The ethmoid sinuses or ethmoid air cells of the

ethmoid bone The ethmoid bone (; from ) is an unpaired bone in the skull that separates the nasal cavity from the brain. It is located at the roof of the nose, between the two orbits. The cubical (cube-shaped) bone is lightweight due to a spongy constructi ...

are one of the four paired

paranasal sinus Paranasal sinuses are a group of four paired skeletal pneumaticity, air-filled spaces that surround the nasal cavity. The maxillary sinuses are located under the eyes; the frontal sinuses are above the eyes; the Ethmoid sinus, ethmoidal sinuses a ...

es. Unlike the other three pairs of paranasal sinuses which consist of one or two large cavities, the ethmoidal sinuses entail a number of small air-filled cavities ("air cells"). The cells are located within the lateral mass (labyrinth) of each ethmoid bone and are variable in both size and number.Illustrated Anatomy of the Head and Neck, Fehrenbach and Herring, Elsevier, 2012, page 64 The cells are grouped into anterior, middle, and posterior groups; the groups differ in their drainage modalities, though all ultimately drain into either the superior or the

middle nasal meatus In anatomy, the term nasal meatus can refer to any of the three meatuses (passages) through the skulls nasal cavity: the superior meatus (''meatus nasi superior''), middle meatus (''meatus nasi medius''), and inferior meatus (''meatus nasi infer ...

of the lateral wall of the nasal cavity.

Structure

The ethmoid air cells consist of numerous thin-walled cavities in the

ethmoidal labyrinth The ethmoidal labyrinth or lateral mass of the ethmoid bone consists of a number of thin-walled cellular cavities, the ethmoid air cells, arranged in three groups, anterior, middle, and posterior, and interposed between two vertical plates of bone ...

Otorhinolaryngology, Head and Neck Surgery, Anniko, Springer, 2010, page 188 that represent invaginations of the mucous membrane of the nasal wall into the ethmoid bone. They are situated between the superior parts of the nasal cavities and the

orbits In celestial mechanics, an orbit (also known as orbital revolution) is the curved trajectory of an physical body, object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an satellite, artificia ...

, and are separated from these cavities by thin bony lamellae. There are 5-15 air cells in either ethmoid bone in the adult, with a combined volume of 2-3mL.

Development

The ethmoidal cells (sinuses) and

maxillary sinus The pyramid-shaped maxillary sinus (or antrum of Nathaniel Highmore (surgeon), Highmore) is the largest of the paranasal sinuses, located in the maxilla. It drains into the middle meatus of the noseHuman Anatomy, Jacobs, Elsevier, 2008, page 209- ...

es are present at birth. At birth, 3-4 air cells are present, with the number increasing to 5-15 by adulthood.

Drainage

* The ''anterior ethmoidal cells'' drain (directly or indirectly) into the

by way of the ethmoidal infundibulum. * The ''middle ethmoidal cells'' drain directly into the

. * The ''posterior ethmoidal cells'' drain directly into the superior nasal meatus at the sphenoethmoidal recess; sometimes, one or more opens into the

sphenoidal sinus The sphenoid sinus is a paired paranasal sinus in the Body of sphenoid bone, body of the sphenoid bone. It is one pair of the four paired paranasal sinuses.Illustrated Anatomy of the Head and Neck, Fehrenbach and Herring, Elsevier, 2012, page 64 T ...

Lamellae

The ethmoidal labyrinth is divided by multiple obliquely oriented, parallel lamellae. The first lamellae is equivalent to the uncinate process of ethmoid bone, the second corresponds the ethmoid bulla, and the third is the basal lamella, and the fourth is equivalent to the superior nasal concha. The anterior and posterior ethmoid cells are separated by the basal lamella (also known as the ground lamella). It is one of the bony divisions of the ethmoid bone and is mostly contained inside the ethmoid labyrinth. The basal lamella is continuous medially with the bony

middle nasal concha The medial surface of the labyrinth of ethmoid consists of a thin lamella, which descends from the under surface of the cribriform plate, and ends below in a free, convoluted margin, the middle nasal concha (middle nasal turbinate). It is rough, ...

. Anteriorly, it vertically inserts into the ethmoid crest; the middle part attaches obliquely into the orbital lamina of ethmoid bone (lamina papyricea) while the posterior part attaches into the orbital lamina horizontally.

Innervation

The ethmoidal air cells receive sensory innervation from the

anterior Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position pro ...

and the posterior ethmoidal nerve (which are ultimately derived from the ophthalmic branch (CN V₁) of the trigeminal nerve (CN V)),

Haller cells

Haller cells are air cells situated beneath the ethmoid bulla along the roof of the

and the most inferior portion of the

lamina papyracea The orbital lamina of ethmoid bone (or lamina papyracea or orbital lamina) is a smooth, oblong, paper-thin bone plate which forms the lateral wall of the labyrinth of the ethmoid bone. It covers the middle and posterior ethmoidal cells, and forms ...

, including air cells located within the ethmoid infundibulum. 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 In neuroanatomy, the optic nerve, also known as the second cranial nerve, cranial nerve II, or simply CN II, is a paired cranial nerve that transmits visual system, visual information from the retina to the brain. In humans, the optic nerve i ...

and

internal carotid artery The internal carotid artery is an artery in the neck which supplies the anterior cerebral artery, anterior and middle cerebral artery, middle cerebral circulation. In human anatomy, the internal and external carotid artery, external carotid ari ...

, 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.Human Anatomy, Jacobs, Elsevier, 2008, page 210

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

External links

* * {{Authority control Bones of the head and neck Rhinology Otorhinolaryngology Sinus surgery