The ethmoid bone is a small unpaired bone, situated in the midline that the anterior cranium – the superior aspect of the skull that encloses and also protects the brain.

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The ax ‘ethmoid’ originates from the Greek ‘ethmos’, meaning sieve. This is reflect in its lightweight, spongy structure.

In this article, us shall look in ~ the anatomy of the ethmoid bone – that is location, relations, and structure.


Anatomical Structure

The ethmoid bone is among the 8 bones of the cranium. It is positioned at the roof that the nasal cavity, and also between the 2 orbital cavities.

It contributes to the medial wall surface of the orbit and forms part of the anterior cranial fossa, where it off the sleep cavity (inferiorly) native the cranial cavity (superiorly). It additionally forms a significant portion that the nasal septum and also lateral nasal wall.

The olfactory nerve (CN I) has actually a near anatomical partnership with the ethmoid bone. Its numerous nerve fibres pass with the cribriform bowl of the ethmoid bone come innervate the sleep cavity through the sense of smell.


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Fig 1 – The anatomical position and also relations of the ethmoid bone.


The ethmoid bone is comprised of three parts – the cribriform plate, the perpendicular plate, and the ethmoidal labyrinth.

The cribriform plate forms the roof of the sleep cavity. It is pierced by numerous olfactory nerve fibres, which provides it a sieve-like structure. Projecting superiorly native the cribriform key is the crista galli, which provides an attachment point for the falx cerebri (sheet that dura mater that separates the 2 cerebral hemispheres).

Another forecast of bone descends from the cribriform bowl – the perpendicular plate. It forms the superior two-thirds the the nasal septum.

Lastly, the ethmoid bone consists of two ethmoidal labyrinths. These are large masses located at either side of the perpendicular plate, i beg your pardon contain the ethmoidal air cells (sinuses). Two sheets of bone kind each labyrinth:


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Fig 2 – The ethmoid bone in ~ the sleep cavity.


Articulations

The ethmoid bone articulates with 13 others:

Paired – sleep bones, maxillae, lacrimal bones, palatine bones, inferior conchae.

Clinical relationship – Ethmoid Fracture

The ethmoid bone deserve to be fractured in cases of face trauma – many commonly hitting the dashboard in a collision, or a loss from height. Part signs and symptoms the fracture are pertained to the anatomy of the ethmoid bone:

Fracture the cribriform plate – branches that the olfactory bulb may be sheared. This may cause anosmia (loss of feeling of smell).Fracture the the labyrinth – may allow communication between the nasal cavity and also the orbit. It is then feasible for air to get in the orbit and cause orbital emphysema.

Clinical relationship – CSF Rhinorrhoea

A fracture come the cribriform key may permit communication in between the sleep cavity and also the main nervous system. Consequently, cerebrospinal fluid (CSF) can enter the nasal cavity and drain out from the nose. This manifests clinically as a clear watery discharge native one next of the sleep – and also is recognized as CSF rhinorrhoea.

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The leaks typically stop spontaneously and also can be controlled conservatively, yet surgery is sometimes required. Spontaneous CSF rhinorrhoea can also occur due to congenital or acquired defects in the ethmoid bone.