éthmoid

The éthmoid bone, commonly referred to as the ethmoid, is a light, spongy bone located between the orbits. It forms part of the anterior skull base, the medial wall of the orbits, and most of the roof and lateral wall of the nasal cavity. The bone consists of two main elements: a vertical perpendicular plate that descends to contribute to the nasal septum, and a horizontal cribriform plate that forms the roof of the nasal cavity and part of the anterior cranial fossa, perforated by numerous foramina for the olfactory nerve fibers. Between these plates lies the ethmoid labyrinth, a network of air-filled cells divided into the lateral masses. The lateral masses give rise to the superior and middle nasal conchae. The orbital surface includes the thin lamina papyracea, forming part of the medial orbital wall.

The ethmoid articulates with the frontal, sphenoid, lacrimal, maxilla, inferior nasal concha, nasal bones, and vomer. Its complex structure contributes to the medial orbital wall and the cranial base, and its air cells are a prominent source of ethmoiditis.

Clinical notes: Ethmoid sinusitis, common in children, can spread to the orbit or cranial cavity. Fractures of the ethmoid, particularly the cribriform plate, may cause cerebrospinal fluid leakage and loss of smell, with risk of meningitis.

Etymology: from Greek ethnos, “sieve,” referring to the perforated cribriform plate.