Definition

A tissue mass or growth that projects (may be on a stalk or flattened) above the mucosal surface lining of the colon or rectum.

Clinical Signs

The following may indicate presence of colorectal (colon-rectum) or anorectal (anus-rectum) polyps.

• Feces that have decreased in size/shape.
• Impaction of feces/constipation.
• Painless rectal bleeding or signs of blood in feces.
• May see signs of testicular swelling, swelling in lower pelvis, discomfort or pain when area touched.
• Progressive weight loss.

*Note: for information on recognizing various signs of pain or discomfort refer to: Signs of Pain In Rats.

Etiology

Polyps attached to the mucosal lining by a stalk are termed pedunculated, and those that have a broad base or flat are termed sessile.
They can be found as singular or multiple formation , and can vary in size.

The polyp’s appearance may depend on type, location, and by the tissue from which it develops. Polyps that are adenomatous develop from the epithelium. Those that are derived from smooth muscle are called myomas, and polyps deriving from blood vessels are called hemangiomas.

Colorectal polyps can be classified as either neoplastic or non-neoplastic. Those classified as neoplastic include the categories adenomas and carcinomas. Polyps which are classified as non-neoplastic include the categories mucosal, inflammatory, and hyperplastic (lymphoid) polyps.
It is believed that chronic inflammation, along with swelling and edema of the mucosal lining may give rise to polyps.

Although their etiology is not clearly understood, it is believed they may be idiopathic (without clear pathogenesis or cause), attributed to an autosomal dominant trait (familial), or from an underlying disease process.

Factors that may contribute to the development of colorectal polyps in rats are:

• genetics
• aging
• diet that includes too much fat
• obesity

While most of these polyps are benign, certain types such as adenomas have the potential to become cancerous (although studies indicate rats have almost no spontaneous development of colon cancer). Not only that, but colorectal polyps in rats also have the potential (due to the polyps’ growth) to block the passage of feces through the colon and rectum. It is recommended and where feasible, depending on the health and age of the rat, to have these growths removed.

Figure

Case History of Rectal Polyp

• Fig 1: Rectal polyp and suspect bacterial orchitis in domestic fawn and white male rat (Reggie)

Diagnostics

Take history from pet owner.

Check feces for frank blood or occult blood.

Visualization of bowel lumen if feasible.

Treatment

Recommended treatment is removal of the growth including base and stem, or if not feasible, then removal of as much as possible under anesthesia. One should be aware that the growth may return.

In the event surgery is an option the following post-op analgesia may be given:

• For severe pain or first 24 hours post-op: Buprenex (buprenorphine), or Torbugesic (butorphanol).

• For mild to moderate pain : Banamine (flunixin meglumine), Metacam (meloxicam), or carprofen. Do not use if a corticosteroid has already been prescribed.
• *Note: for pain not controlled by the use of an NSAID (e.g., Banamine, meloxicam, or carprofen), alone, consider alternating or co-administering with a narcotic (e.g., buprenorphine or butorphanol) or narcotic-like (e.g., tramadol) medication.

If surgery is not an option and the rat is able to pass feces, a nonsteroidal medication (e.g., Sulindac, Piroxicam, or Metacam) may reduce inflammation and swelling providing comfort.

For information pertaining to medications refer to the Rat Medication Guide.

Should condition preclude comfort or quality of life, discuss euthanasia with veterinarian.

Nursing Care

• Maintain healthy diet that includes soy and tofu.
• Monitor and maintain a healthy weight for the rat.

In the event of surgical removal or debulking of polyp provide the following post-op care:

• A hospital cage (small individual cage) that includes clean non-litter bedding such as felt, soft t-shirt type material, or ink-free paper towels. Clean and change bedding daily. Avoid litter-type bedding post-op, until healed, to prevent the chance of wound contamination or infection.
• Provide additional warmth to maintain body temperature within normal limits. It is essential that the rat does not become overheated or dehydrated. The rat should also be able to move away from the heat source if it becomes uncomfortable. If the rat is unconscious or immobile extreme care must be taken to keep the heat low and stable.
  • You can use an isothermic product that is heated in the microwave such as SnuggleSafe®. Make sure to follow the product directions carefully and wrap in a towel before placing in the cage. SnuggleSafe® will provide heat for 12 hours before needing to be reheated. Other similar types of product may vary in re-heat time. Check directions for individual product.
  • If using a heating pad (good for long term use) use only the low heat setting, put a thick towel in between the pad and the cage bottom, and place beneath a corner of the cage.
  • If none of these options are available you can use a plastic bottle filled with hot water, and wrapped in a towel, in the corner of the cage.
• Medicate for post-op pain as needed.
• Encourage fluid intake while recuperating, such as water, Jell-O water , or electrolyte replacement drinks such as Pedialyte or Gatorade (which can be found in local grocery stores). Please note that Pedialyte is only good refrigerated for 24 hours after opened, but can be frozen as ice cubes and thawed as needed.
  *Note: a juicy type of fruit also provides an additional fluid source in the diet.
• Contact veterinarian if any of the following are observed: swelling, redness or pain at the incision site, or if there are signs of increased weight loss, lethargy, or changes in habits.

Outcome

• Bowel function returns to normal
• Comfort increased
• Increased quality of life
• Emotional support for those having to consider euthanasia for their rat

Prevention

While you may not be able to prevent the development of polyps, doing the following may decrease their chance of developing, and increase quality of life.

• Do regular physical health checks of your rat weekly.
• Seek veterinarian care if your rat is ill, and treat appropriately.
• Provide a healthy diet low in fats. Include soy and tofu in dietary regimen.
• Maintain healthy weight for your rat.

Early detection and treatment can help to improve quality of life.

References

1. Corpet, D., & Pierre, F. (2003). Point: From animal models to prevention of colon cancer. Systematic review of chemoprevention in min mice and choice of the model system. Cancer Epidemiol Biomarkers Prev, 12(5), 391-400. Retrieved November 30, 2008, from http://cebp.aacrjournals.org/cgi/content/full/12/5/391.
2. Skinner, S., Penney, A., & O’Brien, P. (1991). Sulindac inhibits the rate of growth and appearance of colon tumors in the rat. Arch Surg, 126(9), 1094-6. Retrieved November 30, 2008, from http://archsurg.ama-assn.org/cgi/content/abstract/126/9/1094.
3. Wenk, M., Ward, J., Reznik, G., & Dean, J. (1981). Effects of three retinoids on colon adenocarcinomas, sarcomas and hyperplastic polyps induced by intrarectal N-methyl-N-nitrosourea administration in male F344 rats. Carcinogenesis, 2(11), 1161-6. Retrieved November 30, 2008, from http://www.ncbi.nlm.nih.gov/pubmed/7318152?dopt=Abstract.