ANATOMY
The sinuses, like the mastoids, are unique, air-filled cavities within the head (Figure1). The sinuses are normally sterile. These structures, as well as the eustachian tube, the middle ear, and the respiratory portion of the pharynx, are lined by respiratory epithelium. The clearance of secretions and contaminants depends on normal ciliary activity and mucous flow.
Fig1. Location of the paranasal sinuses. (From Milliken ME, Campbell G: Essential competencies for patient care, St Louis, 1985, Mosby.)
DISEASES
The pathogens associated with otitis media are the same ones associated with sinusitis; bacteria from the nose and throat make their way to the inner ear and sinuses. Acute sinusitis usually develops during the course of a cold or influenza illness and tends to be self-limited, lasting 1 to 3 weeks, and is usually more prevalent in winter and spring. Acute sinusitis is often difficult to distinguish from the primary illness. Symptoms include purulent nasal and postnasal discharge, a feeling of pressure over the sinus areas of the face, cough, and a nasal quality to the voice. Fever is sometimes present.
Occasionally, acute sinusitis persists and reaches a chronic state in which bacterial colonization occurs and the condition no longer responds to antibiotic treatment. Ordinarily, surgery or drainage is required for successful management. Patients with chronic sinusitis may have acute exacerbations (flare-ups). Other complications include local extension into the orbit, skull, meninges, or brain, and development of chronic sinusitis.
PATHOGENESIS
Most cases of acute sinusitis are believed to be bacterial complications following a viral respiratory infection. The exact mechanisms involved are unknown. About 5% to 10% of acute maxillary sinus infections result from infection originating from a dental source. The maxillary sinuses are close to the roots of the upper teeth, providing a mechanism for dental infections to extend into the sinuses. The primary problems associated with the development of chronic sinusitis include inadequate drainage, impaired mucociliary clearance, and mucosal damage.
EPIDEMIOLOGY AND ETIOLOGY OF DISEASE
Although difficult to access, the actual incidence of acute sinusitis parallels that of acute upper respiratory tract infections (i.e., being most prevalent in the fall through spring).
Most studies of the microbiology of acute sinusitis are associated with maxillary sinusitis because it is the most common type and specimen collection available through puncture and aspiration. Acute viral sinusitis is one of the most common causes of respiratory tract infection and in most cases resolves without treatment. However, published estimates indicate that 0.5% to 2% of cases of acute viral sinusitis in adults are complicated by bacterial sinusitis. This scenario is even more common in children. Bacterial cultures are positive in about three fourths of patients. Studies have indicated that Streptococcus pneumoniae and Haemophilus influenzae are the major bacterial pathogens in adults with acute sinusitis; other species such as beta-hemolytic and alpha-hemolytic streptococci, Staphylococcus aureus, and anaerobes have also been cultured but less frequently. The predominant bacterial organisms associated with chronic sinusitis include S. pneumoniae, H. influenzae, and M. catarrhalis; less frequently isolated organisms include anaerobic streptococci, Prevotella spp., and Fusobacterium spp. Fungal pathogens such as Aspergillus, Fusarum, and Candida albicans have also been identified in cases of chronic sinusitis using culture and polymerase chain reaction (PCR).
Among children, S. pneumoniae, H. influenzae, and M. catarrhalis are most common. Rhinovirus is found in 15% of patients, influenza virus in 5%, parainfluenza virus in 3%, and adenovirus in less than 1%. The major causes of acute sinusitis are summarized in Table 1. M. catarrhalis has been isolated in chronic sinusitis in children.
Table1. Major Infectious Causes of Acute Sinusitis
LABORATORY DIAGNOSIS
In most cases, a diagnosis can be made on the basis of physical findings, history, radiograph studies, and other imaging techniques such as magnetic resonance imaging. However, if a laboratory diagnosis is needed, an otolaryngologist collects a specimen from the maxillary sinus by puncture and aspiration or during surgery. Sinus drainage is unacceptable for smear or culture because this material will be contaminated with aerobic and anaerobic normal respiratory flora; sinus washings or aspirates surgically collected are the specimens of choice. Gram-stained smears and aerobic and anaerobic cultures should be performed on each specimen. Aerobic culture media should include blood, chocolate, and MacConkey agar.
