Your horse’s sinus cavities are complex: A variety of caverns of different sizes and shapes rest just behind the bones of his face, surrounded by soft tissue and abutting his molars. This makes diagnosing and managing equine sinus diseases challenging for veterinarians. In fact, an estimated 47% of horses that undergo sinus surgery reportedly develop some type of postoperative complication.

Before delving into common causes of sinus disease during his presentation at the 2017 American Association of Equine Practitioners Convention, held Nov. 17-21 in San Antonio, Texas, José García-López, VMD, Dipl. ACVS, ACVSMR, reviewed the paranasal sinus anatomy for attendees. García-López, who is director of Equine Sports Medicine from the Tufts University Cummings School of Veterinary Medicine, in North Grafton, Massachusetts, described the frontal, conchal, maxillary, and sphenopalatine cavities, along with the normal “communications” between them (how they’re connected and drain into one another). He did note that there are some “funky crevices” that allow materials to hide, and accessing those areas can be difficult for veterinarians.

“When approaching horses with sinus disease, it is important to know where the communications are between the various sinuses,” emphasized García-López.

He shared several case examples of common culprits behind equine sinus diseases.

Case 1: Primary sinusitis

This case began as a primary infection rather than secondary to another cause, such as a cyst or tooth-root abscess. The veterinarian recognized that equine influenza and even equine herpesvirus-4 can produce sufficient mucus to cause inflammation of the sinus lining (what we know as sinusitis), which can block normal mucus drainage. Inspissated (thickened) pus accumulated in this horse’s sinuses, especially in the ventral conchal sinus.

“In terms of management, lavage (flushing out) is key,” García-López said. “Use between 1 and 3 liters of sterile water with or without dilute Betadine or chlorhexidine once or twice daily.”

Case 2: Unilateral (one-sided) nasal discharge, partially responsive to antibiotics

In this case, a surgeon performed sinusotomy (incising through the bone overlying the sinus to access the paranasal cavities) under general anesthesia and identified a fluid-filled paranasal sinus cyst with a “shell.” Debulking (eliminating all or most of the substance of) the cyst, being sure to remove the lining or shell, typically results in complete resolution. Despite being a relatively common equine sinus disease, responsible for facial swelling, nasal discharge, and even dyspnea (difficulty breathing), these cysts’ underlying cause remains unknown.

“A fair amount of bleeding occurs after removing these cysts, and the nasal cavity needs to be packed,” García-López said. “Be sure to exit the packing through the nose, not the sinusotomy site.”

Case 3: Malodorous, purulent (pus-filled), unilateral nasal discharge, partially responsive to antibiotics

A complete oral examination revealed no abnormalities, but a CT scan showed a large, well-defined mass caused by a tooth root abscess. To manage the secondary sinusitis, the veterinarian performed sinoscopy (using an endoscope to visually examine the abscess) to identify and remove the abscess. In addition, the veterinarian removed the affected tooth and again treated the horse with antibiotics.

“These cases can be frustrating to treat because the walls of abscess can appear similar to normal sinus wall, and if you don’t remove all of the abscess, it will recur,” García-López noted.

Case 4: Unilateral epistaxis

A CT scan identified a progressive ethmoid hematoma (a slowly expanding mass in the mucous lining of a structure called the ethmoid turbinate, located in the back part of the nasal cavity) that was consistent with the horse’s clinical signs: unilateral bloody nasal discharge.

“Be careful with these cases,” said García-López. “About 20% of progressive ethmoid hematomas are actually bilateral (involving both sides), even without clinical signs of bilateral epistaxis. Don’t get blinded by the obvious lesion, missing other abnormalities.”

Again, post-surgical complications can develop, and many progressive ethmoid hematomas recur.