During FESS, the surgeon identifies the basal lamella of the middle turbinate. Which sinus is located posterior to this landmark, and what does its perforation risk?

• A Frontal sinus; risk of CSF leak from cribriform plate injury
• B Sphenoid sinus; risk of internal carotid artery injury
• C Posterior ethmoid cells; risk of injury to the optic nerve in the Onodi cell ✓
• D Maxillary sinus; risk of infraorbital nerve damage

Explanation

The basal lamella (ground lamella) of the middle turbinate divides the ethmoid labyrinth into anterior and posterior cells. Posterior to the basal lamella lie the posterior ethmoid cells. An important anatomical variant — the Onodi cell (sphenoethmoid cell) — is the most posterolateral posterior ethmoid cell that pneumatizes lateral to and around the optic nerve, creating a risk of optic nerve injury if this cell is entered aggressively. This is a critical FESS danger landmark. The sphenoid sinus lies further posterior.

Reference: Dhingra Diseases of Ear, Nose and Throat, 7th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.