Keros Classification - Depth of Olfactory Fossa
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👃 Keros Classification - Depth of Olfactory Fossa
Understanding the depth of the olfactory fossa is essential before performing endoscopic surgery close to the skull base, as breaching it can injure skull base structures.
🧠 Anatomy of the Olfactory Fossa
- The ethmoid labyrinth is covered by the fovea ethmoidalis of the frontal bone, which separates the ethmoidal cells from the anterior cranial fossa
- The cribriform plate of the ethmoid bone separates the olfactory fossa of the anterior cranial fossa above from the olfactory cleft of the nasal cavity below
⭐ The cribriform plate therefore forms the distinction between the anterior cranial fossa above and the nasal cavity below.
What are the contents of the Olfactory Fossa?
📊 Keros Classification
Given by Predrag Keros in 1962, to classify the depth of the olfactory fossa.
⭐ Based on the height of the lateral lamella of the cribriform plate.
| Type | Depth of Olfactory Fossa |
|---|---|
| Type 1 | 1 to 3 mm |
| Type 2 | 4 to 7 mm |
| Type 3 | 8 to 16 mm |
Which is the most common type out of the 3 types of Keros Classification?
Which is the most dangerous type out of the 3 types of Keros Classification?
⚠️ Surgical Importance
1- Risk of Iatrogenic Skull Base Injury
The depth of the olfactory fossa determines the risk of injury during FESS.
👉 The higher the Keros type, the greater the chance of inadvertently breaching the anterior cranial fossa.
2- Injury to the Anterior Ethmoidal Artery
⚠️ The anterior ethmoidal artery lies in this region.
What will injury to Anterior Ethmoidal Artery lead to?
3- Pre-operative Coronal CT Scan
⭐ A pre-operative coronal CT scan must be reviewed to assess the depth of the olfactory fossa in that particular patient before surgery.
What is the clinical implication of Asymmetry of the Olfactory Fossa on both sides?
🧠 Viva Pearls
- Keros classification was given by Predrag Keros in 1962.
- It classifies the depth of the olfactory fossa, based on the height of the lateral lamella of the cribriform plate.
- The fovea ethmoidalis separates the ethmoidal cells from the anterior cranial fossa.
- The cribriform plate separates the olfactory fossa above from the olfactory cleft below.
- The olfactory fossa opens superiorly into the anterior cranial fossa.
- Keros Type 1 is 1 to 3 mm, Type 2 is 4 to 7 mm and Type 3 is 8 to 16 mm.
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