Sinusitis is an inflammation of the sinus lining, often occurring during an upper respiratory infection, caused by either bacteria or viruses. It can also be a complication of tooth infection, allergy or certain infectious diseases.

Horses, to a certain extent, are airheads – they have three pairs of sinuses in their heads, with one of each of the pairs on either side of the head. Only two of these, called the maxillary and the frontal sinuses, are commonly affected with infections and other problems. The frontal and maxillary sinuses communicate with each other, and to make matters even more complicated, the maxillary sinus contains the roots of the last three cheek teeth.

Sinusitis can affect any age horse. Older horses are more likely to have sinusitis from tooth root infections. Young horses are more likely to have a sinus cyst or a primary infection. It is rare, but both young and old horses may also have a tumor in the sinus.

What to Watch For

  • Sinusitis is usually recognized when the horse has a persistent nasal discharge from one side. Rarely, there may be an infection in both sinuses.
  • If the infection is secondary to a dental problem, the nasal discharge will typically be remarkably foul smelling. You sometimes need to get close to the horse to notice the smell, but if the discharge is prolific, then everything touching the horse's nose – including your hands or clothes – will carry the offensive smell.
  • If the infection has been going on for a long time, you may eventually notice a swelling along the side of your horse's face.
  • Some horses find sinusitis very painful and irksome, and will resist the bit, shake their heads, or refuse to eat.


  • Physical examination. Your veterinarian will take an in-depth history and perform a physical examination. She will want to know how long this has been going on, what the discharge looks like, and how old your horse is. During the physical examination, your veterinarian will percuss the sinuses – she will gently but firmly rap on the area overlying the maxillary and frontal sinuses while holding your horse's mouth open. This increases resonance, the drumlike, hollow sound. This will indicate if one side is duller than the other, indicating that it might be full of fluid.
  • Radiographs. X-rays of the head will show the presence of fluid or a mass in the sinuses, and will allow your veterinarian to determine if the tooth roots that protrude into the sinuses are infected.
  • Endoscopy. This will allow your veterinarian to examine the opening to the sinuses – if she sees pus coming from this opening, then sinusitis is very likely. She will also be able to examine other structures, such as the guttural pouches to determine if there is another cause for the nasal discharge. Occasionally, there will be multiple causes that need to be addressed separately.
  • Oral examination. A thorough oral examination of the teeth will allow your veterinarian to look for cracked or missing teeth. This usually requires heavy sedation and the use of a mouth gag (speculum).


    Treatment depends on the underlying cause of the sinusitis, the desired outcome, and in some cases, the age of the horse.

  • In uncomplicated cases, the first approach is to drill a hole into the sinus. This is called trephination, and is done easily under sedation and local anesthesia; it takes less than an hour. This procedure allows your veterinarian to obtain an uncontaminated sample of the pus for bacterial culture and sensitivity to determine which antibiotics will be effective against the bacteria that are found. Culture is also important to rule out strangles (Streptococcus equi var. equi) infection, which can spread to other horses rapidly.
  • When there is a build up of pus in the sinus, it can be very difficult for the antibiotics to get to the infection, so the pus must be removed. To do this, your veterinarian will place a drain into the sinus, and flush it with copious amounts of fluid. Frequently, the drain will be left in for 3-7 days, and you will be able to flush your horse's sinus at home.
  • Your horse will probably stay on antibiotics for a total of 2-4 weeks.
  • In complicated cases, such as with a sinus cyst, an infected tooth, or a tumor, your horse will likely undergo sinus surgery. This is usually the only way to achieve resolution of the problem.
  • Because sinus surgery can be expensive and there can be complications, some veterinarians have successfully managed tooth root infections in older horses by flushing the sinuses 2-3 times per year.

    Home Care

  • You may need to flush your horse's sinuses, according to your veterinarian's directions.
  • Be sure to follow instructions for giving antibiotics EXACTLY. It is very important to give the recommended amount at the right times. It is also very important to finish the entire course of antibiotics. The infection will likely still be present for some time after your horse is looking and feeling healthy. If you stop giving the antibiotics, there will likely be a recurrence.

    Preventative Care

    Be sure to have your veterinarian do a thorough dental examination on your horse every year. You may be able to treat dental problems before they cause a sinus infection.

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