Dogs and cats lack voluntary control of the sacs. Normally, the semi-liquid, fetid material is squeezed out passively when pets defecate, but sometimes things go wrong. Problems associated with anal sacs include impaction, infection, abscess, and neoplasia. Impaction occurs when the duct or tube through which an anal sac empties becomes clogged. Pressure builds in the sac and on surrounding tissue, resulting in painful defecation and, in some cases, constipation.
Bacterial infections cause damage and inflammation resulting in pain and itchiness.
This condition, which Dr. Barber speculates must be far more painful than hemorrhoids, sometimes leads to unusual levels of fear or aggression in pets. Left untreated, infections can abscess. Pain associated with abscesses can become very intense as pressure and inflammation increase. If this stage of the disease is left untreated, the abscess could rupture and drain through the skin, temporarily reducing pain, until the body seals the rupture, causing the process to start over again. Some of these growths are benign and others are very aggressive cancers.