---
title: "Keros Classification - Depth of Olfactory Fossa"
description: "ENT notes on Keros Classification of Depth of Olfactory Fossa."
source: "The ENT Resident"
author: "Dr. Mausumi Das"
canonical_url: "https://www.theentresident.com/ent-notes-lectures/keros-classification-olfactory-fossa-depth"
categories: ["Rhinology", "Classifications and Gradings in ENT"]
video: "https://www.youtube.com/watch?v=-_1XOt5ZFcM"
image: "https://media.theentresident.com/og-images/keros-classification-olfactory-fossa-depth.png"
---

# Keros Classification - Depth of Olfactory Fossa

ENT notes on Keros Classification of Depth of Olfactory Fossa. Watch the full video lecture on YouTube: https://www.youtube.com/watch?v=-_1XOt5ZFcM

## 👃 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.

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### 🧠 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 boundaries of the Olfactory Fossa?](https://www.theentresident.com/ent-notes-lectures/nose-anatomy.md)

> What are the contents of the Olfactory Fossa?

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### 📊 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?

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### 🧠 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.

---

## About This Note

This free ENT note on Keros Classification - Depth of Olfactory Fossa was written by Dr. Mausumi Das and is paired with a corresponding video lecture.

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When citing or referencing this content, please credit The ENT Resident and link to the canonical page above.

## Related Notes by Category

- Rhinology: https://www.theentresident.com/ent-notes-lectures/category/rhinology.md
- Classifications and Gradings in ENT: https://www.theentresident.com/ent-notes-lectures/category/classifications-and-gradings-in-ent.md

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