A common cyst of the horse is the epidermal inclusion cyst of the nasal diverticulm or "false nostril" of the horse. These are sometimes called atheromas because of their soft or fluid, colored, and cloudy contents on aspiration. This usually appears as a soft swelling on the nose just above the horses nostril. In uncomplicated small cysts they have been ignored and larger ones surgically removed. Recently a paper describes a simple procedure for resolving these cysts by a single injection, see insert to the right. This paper describes this procedure and provides a case report including pictures of the recovery.

The appearance of a soft swelling in the false nostril, the nasal diverticula, is fairly diagnostic for this condition. They can range from a barely noticable swelling above the nostril to very large and causing a wistling noise with respiratory effort. They are usually present from birth and usually unilateral, but may enlarge with time.