What is a cyst?
Cysts are hollow spaces within tissues that contain either liquid or solidified materials; the contents may be made up of natural bodily secretions (e.g., sebum – the oily waxy substance secreted by the sebaceous glands – or sweat) or abnormal breakdown products such as dead cells or keratin. There are several types of cysts, including true cysts, follicular cysts, sebaceous cysts, dermoid cysts, and false cysts.
True cysts have a secretory lining (a membrane that lines its inner surface and produces secretions). True cysts often form in glands (such as sweat glands) as a result of blocked ducts. Complete removal or destruction of the lining may be necessary to prevent recurrence of a true cyst. True cysts, especially those that form in the sweat gland, are common in dogs and cats, particularly on the eyelids.
Follicular cysts are dilated hair follicles containing fluid or dark-colored cheesy material. They are prone to becoming infected (pyoderma). Follicular cysts are also known as epidermoid cysts. Dilated pores and comedones (blackheads) 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, with the exception of ‘feline acne’ on the chin.
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, with the exception of ‘stud tail’ on the upper side of the tail.
Dermoid cysts are complex congenital cysts that form long before birth. Dermoid cysts are rare.
False cysts are fluid-filled structures that do not contain a secretory lining. False cysts may be formed by hemorrhage or trauma that leads to tissue death; the fluid within them develops when the dead tissue liquefies. False cysts that develop due to trauma are fairly common in dogs.
What causes cysts to develop?
Comedones and follicular cysts are a consequence of local injury to the follicle(s), blockage of the opening of the pore or the follicle, mechanical or ’pressure point’ 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 not uncommon in dogs with thin coats and little body fat. Multiple and recurrent follicular cysts may develop on the heads of young dogs. Boxer Dogs, Shih Tzus, Schnauzers, and Basset Hounds have a genetic predisposition for follicular cysts, but they can occur in other breeds as well. Comedomes can develop secondary to exposure to drugs such as glucocorticoids (steroids).
Dermoid cysts along the midline of the back develop during embryonic growth. They occur because 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 due to hemorrhage or trauma are common on the flank (the side of the body between the ribs and the hip). Sometimes false cysts occur as a result of reactions to injections.
What are the clinical signs of cysts?
Follicular cysts appear as single round nodules (hard tissue masses) on or underneath the skin. They may be bluish in color and contain thick, yellowish or grey cheesy material (keratin). This material may become secondarily infected with bacteria or yeast and produce a foul smell. They usually occur on the neck, head, or trunk but can appear anywhere.
"Cysts are hollow spaces within tissues that contain either liquid or solidified materials"
Sweat gland (or 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 sweat glands and may ooze a yellow substance. There may be many of them, particularly around the eyes and in the ears.
Sebaceous cysts appear 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 a definitive diagnosis relies on biopsy and microscopic examination of tissue. A biopsy is a surgical excision of a piece of, or the entire cyst. The biopsy is examined by a veterinary pathologist under the microscope. This is called histopathology. Histopathology is not only helpful to make a diagnosis but also 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 types of treatments are available for cysts?
The most common treatment for cysts is surgical removal. If available, laser treatment is useful for sweat gland cysts. Medical (topical) treatment of multiple small follicular cysts may be helpful. Other treatments may be needed to address the primary (or underlying) causes.
If the underlying cause is removed, some cysts will shrink or disappear. Cysts due to trauma may resolve in time.
Depending on the cause, excision often leads to a complete cure. If your pet develops recurrent or multiple cysts, a diagnostic investigation may be necessary to determine the underlying cause. 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.
Is there any special care that I should provide to my pet?
It is important to prevent your pet from rubbing, scratching, licking, or biting the cyst(s), 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.
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 post-surgical care, please contact your veterinarian.