Canines, like other carnivores, have a pair of sacs on either side of the anus, between the internal and external anal sphincter muscles. The walls of these paired structures are lined with large glands that secrete a foul-smelling, yellow-gray or brownish liquid or pasty material. Normally, small amounts of this material are expelled from the anal sacs when the dog defecates and also when it is startled or suddenly becomes fearful. Anal sac disease is not a single "disease" per se, but refers to a number of conditions that occur when a dog's anal sacs become infected, inflamed, impacted, abscessed or affected by tumors. When these problems are present, the glands lining the anal sacs cannot eliminate the material that they normally produce or, in cases of infection, the sacs become filled with abnormal substances such as pus or blood. The result is that material builds up inside the anal sacs much like a balloon filling with water or air, causing discomfort, pain and possible anal sac rupture.
Causes of Anal Sac Problems
The underlying causes of anal sac problems are largely unknown. Several predisposing factors have been suggested, including obesity, recent diarrhea, poor perianal muscle tone, chronically soft feces and excessive or retained anal glandular secretions. These conditions are thought to promote the overgrowth of bacteria that normally is present within the anal sacs, thereby increasing the chances of inflammation, infection, impaction and formation of pus-filled abscesses. The reason that tumors develop in the perianal area, like the reason for tumor development elsewhere in the body of dogs or other mammals, is not well understood. However, both benign and malignant tumors can occur in or around the anal sacs, causing symptoms similar if not identical to those caused by more temporary and treatable problems such as bacterial infection or physical impaction by a removable source.
Prevention of Anal Sac Problems
One of the best ways to prevent anal sac problems is to feed dogs a high quality diet that is low in saturated fats and has enough dietary fiber to increase stool bulk and reduce the occurrence of loose or sloppy stools. The material normally found inside the anal sacs cannot be evacuated naturally unless there is a sufficient amount of appropriately firm feces passing through the dog's rectum. Overweight dogs should be put on a weight loss regimen, as obesity can contribute to anal sac problems as well. Routine manual expression of the anal sacs by veterinarians or by owners should not be necessary in normal dogs but may become appropriate in certain situations, which the treating veterinarian is best suited to assess. Of course, good routine hygiene can help prevent abnormal accumulation of bacteria and other microorganisms around the anal area. Unfortunately, there is no way given the current state of medical knowledge to prevent perianal tumors. Research into the causes and treatment of cancer remains in the forefront of both human and veterinary medicine.
The prognosis for dogs with non-cancerous anal sac problems is quite good. However, if surgical removal of the anal sacs becomes necessary for any reason, the prognosis worsens. If cancer is diagnosed, the prognosis is mixed to guarded, depending upon the tumor type, malignancy and the stage of the disease.
Anal sac disorders are relatively common in dogs, especially in small breeds. The anal sacs are paired structures on either side of a dog's anus that normally secrete a very smelly substance during defecation, probably as a form of territorial marking. When these sacs become irritated, inflamed, impacted or infected – which can occur for a number of reasons – the contents of the sacs are unable to drain normally, which causes affected animals to suffer discomfort, itchiness and pain that can range from quite mild to extremely severe.
Symptoms of Anal Sac Problems
Dogs with anal sac disorders usually show signs of physical discomfort at or near the area around their anus (called the perianal or perineal region). The affected area may be swollen and red, and there may be visible blood and pus on fecal matter or around the anus, especially when an anal sac abscess has ruptured. Signs suggesting that something is wrong with one or both of a dog's anal sacs may include all or some of the following:
Licking and biting at the anal area
Straining to defecate
"Scooting" the rear end along the ground
Reluctance to sit
Fresh blood on the feces
Visible swelling and redness around the anus
An open, weeping wound adjacent to the anus, with or without evidence of pus or blood
An unusually foul odor in the anal area
Possible fever, if infection is present
These symptoms are caused by the pain, itchiness and general discomfort that accompanies anal sac disorders. If tumors are present, owners may (or may not) notice a visible mass or bulge near their dog's anus. Owners often report an unpleasant "fishy" odor around their dog's perianal region and possibly around its mouth (from the dog's licking and biting at its rear end).
