Selected Disorders of the Equine Paranasal Sinuses

Aubre Harper

Hal Traxler

Dr. Ame Walesby

In the horse, there are 6 pairs of paranasal sinus cavities: the frontal, maxillary, sphenopalatine, and the dorsal, middle, and ventral conchal. The picture below illustrates the approximate location of these sinus cavities. The picture represents a view of the left side of a horse’s skull. The horse’s nose would be to the left, and the ears would be to the upper right. The eye would be located in the area labeled ‘orbit’. Only the upper jaw is represented (the upper cheek teeth are along the bottom of the picture). Fluid and debris drain through various openings between the sinuses and eventually into the nasal cavity and out through the nostrils. In some areas the openings between sinuses may be very small, limiting the amount of fluid that can drain through. The roots of the upper cheek teeth project into the maxillary sinus cavity and can also hinder the drainage of fluid.

Unfortunately, the complex anatomy of these sinuses combined with their less than ideal drainage system predispose the horse to developing a wide variety of sinus disorders (usually within the frontal or maxillary sinuses). These disorders can become very serious by destroying the normal tissue in and around the nasal cavity, or by causing an obstruction of the horse’s airway. The horse is an obligate nasal breather, meaning that it is only able to breathe through the nose (not through the mouth like other animals). Therefore, any obstruction in the nasal cavity of a horse can be a life-threatening situation. It is imperative that the horse owner be able to recognize the clinical signs associated with early sinus disease so that treatment may be started as soon as a diagnosis is reached.

Sinus Cysts

Sinus cysts are an uncommon, but well recognized condition affecting the paranasal sinuses of the horse. The cysts are cavities filled with a thick, amber-colored, honey-like fluid. They are seen primarily in the maxillary sinuses of relatively young horses. The exact cause is unknown, but it has been hypothesized that the cysts are congenital anomalies present at birth, or that the cysts may have their origin in dental tissues. The cysts grow at such a slow rate that the facial bones and other surrounding structures are forced to remodel themselves around the developing cyst. For this reason, the most common clinical sign associated with sinus cysts is progressive facial swelling and deformity. The growing cyst may also cause abnormal changes in the roots of the upper cheek teeth, leading to development of secondary dental disease. Over time the cyst may invade the neighboring nasal cavity and obstruct air flow to the lungs. A horse with such an obstruction will exhibit respiratory difficulty and/or exercise intolerance. Additionally, sinus cysts are associated with a unilateral clear to mucoid nasal discharge.

Diagnosing sinus cysts is relatively simple. Generally, the horse’s history and clinical signs are enough to support a diagnosis of sinus cysts. For confirmation, radiographs (x-rays) may reveal abnormalities of the tooth roots or a fluid-filled cavity in the area of the maxillary sinus. Endoscopy may also be performed in order to visualize the cyst and/or the deformed sinus cavities. Once it is located using the endoscope, the veterinarian may opt to drain the cyst as a temporary solution. But it should be noted that the cyst will redevelop to its original size relatively quickly. Left untreated, the sinus cyst will continue to grow, progressively deforming the facial bones and imposing on the airway. The only acceptable method for complete resolution of a sinus cyst is surgery.

Recurrence of the sinus cyst is uncommon. Following successful surgical extraction, the overlying facial bones may gradually remodel to a more normal appearance. The prognosis for a complete return to normal athletic performance is fair to guarded. There is a chance that the horse will suffer some ongoing health problems, depending on the size and severity of the sinus cyst. Most commonly, the horse may experience a chronic nasal discharge. If the cyst grew large enough to cause obstruction of the nasal passages, the horse may suffer persistent respiratory obstruction and difficulty (this condition may improve in younger horses that are still growing). And in some cases, the upper tooth roots are so affected that the horse may continue to have dental abnormalities for the remainder of its life.

Paranasal Neoplasia

Although neoplasia (cancer) of the oral cavity is extremely rare, it does occur. There are no breed or sex preferences shown by certain types of tumors. However, there is an age predilection. Oral tumors do occur in all ages of horses, but most are congenital and identified when the horse is young.

Clinical signs associated with oral neoplasia vary depending on the location, type and size of the tumor in the oral cavity. The anatomy of the oral cavity allows for advanced development of the tumor before the horse develops outward clinical signs. Clinical signs range from difficulty swallowing or chewing food, bad breath, oral or a nasal discharge, and swollen lymph nodes.

Physical exam reveals a slowly developing, firm, immobile swelling of the upper or lower jaw bones. The mucus membrane over the mass is often ulcerated and the teeth associated with the mass can be loose. Sedation or general anesthesia may be required to do a thorough accurate exam. Radiographs are essential to assess the size and extent of the mass, and to differentiate the mass from a primary dental problem. Endoscopy can be used to determine the degree of sinus involvement. Biopsies can be performed to identify the tumor and plan therapy. Surgical removal is indicated. The possibility of complete removal and cure depends on the size and location of the tumor. Recurrence is more common when the tumor is located on the lower jawbone. Cryosurgery, the freezing of tissue to kill tissue cells, has been used to supplement surgical excision by removing neoplastic cells without removing additional bone.

Successful treatment depends on successful removal and the type of tumor present. Should the tumor prove to be aggressive and destructive then euthanasia is indicated.

