Anal glands are pouches or sacs, which are located near the anus. Every dog and cat has a pair of anal glands, one gland located on each side of the anal region. The openings to these glands are located just inside the anus very near the juncture between the anus and the skin at approximately 4 o’clock and 8 o’clock position. Anal glands in dogs and cats secrete a liquid substance, which is held inside of the sac until the animal defecates. In dogs and cats with normal anal glands, this liquid is normally expressed from the glands along with the bowel movement. Many animals will also express the contents of these glands when they become frightened, nervous, or excited. This expression will result in a foul smelling, dark colored liquid substance being seen near the rectum of the animal, under the tail, or on the floor or ground near the pet.
Dogs are more commonly affected with anal sac disease than cats, and small breed dogs are more commonly affected with anal sac impaction than large breed dogs. Older female dogs are more commonly affected with anal sac tumors. If the sacs do not empty normally, an impaction can occur. Symptoms of an impaction include “scooting” along the floor to attempt to empty the overfull sacs. This is more common in smaller breeds, but it can happen to any dog. Usually, it occurs because recurrent loose stools do not supply enough sphincter pressure to empty the sacs. It can also be caused by small anal sac openings or overactive glands. Other symptoms commonly noted are frequent licking of the anus or tail base, reluctance to sit, or sitting asymmetrically to avoid pressure on the painful anal sac, straining to defecate, difficulty defecating, production of ribbon-like stools, and painful swelling at the 4 o’clock or 8 o’clock locations around the anus.
When the anal glands become over-filled, it is possible to manually express them. External manual expression involves squeezing the area on either side of the anus to milk the fluid out of the glands. When expressed properly, the fluid from the glands will be visible exiting through the openings near the anus. Internal manual expression involves inserting a finger inside of the rectum of the dog and milking the fluid from the anal glands between two fingers, one inside the rectum and one outside. Similar to the external method, fluid will be visible exiting the anal gland openings when expression is accomplished successfully.
If intervention does not occur to empty the over-filled anal glands, eventually the fluid inside of the anal glands begins to change in consistency, becoming much thicker and more difficult to express. Left unexpressed, anal glands can eventually become infected and may even abscess and rupture, leaving an open, painful wound near the anus.
Treatment for anal gland infections and/or abscesses may involve flushing the anal gland and treating with antibiotics, either systemically, topically, or both. Culture and sensitivity testing will determine the most appropriate antibiotic regime indicated to resolve the infection as expediently as possible. Flushing the diseased anal gland may require sedation for the affected pet. In addition, pain medication may be necessary to relieve the discomfort for these dogs and cats. It is possible to surgically remove the anal glands from pets experiencing repeated anal gland issues. The staging of surgical removal is important as surgical removal in the presence of an acute rupture or infection increases the chances of complications, including but not limited to incomplete removal of anal gland tissue and spreading infection into previously unaffected tissue. Surgery is best performed after the infection is under control as visualization of the affected tissues is much more precise. Surgical removal of anal glands can lead to complications, which may include fecal incontinence if the nerves in the area of the anal glands are disrupted during the course of the surgery. This incontinence may be temporary or permanent. For this reason, an experienced surgeon is best equipped to perform the procedure in order to decrease the chance of postoperative complications.
Tumors of the anal sacs are uncommon in dogs, but can become serious problems because they can invade local tissues, such as the rectum, or metastasize to other organs, even when the primary tumor is still very small. Additionally, these tumors can cause increased blood calcium levels (hypercalcemia of malignancy) that can lead to kidney failure. Hypercalcemia of malignancy is detected in approximately 25% of dogs with anal sac carcinoma. Clinical signs may be associated with the primary tumor or with kidney disease resulting from hypercalcemia. Clinical signs associated with a primary tumor are similar to the signs observed for anal sac infections and include constipation, pain when defecating, straining to defecate, and bloody feces. Clinical signs associated with kidney failure from high blood calcium include lethargy, loss of appetite, vomiting, increased water intake, and increased urinations.
If a mass is felt in the area of the anal sac, it can be aspirated to determine if cancer cells are present. If anal sac carcinoma is confirmed, thoracic and abdominal radiographs and ultrasounds should be performed to search for evidence that the tumor has spread to the regional sublumbar lymph nodes or lungs. Blood chemistries and urine are tested to check for high calcium and any evidence of kidney damage since high blood calcium and subsequent kidney failure are associated with poor survival rates in animals with anal sac tumors.
Although a variety of treatment combinations have been reported, surgery is the only method that has been proven to influence survival of dogs with anal sac carcinomas. Surgical treatment includes removal of the primary tumor and, in some cases, also the sublumbar lymph nodes in the abdomen, which are affected by metastatic disease in half of dogs. In addition to surgery, many oncologists recommend radiation and chemotherapy in an attempt to prolong survival of affected dogs. Due to the highly invasive nature of anal sac carcinomas and the possibility that aggressive surgical removal may lead to fecal incontinence, radiation is commonly used when complete (clean) surgical margins cannot be achieved. Animals that present with hypercalcemia may need to be treated before surgery with intravenous fluid therapy, diuretics (to increase urine production), and corticosteroids or bisphosphonates to decrease blood calcium concentrations.
Prognosis and survival depend on factors such as the type of treatment, size of the mass, and presence of hypercalcemia and metastatic disease. In a recent study of dogs with anal sac adenocarcinoma, overall median survival was 584 days. Dogs not treated surgically had shorter survival times (median, 402 days). Median survival is poorer in dogs with tumors larger than 4 inches (median survival, 292 days), hypercalcemia (median survival, 256 days), and spread to the lungs (median survival, 219 days). Interestingly, metastasis to the abdominal lymph nodes was not found to affect survival.
In summary, because many of the clinical signs associated with anal gland infection can mimic those of an anal gland tumor or cancer, prompt and thorough evaluation of the rectal area is indicated whenever a pet is exhibiting signs of pain and discomfort in this region.
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