Types of Sinuses

The sinuses are small air-filled spaces located in the bones of the skull that humidify the air passing through the airways. Many of the sinuses make mucus that helps to protect the airway and clean the air passing through it. Others resonate as certain vibrations pass through the airway, changing the volume and tone of the human voice. Most simply, sinuses also serve to reduce the weight of bones that they occupy.

There are four main locations for sinuses in the skull. The frontal bones, sphenoid bones, ethmoid bones, and maxillary bones. 

The frontal sinuses are situated behind the brow ridges and directly above the orbits. The frontal sinuses are often different sizes between left and right. They have ducts that connect them to the nasopharynx. This passage can become blocked resulting in fluid and bacteria buildup, this causes the classic "sinus headache."

The sphenoid sinuses are the most posterior sinuses. They lie near the optic nerve and the pituitary gland, two structures that are close to the center of the head.

The ethmoid sinuses are situated just behind the nose. Like the frontal sinuses, they are variable in size. The ethmoids are extremely small and vary in number as well. They are the most difficult to palpate during an extraoral or facial examination.

The maxillary sinuses are the largest of the paranasal sinuses. They are situated below the eyes and on either side of the nose directly behind the cheekbones.