Anyone who has watched dogs say hello to each other has probably wondered why sniffing rear ends is part of the ritual. It might seem a little forward to our human sensibilities, but there is a perfectly good reason from their point of view. Smells are much more important to our canine companions than to us, and they use olfactory communication in addition to body language and vocalizing. Some of these smells are produced by a set of glands near the rear end—the anal glands. Two pea sized glands are located on either side of the anus, and produce an oily, strong smelling secretion. For healthy dogs, these secretions contribute to the unique set of smells that helps them identify each other. However, anal glands can also be involved in some common health issues for pets.
Both cats and dogs have anal glands, although dogs are more likely to have medical issues with them. The glands are located next to the anus, between the internal and external anal sphincters. Their secretions are usually liquid or pasty, and very foul smelling to humans! Each gland empties into a small pouch, called an anal sac. This sac is connected by a short tube, called a duct, to the anus. The anal glands’ secretions are stored in the sacs. When a dog defecates, the pressure causes the sacs to empty through the ducts into the anus. The anal sacs can also be expressed if a dog is very scared or excited. A normal, healthy dog should not need any help emptying these sacs.
Just like any other part of the body, things can go wrong with the anal sacs. If the sacs become too full or irritated, there are a few typical signs that a dog will display. One of the most common is “scooting” or rubbing his bottom along the floor. He may also lick or chew excessively at his rear end, or strain to defecate. In some cases, there might be a visible sore near the anus, or bloody discharge. Any of these signs is a good reason to head to the vet!
Some of the most common disease processes that can occur in the anal sacs are impaction, sacculitis, and abscessation. These are often related and can occur concurrently. An impacted anal sac contains a thick material that is not easily expressed, and may become distended or painful. Sacculitis is inflammation of the anal sacs, and may occur with or without impaction. It may involve a bacterial infection. In some cases, bacterial sacculitis can progress to an abscess, or a focal area of pus. Abscessed anal sacs are often quite painful, and affected pets may vocalize, bite at the area, or display other signs of discomfort. They can rupture, creating a draining tract or hole to the outside of the body, usually slightly below and to the side of the anus. These conditions are typically diagnosed on physical exam. A complete physical exam should always include a rectal examination and palpation of the anal sacs, especially if any of the previous clinical signs are present. If your veterinarian thinks that the glands feel full or abnormal, he or she will typically express them manually. If sacculitis is present, the expressed material may include pus or blood.
One question many owners ask is why their pet developed anal sac impaction or sacculitis. There are multiple possible causes, and it is not always possible to completely identify what triggered the episode. Abnormal defecation, such as diarrhea or constipation, can prevent the sacs from emptying appropriately. Pets with poor muscle tone, such as obese dogs or dogs with neurologic issues, may also be predisposed to impacted anal sacs. Additionally, if the ducts emptying from the sacs are obstructed, the sacs will continue to fill. Certain endocrine and dermatologic diseases may cause hypersecretion of the anal glands, which can lead to impaction and sacculitis. Dogs with allergies, including environmental and food allergies, may be predisposed to anal sacculitis. However, for some pets with chronic anal sac impaction or sacculitis, the underlying cause is unclear.
The treatment for anal sac disorders depends on the severity, as well as reason for the problem. For simple impaction, manual expression of the sacs by a veterinary professional will relieve the discomfort. If sacculitis is present, treatment may involve oral antibiotics or anti-inflammatories, or flushing of the sacs with instillation of a topical medication. Flushing and application of local medications may need to be repeated at multiple visits. In an abscess is present, it will need to be manually lanced and flushed, or just flushed and cleaned if it has already ruptured. Typically, treating an anal sac abscess requires at least light sedation, as the area can be quite sensitive. After the initial treatment, applying warm compresses to the area at home can improve comfort and promote healing.
In the long term, dogs with repeated anal sac impactions may benefit from adding fiber to their diet to bulk up stools and promote normal emptying of the sacs. This could take the form of a tablespoon or two of canned pumpkin with food, or even a commercial fiber powder supplement. A regular exercise regimen can also improve muscle tone, which can lead to better empting of the anal sacs. For dogs with recurrent impaction but not sacculitis, regular manual expression of the glands by a veterinarian or technician may be all that is needed to control the issue. If issues continue to recur, more testing may be indicated in order to investigate underlying problems. This could include bloodwork to check for endocrine diseases, or a full dermatologic workup if it occurs with other skin issues. Your veterinarian may suggest a trial of medication for allergies, or a diet trial to rule out food allergies.
