Sinusitis means that there is an inflammation or infection of a sinus cavity. While there are other sinuses in the body this article will restrict itself to the paranasal sinuses. The paranasal (meaning near the nose) sinuses are all located in the head of the horse and in this article when I say sinus (which they are most commonly referred to as) I am referring to the paranasal sinuses.
What is sinusitis?
Sinusitis means that there is an inflammation or infection of a sinus cavity. While there are other sinuses in the body this article will restrict itself to the paranasal sinuses. The paranasal (meaning near the nose) sinuses are all located in the head of the horse and in this article when I say sinus (which they are most commonly referred to as) I am referring to the paranasal sinuses. Horses have five sinuses of which the maxillary is the largest. All these sinuses are located in the upper part of the head just below and above the eyes. The sinuses are the maxillary (divided into caudal and rostal), frontal, sphenopalatine, and conchal. Of these, the frontal and maxillary are the two that cause the veterinary practitioner the most concern when sinusitis develops. The size of the sinus changes with the age of the horse. In young horses the reserved crown and roots of the upper cheek teeth occupy part of the maxillary sinus. As the horse ages the teeth erupt (downward into the mouth and are worn away by attrition) and move forward towards the nose.
There are two main classifications of sinusitis in the horse, primary and secondary. Primary sinusitis refers to when there is an inflammation or infection of the sinus of which the offending pathogen is usually just one type of bacteria (Streptococcus zooepidemicus). Secondary refers to when there are many offending pathogens and the disease process is most commonly associated with a tooth infection, facial fractures, granulomatous lesions and neoplasms.
The most common clinical sign of sinusitis is a nasal discharge (Figure 1). The nasal discharge is usually unilateral and rarely is bilateral. It ranges from being vary slight and clear in nature too copious and purulent. Halitosis (bad breath) is another vary common clinical sign. In people headaches are very common but we don’t know if horses get headaches but it can be assumed that an inflamed sinus filled with fluid has to be uncomfortable. However, horses do seems to cope as they don’t exhibit any obvious behavioral signs (head pressing, head tossing, kicking, pawing, colic, etc) when they do have sinusitis. Again, how does the owner find out if their horse has sinusitis? In most cases they observe a unilateral nasal discharge and halitosis. If there is no nasal discharge the owner might notice the halitosis which might from the mouth.
Percutaneous sinus centesis (taking a sample of the fluid within the sinus) is done in the standing sedated horse. The fluid sample is cultured for aerobic and anaerobic bacteria and, if suspected fungi. Cytology of the fluid is also examined for bacteria, fungi, inflammatory and neoplastic cells. If any plant or feed stuff is found upon cytological examination a disease tooth is most likely the problem or the horse has a oral-nasal fistular (a communication between the mouth and the sinuses).
Often the veterinarian will discover a disease tooth upon oral examination and if not and cannot determine the cause for the halitosis then they will take radiographs of the head. Frequently, these radiographs will not only show an associated sinusitis (fluid in the sinus) but a disease tooth. In cases where a diseased tooth is the nidus of infection, the tooth must be extracted or repelled. In order for the sinusitis to resolve with treatment it must be started early in the course of the disease.
In primary sinusitis treatment involves taking a sample of the exudate (fluid in the sinus) and performing a culture (growing the bacterial organism) and sensiverity (determining which antibiotic will kill the bacterial infection).
Once the antibiotic of choice is determined it is administered systemically and the sinus flushed (by inserting a tube in the sinus) daily for a few days.
Secondary sinusitis treatment is the same for a primary case except that the offending factor (eg, tooth) must be determine and treated first. In the case of a disease tooth the tooth must be removed. Prolonged cases of sinusitis (primary or secondary) can be difficult to treat. The mucus membranes that line the sinus become infected and subsequently the bone of the sinus and it is vary hard if not impossible to removed the infection in some horses. Some horses with prolonged sinusitis may never fully recover.