the size of the incision, the eyelid may be slightly smaller after surgery, and the eye may appear slightly narrowed.

Following surgery, your dog will need to wear an Elizabethan collar (cone) to prevent scratching while the area heals. Pain medication, oral antibiotics, or medicated eye drops or ointment may also be prescribed. Your veterinarian will schedule a follow-up appointment to assess healing and possibly remove the stitches.

The removed tissue should be examined by a pathologist to confirm the diagnosis and make sure it is not a more serious form of eyelid tumor. This examination can also help determine whether the mass was completely removed or how likely it is to regrow.

What is the prognosis?

The prognosis is very good. Removal of the meibomian gland adenoma is considered curative. However, the tumor can grow back if not all the affected tissue is removed during surgery.

Treatment is more likely to be successful when the tumor is removed while it is small. Removing a smaller tumor allows the veterinarian to obtain good surgical margins (healthy tissue around the tumor) while leaving enough eyelid tissue to close the incision.