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The paranasal sinuses are aerated cavities in the bones of the face that develop as outpouches of the nasal cavity and communicate with this cavity throughout life.(1) The maxillary and ethmoid sinuses are fully developed at birth, but the frontal sinus develops after age 2 and the sphenoid sinus after age 7. The nose and sinuses are lined with ciliated pseudocolumnar epithelium that includes mucous producing goblet cells. Small tubular openings called the sinus ostia connect the sinus cavities and facilitate drainage of the sinuses into the nasal cavity through the activity of ciliated cells.(2) The mucous blanket is carried toward the sinus openings (ostia) at a speed of up to 1cm/minute by the beating of cilia.(1) The mucous blanket changes two to three times an hour, and under normal circumstances does not accumulate in the sinus cavities. It is frequently the delay in the mucociliary transport time or obstruction of the ostia that may lead to sinusitis. The paranasal sinuses are frequently involved in the common cold. Computed tomographic study of patients with the common cold reveals that over 85 percent have a self-limited paranasal sinusitis that resolves without treatment.(3) Actually, rhinosinusitis is a more accurate term for what is commonly called sinusitis, since, as already described, the mucous membranes of the sinuses and the nose are contiguous.
The sinusitis that occurs with the most frequency involves the maxillary sinuses, followed by ethmoid sinusitis, then frontal and sphenoid sinusitis. The most common precursor to sinusitis is a viral upper respiratory tract infection; however, the frequency of which a clinically evident complication of acute bacterial sinusitis occurs, is very small, (only about 0.5% of viral upper respiratory infections). The development of sinusitis occurs most frequently from obstruction of the ostia due to mucosal edema. Viral infections also increase the amount of mucous, which may cause damage to ciliated cells and prolong transport time.
Acute sinusitis can be classified into various categories on the basis of several characteristics including its occurrence in the community or hospital setting; the immune status of the patient; its infectious or noninfectious cause; and its viral, bacterial, or fungal cause.(4) For example, in a non-hospitalized patient with normal immunity, sinusitis may be viral, bacterial, a combination of both viral and bacterial, or non-invasive fungal. It may also be allergic or non-allergic. In a hospitalized patient, nosocomial sinusitis is usually bacterial or fungal. Non-infectious causes include allergic or toxic sinusitis. In the immunocompromised patient, sinusitis may have a viral, or bacterial origin, and sometimes may be caused by an invasive fungal pathogen.
The paranasal sinuses, although directly connected to the nasal passages, which are colonized with bacteria, are themselves sterile under normal conditions. Sterility is maintained in the sinus by mechanisms that are not fully understood but are believed to include mucociliary clearance, the immune system, and possibly antibacterial concentrations of nitric oxide gas in the sinus cavity.(4)
The bacteriology of acute community-acquired maxillary sinusitis has been well defined by studies using direct sinus puncture and aspiration.(1) Streptococcus pneumoniae has been shown to cause about one-third of cases, while Haemophilus influenzae (not type b) causes one-fourth of cases. Moraxella catarrhalis, is also an important pathogen, especially in children and causing about 20 percent of pediatric sinusitis. Gram-negative bacilli play a role in approximately 9 percent of adult cases, and anaerobes are found in 6 percent. Anaerobes may be particularly important in patients with dental infections. In about one-fifth of adult cases, the presence of rhi
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