A perianal adenoma (also known as circumanal adenoma and hepatoid adenoma) is a common tumor that arises from the sebaceous glands surrounding the anus. It's so common that it accounts for 80% of all tumors that occur in the perianal area.
This kind of tumor is considered very rare in cats, primarily because cats don't have perianal sebaceous glands. Dogs, however, have plenty of these.
Perianal adenomas are particularly common in intact males. However, they can also be seen in spayed female dogs. That's because estrogen, at low levels in spayed females, tends to inhibit these tumors.
These tumors may also be associated with testicular interstitial tumors in intact male dogs, hyperadrenocorticism (Cushings disease), and with adrenal tumors that produce excessive amounts of testosterone.
The malignant version of this disease is called perianal adenocarcinoma and it's considered far less common than the perianal adenoma. In most cases, perianal adenoma carries a good prognosis (after treatment, they recur in less than 10% of patients). By contrast, perianal adenocarcinoma is considered an aggressive tumor type and carries a fair to guarded prognosis.
Symptoms and Identification
Perianal adenomas appear as slow-growing, non-painful masses around the anus. They usually emerge in the hairless area of the perineum, but technically, they can appear in the prepuce, scrotum, and under the tail. They're typically superficial and are only rarely adhered to deeper tissues.
They can arise as single, multiple, or diffuse masses, though they're typically single and small in females. Occasionally, they'll be ulcerated and infected on their surface.
Though perianal adenomas are considered benign (they don't spread to distant sites and aren't typically locally invasive, some perianal adenomas can be classified into an intermediate category called invasive perianal adenoma. These tumors can act somewhat invasively.
Diagnosis of perianal adenomas is typically achieved by biopsying the tissue, as simple cell analysis (cytology) is usually unable to differentiate between a benign and malignant tumor type.
The treatment for a perianal adenoma in males typically includes castration. Local resection of the mass is usually recommended as well. However, if the mass is close to the anal sphincter, or if its borders should be indistinct or diffuse, the tumor may be left surgically untreated. In these cases, resection may be considered after the mass is no longer being stimulated by testosterone and has reached a more manageable size (after several months).
Radiation therapy may be elected in some cases, as may cryosurgery for small tumors (less than an inch in diameter). In some cases, administration of systemic estrogens may lead to tumor regression. However, this approach is seldom undertaken given that bone marrow suppression is considered a serious side effect of estrogen therapy in dogs.
The cost of treating perianal adenomas depends on the location and size of the tumor as well as the level of care elected and the geographic region. For most, castration and resection with a biopsy runs about $500 to $1500. For those that require additional treatments, including radiation therapy (only rarely required), treatment may cost upwards of $5,000 or more.
These tumors are largely preventable by castrating male dogs and, technically, by leaving females intact. However, care should be taken to consult with a veterinarian by way of assessing all the risks and benefits of sterilization for both males and females.
Berrocal A. Vos, J.H. van den Ingh, T.S.G.A.M. Molenbeek, R.F. vanSluijs,F.J. Journal of Veterinary Medicine Series A. Volume 36, Issue 1-10, pages 739-749, February-December 1989.
Vail, D. M.; Withrow, S. J.; Schwarz, P. D.; Powers, B. E. Perianal adenocarcinoma in the canine male: a retrospective study of 41 cases. Journal of the American Animal Hospital Association 1990 Vol. 26 No. 3 pp. 329-334.
Wilson GP, Hayes HM Jr. Journal of the American Veterinary Medical Association [1979, 174(12):1301-1303].