The ethmoid sinuses or ethmoid air cells of the ethmoid bone are one of the four paired paranasal sinuses. The cells are variable in both size and number in the lateral mass of each of the ethmoid bones and cannot be palpated during an extraoral examination. They are divided into anterior and posterior groups. The ethmoid air cells are numerous thin-walled cavities situated in the ethmoidal labyrinth and completed by the frontal, maxilla, lacrimal, sphenoidal, and palatine bones. They lie between the upper parts of the nasal cavities and the orbits, and are separated from these cavities by thin bony lamellae.
Frontal view of paranasal sinuses
Coronal section of nasal cavities.
|Nerve||posterior ethmoidal nerve|
|Latin||Cellulae ethmoidales, |
|Anatomical terms of bone|
Groups of sinuses
- The posterior group the posterior ethmoidal sinus drains into the superior meatus above the middle nasal concha; sometimes one or more opens into the sphenoidal sinus.
- The anterior group the anterior ethmoidal sinus drains into the middle meatus of the nose by way of the infundibulum.
The two groups are divided by the basal lamella. This is one of the bony divisions of the ethmoid bone and is mostly contained inside the ethmoid labyrinth. Medially the lamella becomes the bony part of the middle concha.
The ethmoidal air cells receive sensory fibers from the anterior and posterior ethmoidal nerves, and the orbital branches of the pterygopalatine ganglion, which carry the postganglionic parasympathetic nerve fibers for mucous secretion from the facial nerve.
Acute ethmoiditis in childhood and ethmoidal carcinoma may spread superiorly causing meningitis and cerebrospinal fluid leakage or it may spread laterally into the orbit causing proptosis and diplopia.
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