Ethmoidal cells

Anatomy

The ethmoid bone gets its name from the ethmoid plate (lamina cribrosa), which like a sieve has numerous holes and is found in the facial skull (viscerocranium). The ethmoid bone (Os ethmoidale) is a bony structure between the two eye sockets (orbitae) in the skull. It forms one of the central structures of the paranasal sinuses.

The inner structure is formed by the aerated (pneumatized) ethmoidal cells (Cellulae ethmoidalis). The labyrinth of these cells (Labyrinthus ethmoidale) is separated by bony septums (septa). The ethmoidal cells can be divided into anterior and posterior (Cellulae ethmoidales anteriores and Cellulae ethmoidales posteriores).

The anterior ethmoid cells are connected to the middle nasal passage (Meatus nasi medius), the posterior cells to the upper nasal passage (Meatus nasi superior). Some authors differentiate further and call them middle ethmoid cells (Cellulae ethmoidales mediale). The ethmoid cells border (at the back) at the bottom on the sphenoid sinuses (Sinus sphenoidales), at the top on the anterior base of the skull, the frontal bone (Os frontale) and on the ethmoid plate (Lamina cribrosa), at the sides are the two eye sockets, at the front are the middle eye angles (Angulus oculi) and at the back are the middle and frontal fossa.

Here there is anatomical proximity to the optic nerve (nervus opticus). Due to the “paper-thin” wall (Lamina papyracea) between the eye sockets and the ethmoid cells, inflammation and tumors can spread in both directions. In the area of the thin ethmoid plate, inflammations can rise into the interior of the skull due to damage. There are variants regarding the position of ethmoidal cells, which have proper names. The Haller cells are located in the maxillary sinus and the Onodi cells are located in the sphenoidal sinus, where they lie around the optic nerve canal (Canalis opticus).

Function and tasks

The ethmoid bone stabilizes the bony eye sockets, connects them with the olfactory bulb (Bulbus olfactorius) and the frontal region and separates the cranial cavity and nasal cavity from each other. Together with the nasal septum, it separates the main nasal cavity into two mirror-like areas, thus enabling a degree of directional olfaction. Due to the holes in the ethmoidal plate, it is possible for the olfactory filaments (Fila olfactoria) and blood vessels (A. ethmoidalis anterior, A. ethmoidalis posterior) to enter the nose to allow blood circulation and sensitivity of the nose.

The ethmoidal cells also allow the passage of the nasociliary nerve, a branch of the fifth cranial nerve (trigeminal nerve). This plays an essential role in the transmission of stimuli between the eyes, upper jaw (maxilla), lower jaw (mandible) and brain. A bony groin, the cockscomb (Crista galli) partially divides the sieve plate and serves as attachment of the cerebral falx (Falx cerebri).

As the central structure of the paranasal sinuses (Sinus paranasales), the ethmoidal cells participate in the air conditioning and thermal insulation of the airways. The formation of cavities saves bone and weight. Together with the central nasal passage and the openings to the maxillary sinuses, the anterior ethmoidal cells are part of a functional unit (ostiomeatal unit), which contributes to a physiological drainage of secretions. These and other functions and tasks are controversially discussed and are part of scientific research that is not yet complete.