Primary Sinusitis

The term ‘sinusitis’ refers to any inflammatory process occurring within the paranasal sinuses. Sinusitis may develop as a result of a wide variety of insults, such as dental disease, trauma, sinus cysts, or neoplasia. These insults disrupt the normal architecture and immune mechanisms of the sinuses and allow the establishment of secondary bacterial or fungal infections. In contrast, the term ‘primary sinusitis’ is generally reserved for those conditions due to direct invasion of the sinuses by the pathogens themselves (usually the bacterium Streptococcus spp.) or due to extension from an upper respiratory infection. Horses 1 – 5 years of age are most commonly affected with primary sinusitis due to their increased susceptibility to bacterial or viral upper respiratory infections. Older horses are more likely to develop dental disease or neoplasia (cancer), and are therefore more likely to develop sinusitis secondary to these conditions.

The clinical signs associated with primary sinusitis will vary based on the location, severity and chronicity of the disorder. Unilateral nasal discharge suggests that only one side of the sinuses is involved, whereas bilateral nasal discharge indicates infection in both the left and right sinuses. This nasal discharge may range from clear and mucoid, to thick and blood-stained, to yellow, purulent, and foul-smelling, depending on the pathogen causing the infection. Fever, weight loss, respiratory difficulty, and exercise intolerance are all common signs seen in horses with sinusitis. In more chronic conditions, the infection may extend into surrounding tissues and cause neurologic signs or meningitis.

A presumptive diagnosis of primary sinusitis may be made based upon the history and clinical signs. A thorough physical exam along with radiography (x-rays), endoscopy, and/or sinuscentesis can aid in confirming the diagnosis. Percussion (tapping sharply on the bone overlying the sinuses) may reveal dullness, an indication of an accumulation of fluid or a mass in the sinuses. Radiographs are helpful in establishing the location or extent of the sinus disease. Affected sinuses will appear fluid-filled, and nearby bone may be deformed as well (a sign of a more aggressive, chronic disorder). Endoscopy may allow visualization of draining purulent matter from the suspected infected sinus as well as an evaluation of the architecture of the nasal cavity (severe sinusitis may deform nearby tissues and structures). In performing a sinuscentesis, a fluid sample is obtained via a needle introduced through the skin and bone into the affected sinus. This sample may then be analyzed in order to determine the cause of the sinusitis.

There are a variety of treatment protocols available for primary sinusitis based on the severity of the disorder. Initially, systemic antibiotics (usually Penicillin) are administered to the horse until results from the sinuscentesis sample are obtained. If the results show that the causative pathogen is susceptible to the antibiotic already being administered, this course of therapy continues for at least 14 more days. If not, then the systemic antibiotic should be changed to one that is specific for the causative pathogen and should be administered for at least 14 days. Daily lavage (rinsing with fluid) of the affected sinus is also an appropriate treatment. A catheter is placed into the sinus and about 1 liter of fluid (with the previously chosen antibiotic added into the fluid) is flushed into the sinus cavity for the removal of purulent matter and debris. If these therapies are not successful in resolving the sinusitis, surgery may be necessary. The surgical procedure involves entering the sinus cavity via the overlying facial bone and manually removing the fluid and necrotic tissue.

For those cases of sinusitis that respond quickly to systemic antibiotics and daily lavage, the prognosis tends to be favorable. In more chronic cases (those lasting longer than 6 months without successful resolution of the condition), the prognosis is poor and recurrence is common.

Tooth Root Abscesses

Sinusitis is commonly seen in the frontal or maxillary sinus in the horse. The sinuses are closely associated with the tooth roots. As a result, food and bacteria from an infected tooth can enter the sinus resulting in infection of that sinus. Clinical signs include a purulent nasal discharge from one side of the nose. The color of the discharge varies from yellow to green and is usually foul smelling. In addition, the discharge can be intermittent or continuous lasting days to weeks. Other clinical signs include swelling of the lymph nodes under the jaw and a foul smell to the breath.

Tooth root abscesses frequently occur in young horses when teeth are erupting, but can occur in horses of any age. Infection can be caused by either a delay in tooth eruption, caused by a baby tooth or trauma, which may cause the break down of blood vessels in the bone around the tooth, or the development of a central canal of necrosis in the tooth. It is proposed that bacteria that normally do not cause problems take advantage of the situation and invade the disturbed tissues initiating infection.

Diagnosis is based on history, clinical signs, oral examination and radiographs. Radiographs help to locate the affected tooth.

Once the diseased tooth has been identified, several options for treatment exist. If there is a retained baby tooth it should be removed and the adjoining teeth filed to provide enough room for the growing tooth. If there is a draining tract associated with the diseased tooth, the draining tract should be surgically cleaned and flushed. Antibiotics and antiinflammatory drugs should also be given. If the problem reoccurs after the drug treatments have been stopped, then a root canal surgery or extraction of the affected tooth is indicated. Root canal surgery preserves the function of the tooth while removing the disease portion of the tooth. Extraction is started by elevating the gums on the tongue and cheek sides of the tooth with a periodontal probe. Extraction forceps with wide, short jaws are then positioned on the cheek and tongue sides of the tooth and tightened into position. A slow side-to-side motion is started and as loosening begins the motion and the force is increased. As the tooth really begins to loosen a sucking noise caused by the motion of the tooth and the blood in the tooth socket will be heard and a twisting or rocking motion can be applied to the forceps. When the handles of the forceps rock freely a fulcrum is positioned to elevate the tooth out of the socket. With older horses the wound is left open to heal and with younger horses cleaning and lavage of the wound is required. To perform this extraction great patience is a necessity because if the time required to do the extraction is not taken the tooth can be broken and the whole process will be made more difficult.

Sinusitis secondary to dental disease can be prevented with regular veterinary dental care.