In severe, chronic cases, medical management may be unsuccessful. In that case, the step would be surgical removal of the anal sacs, a procedure known as an anal sacculectomy. For dogs with recurrent, painful anal sacculitis, the procedure can be highly effective. As with any surgery, there is a low risk of complications, which include fecal incontinence, infection, or formation of a draining tract (an opening from the site of the anal gland to the skin). The decision for when to proceed to surgery is not straightforward, and will depend on the individual patient and owner.
There is another major category of anal sac disease: neoplasia, or cancer. The most common type of cancer in that area is anal sac adenocarcinoma. This is an aggressive cancer, with a high rate of metastasis (spread to distant sites). There are often no clinical signs initially, and a nodule or firm, inexpressible gland may be noted on a routine rectal examination. If the cancer has already spread to nearby lymph nodes, dogs may show signs from enlarged lymph nodes in front of the pelvis. Signs may include straining to defecate, ribbon like stools, or constipation. Due to hormones released by the cancer cells, the tumor may cause excessively high calcium levels in the blood. This can lead to increased thirst and urination, vomiting, weakness, and lethargy. Some dogs may also display scooting or excessive licking of the area. Cats are more likely to show signs such as bloody discharge or ulceration of the anal sacs, but may also display straining to defecate.
If there is a suspicion of an anal sac tumor on physical exam, additional tests may be suggested. This could include bloodwork to check for other diseases, and to assess blood calcium levels. Radiographs (x-rays) can be performed of the abdomen to look for enlarged lymph nodes, or of the chest to check for metastasis to the lungs. An abdominal ultrasound may be suggested to investigate lymph nodes and other internal organs for masses. Sometimes, a fine needle aspirate and cytology of the mass may be performed. This involves sticking a needle into the mass to get a sample of cells, and examining them under a microscope for signs of malignancy. The only definitive way to determine if the mass is cancerous is to surgically remove the anal sac and gland, and to submit them for histopathology. This involves examining thin slices of the tissue microscopically.
Treatment for an anal sac adenocarcinoma depends on how far the disease has spread, as well as the goals and expectations of the owner and the condition of the pet. Up to eighty percent of dogs with this type of cancer already have metastasis to other organs at the time of diagnosis. Typically an anal sacculectomy is the first step, unless widespread metastasis is already present. If lymph node metastasis is present, those should be surgically removed as well, which is a much more involved procedure, typically requiring a specialist. The best way to prolong survival time after surgery is to follow it with radiation of the area, but this can only be performed at certain speciality hospitals or universities. In some cases, chemotherapy may also be beneficial. Certain medications, such as anti-inflammatories, may relieve clinical signs and even slow progression of disease. Other medications may help lower calcium levels, which can make pets more comfortable. The prognosis depends on the stage of disease and the choice of treatment, but may be several years if it is caught early.
To sum up, anal sac disorders are quite common in dogs, and can occur in cats as well. A basic understanding of the common diseases and treatments is useful for owners, as it can help to make informed decisions about pet care. It is vital to realize that these issues can range from a mild irritation to a life threatening disease. Given this fact, it is important that any anal sac-related issues be assessed promptly by a veterinarian, in order to have the best chance of resolving them.
Grossman, M. (2012, October 11). Anal Sac. Retrieved July 5, 2019, from https://www.vin.com/doc/?id=5612395&pid=11200.
Rubin, S. (2019). Anal Sac Disease. Retrieved July 5, 2019, from www.merckvetmanual.com.
Shell, L. (2008, September 18). Anal Sac Impaction and Infection. Retrieved July 5, 2019, from https://www.vin.com/Members/Associate/Associate.plx?DiseaseId=102.
Shell, L., & Waltman, S. (2018, March 1). Anal Sac Adenocarcinoma. Retrieved July 5, 2019, from https://www.vin.com/Members/Associate/Associate.plx?DiseaseId=1197.