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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.

Region: Head & Skull

Clinical Relevance

Clinical Notes

The posterior ethmoidal nerve is relevant in endoscopic skull base surgery where the posterior ethmoidal foramen (and the accompanying posterior ethmoidal artery) marks the posterior limit of the ethmoid labyrinth and the anterior limit of the optic canal — the critical relationship described as the optic nerve being just 2-5 mm posterior to the posterior ethmoidal foramen. Electrosurgery near the posterior ethmoidal foramen risks inadvertent optic nerve injury from transmitted current or thermal spread.

Pathology

Common Injuries & Conditions

Posterior Ethmoidal Foramen as Optic Canal Landmark

During FESS and endoscopic skull base surgery, the posterior ethmoidal foramen and its artery mark the posterior limit of safe ethmoid dissection; the optic nerve lies only 2-5 mm posterior to this foramen, so any instrumentation posterior to the foramen risks optic nerve injury with permanent visual loss.