The anterior ethmoidal nerve is a branch of the nasociliary nerve (from V1) that passes through the anterior ethmoidal foramen in the medial orbital wall to enter the anterior cranial fossa, then descends through the cribriform plate to enter the nasal cavity, where it supplies the anterior nasal septum and lateral nasal wall. A small external nasal branch exits between the nasal bone and the upper lateral cartilage to supply the skin of the nasal tip and alae.
| Origin | Nasociliary nerve, from the ophthalmic division of the trigeminal nerve (V1) |
|---|---|
| Course | Passes through the anterior ethmoidal foramen, crosses the cribriform plate in the anterior cranial fossa, descends into the nasal cavity, and ends as the external nasal nerve between the nasal bone and the lateral nasal cartilage |
| Sensory |
|
The anterior ethmoidal nerve provides the sensory supply to the anterior nasal cavity and the skin over the nasal tip. Local anaesthetic near the anterior ethmoidal foramen blocks anterior nasal sensation for nasal procedures. In herpes zoster ophthalmicus, vesicles on the side or tip of the nose (Hutchinson sign) show involvement of the nasociliary territory through the external nasal branch and predict eye involvement. The nerve and its artery cross the thin lateral lamella of the cribriform plate, so in sinus surgery a deep olfactory fossa (Keros type 3) raises the risk of skull base injury and CSF leak. The external nasal branch can be injured in open rhinoplasty, usually with recovery of tip sensation.
The external nasal branch emerging between the nasal bone and upper lateral cartilage can be injured during open rhinoplasty, producing nasal tip numbness that usually recovers within 6-12 months.
Vesicles on the nasal tip or side of the nose reflect shingles in the nasociliary territory and signal a high risk of eye involvement, so urgent eye assessment is needed.
Where the olfactory fossa is deep (Keros type 3), the thin lateral lamella of the cribriform plate along the anterior ethmoidal nerve and artery is easily breached during ethmoidectomy, causing a CSF leak.
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