Pathophysiology

Failure of normal mucus transport and decreased sinus ventilation are the major factors contributing to the development of sinusitis. Obstruction of the sinus ostia occurs with mucosal edema or any anatomic abnormality that interferes with drainage. Bacterial and viral infections also impair the mucus transport system. The frequency of ciliary beats (normally 700 per minute) decreases to less than 300 per minute during periods of infection.

Inflammation causes 30 percent of the ciliated columnar cells to undergo metaplastic changes to mucus-secreting goblet cells. The obstruction and decreased transport results

in stagnation of secretions, decreased pH and lowered oxygen tension within the sinus, creating an excellent culture medium for bacteria.

A number of factors can contribute

to the development of sinusitis. The most common cause of acute bacterial sinusitis is a viral upper respiratory infection. Up to 0.5 percent of upper respiratory infections in adults develop into documented sinusitis. Children experience six to eight colds per year, and approximately 5 to 10 percent of these infections are complicated by sinusitis.

Allergic rhinitis has also been considered a contributing factor to sinusitis; however, no causal relationship has been proven, and it is now believed to be a rare initiating factor. Iatrogenic factors include mechanical ventilation, nasogastric tubes, nasal packing and dental procedures. Pregnancy, hormone changes associated with puberty, and senile rhinorrhea may be contributing factors. Anatomic variations include tonsillar and adenoid hypertrophy, deviated septum, nasal polyps and cleft palate. Smoking and intranasal cocaine use also predispose to sinusitis.

Computed tomographic (CT) scanning in humans has shown that most uncomplicated colds are associated with some radiographic findings of sinus involvement, the great majority of which do not progress to florid sinusitis. Experimentally-produced rhinovirus infections can generate abnormalities of the sinuses (as detected by MR imaging) accompanied by increased nasal secretion but without any evidence for bacterial involvement. Thus, prophylactic antibiotics for colds are never indicated, although they are frequently administered.

Viral URI most common cause.

Nasotracheal or nasogastric tubes can predispose to sinusitis.

Prophylacticantibiotic not indicated.

The bacteria responsible for sinusitis vary with the clinical setting:

The major causes of typical acute bacterial sinusitis include Streptococcus pneumoniae, Haemophilus influenzae, Streptococcus pyogenes, and (less often) Staphylococcus aureus.

Patients with chronic sinusitis are more likely to be infected with obligate anaerobes which are part of the usual mouth flora.
Nosocomial sinusitis involves bacteria and fungi that enter the sinus after becoming part of the patient's respiratory tract flora. This includes methicillin-resistant S. aureus (MRSA), various gram-negative bacilli (such as Escherichia coli and Pseudomonas aeruginosa), and yeasts such as Candida albicans.