Perianal fistula is a specific disease of the canine characterized by ulcerating fistulous tracts, often with a malodorous
purulent discharge around the anal orifice. The tracts are usually infected and filed with chronic inflammatory tissne. The
extremely severe and chronic cases the tracts may extend to the lumen of the rectoanal canal, becoming true fistulas.
This disease is most commonly seen in the German shepherd with a few cases reported in Setters and Retrievers. Dogs of either
sex can be affected and there seems to be some age correlation with older dogs, over seven years, being most often affected.
Although the etiology of this disease is not clear, many possibilities have been advanced. The conformation of the German
shepherd may be a predisposing factor in that the broad-based tail is held close to the anal region and thus maintains a film
of fecal material and anal sac secretion over the perianal region. This conformation and the poor ventilation afforded by
such tail carriage may provide a suitable environment for establishment of infection of circumanal glands, hair follicles,
and other glands in the perianal region. This conformation and. the poor ventilation afforded by such tail carriage may provide
a suitable environment for establishment of infection of circumanal glands, hair follicles, and other glands in the perianal
region, and thus abscessation fistulization. This author feels the deep folds just inside the anus also play a major role
in this disease and lead to collection of feces in rectal glands and resulting fistulous tracts.
Many of the dogs affected may also have a generalized skin problem and be hypothyroid; some may also have poor T-cell function.
Thus some suspect that perianal fistulas are an expression of generalized skin and systemic problems.
The anal sacs have been shown to be only secondarily involved in the disease process. Statistically, anal disease is seen
less frequently in German Shepherds. However, the infection can spread to deeper structures which can eventually canse severe
problems for the dog. One of these structures is the external anal sphincter, which plays a vital role in fecal continence;
rarely do the tracts extend to the bowel lumen.