d) Ethmoidal Air Cells

The ethmoidal air cells are unique among the paranasal sinuses due to their small size and number.

Structure

Location and Boundaries

The ethmoidal air cells are between three and eighteen paired cavities that lie in the substance of the ethmoid bone, between the orbit and the nasal cavity. The are divided into anterior and posterior groups based on their communication with the nasal cavity.

Relations

Laterally, with the orbit (there is a very thin layer of bone dividing these two structures)
Medially, with the superior part of the nasal cavity.
Superiorly, with the frontal sinus and anterior cranial fossa.
Inferiorly, with the maxillary sinus, nasal cavity and middle concha.
Posteriorly, with the sphenoidal sinuses.
Anteriorly with the nose.

Macroscopic Features

The air cells are divided by very thin and incomplete septa. There is a major division between an anterior and posterior group, causing them to communicate with the nasal cavity by different apertures. They are lined by pale pink mucosa.

Microscopic Features

The lining epithelium is of pseudostratified columnar / respiratory type with cilia and goblet cells.

Physiological Variations

The ethmoidal air cells are present at birth, enlarging through childhood and puberty.

Neurovascular Supply

Arterial Supply

By branches of the anterior / posterior ethmoidal arteries (branches of the ophthalmic artery) and nasal branches of the sphenopalatine artery.

Venous Drainage

Named veins accompany the arteries to either the superior ophthalmic vein or pterygopalatine venous plexus.

Lymphatics

The anterior air cells drain to submandibular nodes. The posterior air cells drain to retropharyngeal nodes.

Innervation

The anterior and posterior ethmoidal nerves, branches of the nasopalatine nerve (V1), carry general sensory information. Secretomotor supply is via the orbital branches of the pterygopalatine ganglion (through the greater petrosal nerve, a branch of VII).

Routes of Cancer Spread

Local Invasion

Like other paranasal tumours, carcinoma of the ethmoidal air cells tends to undergo extensive local invasion with minimal distant spread. Invasion may occur laterally into the orbit (causing proptosis), infero-medially into the nasal cavity causing epistaxis, or superior into the brain causing meningitis.

Lymphatic Spread

Tumours from the anterior ethmoidal air cells will tend to pass to submandibular nodes, whereas those from the posterior cells will pass posteriorly and inferiorly to the retropharyngeal nodes.

Neurological Spread

Tumours may invade along nerves, typically into the nasopalatine nerve and the ophthalmic nerve (V1).


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