Ethmoid Bone

Key Features & Anatomical Relations

The ethmoid bone is a single, small, cube-like bone that is located centrally within the cranium. It is classified as an irregular bone. The cribriform plate is the only part of the ethmoid bone that contributes to the formation of the neurocranium, while the rest of the bone contributes to the formation of the viscerocranium. The ethmoid bone consists of ethmoidal air cells and includes the following bony features:

- parts: cribriform and perpendicular plates, crista galli, and ethmoidal labyrinths;

- surfaces: anterior, posterior, and inferior borders of perpendicular plate, lateral surfaces of perpendicular plate, and orbital plate;

- landmarks: superior and middle nasal conchae, alae of crista galli, uncinate processes, and anterior and posterior ethmoidal grooves.

More information regarding these bony features can be found in the Parts, Surfaces and Landmarks tabs for this bone.

The ethmoid bone is located:

- anterior to the sphenoid bone;

- posterior to the nasal and lacrimal bones;

- superior to the palatine bones, maxillae, vomer, and inferior nasal conchae;

- inferior to the frontal bone.

It articulates with the:

- sphenoid bone at the sphenoethmoidal suture;

- lacrimal bones at the ethmoidolacrimal sutures;

- palatine bones at the palatoethmoidal sutures;

- maxillae at the ethmoidomaxillary sutures;

- frontal bone at the frontoethmoidal suture.

- inferior nasal conchae;

- nasal bones;

- vomer.

Ossification

Ossification of the ethmoid bone occurs at three ossification centers, these are found in the:

- right and left ethmoidal labyrinths, with one center found in each, which appear in utero during the fourth to fifth months;

- perpendicular plate, which appears during the first year after birth.

The ossification centers for the ethmoidal labyrinths and perpendicular plate fuse with each during the second year (Standring, 2016).

Variations

In some individuals;

- the crista galli may be present in a pneumatized form (i.e., contain air-filled cavities);

- the superior nasal conchae may be present in a pneumatized form;

- accessory ethmoidal foramina may be present (Tubbs, Shoja and Loukas, 2016).

List of Clinical Correlates

- Fracture of ethmoid bone

References

Standring, S. (2016) Gray's Anatomy: The Anatomical Basis of Clinical Practice. Gray's Anatomy Series 41st edn.: Elsevier Limited.

Tubbs, R. S., Shoja, M. M. and Loukas, M. (2016) Bergman's Comprehensive Encyclopedia of Human Anatomic Variation. Wiley.