A Review of Nasal Cavity Disorders Associated with Equine Sinus Disease

Introduction
In recent years, it has become increasingly recognized that many cases of equine sinus disease are accompanied by nasal cavity disorders. Together, they can be more accurately referred to as sinonasal disorders.
Nasal conchal bulla disorders
Sinus-associated nasal disorders include empyema or distortion of the ventral and dorsal nasal conchal bullae. These anatomical structures have often been neglected in the equine literature. Nasal conchal bulla changes are observed in more than 50% of horses with sinus disease, particularly in cases with purulent sinusitis, such as primary and dental sinusitis.
Whilst computed tomography imaging (CT) is the most reliable method for detecting such changes, financial and practical limitations often restrict its use. These conchal bulla changes can usually be endoscopically identified in the lateral aspect of the middle meatus as a swollen, rounded structure, possibly fistulated. A smaller (typically less than 10 mm diameter) flexible endoscope is best for this examination. With appropriate training, nasal conchal bulla changes can also be recognized on lateral-oblique head radiographs. Anatomical, endoscopic, and diagnostic imaging examples of normal and diseased nasal conchal bullae will be presented, and their treatment discussed.

Sinonasal fistulation
Another common concurrent sinus and nasal disorder is spontaneous sino-nasal fistulation, which mainly occurs between the lateral aspect of the middle meatus and the rostral or rostro-medial aspects of the ventral conchal sinus. When identified, this fistula can sometimes be used as a portal to lavage the sinuses. However, direct endoscopic access to the rostral maxillary sinus from this portal may be difficult in young horses.

Inspissated Exudate and Sequestra in the Middle Meatus
In many cases of sinusitis (44% in a recent large study), the middle meatus, particularly its lateral aspect, develops an accumulation of inspissated exudate, and/or sequestered nasal conchal or nasal bulla bone, sometimes with overlying secondary, dark fungal plaques. These lesions are best detected using a small endoscope as described above, which can actually be more sensitive than CT imaging in identifying these lesions.
In some cases, visualization of the middle meatus may be obstructed by large amounts of exudate present at this site. Vigorous flushing of this area transendoscopically, using high volumes of lukewarm water or 1% saline solution using a diastema pump, can remove exudate and allow clearer visualization of the remaining area. Most such exudate can be lavaged into the nasopharynx or common nasal passages, as described earlier. Firmer areas of inspissated exudate can be “flicked” down into the nasal passages by flexing the endoscope tip, where they may be swallowed or snorted out of the nostrils. Irregular pieces of the thin, lacelike bone can be transendoscopically grasped with biopsy forceps and retracted back through the middle meatus and then nostrils or pushed into the common nasal meatus if too large. Examples of these middle meatus lesions will be presented.

Triadan 06 and 07 Infections and Sinus Disease
Because their apices normally lie outside the sinuses, apical infections of Triadan 06 and Triadan 07 cheek teeth do not directly cause equine sinus disease. However, infections of these teeth may be present along with apical infections of adjacent Triadan 07 and 08 teeth, particularly of the 08, and so be associated with sinusitis. There are also documented instances where apical infection of the Triadan 07 teeth led directly to sinusitis, and some examples will be presented

Sino-Nasal Fistulation and Sinus Disease
The formation of an oro-nasal fistula following the extraction of Triadan 06 or Triadan 07 teeth allows food material to enter the nasal cavity. This will lead to foreign body rhinitis, which can become severe in some horses and can subsequently result in ipsilateral sinusitis.