the air-filled spaces, lined with mucous membrane, within some of the bones of the skull. They open into the nasal cavity, via the meatuses, and are named according to the bone in which they are situated. They comprise the frontal sinuses and the maxillary sinuses (one pair of each), the ethmoid sinuses (consisting of many spaces inside the ethmoid bone), and the two sphenoid sinuses. See illustration.
Sited within some of the bones of the SKULL, these are spaces ?lled with air and lined by MUCOUS MEMBRANE. The sinuses comprise frontal and maxillary (a pair of each), ethmoidal (a group of small spaces), and two sphenoid sinuses. They drain into the nasal cavities (see NOSE). When a person has an upper respiratory infection, the sinuses sometimes become infected: this causes pain, purulent discharge from the nose and obstruction of the nasal passages (see SINUSITIS). Generally all that is required is a decongestant and antibiotic but, occasionally, infection may spread to produce a cerebral abscess or cerebral venous sinus thrombosis (see BRAIN, DISEASES OF).... paranasal sinus
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