ethmoid

The ethmoid bone is a light, spongy cranial bone located between the eyes at the roof of the nasal cavity. It contributes to the medial walls of the orbits, forms part of the nasal septum, and helps delineate the anterior cranial fossa. Its thin orbital plate (lamina papyracea) forms part of the medial wall of the orbit and is intimately related to the orbital contents.

Anatomy and parts

The ethmoid consists of three main parts: the perpendicular plate, the cribriform plate, and the ethmoidal labyrinth. The perpendicular plate descends within the nasal cavity to form part of the nasal septum. The cribriform plate is a sieve-like horizontal surface that contains many foramina for the olfactory nerves as they pass from the nasal mucosa to the olfactory bulbs. The ethmoidal labyrinth is a complex set of air cells that extend into the orbital and nasal regions, giving rise to the superior and middle nasal conchae (turbinates).

Relations and function

The ethmoid articulates with the frontal bone anteriorly, the sphenoid behind, and with the lacrimal, nasal, and maxillary bones. It also forms part of the nasal cavity and the orbital walls. Its air cells and conchae increase the surface area of the nasal mucosa, aiding humidification, filtration, and airflow regulation. The bone also supports olfactory structures via the cribriform plate.

Clinical notes

Fractures of the cribriform plate can cause cerebrospinal fluid leakage and pose a risk to the olfactory nerves and brain. Ethmoiditis refers to infection of the ethmoidal air cells and can have orbital or intracranial complications. The ethmoid bone is primarily formed by neural crest-derived tissue during development.