Pathogenesis of Sinusitis

The anatomy of the sinuses does not promote passive gravitational drainage and therefore the cilia of the sinonasal mucosa must function properly. Without the constant movement of mucus from the sinuses into the nose, accumulation and eventual infection is inevitable. This fact is illustrated by disorders such as Kartagener syndrome, in which ciliary movement is abnormal.

The cilia of the maxillary sinus propel mucous toward the natural ostia of the sinus, explaining why large openings made into the maxillary antrum at places other than the natural ostia (eg, in the inferior meatus) are ineffective at draining the sinus.

Acute sinusitis may begin with edema of the nasal mucosa and the resultant blockage of the sinus ostia, which then results in stasis and infection. The most common organisms responsible for acute sinusitis include Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis. Depending on the geographic location, approximately one third of S. pneumoniae isolates are resistant to penicillin and one third of H. influenzae produce -lactamase. Nearly all isolates of M. catarrhalis produce -lactamase.

Chronic sinusitis arises from longstanding inflammation of the sinonasal mucosa and is often caused by bacteria different from the bacteria that produce acute sinusitis. Laboratory studies in which maxillary mucopus was cultured during endoscopic surgery showed a high percentage of coagulase-negative Staphylococci, Staphylococcus aureus, and Streptococcus viridans.

Corynebacterium and anaerobes were also isolated. Although coagulase-negative Staphylococcus is often considered a contaminant, the organism may have a pathologic role in chronic sinusitis. Also of note, the coagulase-negative Staphylococcus isolated displayed significant antimicrobial resistance. In other studies of chronic sinusitis bacteriology, a similar range of organisms was cultured except that Pseudomonas was identified in a significant number of the isolates. One half of these Pseudomonas isolates were resistant to quinolones.

Fungus may also infect the paranasal sinuses, causing a wide range of disease. Certain species, specifically Mucor, cause invasive fungal sinusitis. Invasive fungal sinusitis is typically seen in the diabetic or immunocompromised patient and is characterized by a rapidly progressive course. The skull base and orbit are frequently involved, necessitating aggressive surgical and medical management. Fungus can also stimulate an immune response from the sinonasal mucosa, resulting in allergic fungal sinusitis. Typically, polypoid tissue is seen anterior to a mass consisting of mucin, fungal elements, Charcot-Leyden crystals, and eosinophils. Sinus expansion and bony remodeling are hallmark features of this process. Even though this is not an invasive, infectious process, the treatment is surgery with immunotherapy as a critical adjunct.