Cysts

What is a cyst?

Cysts are hollow spaces within tissues that contain either a liquid or a solidified material; the contents may be a natural bodily secretion or an abnormal breakdown product. Occasionally cysts will develop within a cancerous lump, but only non-cancerous cysts will be considered here. Non-cancerous cysts include true cysts, follicular cysts, dermoid cysts and false cysts.

"True cysts have a secretory lining." 

True cysts have a secretory lining (a membrane that lines its inner surface and produces secretions). Often, true cysts form in glands as a result of blocked ducts. Complete removal or destruction of the lining may be necessary to prevent recurrence of a true cyst. In animals, a common type of true cyst is the one that forms in sweat glands.

 Follicular cysts are dilated hair follicles containing fluid or dark-colored cheesy material. They are predisposed to developing a secondary infection (pyoderma). Follicular cysts are also known as epidermoid cysts. Dilated pores and comedones (blackheads) are related to follicular cysts but have wide openings on the surface.

Sebaceous cysts fill with sebum and develop in and around sebaceous glands that are associated with hair follicles. These common cysts are also prone to secondary infections. 

Dermoid cysts are complex congenital cysts.

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. 

What do we know about the cause?

Comedones and follicular cysts are secondary problems that occur because of local injury, blockage of the opening of the pore or the follicle, mechanical or "pressure point" damage, sun radiation damage or follicular inactivity (e.g. Mexican hairless and Chinese crested dogs). Some follow treatment with drugs such as glucocorticoids ("steroids"). Others may form due to a lack of oily secretions in diseases such as sebaceous adenitis. There is an inherited predisposition to cysts as in breeds such as Schnauzers and Yorkshire terriers.

"There is an inherited predisposition to cysts as in breeds such as Schnauzers and Yorkshire terriers."

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. Boxers have a predilection for these cysts but they are also seen in other breeds.

Dermoid cysts along the midline develop during embryonic growth and occur because the epidermis fails to close properly; the result of this developmental abnormality is that isolated islands of the outer epidermal tissue become trapped within the deeper tissue. Dermoid cysts occur most frequently in the Rhodesian Ridgeback dog.

False cysts due to hemorrhage or trauma are common on the flank. A few are idiosyncratic reactions to injections.

Why has my pet developed a cyst?

In some species, particularly the dog, genetic factors favor the formation or persistence of follicular cysts in some species. As noted, above, some breeds have a predilection for certain types of cysts, as noted above.

Are these common tumors? 

Follicular and sebaceous cysts are common in dogs but unusual in cats, with the exception of "feline acne" on the chin and "stud tail" on the upper tail. Dermoid cysts are rare. Cysts due to trauma are moderately common in dogs. Sweat gland cysts are common in dogs and cats, particularly on the eyelids.

How will these affect my pet?

Follicular and dermoid cysts are unsightly and may fill with an unpleasant, soft cheesy material (keratin). This material may become secondarily infected with bacteria or yeast, producing a foul smell.

Sweat gland cysts are nodules or vesicles, approximately 1/8 of an inch in diameter. They are usually slightly translucent and blue or dark in color; often the surrounding hair will be lost. They may be multiple, particularly around the eyes and in the ears. Multiple tumors are sometimes called "apocrine cystadenomatosis".

Cysts filled with blood often look dark. With the naked eye they may be difficult to distinguish from cancers.

How are these diagnosed?

"...accurate diagnosis relies upon microscopic examination of tissue."

Clinically, your veterinarian may suspect that a tumor is a cyst, but accurate diagnosis relies upon microscopic examination of tissue. Cytology, the microscopic examination of individual cells, is not diagnostic for cysts. Histopathology, the microscopic evaluation of tissues, is necessary for the accurate diagnosis of these benign tumors. Your veterinarian will either take a biopsy of the tissue or remove the entire lump and submit the tissue to a specialized laboratory for evaluation by a veterinary pathologist. If the sample is the complete lump, the pathologist will be able to assess whether the entire mass was successfully removed. Histopathology may also help determine the cause of the cyst, predict the behavior of the tumor (prognosis) and rule out other forms of cancer. 

What types of treatment are available?

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 can be used. Other treatments may be needed to address the primary causes.

Can this problem disappear without treatment?

If the underlying cause is removed, some cysts will decrease in size or disappear. Cysts due to trauma can resolve in time.

How can I help my pet?

Preventing your pet from rubbing, scratching, licking or biting cysts will reduce inflammation, infection and bleeding. If the cyst becomes ulcerated, 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 ask.

How will I know if the cyst has been permanently cured?

"In many cases, excision leads to a complete cure."

This depends on the cause and whether this is a single or multiple problem. In many cases, excision leads to a complete cure. If your pet develops recurrent or multiple cysts, it is necessary to determine the underlying cause by means of diagnostic investigation. In cases where the cysts are a genetic characteristic (e.g. Mexican hairless dogs), there will always be a tendency to develop further cysts.