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:
8/31/2007
Reviewed By:
Harvey Simon, MD, Editor-in-Chief; Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital.

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