My dog has a perianal adenoma. What is this?
Category: Canine

An eight-year old unneutered male dog I have bred over the years has been diagnosed with perianal adenoma. He has a small lump near the rectum with a scab covering that falls off with bathing. The veterinarian recommended surgery and neutering. I am not familiar with this type of problem. What is it? Can it be cancer? Will neutering the dog help in some way? Thank you.

A benign tumor of the sebaceous glands around the anal area.


Perianal adenomas are benign, slowly growing tumors that arise from the cells of sebaceous (oil) glands around the tail area. These tumors are confined to the skin and are not attached to underlying structures. The lesions may occur as single or multiple masses or as diffuse, relatively flat sheets of sebaceous tumor cells. They range in size from about 0.2 to 1.2 inch in diameter. These growths frequently ulcerate and the resulting broken skin may become infected. Perianal adenomas may quietly grow for months or even years. Perianal tumor cells are stimulated by testosterone, a male hormone produced mostly by the testes and to a much lesser extent by the adrenal glands. Perianal adenomas most frequently affect intact, middle-aged and older male dogs. Female dogs develop these tumors only infrequently; most affected female dogs have been spayed. Perianal adenomas are not painful, although they may stimulate licking of the affected area or possibly scooting. A small percentage of perianal gland tumors will be malignant (adenocarcinoma), which are treated differently, so differentiating these from benign tumors is of critical importance. Perianal adenocarcinomas tend to adhere to structures underlying the skin, but a definite diagnosis of benign versus malignant may only be made with a microscopic examination of a tumor tissue sample. The tissue may be sampled either by a fine-needle aspirate technique or by surgical biopsy. The former procedure involves inserting a needle attached to a syringe into the tissue and withdrawing a sample into the needle. Surgical biopsy entails excising a sample of the tumor or removing it entirely, along with surrounding margins of normal tissue. The resulting tissue samples are examined under a microscope for tumor identification. Discriminating between benign and malignant processes may be difficult in some cases. Pathologists often suggest that a tumor sample may be either adenoma or adenocarcinoma, depending on the tumor's biologic behavior. The treatment of choice for intact male dogs with confirmed, benign perianal adenoma is castration and surgical removal of the tumors. If the tumors are relatively small, they may be removed by cryotherapy (cryosurgery). Cryotherapy involves freezing the tumors with liquid nitrogen. If the tumors are large, after castration they will be monitored for one to two months before surgical excision is performed. The reason for the waiting period is that as testosterone levels decline after neutering, the tumors will shrink and thus removal will be easier and less traumatic. In some cases, the tumors will completely disappear and no surgery will be needed. Perianal adenomas in female dogs are removed with cryosurgery or excisional surgery. Treatment is highly successful and the prognosis is good. In 10 to 20 percent of treated cases the lesions may recur, but these may be treated again. Castration eliminates the major source of testosterone. Generally, neutering male dogs early in life will help prevent the original development of perianal adenomas and adenocarcinomas and other such growths. In some exceptional situations, where castration is not a considered option, estrogen may be administered to shrink the tumors. The major drawback to this treatment approach is that the hormone may cause bone marrow suppression, which could be life threatening. These tumors can get very large and problematic to remove, so this problem should be dealt with promptly. You may wish to review our VetCentric Encyclopedia article, "Neutering, Canine."



Main Hospital
133 East 39th Street
New York, NY 10016
212. 889.7778
Chelsea Clinic
32 West 25th Street
2nd Floor
New York, NY 10010