Dogs, cats and many other small mammals have a pair of anal sacs, also called anal glands, located just under the skin on both sides of the rectum. These glands are actually scent glands.
In the domesticated dog and cat they serve no particular purpose and can often become impacted or inflamed.
Location and function of the anal sacs
These small sacs are located at the 8 o’clock and 4 o’clock positions, slightly
below the rectum. Each sac is lined with many sebaceous and sweat glands. The sacs empty through a short, narrow duct to the surface near the inside edge of the rectum. Every time a stool is passed, it should put enough pressure on the anal sacs that some of the secretion is deposited on the surface of the stool.
The scent produced by the animal’s anal sac secretions are unique to that animal and acts as an identifier to other dogs and cats. That is why dogs and cats smell each other’s anal area when they meet.
The secretion from the anal sacs is a semi-oily to creamy, brownish fluid that has an offensive odour to humans.
Causes of anal sac problems
Anal sac impaction, infection and abscesses are a common problem in dogs, and occasionally in cats.
For unknown reasons, some dogs’ anal sacs produce a rather thick, semi-solid material that the sac is unable to secrete through the narrow duct. This causes the sacs to become impacted, causing discomfort. This can cause the secretion to continue building up inside the sac, causing it to swell and become uncomfortable/painful. If it remains impacted for a long enough period, it will become infected and continue to burst, forming an anal sac abscess.
When the anal sacs become impacted the dog, or cat, will drag its bottom along the ground (scooting), licking or chewing at the anal area excessively. This can cause injury to the area and cause bacteria to enter the anal sac through the ducts, leading to infection.
Tumours can also form inside the anal sac. The cause for tumour formation is often unknown, but may be the result of chronic irritation. Small tumours may cause no discomfort, while larger, more advanced tumours may cause swelling and/or cause problems with defecation.
Treatment of anal sac problems
When the anal sacs become impacted, a veterinarian must “express” them. This is done by applying pressure with the fingers, starting below the anal sac and then pushing up, emptying the sacs of all material. If signs of an infection is present, a course of antibiotics may be prescribed.
An anal sac abscess must be lanced and flushed, under anesthetic, by a 
veterinarian. The patient will also be sent home with medication. Using warm compression on the area often helps to relieve some of the pain and reduce the swelling. Secondary problems can sometimes occur with abscesses, causing scar tissue or other damage that may affect the nerves and muscles in the area.
If the anal sac impaction is recurrent, a diet change may be prescribed that will help bulk up the stool which puts more pressure on the sacs and, hopefully, leads to the sacs expressing themselves.
Only in extreme cases are anal sacs surgically removed. Even though it is a fairly simple procedure, complications such as fecal incontinence can occur.
Are some dogs/cats more prone to anal sac problems?
There is no age or sex predisposition to anal sac pathology. Some dogs may be born with narrower anal sac ducts or may have developed problems due to trauma to the anal area.
Anal sac impactions are often more common in small breed dogs.
If your pet is scooting his bottom on the ground, frequently licks or bites at his anal region or displays discomfort when defecating, it is advisable to have him checked by a veterinarian.
