The anus* is not generally a popular body part to talk about. However, just as with other areas of a rabbit’s body, the anus has its potential health problems. Knowing about these problems can help prepare you if you see your rabbit straining in the litter box, blood on the floor, or a mass protruding from your rabbit’s bottom. This article will outline some of the problems that may be seen in the rabbit’s anal area. If you see any abnormalities in this area it is important to take your rabbit to a veterinarian for diagnosis and treatment.
One of the most common “ailments of the anus” is a polyp. An anal polyp is an overgrowth of the mucus membrane within the rectum that protrudes through the anus. A polyp is almost always benign, although the possibility of it growing large enough to block the rectum does exist, in which case surgery is required to remove it. Polyps range in color from pink to red to brown and occur because of inflammation or changes in rectal or anal tissue. One example is a rabbit not getting enough fiber in her diet, which can change the shape or texture of the stool, which in turn can inflame the delicate tissue that rabbits have in this area. Multiple polyps can also be present, in which case you may see stool coming out from in between them. If there is no anal blockage and your rabbit is not in pain, it is usually only necessary to monitor the situation. Surgery may be needed if the polyps interfere with stool passage or are causing pain.
The term polyp is often used as a generic term for any type of growth or mass. However, a polyp does differ from other masses such as a hemorrhoid or papilloma.
While a polyp is made of solid matter, a hemorrhoid is filled with blood. A hemorrhoid is a swollen, inflamed vein in the anus or rectum, caused by too much pressure on the vein. A hemorrhoid can be hard to differentiate from a polyp, unless you can actually see a purple color within, which is blood. To reduce inflammation, a topical anti-inflammatory medication can be used, upon recommendation by your rabbit veterinarian. A hemorrhoid is very rare, and is usually small and resolves on its own. Hemorrhoids don’t typically cause enough swelling to block the rectum; however, if they are large, they can be surgically removed.
A papilloma is a small, often benign tumor of the skin that looks like a cauliflower or a bunch of grapes. It resembles a plantar wart in a human. Papillomas develop at the rectoanal junction and can protrude out of the anus. When small, because they are internal, you can’t see them unless pressure is applied, such as when a stool is being passed. However, as they grow and begin to protrude, they are visible. Papillomas, which are white or pink, bleed easily. A papilloma can become crusty or ulcerated, and, like a polyp, if it grows large enough it can block the anus.
A viral papilloma caused by the Shope papallomavirus is a benign condition occasionally seen in wild cottontail rabbits but is rare in pet rabbits. In domestic rabbits it may cause a malignant squamous cell carcinoma-like growth. Surgical removal is the only treatment.
Rabbit syphilis caused by the bacteria Treponema cuniculi can cause lesions that resemble papillomas but are in fact inflamed areas of tissue around the mucocutaneous junction of the lips, nose, eyes, urogenital, and anal openings in a rabbit. These lesions are crusty and raised early in the disease but may develop into large papillary nodules that ulcerate and bleed as the disease progresses. Rabbit syphilis is transmitted when rabbits have anogenital or oral contact with an infected rabbit. In newborn rabbits it can be transmitted as they pass through the birth canal. Some rabbits can carry the infection for months or years before they show external signs. Infected rabbits should be isolated until they complete antibiotic treatment. Injectable penicillin is the most effective antibiotic. Please note that oral penicillin should never be used in a rabbit and even injectable penicillin, if used improperly or in a seriously compromised animal, has risks. A veterinarian should always supervise these cases.
Less common ailments
Other ailments of the anus are rare and include anal fissures, rectal prolapse, imperforate anus, and anal cancer. An anal fissure is a small laceration in the thin, moist tissue lining the inner-most part of the anus, usually in a small fold or pocket of the skin. Anal fissures are usually never noticed and resolve on their own.
Rectal prolapse is a condition in which all layers of rectal tissue and the rectal lining protrude. Prolapse can be incomplete, in which a small portion of the rectal lining is visible when a rabbit passes stool and after which it subsides, or complete, in which a mass of tissue persistently protrudes from the anus. In the chronic complete stage, this tissue might be black or blue. This indicates an emergency condition, because a rabbit can quickly go into shock and die. Prolapse develops when a rabbit strains while passing stool, because of issues such as constipation, intestinal foreign bodies, rectal or anal tumors, intestinal intusuception (intestine folds in on itself), or polyp blockage. When a prolapse occurs, surgery is required to replace the tissue in its proper anatomical position.
Imperforate anus is something that house rabbit caregivers would rarely see. Imperforate anus is when the opening to the anus is blocked (or missing). This condition is almost always congenital (present from birth). However, it can occur from scar tissue building up around the anus. This can happen if a rabbit has been involved in fights and was bitten in the anal area. As the area heals, scar tissue can form and gradually block the anus. Treatment involves surgery to create a new or larger anal opening.
Rabbit anal cancer is also rare. In addition to one or more tumors in the anal area, signs can include bloody urine, lethargy, loss of appetite, weight loss, and anal bleeding. In addition, tumors can be present on other parts of the body if the cancer spreads. Blood work and radiographs of the chest and abdomen are recommended to look for metastasis (whether the cancer has spread). Surgical removal of the tumors and radiation therapy post surgery are the most common treatments.
Ailments of the anus in rabbits are rare, involving approximately 4-5 percent of cases brought to veterinarians. Seeing blood or a mass on your rabbit’s bottom can be scary but in most cases it is not an emergency. However, consult your veterinarian as soon as possible because some of these conditions can be painful or may progress to become more serious conditions.
*The anus is not the same thing as the rectum. The rectum is the last inch or so of the rabbit’s colon before it reaches the anus. The anus is the opening of the rectum to the outside.
By Amy Bremers
In consultation with Laura Wade, DVM, ABVP owner of Specialized Care for Avian & Exotic Pets in Lancaster, New York
HRJ Vol. 5, No. 7, Winter/Spring 2011