Sinuses are air-filled sacs (empty spaces) on either side of the nasal cavity that filter and clean the air breathed through the nose and lighten the bones of the skull. There are four paired sinuses in the head. The most posterior (farthest toward the back of the head) of these is the sphenoid sinus.

The sphenoid sinuses are located in the sphenoid bone near the optic nerve and the pituitary gland on the side of the skull. There are seven bones that form the orbit (eye socket), and the sphenoid is one of these bones. The pituitary gland, which produces many different hormones that control other glands, is housed in the sphenoid bone. It is also housed in the sella turcica.

Like the nasal cavity, the sinuses are all lined with mucus. The mucus secretions produced in the sinuses are continually being swept into the nose by the hair-like structures on the surface of the respiratory membrane (lung lining tissues). This serves to moisten the air we breathe through our noses. The hollow sinuses also act to lighten the bones of the skull and serve as resonating chambers for speech.

The paired and often asymmetrical sinuses are small or rudimentary at birth but grow as the skull grows. They are fairly well developed by age 7 to 8, but don’t reach their maximum size until after puberty. In adults, the sinuses vary considerably in size and shape.

Sinuses are susceptible to infection. Sinusitis is inflammation of a sinus caused by a bacterial infection that can follow a viral infection. This causes pus and mucus to accumulate within the sinus. Symptoms can include fever, headache, sinus pain, stuffy nose, and impaired sense of smell.