Paranasal sinuses. Three diagnostic head X-rays carried out to check the paranasal sinuses in a 76-year-old man. At left, the head is tilted backwards. At centre, the head is seen from the front. At right is a left-facing side view of the head. The paranasal sinuses (frontal, ethmoidal, sphenoidal, and maxillary) are spaces in the bones surrounding the eyes and nose, and the cheek bones of the upper jaw. They lighten the bones of the skull and reduce the weight of the head. Connected to the nasal passages and lined with mucous membranes, they can fill with fluid and secrete mucus during an infection, when they show as opaque areas on an X-ray.
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