Ethmoid sinus

The ethmoid air cells consist of numerous thin-walled cavities in the ethmoidal labyrinth that represent invaginations of the mucous membrane of the nasal wall into the ethmoid bone. Development The ethmoidal cells (sinuses) and maxillary sinuses are present at birth. At birth, 3-4 air cells are present, with the number increasing to 5-15 by adulthood. These may arise from the anterior or posterior ethmoidal sinuses. Onodi cells Also known as a sphenoethmoidal air cell, an Onodi cell is a posterior ethmoidal air cell that lies superolateral to the sphenoid sinus, often extending into the anterior clinoid process. Onodi cells are clinically significant because they lie in close proximity to the optic nerve and internal carotid artery, so surgeons should be aware of their existence when performing surgery on the sphenoid sinus so as not to damage these important structures. A central Onodi air cell is a variation in which a posterior ethmoid cell lies superior to the sphenoid sinus in a midline position with at least one optic canal bulge. ==Clinical significance==

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. ==Additional images==

File:Slide2ROMA.JPG|Ethmoid sinus. Ethmoidal air cells. Deep dissection. Superior view. File:Diagram showing ethmoid sinus cancer that has spread to the lymph nodes CRUK 121.svg|Ethmoid sinus cancer that has spread to the lymph nodes ==References==