Located within this framework of cartilage, bones, and turbinates are the four sinus cavities of the paranasal region. They function to humidify incoming air, filter out particulate matter present in respiration, aid in resonance, lighten the weight of the skull, and protect the brain and tissues from direct trauma. All the paranasal sinuses are connected to the nasal cavity via an opening in their tissue called the ostium. This small aperture allows for release of pressure and for drainage of superfluous liquid and mucus from each of the cavities. Since the ostium is the only means by which mucus and fluid can drain from the sinus, if this opening narrows or becomes blocked due to inflammation or disease state, opportunistic organisms can flourish in the cavities, resulting in an infection (Van Alyea, 1939; Baraniuk, 1994; Citardi, 2003).
Each sinus is named by the bone it rests in or on, resulting in the frontal, sphenoid, ethmoid, and maxillary cavities (Fig. 1.1). The frontal cavities, small to medium in size, rest above the eye orbits on both sides of the face and drain into the middle mea-tus via the frontomasal duct and ethmoidal infindibulum. The two cavities usually lie asymmetrical to one another, though cases have been seen in which the cavities lie behind one another or are connected (Cooper, 1994).
The next set of sinuses are the ethmoid cavities which have a honeycomb appearance and contain anywhere from 6 to 12 air cells within their structure (Van Alyea, 1939; Citardi, 2003). They flank the upper area of the nose and lie in close proximity to the frontal sinuses.
They drain into the ethmoidal infindibulum via several openings.
Posterior to the ethmoid sinuses, near the middle of the skull, rest the two asymmetrical sphenoid cavities. Drainage occurs via the sphenoidal ostium into the sphenoeth-moid recess, which is the space between the superior turbinate, septum, and sphenoid sinus wall (Citardi, 2003).
Lastly, the largest sinus, the maxillary, lies beneath the cheeks on each side of the face. The sinus drains into the ethmoid infindibulum just as the other cavities, however, the ostium on the maxillary tends to be reasonably smaller due to the surrounding mucosa on the bone (Cooper, 1994).
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