Sinuses

Sinuses: Air Spaces in Your Head

Sinuses are air spaces in your skull lined with mucous membranes. You have four sets of nasal sinuses:

• two frontal sinuses in the forehead above the eyes

• two maxillary sinuses, one inside each cheek bone (dark triangles seen in this CAT scan)

• ethmoid sinuses: a beehive of 18 to 22 cavities behind the bridge of the nose (also shown here)

• sphenoid sinuses, behind the nose and underneath the brain