Yarmouth Veterinary Center

75 Willow Street
Yarmouth , ME 04096





~ The anal sacs are part of the normal anatomy of dogs and cats.

~ They are two small pouches deep under the skin in between the muscle layers of the anal sphincter. They empty into the anus through small ducts, one for each sac, located at 4 o’clock and 8 o’clock of the anus.

~ The anal sacs normally vary in size from a small raisin to a very large grape.

~ They fill with a secretion secreted by the glands in the skin that lines the sacs. This secretion normally varies in consistency from thin liquid, to liquid with tiny chunks, to thick paste. (Sometimes anal sacs are referred to as anal glands, but this is a misnomer; the glands are in the skin that lines the sacs, the sacs are the pouches that hold the glands’ secretion.)

~ Anal sacs empty a bit at a time when the pet defecates. They may also empty quickly if the pet suddenly contracts its anal sphincter when it is startled, frightened, or excited. Sometimes they will empty when the pet is deeply sleeping.

~ How quickly or slowly normal anal sacs fill varies from pet to pet and, for any individual pet varies over time. Most dogs and cats with normal anal sacs never need them emptied. Please see the notes below about about risk factors and causes of anal sac problems.

~ The anal sacs serve no purpose for our pets; they may have been involved in scent marking for ancient dogs and cats.


~ Frequent filling requiring manual emptying

~ Impaction - obstructed anal sacs that are overly full

~ Abscess, either ruptured to the outside or not

~ Cancer, especially anal sac adenocarcinoma

~ Problems are more common in dogs than cats


~ The cause of a pet’s anal sac problems, including the problem of frequent filling with normal secretion, often cannot be diagnosed. Occasionally, however, we find one or more of the following factors:

~ Anal sacs that are located especially deep in the muscle layers of the anal sphincter, and/or that are exceptionally large.

~ Inactivity and decreased mobility due to other health problems that leads to decreased anal sphincter muscle tone.

~ Obesity: in our experience pets that have chronic problems with their anal sacs are often significantly overweight.

~ Changes in fecal consistency and volume with constipation or diarrhea

~ Allergic skin diseases: allergy in pets usually causes skin problems; one of these problems is increased secretions from the glands of the skin. If the glands of the skin that lines the anal sacs produce a larger than normal amount of secretion, the sacs will fill more quickly and more often, and to a greater size.

~ Non-anal sac tumors and other problems in the skin of the anus near the anal sac duct may obstruct the duct.


~ Dogs: licking at the anal area; cats: licking fur off the back half of the body

~ Scooting

~ Reluctance to sit

~ Foul odor from the pet’s anal area

~ Foul breath odor, from licking the anal area

~ Straining to defecate, bloody discharge


~ Diagnosis of anal sac problems is often straightforward, based on the pet’s history and physical exam.

~ It is important that we distinguish an anal sac problem from a non-anal sac problem that has the same symptoms, including these possibilities:

    ~ Inflammation and infection of the skin of the anus

    ~ Hernias in the anal region

    ~ Perianal fistulas

    ~ A large variety of dermatologic, nutritional, and intestinal problems

~ Depending on the particular anal sac problem, the pet’s general health status, and the treatment plan being considered, other diagnostic tests can be important:

    ~ Blood tests

    ~ Diagnostic imaging: x-rays, ultrasound, endoscopy

    ~ Tissue sampling: biopsy, cytology

    ~ Bacterial culture and sensitivity testing

    ~ Allergy testing


~ Expressing, or emptying anal sacs that are not impacted, obstructed, or otherwise diseased, is a relatively quick outpatient service that we provide. The YVC price for this service is $21 (this price may have changed since this article was written.)

~ Expressing impacted anal sacs often requires general anesthesia.

~ We can infuse inflamed or infected anal sacs with an antibiotic/anti-inflammatory lotion. This brief procedure sometimes requires sedation or anesthesia.

~ Anal sac abscesses are lanced, drained, and flushed and the pet is subsequently treated with antibiotics and anti-inflammatory medications.

~ A variation of anal sac trouble that we occasionally encounter is a severe inflammation, represented by a large, hard, painful swelling in the region of the sac, that has not yet turned into an abscess. Treatment with antibiotics and anti-inflammatory medicine will sometimes (but not always) resolve the problem before an abscess that requires drainage forms.


~ Anal sacs can be surgically removed. In our experience with this surgery at YVC the prognosis is very good for a complete resolution of the problem (except when the problem is cancer or perianal fistula).

