Posterior cells of ethmoid bone

At a glance

English

Posterior cells of ethmoid bone

Latin (TA2)

Cellulae posteriores ossis ethmoidei

System

Bone

Region

Whole body

Side

Paired, left and right

About the posterior cells of ethmoid bone

The posterior ethmoidal cells form the rear part of each ethmoidal labyrinth, behind the middle cells and directly in front of the body of the sphenoid bone. They lie between the upper back part of the nasal cavity and the deep part of the medial orbital wall, beneath the floor of the anterior cranial fossa. They are usually fewer than the anterior cells but larger, and they vary in shape and extent between people.

Their walls are thin plates of bone lined with mucous membrane continuous with that of the nose. The orbital plate of the ethmoid forms their outer wall, the frontal bone completes their roof, and behind they are closed by the sphenoidal concha and the front of the sphenoid body; the orbital process of the palatine bone may also close a cell below. Close to their outer side, at the back of the orbit, runs the optic nerve in its canal, and the posterior ethmoidal foramen lies at the junction of their roof with the orbital wall.

The posterior cells open into the superior meatus of the nose, beneath the superior concha. Just behind and above them is the sphenoethmoidal recess, into which the sphenoidal sinus drains, so the two systems lie next to each other at the back of the nose. The cells are present at birth in a small form and enlarge through childhood.

Clinically, these cells are the closest of the ethmoid group to the optic nerve. In some people a posterior cell extends backward beside or above the sphenoidal sinus and comes to surround the optic nerve or lie against the internal carotid artery; this sphenoethmoidal (Onodi) cell is important to recognise on scans before surgery, because entering it carelessly can injure either structure. Infection in the posterior cells can also involve the optic nerve, giving blurred vision.

Function and supply

Nerve supply

The posterior ethmoidal nerve, from the nasociliary branch of the ophthalmic nerve, supplies the lining, together with orbital and nasal branches from the pterygopalatine ganglion that carry maxillary nerve and secretory fibres.

Blood supply

The posterior ethmoidal artery from the ophthalmic artery and branches of the sphenopalatine artery from the maxillary artery.