Sinusitis is an infection of one or all sinus cavities, usually caused by an upper respiratory tract infection (primary sinusitis). Other causes of sinusitis include dental disease, cysts, tumours, fungal infections, and even head trauma.
The horse’s paranasal sinuses are linked air-filled chambers which connect with the nasal cavity and are lined with a mucous membrane which produces fluid and mucus. While it would make sense for the drainage point for this fluid to be located on the floor of the sinuses, it is actually positioned towards the upper area, causing the sinuses to be overwhelmed during increased mucus production. As nasal breathers, horses require the ability to breathe in large quantities of air and if this function is compromised due to excessive mucus or inflammation, performance and general health will suffer.
- Nasal discharge (pus or blood)
- Halitosis (foul breath)
- Difficulty eating
- Laboured breathing
- Poor performance during exercise
- Facial deformity over sinus area
- Discharge from eyes
- Head shaking
An endoscope can be navigated through the nasal cavity to determine the cause of the drainage. Fluid samples are cultured for aerobic/anaerobic bacteria and fungi, and x-rays may be ordered if halitosis is present to detect and remove any diseased teeth. In sinusitis caused by tumours or injury, the underlying cause must first be treated.
Antibiotics are the usual course of treatment for primary sinusitis. Steam inhalation and light exercise will help the horse return to normal health. Chronic cases may require surgical lavage (flushing), where a small hole is drilled in the uppermost sinus cavity under sedation or local anaesthetic (lower cost and no anesthesia risk) and a catheter is stitched in place. Five litres of lukewarm saline, very dilute povidine iodine, or chlorohexidine solution are administered two or three times daily for about a week until symptoms subside.
Delayed or ineffective treatment can result in primary sinusitis progressing to osteomyelitis and necrosis, destroying soft tissue and bone. In these cases, surgical debridement and curettage (removal of diseased tissue) may be necessary, and in more severe cases, sinusotomy (creating a permanent opening from the frontal sinus into the nasal cavity) may be the only option.