The guttural pouches are paired outpocketings of the upper airway (pharynx). They are located near the throatlatch region of the neck. Major vessels and nerves supplying the head course through the walls of the pouch.

The guttural pouches are thought to be involved in cooling blood that passes to the brain through the large carotid arteries. They may also have a role in equalizing air pressure on the tympanic membrane. The guttural pouch volume in an average horse is 300-500 ml each.

In young horses, air can becomes trapped in one or both pouches through a one-way valve effect. There usually is a congenital defect in the guttural pouch opening that results in this condition. Air accumulation in the pouch results in a large, firm air-filled swelling in the throatlatch area of the neck.

Usually this does not cause the horse much distress, although in very severe cases, the swelling can cause difficulty breathing. In some cases, the pouch may deflate on its own intermittently.

Treatment is usually surgical, although in some cases, catheterization of the pouch may resolve the issue. The pouch is accessed with an endoscope through a small slit in the pharynx.