What is a cyst?
True cysts are abnormal pockets in tissue that are filled with either liquid or solidified material. They have a membrane that lines the inner surface and produces secretions, including natural bodily secretions (e.g., sebum — the oily, waxy substance secreted by the sebaceous glands) and contains abnormal breakdown products like dead cells or keratin. There are several types of true cysts, including follicular cysts, apocrine cysts, sebaceous cysts, dermoid cysts, and false cysts.
Follicular Cysts
Follicular cysts (also known as epidermoid cysts) are sacs that form in hair follicles and contain fluid or dark-colored cheesy material. They are prone to becoming infected (pyoderma). Dilated pores and blackheads (comedones) are related to follicular cysts but have wider than usual openings on the surface of the skin. Follicular cysts are common in dogs but unusual in cats, except for severe cases of feline chin acne.
Follicular cysts and comedones are caused by injury to the hair follicle, blockage of the opening of the pore or the follicle, mechanical damage, sun damage (UV damage), or inactivity of the hair follicles in hairless breeds (e.g., Mexican hairless dog and Chinese crested dog). Comedones on the sternum and other pressure points are common in dogs with thin coats and little body fat.
Multiple and recurrent follicular cysts may develop on the heads of young dogs. Certain breeds have a genetic predisposition for follicular cysts (e.g., Boxers, Shih Tzus, Schnauzers, and Basset hounds), but they can occur in any breed. Comedones can develop due to exposure to drugs such as glucocorticoids, hypothyroidism (underactive thyroid gland), Cushing’s disease, or secondary to allergies.
Apocrine Cysts
Apocrine cysts form from the apocrine skin sweat glands and contain clear fluid. They are more commonly found on the head as raised, hairless, round lumps in the skin but may be found throughout the body. They are uncommon in cats and dogs and their cause has not been determined.
Sebaceous Cysts
Sebaceous cysts fill with sebum and develop in and around sebaceous glands that are associated with hair follicles. These cysts are also prone to secondary bacterial infection. Sebaceous cysts are common in dogs but unusual in cats.
Dermoid Cysts
Dermoid cysts are complex congenital cysts that form long before birth. They are rare in dogs and cats. Dermoid cysts form along the midline of the back and develop during embryonic growth when the epidermis (outer layer of the skin) fails to close properly. These cysts are seen most frequently in Rhodesian ridgebacks and Kerry blue terriers.
False Cysts
As the name suggests, false cysts are not actually cysts. They are fluid-filled, like true cysts, but they do not contain a secretory lining, as true cysts do. False cysts may be formed by hemorrhage or trauma that leads to tissue death; the fluid inside develops when the dead tissue liquefies. False cysts that develop due to trauma are common in dogs and often occur on the flank (the side of the body between the ribs and the hip). Sometimes false cysts occur because of reactions to injections.
What are the clinical signs of cysts?
True cysts often appear as nodules or vesicles. They are slightly translucent and blue or dark in color and may cause the surrounding hair to fall out. They are filled with fluid produced by the glands and may ooze a yellow substance. There may be many of them, particularly around the eyes.
Follicular cysts appear as single, round nodules (hard tissue masses) on or under the skin. They may be bluish and contain thick, yellowish or grey cheesy material (keratin). This material may become secondarily infected with bacteria or yeast and produce a foul smell. Follicular cysts usually occur on the neck, head, feet, and trunk but can appear anywhere. They may rupture within the skin, which creates secondary inflammation and pain.
A sebaceous cyst appears as a single, raised bump that may seem white or slightly blue in color. If it bursts, it will ooze a grayish-white, brownish, or cottage-cheese-like discharge. These cysts usually develop on the head, neck, torso, or upper legs.
False cysts (those filled with blood) often look dark.
How are cysts diagnosed?
Your veterinarian may suspect that your pet’s condition is a cyst, but they must test to know for sure. They can take a sample of the cyst’s contents with a needle and analyze it microscopically (cytology) to determine what type of cyst it may be, but a definitive diagnosis relies on biopsy and microscopic examination of tissue.
A biopsy is a surgical excision of the cyst or a piece of it. The biopsy is examined by a veterinary pathologist under the microscope in a process called histopathology. Histopathology helps make a diagnosis and allows the pathologist to assess whether the entire cyst was successfully removed. Histopathology may also help determine the cause of the cyst and rule out other diseases, including cancer.
What treatments are available for cysts?
- The most common treatment for cysts is surgical removal (excision). Depending on the cause, excision often leads to a complete cure. Complete removal or destruction of the lining may be necessary to prevent recurrence of a true cyst.
- Laser treatment is useful for true cysts.
- Cysts due to trauma may resolve over time.
- Medical (topical) treatment of multiple small follicular cysts may be helpful.
- In cases where the cysts are a characteristic of the breed (e.g., with hairless breeds), there will always be a tendency for further cysts to develop.
If your pet develops recurrent or multiple cysts, a diagnostic investigation may be necessary to determine the underlying cause, and other treatments may be needed to address the primary causes. If the underlying cause is removed, some cysts will shrink or disappear.
Is there any special care that I should provide for my pet?
It is important to prevent your pet from rubbing, scratching, licking, or biting the cysts, all of which can cause inflammation, infection, and bleeding. If the cyst ulcerates (opens), it will need to be kept clean, and your pet may require a protective bandage over the area until it heals. A head collar (Elizabethan collar) may be recommended to prevent licking.
After surgery, the incision site needs to be kept clean and dry, and your pet should not be allowed to interfere with the site. Report any significant swelling, bleeding, or loss of sutures to your veterinarian. If you require additional advice on postsurgical care, contact your veterinarian.
