Anal sacs are paired small pouches located on either side of the anal opening in dogs, cats, ferrets and other animals. The lining of the sacs produces a smelly brown liquid that is usually eliminated in small quantities during defecation. The purpose of the anal sac is unknown, but it is thought that they function in communication about the animal or its territory.
Anal sacs can become inflamed, infected, or impacted (blocked). With these conditions, it is common for your pet to scoot their bottom on the ground and lick or chew at the area.
Tumours of the anal sacs (apocrine gland adenocarcinoma is the most common tumour type) are a serious but uncommon problem because they tend to invade surrounding tissues and metastasize (spread to distant tissues) even when the primary tumour is very small. The tumours are almost always only on one side. In approximately 25% of cases, the tumour can cause hypercalcemia (elevated blood calcium) which can cause kidney failure.
Anal sac tumours occur in male and female dogs with roughly an equal incidence. They occur in any breed but are more common in Spaniel breeds. Ten years is the average age of affected dogs. Anal sac tumours are very rare in cats.