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Posterior Ethmoid Nerve

nervus ethmoidalis posterior

The posterior ethmoid nerve is the smaller terminal branch of the nasociliary nerve (V1), passing through the posterior ethmoid foramen to supply the posterior ethmoid air cells, the posterior superior nasal septum, and the sphenoid sinus. It accompanies the posterior ethmoid artery through the posterior ethmoid canal, approximately 5-10 mm anterior to the optic canal — the same anatomical relationship that makes the posterior ethmoid artery a surgical landmark for optic canal identification.

Region: Head & Skull

Clinical Relevance

Clinical Notes

The posterior ethmoid nerve supplies the posterior nasal septum and posterior ethmoid sinuses, making it the sensory nerve of the posterior sinonasal region at risk during sphenoethmoidectomy. Its foraminal position anterior to the optic canal makes it a depth landmark in endoscopic posterior ethmoid dissection. Division of the posterior ethmoid nerve during sphenoethmoidectomy produces posterior septum hypoaesthesia, which is usually asymptomatic. The nerve's septal branches contribute to the sensory supply of the posterior epistaxis zone.

Pathology

Common Injuries & Conditions

Posterior Ethmoid Nerve as Optic Canal Depth Marker

The posterior ethmoid nerve and its accompanying artery exit the orbit through the posterior ethmoid foramen 5-10 mm anterior to the optic canal; endoscopic identification of the posterior ethmoid artery/nerve complex confirms that the sphenoethmoid dissection is anterior to the optic nerve, preventing optic canal violation during posterior ethmoidectomy.