By the ethmoid bone, physicians mean a multi-unit cranial bone of the bony orbit. The ethmoid bone is involved in the anatomic structure of the orbits, as well as the nasal cavities and the frontal sinus, and serves as an attachment point for the olfactory system. The ethmoid bone can be affected by fractures, inflammation, and nerve damage.
What is the ethmoid bone?
The ethmoid bone is a small, light, and externally invisible bone of the skull. This anatomical structure is also known as the os ethmoidale and is located at the end of the nasal cavity. There, at depth, it forms the boundary with the cranial cavity. Thus, the ethmoid bone is a part of the base of the skull, but also of the nasal roof and orbits. The bone consists of several sections: the lamina cribrosa, the lamina perpendicularis, and the paired labyrinth. Each of these sections performs a different function. The ethmoid bone is often referred to as the perforated bone plate, through whose holes nerve cords of the olfactory brain extend toward the nose. In this context, the separation of the nasal cavity from the cranial cavity is often cited as the main function of the anatomical structure.
Anatomy and structure
The lamina cribrosa is one of the four parts of the ethmoid bone. A bicuspid bony prominence projects from its center. This projection is also known as the cockscomb. One of the edges of this cockscomb articulates with the frontal bone. Its two wings thereby correspond with the depressions of the frontal bone, forming the blind-ending opening in the tissues of the frontal sinus. The lamina perpendicularis is the second structure of the ethmoid bone. This bone lamina forms the nasal septum. The second bone of the ethmoid also articulates with the nasal bone, the sphenoid bone, and the ploughshare bone. The bipartite and symmetrically arranged labyrinth is the third structure of the ethmoid bone, which carries different types of the so-called ethmoid cells. The labyrinth is involved as a structure on the walls of the orbeitae and the nasal wall, as well as on the sphenoid bone. Overall, the surface of the ethmoid bone is rather smooth. Only the attachment points of the individual nerves and blood vessels are not of smooth structure.
Function and tasks
The ethmoid bone primarily provides stability to the bony orbit. It serves as a connector between your individual structures of the olfactory bulb, orbit, and frontal area. However, the ethmoid bone is also responsible for structural separation. For example, the bone structures of the ethmoid separate the cranial cavity from the nasal cavity. An edge of the cockscomb is also the attachment point for the separation structure of the two cerebral hemispheres. Similarly, the two sides of the nose are divided by the ethmoid bone. This plays an important role in the perception of smell. It is only through the two nasal cavities, for example, that humans can assess in which direction the source of an odor is located, as seen from their point of view. It is not only because of this function that the ethmoid bone plays an important role for the entire olfactory system and general olfactory perception. The second ethmoid bone serves as an attachment point for many olfactory nerves in the upper region. Moreover, without the holes in the ethmoid plate, the olfactory nerve and the blood vessels of the mucosa could not even pass through to the nose. To the sides of the cockscomb the first ethmoid bone carries additionally one pit each for the support of the right and left olfactory bulb and by the fine bone tubules in this structure the nerve fibers of the smell perception pull themselves only up into the olfactory bulb out. In addition, the nasociliary nerve, i.e. a part of the fifth cranial nerve, passes through a notch of the first ethmoid bone. The fifth cranial nerve is responsible, among other things, for the transmission of stimuli between the eyes, the upper jaw, the lower jaw and the brain and thus enables, for example, the chewing movement during eating.
Diseases
One of the most common conditions of the ethmoid bone is a fracture. When there is a fracture to one of the structures involved, it is usually related to a blow to the orbit. The ethmoid bone may be in danger of subsidence as part of this. If this risk occurs, then the bony orbit and the nasal wall may no longer have stability. A fracture of the ethmoid bone can possibly be corrected surgically or minmal invasive. If such correction does not occur, the anatomical structure of the face may permanently shift from the frontal sinus downward.Since the fifth cranial nerve and the olfactory nerves dock at the level of the ethmoid bone, nerves are sometimes involved in a fracture of the ethmoid bone. Most often, the nerves of the olfactory system are involved. This phenomenon can cause, for example, confused olfactory sensations. In this case, surgical release of the affected nerve structures is indispensable. However, nerves that have been trapped for a longer period of time usually die. This death causes permanent restriction of nerve function. Even freeing a pinched nerve may not fully restore its function. In addition to fractures, the ethmoid bone and especially the ethmoid cells may also be affected by inflammatory processes. Such inflammation is also known as “sinusitis ethmoidalis”. Because of the connection to the cerebral hemispheres, inflammation of the ethmoidal cells often spreads to the meninges, possibly causing meningitis. Just as frequently, inflammation of the ethmoidal cells results in an abscess of the orbits if the course is unfavorable.
