What types of tumors affect the eyelids, conjunctiva, and periocular tissues?
The eyelids and surrounding tissues (e.g., conjunctiva) are considered extensions of the skin. Therefore, the types of tumors that can develop in the skin can also develop in these tissues.
In general, tumors develop from the abnormal growth and unregulated replication of cells that make up body tissues. The eyelids and surrounding tissues are made up of many kinds of cells.
The edges of the eyelids, for example, have tiny glands, called meibomian glands, containing cells that produce secretions to lubricate the eye. If these cells over-multiply, they develop into benign tumors called meibomian gland adenomas (non-cancerous) or meibomian gland adenocarcinomas, a less common malignant tumor.
The edges of the eyelids also have melanocytes, cells that produce pigment. If these cells over-multiply, they cause tumors called melanomas. And when skin (squamous) cells over-multiply, they cause squamous cell carcinomas (SCC). Similarly, the conjunctiva contains lymphoid tissue cells, and if these over-multiply, they cause lymphomas or mast cell tumors. Other types of tumors can affect the eyelids, conjunctiva, and periocular tissues, but the ones listed above are the most diagnosed tumors.
What causes these types of tumors?
Why a pet may develop these types of tumors, or any cancer, is not straightforward. Very few cancers have a single known cause. Most seem to be caused by a complex mix of risk factors, some environmental and some genetic or hereditary.
"Very few cancers have a single known cause."
Squamous cell carcinoma has been attributed to exposure to ultraviolet rays/sunlight. Breeds with light-colored haircoats and breeds that are hairless are especially at risk. Otherwise, the causes of these types of tumors are not clear.
What are the signs of these types of tumors?
The signs of these tumors can vary, depending on the type of tumor, where it grows, and whether it is benign or malignant. Benign tumors tend to be polyp- or cauliflower-like in appearance. They may grow on the inside or outside the eyelids. If they come into contact with the clear surface of the eye (the cornea), they can cause painful corneal scratches that can lead to corneal ulcers.
They can also cause general irritation and inflammation, leading to eye infections. Malignant tumors tend to be irregular or nodular in appearance. They may ulcerate (break open) and bleed, and become inflamed, infected, and painful.
Other signs that your pet may have a tumor of the eyelid, conjunctiva, or periocular tissue include:
- squinting
- eye discharge
- protrusion of the third eyelid
- roughening/thickening of the conjunctiva
- repeated pawing or rubbing the eye
How are these types of tumors diagnosed?
Your veterinarian may use a procedure called fine needle aspiration (FNA) to make a diagnosis. FNA involves taking a small needle with a syringe and suctioning a sample of cells directly from the tumor and placing them on a microscope slide. A veterinary pathologist then examines the slide under a microscope.
In some cases, when the results from FNA are not entirely clear or when surgical removal of the tumor is otherwise indicated, the entire tumor is removed and assessed to get a definitive diagnosis. The tumor is examined by a veterinary pathologist under the microscope. This is called histopathology. Histopathology helps to make a diagnosis and can also indicate how the tumor is likely to behave.
How do these types of tumors typically progress?
Depending on the type of tumor, its location, and whether it is benign or malignant, these types of tumors may be slow- or fast-growing and may or may not metastasize (spread elsewhere in the body). Tumors in the conjunctiva are likely to grow more quickly than tumors of the eyelids and tend to invade the surrounding tissue and spread to other sites.
Benign tumors typically grow slowly and locally. Malignant tumors can grow more quickly and growth depends on the type of tumor – and even the type of pet. For example, in dogs, squamous cell carcinomas do not tend to metastasize, while in cats, they do. Malignant tumors can spread locally, extending into the underlying tissues, or to other areas of the body, including the nearby lymph nodes, lungs, and bone.
Depending on the type of tumor (benign or malignant), staging is sometimes recommended (searching for potential spread to other locations in the body). Staging may include X-rays (radiographs) of the lungs, bloodwork, urinalysis, and possibly an abdominal ultrasound or CT scan. If the lymph nodes appear to be affected, they may be sampled by FNA to determine if spread has occurred.
What are the treatments for these types of tumors?
The treatments for these types of tumors vary with the type of tumor, its location, and its size, and may include surgical removal, radiation therapy, and freezing (cryotherapy). In some cases, medical therapy (antibiotics, anti-inflammatories) may be indicated to control pain and clear secondary bacterial infections.
"Prompt removal helps to prevent secondary problems and, in cases of malignancy, reduces the chance for metastasis."
These tumors are usually surgically removed because they tend to be disfiguring, bothersome, sometimes painful, and may predispose the pet to secondary problems such as eye infections and corneal ulcers. Prompt removal helps to prevent secondary problems and, in cases of malignancy, reduces the chance for metastasis. Tumors of the conjunctiva typically require more extensive surgery to remove than do tumors of the eyelids. After surgery, regular rechecks are advisable, as conjunctival tumors may regrow.
In many cases, these tumors may be removed by your veterinarian; however, a referral to an ophthalmologist may be recommended. Surgery on the tissues around the eye may cause side effects, including: irritation of the cornea from exposed suture, entropion (rolling in of the eyelid), incision breakdown, abnormal eyelash direction causing corneal irritation (trichiasis), reduced tear production (dry eye), and inability to fully close the eye, causing exposure irritation.
What is the prognosis?
The prognosis for tumors of the eyelids, conjunctiva, and periocular tissues depends on the type of cancer, its location, and whether it is benign or malignant. It also depends on how early the tumor is identified and treated. As with all cancers, early intervention offers the best prognosis.
