Cats have 2 anal sacs located on either side of the anus at the 4 and 8 o’clock positions.
The sacs are small pockets beneath the skin that are lined by glands that produce foul-smelling (to us!) secretions. This scent is stored in the sac, but it’s milked out through narrow ducts each time the cat moves her bowel.
This marks the feces — a “calling card” of sorts — and helps other cats know who is in the area. It’s almost the same idea as a skunk producing scent to warn predators, only cats use smell in a more sociable way to let one another know who’s around.
Sometimes the secretion dries out in the ducts, forming a plug like a cork in a bottle. This can make the sacs uncomfortably full, which leads to itchiness and discomfort.
Sometimes the bacteria trapped in the secretion leads to infection, in which case an anal sac abscess can form. Infections, however, are much rarer in cats’ anal sacs than in those of dogs.
A cat with a blocked anal sac experiences discomfort around her anus. She may scoot, trying to relieve the blockage, or bite and lick at her rear. Sometimes the cat becomes obsessed and licks so much that she damages the fur and causes bald patches around the tail base.
Anal sac infection is painful. Even a placid cat may be unhappy if you try to see what’s wrong. If an abscess forms, swelling may be visible beside the anal ring.
If the pressure builds up within the sac, the abscess may rupture, and then you see a sore, ulcerated, inflamed area beside the anus that discharges bloodstained pus.
The anal sacs are designed to empty with the normal muscular contractions of the bowel. Soft feces do not need as much muscular effort to pass, and so the sacs can fail to empty fully.
A classic scenario is a cat with a tummy upset that develops impacted anal sacs 1 week later. This is because secretion built up in the gland, then dried out and caused a blockage.
Bacteria in the anal sac are usually flushed out each time the sac empties.
An impacted sac also implies that bacteria are stuck inside the sac, and this can lead to infection and an eventual abscess.
Diagnosis is nothing more sophisticated than your veterinarian getting a good look at the cat’s nether regions.
Digital exploration of the rectum (ahem — putting a finger up the cat’s bottom) enables the vet to feel the full, hard sacs. To empty them, she then applies moderate pressure until the contents squeeze out — like toothpaste from a tube.
Relieving impaction can usually be done in the clinic by gently squeezing the sacs. If the cat is sore, a brief anesthetic is a kind remedy.
If the secretion is infected, your vet may suggest culturing it to find the most suitable antibiotic to kill the bugs. Pain relief, usually a non-steroidal anti-inflammatory such as meloxicam, is prescribed to ease discomfort until the antibiotic kicks in.
A good, firm bowel movement is the best preventive measure against anal sac impaction. Also, keeping your cat at a healthy weight can help, because overweight animals have the cat equivalent of a weak pelvic floor, which makes it more difficult to empty the anal sacs.
It is unusual for a cat to have regular anal sac problems and even rarer to have the anal sacs surgically removed. This is a technically demanding procedure, and carries a risk of permanent fecal incontinence after surgery.
- Small Animal Internal Medicine. Nelson & Couto. Publisher: Mosby. 5th edition.
This pet health content was written by a veterinarian, Dr. Pippa Elliott, BVMS, MRCVS. It was last reviewed Oct. 1, 2015.