Definition

An abnormal, rapid, and invasive growth of cells on the testicles.

Clinical Signs

• An irregular shape or appearance of the testicle.
• A hard lump/mass felt on the testicle.
• A non-tender swelling on testicle.

Etiology

The testicles in rats (also known as testes, or, if referring to one testicle, as testis, orchis, or orchid), as in most mammals, are part of the reproductive system. They are normally contained in a sac called the scrotum. The scrotum lies caudal to the penis and ventral to the anus. Unlike humans and many other mammals, where the inguinal canal closes shortly after birth preventing the testicles from moving back into the abdomen, rats have an open inguinal canal allowing the testicles to migrate easily in and out of the abdominal cavity. This is an important fact for veterinarians to remember when deciding to perform an orchiectomy (neuter), in the male rat, for behavioral or health reasons.

The etiology or exact cause of testicular tumors is unknown, however, factors that are believed to contribute to their development in rats are: congenital cryptorchidism (undescended testicle), and aging.

Testicular tumors can be both benign or metastatic. While these tumors are not uncommon in the aging male rat, they are rarely found to have spread or metastasized to other organs or areas of the body.

Testicular cancer or tumors are primarily found to arise from primordial germ cells (undeveloped or “seed” cells that develop into sperm). They are then divided into types: seminomas which contain primitive less specialized cells, and nonseminomas which contain more specialized cells from which cancers such as embryonal carcinoma, yolk sac carcinoma, choriocarcinoma and teratomas develop. Those tumors that contain both seminoma and nonseminoma types are mixed germ cell tumors.

In addition those tumors that develop from supportive and hormone producing tissues in the testicles are called stromal tumors. Stromal tumors are further divided into two types of testicular tumors: leydig cell (found in the interstitium of the testicles and primary site for the biosynthesis of testosterone) and sertoli cell (nurse cells that regulate intratubular and intercellular environment in the testicles). The leydig cell tumors and sertoli cell tumors are the types most often seen in male rats. Both types of tumors generally do not metastasize.

Secondary testicular tumors can develop when metastasis has occurred from another area of the body. Metastatic conditions that can be responsible for secondary tumor development in the testicles are lymphoma and leukemia.

Even though it is rare in rats for testicular tumors to metastasize to other areas of the body; the recommended treatment for these tumors is orchiectomy (neutering or removal of the testicles). This is because the inevitable growth of these tumors can cause ureteral and bowel obstruction.

Figures

• Fig 1: Testicular tumor in 2-year 2-month-old male rat (Rumpus)

Scrotal neuter (orchiectomy) procedure

• Neuter Fig 1: Shows procedure for male rats (Turing and Angelus)

Diagnostics

Obtain history from pet owner.

Palpate for testicular mass.

Gross examination of testicular tissue, where orchiectomy is performed, may indicate cell type/origin.

Treatment

Recommended treatment in an otherwise healthy male rat is orchiectomy (neuter).

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

Rats do experience pain with surgical procedures. The type of pain medication used post-op should be determined based on extent of procedure and the anticipated severity of pain.

Recommended post-op analgesics:

• 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.

Because there is the potential for wound infection, seroma, or hematoma when an orchiectomy (neuter) is performed via the scrotum on a rat, a broad-spectrum antibiotic prescribed post-op is encouraged.

For information regarding medications refer to the Rat Medication Guide.

Nursing Care

Provide the following post-op care:

• A hospital cage (smaller individual cage) that includes clean non-litter bedding such as felt, soft t-shirt type material, or ink-free paper towels. Clean cage and 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.
• Give antimicrobial if or as prescribed.
• 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.
• Because there is the potential for wound infection, seroma, or hematoma when an orchiectomy (neuter) is performed via the scrotum on a rat, it is important to contact the veterinarian if any of the following occurs: swelling, redness, or pain at the incision site, or if there are signs of increased weight loss, lethargy, or changes in habits.
• If condition precludes comfort or quality discuss euthanasia with veterinarian.

Outcome

• Comfort is 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 testicular tumors, doing the following may increase quality of life:

• Do regular physical health checks of your rat weekly. Early detection and treatment can help to improve quality of life.
• If the rat was born with the condition cryptorchidism (undescended testicle) discuss the benefit versus risk of neutering with a trained veterinarian.
• Seek veterinarian care if your rat is ill, and treat appropriately.

Note to Breeders: Since cryptorchidism tends to be familial and may contribute to testicular tumor formation the continuation / direction of the lines involved may need to be evaluated.

References

1. Chandra, M., & Riley, M. (1994). Rarely occurring spontaneous metastasizing testicular tumors in rats. Histopathologic and ultrastructural features. Exp Toxicol Pathol, 46(2), 155-61. Retrieved December 22, 2008, from the PubMed database.
2. Ertugrul, A., Cam, K., Tarcan, T., Akdas, A., & Turkeri, L. (2002). Nuclear accumulation of protein p53 and histological changes in the rat model of unilateral cryptorchidism. Braz J Urol, 28, 57-63. Retrieved December 22, 2008, from http://www.brazjurol.com.br/january_fabruary_2002/Ertugrul_ing_57_63.htm.
3. Tena-Sempere, M., Kero, J., Rannikko, A., & Huhtaniemi, I. (1999). Experimental cryptorchidism induces a change in the pattern of expression of LH receptor mRNA in rat testis after selective Leydig cell destruction by ethylene dimethane sulfonate. J Endocrinol, 161(1), 131-41. Retrieved December 22, 2008, from http://joe.endocrinology-journals.org/cgi/reprint/161/1/131.