Middle cells of ethmoid bone

At a glance

English

Middle cells of ethmoid bone

Latin (TA2)

Cellulae mediae ossis ethmoidei

System

Bone

Region

Whole body

Side

Paired, left and right

About the middle cells of ethmoid bone

The middle ethmoidal cells lie in the centre of each ethmoidal labyrinth, between the anterior cells in front and the posterior cells behind. Like the rest of the labyrinth they sit between the upper nasal cavity and the medial wall of the orbit, beneath the floor of the anterior cranial fossa. They are fewer than the anterior cells and vary in size and number from person to person.

The best-known member of the group is the ethmoidal bulla, a rounded swelling on the inner wall of the labyrinth produced by one or more large middle cells pushing towards the nose. It lies under cover of the middle concha, just behind the semilunar hiatus. The outer walls of these cells are formed by the thin orbital plate of the ethmoid, and their roofs by the orbital part of the frontal bone, so they lie close to both the orbit and the cranial cavity.

The middle cells open into the middle meatus, on or just above the ethmoidal bulla, by one or several small openings. They therefore share the crowded drainage region of the middle meatus with the anterior ethmoidal cells and the frontal and maxillary sinuses. The cells are present at birth in a small form and grow with the face through childhood, reaching full size in the late teens.

Clinically, the bulla is a key landmark in endoscopic surgery of the sinuses: removing it opens the middle cells and exposes the route back towards the posterior cells and sphenoidal sinus. Because the cell walls facing the orbit and the skull are thin, infection in the middle cells can spread outward into the orbit or, more rarely, upward towards the meninges. Blockage of their small openings by swollen lining is a common part of chronic sinusitis.

Function and supply

Nerve supply

The anterior and posterior ethmoidal nerves, branches of the nasociliary nerve from the ophthalmic nerve, give sensation to the lining, with nasal branches of the maxillary nerve; secretory fibres come from the pterygopalatine ganglion.

Blood supply

The anterior and posterior ethmoidal arteries from the ophthalmic artery and nasal branches of the sphenopalatine artery.