Keros classification of the olfactory fossa depth is important for surgical safety during ethmoidectomy. Which Keros type carries the highest risk of CSF leak during FESS?

• A Keros type III (8–16 mm depth) ✓
• B Keros type I (1–3 mm depth)
• C Keros type II (4–7 mm depth)
• D Keros type IV (asymmetric olfactory fossa)

Explanation

Keros type III has the deepest olfactory fossa (8–16 mm), meaning the lateral lamella of the cribriform plate — a very thin bony wall — is very tall and more prone to fracture or inadvertent penetration during aggressive ethmoidectomy. The deeper the fossa, the longer and more vulnerable the lateral lamella. Keros type I is actually the safest. Keros type IV refers to asymmetry between the two sides and increases risk on the deeper side, but the inherent risk per depth remains greatest in type III.

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

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Written and medically reviewed by the StethoPrep medical team.