Sinusitis, Secondary
Basic Information 
Definition
Secondary sinusitis is an inflammatory disease process localized to the paranasal sinus system in response to a variety of different primary pathologies, including:
Epidemiology
Species, Age, Sex
The age distribution of secondary sinusitis depends on the underlying disease process but can span a wide range. Whereas dental sinusitis is less common in horses younger than 4 years of age, sinus neoplasia has been found in foals. The mean age with which horses are presented with secondary sinusitis ranges between 7 and 14 years.
Risk Factors
• As with primary sinusitis, horses with a compromised immune system (Cushing’s disease) appear to be more prone to developing dental sinusitis.
• Because dental sinusitis is the most common form of secondary sinusitis, any dental pathology involving the fourth premolar through the third molar in the maxilla (108–111, 208–211 according to the Triadan system) may lead to secondary sinusitis.
Associated Conditions and Disorders
• Space-occupying processes such as neoplasia, sinus cysts, and progressive ethmoid hematoma may lead to obstruction of one or both (if bilateral) nasal passages. Consequently, these animals exhibit abnormal respiratory noises. In rare cases of severe airway obstruction, a tracheotomy may become necessary. The space-occupying processes may not only compromise airflow but are also responsible for the considerably higher incidence of facial distortion and swelling in secondary compared with primary sinusitis. The expansion of neoplasia, sinus cysts, or progressive ethmoid hematomas may also cause pressure necrosis of various tissues within the sinus system or nasal cavity.
• Tooth root infections and abscesses may progress to the surrounding bone, causing osteitis.
• Disease processes that are localized in close proximity to the cribriform lamina, such as progressive ethmoid hematoma or trauma, may cause neurologic symptoms and may even lead to life-threatening meningitis.
Clinical Presentation
Disease Forms/Subtypes
Secondary sinusitis is the common feature of the above-mentioned underlying pathologic processes; however, each original process leading to secondary sinusitis must be recognized as a distinct disease that requires specific treatment.
History, Chief Complaint
Owners may observe nasal discharge of different quantity and variable character ranging from purulent or mucopurulent and malodorous (dental sinusitis) to bloody or blood tinged in progressive ethmoid hematomas. Facial swelling is more likely present in secondary than in primary sinusitis cases. Other clinical signs the owners may observe are epiphora and abnormal respiratory noises. In some cases of dental sinusitis, the primary dental pathology may cause an abnormal chewing pattern or result in a prolonged time period the horse needs to finish a meal.
Physical Exam Findings
• Unilateral nasal discharge is most commonly observed followed by facial swelling. The character of the nasal discharge may give a hint to the underlying pathology. Facial swelling frequently accompanies secondary sinusitis caused by sinus neoplasia, sinus cyst, and dental sinusitis in decreasing order. When the disease involves the maxillary sinus, epiphora is more likely.
• Horses with sinonasal growths (neoplasia, cysts, and progressive ethmoid hematoma) can have a partial nasal airflow obstruction, leading to abnormal respiratory noises. Lymphadenopathy of the ipsilateral mandibular lymph nodes is more common in neoplasia, mycotic sinusitis, and dental sinusitis than in cases with progressive ethmoid hematoma.
Etiology and Pathophysiology
• Depends highly on the underlying pathology
• Commonly isolated microorganisms are Streptococcus equi subsp. equi, Streptococcus equi, subsp. zooepidemicus, and Staphylococcus spp., similar to primary sinusitis.
• Direct infection of the sinus system: Ascending pathway in dental sinusitis or direct penetrating wounds in traumatic sinusitis.
• Indirect infection of the sinus system: Sinus cysts, neoplasia, polyps, and progressive ethmoid hematomas may cause indirect infection by diminishing the mucociliary clearance of the respiratory mucosa with subsequent decreased local immunity.
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