The sinuses are air-filled cavities within the head of the horse. The sinuses also accommodate some of the maxillary premolar and molar tooth roots (upper cheek teeth), facilitate passage of facial nerves, and extend around (above and below) the horse’s eyes and end around the facial crest. The horse’s head has uniquely adapted itself and developed six pairs of paranasal sinuses—the frontal, sphenopalatine and maxillary sinuses, and the dorsal, middle and ventral conchal sinuses. The maxillary sinus is the largest paranasal sinus and is divided into two parts (rostral and caudal) by a thin septum. Many of the sinuses also communicate with one another: the maxillary sinus communicates with the front sinus, and the frontal sinus has a large communication with the dorsal conchal sinus. In healthy horses, mucus produced by the lining of the sinuses flows freely through the sinuses and into the nasal passages. The bone overlying the sinuses is very thin, and can be easily distorted by disease.
Sinusitis refers to inflammation or infection of one or more of the paranasal sinuses, and is the most commonly encountered disease of the paranasal sinuses. It is classified as either primary or secondary, and acute or chronic. Primary sinusitis is defined as infection in the sinus as the result of a bacterial infection invading the lining of the sinus that causes a buildup of pus within the sinus. Primary sinusitis is typically the result of an infection in the upper respiratory tract and is most frequently caused by Streptococcus species of bacteria. It usually involves all paranasal sinus cavities, but may be confined to the ventral conchal sinus. More commonly however is secondary sinusitis, which is infection as a result of another primary cause, such as tooth root infection, bone fracture or sinus cyst. The last four cheek teeth are most likely to cause a secondary sinusitis, as these teeth are contained within the maxillary sinuses. Empyema refers to purulent exudate within the sinus, but is not necessarily synonymous with chronic sinusitis.
The most common sign of sinusitis (either primary or secondary) is nasal discharge. The nasal discharge usually occurs on the side of the affected sinus (unilateral) only (Figure 1). The appearance and character of the discharge is variable, and may contain pus or blood, with or without an odor. Other clinical signs include:
- Unilateral facial swelling (Figure 2)
- Epiphora (squinting of the eye)
- Dull percussion of the sinuses
- Inspiratory noise
Your veterinarian will start by performing a complete physical examination before any other diagnostics.
- Endoscopy: can help characterize where the nasal discharge is originating, as purulent material, a mass, or blood can be seen in the nasal passages originating from the nasomaxillary opening (Figure 3).
- Radiographs: (X-rays) of the skull may reveal fluid lines, sinus cysts, solid masses, or lytic or proliferative bone associated with dental disease or neoplasia (Figure 4). If there is a large amount of exudate, it may be difficult to identify the cause of the sinusitis on radiographs, and the exudate may need to be removed to enhance radiographic and endoscopic evaluation.
- CT: In some cases and when possible, CT can help characterize sinus disease most completely, but typically requires general anesthesia and is rarely indicated in the initial stages of diagnosis.
- Sinoscopy: either standing or under general anesthesia may be helpful to obtain a sample of fluid (sinocentesis) for cytologic examination, bacterial culture and antibiotic sensitivity testing. Typically this procedure is done standing, using sedation and local anesthesia, and a small opening is made into the sinus, a flexible endoscope is used to evaluate (and potentially treat) the underlying condition.
Anti-inflammatories are typically used for all cases of sinusitis, to help reduce any swelling or discomfort associated with the condition or surgical procedures. Ideally bacterial culture and sensitivity are used to select an appropriate antibiotic for lavage of the affected sinus(es). In some cases, systemic antibiotics or antifungal medications may also be indicated.
The duration of hospitalization for sinusitis depends on the underlying cause for the condition, and ranges from less than a day to a range of 3–7 days. Repeat evaluation is likely to confirm the sinusitis has completely resolved. If the cause for the sinusitis was related to a tooth, repeat dental evaluation will likely be necessary.
Overall, the cosmetic results of equine sinus surgery and usually good. A small depression may be palpable at the surgical site, but is typically not noticeable to the naked eye. Horses with primary or secondary sinusitis typically have a good to excellent prognosis for return to function/athletic performance after appropriate treatment. If the cause of the sinusitis is treated appropriately and completely, it is unlikely the condition will recur in the future.