Primary Sinusitis

This is an infection of the horse’s sinus, similar to how humans can get sinus infections. These are usually caused by bacteria, but can be caused by fungus. An upper respiratory virus can predispose a horse to developing a primary sinusitis infection. Clinical signs include mucoid (whitish, yellowish) nasal discharge out of one or both nostrils, swelling or bulging of the facial bones, decreased appetite, lethargy and/or weight loss.

Paranasal sinus disease


Radiographs of the skull, CT of the head (Gives the most diagnostic detail), video endoscopy, oral/dental exam


In acute cases the horse is usually medicated with systemic antibiotics and anti-inflammatory medication, and re-evaluated in 2 weeks. If the sinus infection does not get better in 2 weeks then surgical options need to be explored. In chronic cases or cases with thick puss in the sinus, surgical options also need to be explored. One surgical option is to do a trephination into the infected sinus. This involves drilling a hole that is approximately ¾ inch in diameter, with the horse sedated and standing. The puss within the sinus can be flushed through the trephine hole. This may need to be repeated several days in a row to resolve the sinus infection. In more severe cases a sinus flap is performed to allow instruments to be placed in the sinus and aid remove puss and debris from the infected sinus. A sinus flap involves opening a flap of bone into the sinus that is 2-3 inches in width and 4-5 inches in length. The horse is placed under general anesthesia while a sinus flap is made. In cases with trephination or sinus flaps the horse’s face heals with minimal cosmetic defects.