~ Other than cancer, the most common reason our clients consider having the anal sacs removed is long-term, persistent problems that require regularly repeated medical therapy.

~ If there is an abscess and/or a lot of inflammation around the anal sac(s) we will sometimes treat medically until these problems are under control before surgery.

~ At YVC anal sac surgery is usually a day procedure; pets are admitted in the morning and discharged late in the afternoon. Infrequently but occasionally we will keep the pet hospitalized overnight.

~ We routinely remove both anal sacs, even if there is a problem in only one.

~ The YVC price for anal sac removal is $900 (this price may have changed slightly since this article was written). If the anal sacs are badly swollen, abscessed, or there is a tumor this price may not apply.

~ In our experience surgical complications are rare. Still, we believe it is very important for pet owners to be aware of the possible complications. They include:

    ~ Minor bleeding from the incisions that persists for a day or two after surgery

    ~ Scooting after surgery

    ~ Dehiscence - opening of the incision

    ~ Persistent draining site in the skin near the incision due to a remnant of anal sac

        that was accidentally not removed

    ~ Fecal incontinence


~ The most common tumor of the anal sacs

~ Common in dogs, rare in cats

~ Usually older dogs

~ Pets with ASA may have any of the symptoms of anal sac disease noted previously.

~ Hypercalcemia (persistently high blood levels of calcium) occurs in as in many as 50% of patients with anal sac adenocarcinoma. Hypercalcemia is a significant complication that often requires treatment separate from the treatment for the tumor itself; symptoms include:

    ~ increased thirst and urination

    ~ vomiting

    ~ lethargy

    ~ weakness

    ~ loss of appetite

~ In our experience, ASA are frequently found on routine physical exam or routine emptying of anal sacs

~ Metastasis occurs early; sites for metastasis include lymph nodes, liver, lung, and spleen; more than half of pets with ASA have metastasis at the time of diagnosis, so we believe it is very important to screen for it.

~ Other problems can have the same symptoms as ASA. In particular, inflammation and anal sac abscess can present as a large, hard, painful swelling in the region of the anal sac.

~ We use diagnostic tests to determine the likelihood that a mass in the region of an anal sac is is an ASA and not another problem, to search for evidence of metastasis and hypercalcemia, and to establish the pet’s general health status:

    ~ blood tests

    ~ x-ray chest and abdomen

    ~ ultrasound abdomen

    ~ cytology

    ~ biopsy - the only way to definitively confirm an anal sac mass is ASA

~ Surgery is the most worthwhile mode of treatment for ASA.

~ Most ASA can be surgically removed, but some cannot. This cannot be determined without attempting the procedure, so there is an exploratory aspect to surgery to remove an anal sac tumor.

~ The details of surgery to remove an anal sac tumor are similar to the details of anal sac surgery described previously. The differences are that the surgery is, to some lesser or greater degree, more complex, and thus the risk of complications is somewhat higher.

~ There are no studies that we are aware of that address whether or not dogs that have ASA in one sac eventually develop one in the other sac, but we have had this happen to more than one patient. We now will routinely remove the anal sac with the tumor in it and the other anal sac when it is reasonable to do so (sometimes the tumors are very large and difficult to remove; in those cases we will usually remove only the affected anal sac.

~ Surgery to remove an anal sac tumor relieves pain and other tumor-related symptoms, and also often relieves the symptoms of hypercalcemia, even when metastasis is detected on pre-surgical testing.

~ For tumors that cannot be completely removed radiation therapy is the best medical option. At the time this article is written, the closest veterinary specialty practices offering radiation therapy are in New Hampshire and Massachusetts.

~ Chemotherapy might help but, in our opinion and experience, has not proven to be very worthwhile.

~ A somewhat popular, relatively new anti-cancer drug, toceranib, has been shown to produce significant tumor regression in 25% of pets with ASA.

~ Regular recheck physical exams to look for tumor regrowth and blood profiles to check for hypercalcemia are the most important follow-up to surgical removal of ASA.

~ Prognosis:

    ~ The overall prognosis for all pets with ASA is 18 months survival.

    ~ When hypercalcemia is present, the survival time decreases to 6 to 9 months.

    ~ Metastasis to lymph nodes does not necessarily worsen the prognosis.

    ~ Tumors larger than 10 cm diameter have a worse prognosis.

    ~ ASA that has metastasized to the lungs has a worse prognosis.