Dogs At Increased Risk
Small breed dogs develop anal sac disorders more commonly than do large breeds – particularly Miniature Poodles, Toy Poodles and Chihuahuas. Overweight animals are at a higher risk, as well. Female dogs of advanced age seem particularly predisposed to developing anal sac tumors, which may or may not be malignant or visible to the naked eye. Dogs suffering from chronic diarrhea and those with soft feces and poor rectal muscle tone are predisposed to anal sac problems.
Anal sac problems are rather common in domestic dogs and are not particularly difficult to diagnose. It is important for owners to take these problems seriously and to seek veterinary assessment and advice, because without treatment the problems can progressively worsen.
How Anal Sac Problems Are Diagnosed
A thorough history and physical examination are essential when anal sac problems are suspected. After taking a complete history, the attending veterinarian will evaluate the rectal area visually and digitally (by hand). The digital examination can be quite painful, depending upon the cause of the problem, and sedation or even general anesthesia may be required to complete the physical examination without causing significant discomfort to the patient. Normal anal sac secretions are clear to pale yellowish-to-grayish brown. Impacted anal sacs often are plugged with a thick, pasty brown material, and inflamed sacs can eontain a creamy yellow or thin greenish secretion. Abscessed anal sacs will discharge a reddish-brown material, typically accompanied by a fever and obvious swelling and redness around the anal area.
The results of blood work (a complete blood count and serum chemistry panel) and a urinalysis are typically normal in most cases of anal sac disorders, although there may be noticeable abnormalities on blood work if anal sac abscesses have ruptured and the infection has spread. The attending veterinarian may recommend thoracic and pelvic radiographs (x-rays), and possibly an abdominal ultrasound, to rule out neoplasia (cancer) that may have metastasized. The veterinarian will take samples of the anal sac contents during the digital examination and will examine these under a microscope to look at what types of cells are in the anal sac material. This is called "cytology." It may or may not be appropriate to culture the contents taken from the anal sacs, because the culture results can be difficult to interpret due to the normal presence of a great number of bacteria (called "normal flora")in that region. However, a diagnosis of bacterial infection becomes much more likely if a single bacterial species is cultured from the sample.
It may be appropriate to assess the levels of parathyroid hormone-related protein levels in the dog's blood, because they can be elevated in dogs with certain types of anal sac tumors. Abnominal ultrasound may also be helpful to assess whether the lymph nodes have been affected by metastatic disease.
Most anal sac problems in our companion dogs are not especially serious. The diagnosis of anal sac disorders is not unusually difficult in most cases, since the area involved is so isolated and accessible.
When an owner suspects that her dog may have "something unusual going on" in the area around the anus, she should take her pet to the veterinarian as soon as possible. In most cases, anal sac problems are not emergencies. However, if left untreated, the conditions can worsen rapidly and become more difficult to treat once diagnosed. The goals of treatment are to relieve pain, empty the anal sacs, reduce inflammation, control any infection and remove tumors surgically if necessary or appropriate.
Acute treatment for dogs with impacted anal sacs involves gentle manual expression of the contents of the anal sacs, which typically is done by a veterinarian or veterinary technician. In cases that recur frequently, the owner can be taught how to perform this procedure at home. If infection is present, the veterinarian will flush the sacs with sterile saline and apply an antibiotic or antiobiotic/steroid ointment or cream directly into the affected sacs. Sedation or anesthesia are usually necessary for those procedures. Anal sac abscesses that have ruptured are treated the same way, using saline, antibiotics and topical steroid treatments. Systemic antibiotics are frequently recommended as well. If the abscess has not yet ruptured, application of topical hot packs several times daily can help bring the abscess to a head. Then, the veterinarian can lance the abscess to establish drainage and relieve the dog's discomfort.
Chronic treatment for recurrent cases includes weight management, increased dietary fiber intake and possible surgical removal of the anal sacs or any tumors that are present.
With appropriate medical treatment, the prognosis for dogs with non-cancerous anal sac disorders is good. Most affected dogs respond well to non-surgical medical management of the condition. If the anal sacs must be removed, whether due to cancer or for some other reason, the prognosis becomes more guarded. The prognosis is also guarded if no treatment is undertaken.