Sinusitis refers to inflammation of the sinus cavities, which are moist, hollow spaces in the bones of the skull. There are four pairs of sinuses: Frontal sinuses Maxillary sinuses Ethmoid sinuses Sphenoid sinuses (not shown in illustration) If the opening from a sinus cavity becomes plugged, the flow of mucus is blocked and pressure builds up, causing pain and inflammation.

Review Date: 7/3/2002 12:00:00 AM Reviewed By:A.D.A.M. Medical Illustration Team

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