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Definition

noun, plural: ethmoidal sinuses

Any of the many discrete paranasal sinuses within the ethmoid bone, between the nose and the eyes.

Supplement

Collectively, they are called ethmoid air cells. They are separated from the nasal cavities and the orbits by thin bony laminae.

They may be grouped based on their anatomic location:

• posterior sinuses – drain into the superior meatus under cover of the superior nasal concha
• middle sinuses – drain into the middle meatus of the nose on or above the bulla ethmoidalis
• anterior sinuses – drain into the middle meatus of the nose by way of the infundibulum.

Variant: ethmoid sinus or sinus ethmoidales