Ethmoidal air cells

The ethmoidal air cells, also known less commonly as the ethmoidal sinuses, form one of the four pairs of paranasal sinuses. They are located within the single, midline ethmoid bone.

Summary

• location: between the orbit and the nasal cavity, within the ethmoid labyrinth of the ethmoid bone
• blood supply: supraorbital, anterior and posterior ethmoidal and sphenopalatine arteries
• innervation: anterior and posterior ethmoidal and supraorbital nerves

Gross anatomy

A collection of air cells (3-18 in number) separated by bony septa within each side of the lateral mass, or labyrinth, of the ethmoid bone. 

They are separated into anterior and posterior groups by the basal lamella, the lateral attachment of the middle turbinate to the lamina papyracea. Historically the ethmoid sinuses were subdivided into 3 groups of air cells: the anterior, middle and posterior ethmoidal air cells. The middle group are now incorporated into the anterior group.

The anterior ethmoidal air cells drain to the hiatus semilunaris and middle meatus via the ethmoid bulla, which forms parts of the ostiomeatal complex. The posterior ethmoidal air cells drain to the superior meatus and sphenoethmoidal recess ².

Some of the ethmoidal air cells have been given specific names, because of their importance in surgical procedures or involvement in head and neck pathologies:

• frontal recess cells, including the agger nasi cells
• ethmoid bulla
• Haller cells
• Onodi cells

Arterial supply

From the ophthalmic branch of the internal carotid artery, the supraorbital, anterior and posterior ethmoidal arteries supply the ethmoid air cells with the sphenopalatine artery (a branch of the maxillary artery) also contributing. Thus, the ethmoid air cells are supplied by branches of both the internal and external carotid arteries. 

Lymphatic drainage

Lymph from the ethmoid air cells drains to the submandibular and retropharyngeal group of nodes.

Innervation

The posterior ethmoidal air cells, along with the sphenoid sinus, are supplied by the posterior ethmoidal nerve, whereas the anterior ethmoidal nerve supplies the anterior ethmoidal air cells. Both these nerves are extraconal branches of the nasociliary nerve, a branch of the ophthalmic division of the trigeminal nerve.

Development

They are present at birth, and they develop rapidly from 0-4 years of age. They further mature from 8-12 years of age through puberty.