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Posterior Ethmoidal Nerve

nervus ethmoidalis posterior

The posterior ethmoidal nerve is a branch of the nasociliary nerve (from V1) that exits the orbit through the posterior ethmoidal foramen medially and supplies sensory innervation to the posterior ethmoid air cells and the sphenoid sinus mucosal lining. It accompanies the posterior ethmoidal artery.

Anatomical Data

Course & Distribution

Origin	Nasociliary nerve, from the ophthalmic division of the trigeminal nerve (V1)
Course	Leaves the medial orbital wall through the posterior ethmoidal foramen
Sensory	Posterior ethmoidal air cells Sphenoidal sinus

Clinical Relevance

Clinical Notes

The posterior ethmoidal nerve and the posterior ethmoidal artery pass through the posterior ethmoidal foramen, which lies only about 6 mm in front of the optic canal (the 24-12-6 rule along the medial orbital wall). In endoscopic sinus and skull base surgery this foramen marks the posterior limit of safe ethmoid dissection. Dividing the nerve during sphenoethmoidectomy causes only minor, usually unnoticed, loss of sensation in the posterior sinuses. Electrosurgery near the foramen risks thermal injury to the nearby optic nerve.

Pathology

Common Injuries & Conditions

Posterior Ethmoidal Foramen as Optic Canal Landmark

During endoscopic sinus surgery the posterior ethmoidal foramen and its artery mark the posterior limit of safe ethmoid dissection; the optic canal lies only about 6 mm behind it, so instrumentation beyond this point risks optic nerve injury and permanent visual loss.

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