Sinusitis, Primary
Basic Information 
Definition
An inflammatory process of the paranasal sinus system caused by bacterial upper respiratory tract infection
Epidemiology
Species, Age, Sex
Primary sinusitis can affect horses of all ages with a reported higher incidence in 6- to 8-year-old animals.
Risk Factors
• Viral infections of the upper airway can cause swelling of the respiratory mucosal lining of the paranasal sinuses that is severe enough to occlude the nasomaxillary opening and therefore prevent drainage of mucus from the sinus system into the nasal cavity. The accumulation of discharge within the sinuses can cause sinusitis and is more commonly observed in young horses.
• Horses with a compromised immune system (eg, Cushing’s disease) also appear to be more prone to develop sinusitis.
Clinical Presentation
Disease Forms/Subtypes
• Horses present with different degrees of pathology. Horses with mild and early diagnosed forms may respond well to treatment with the appropriate antimicrobial medication alone.
• Horses with more severe or more chronic sinusitis require more aggressive therapy ranging from repeated lavage to sinotomy and surgical debridement.
History, Chief Complaint
Purulent or mucopurulent nasal discharge is the major presenting complaint in primary sinusitis. Only rarely is the nasal discharge bilateral. The owner may notice the nasal discharge during or after exercising the horse or while the animal holds its head down or even at rest with a normal head position.
Physical Exam Findings
• Unilateral nasal discharge is most commonly observed. In primary sinusitis, facial swelling is rare and, if present, may not be noticed by the owner. About 20% of cases with primary sinusitis have epiphora caused by interference with the nasolacrimal duct.
• If the ventral concha is affected, a partial nasal obstruction with subsequent respiratory noise may be detectable. The presence of discharge within the maxillary or frontoconchal sinuses changes the character of sound upon percussion of the respective regions. In about two-thirds of primary sinusitis cases, the submandibular lymph nodes are enlarged.
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