Endoscopic Anatomy of the Nose for FESS

👃 Endoscopic Anatomy of the Nose

This post covers the anatomy that is relevant while performing Functional Endoscopic Sinus Surgery (FESS).

🔍 Middle Turbinate

⭐ The middle turbinate is a boomerang shaped structure, bending in different planes.

It has three parts, each lying in a different plane with a different attachment.

What is Basal Lamella or Ground Lamella? What is the clinical significance of Basal Lamella?

🔍 Osteomeatal Complex (OMC)

⭐ A key structure in the endoscopic anatomy of the nose.

It is the area into which the frontal sinus, maxillary sinus and anterior ethmoidal sinus drain.

Structures Forming the Osteomeatal Complex

1️⃣ Uncinate process

A sickle shaped bone running from an anterosuperior to a posteroinferior direction.

What are the different variations of the Superior Attachment of the Uncinate Process? How does this impact the drainage of the Frontal sinus?

What is Recessus Terminalis?

2️⃣ Bulla ethmoidalis

An anterior ethmoidal cell lying just behind the uncinate process.

⭐ It is the largest and most constant anterior ethmoidal cell, and is usually well pneumatized.

What are the variations of the Bulla Ethmoidalis seen?

3️⃣ Hiatus semilunaris Inferioris

A semilunar groove between the uncinate process in front and the bulla ethmoidalis behind.

⭐ It is a two dimensional space, about 1 to 2 mm wide.

⭐ The hiatus semilunaris leads into the infundibulum.

4️⃣ Ethmoidal infundibulum

⭐ A three dimensional space.

What are the boundaries of Ethmoidal infundibulum?

Which sinuses drain into the Ethmoidal infundibulum?

🔍 Ethmoidal Complex

⭐ The basal lamella divides the ethmoidal complex into anterior and posterior ethmoidal cells.

Name the ethmoidal cells extending towards Maxillary, Frontal & Sphenoid sinuses.

🔍 Sinus Lateralis of Grunwald

Formed by two recesses around the bulla ethmoidalis:

👉 Together these form a semilunar space, the Sinus Lateralis of Grunwald.

Where does the Sinus Lateralis of Grunwald open into?

What are the Boundaries of the Sinus Lateralis of Grunwald?

🔍 Agger Nasi Cell

A bony mound on the ethmoid, situated at the point where the middle turbinate attaches to the lateral nasal wall.

👉 When this bony mound becomes pneumatized, it forms the agger nasi cell.

What does the Agger nasi cell look like on endoscopy?

What is the clinical significance of Agger nasi cell?

🔍 Haller Cell

An anterior ethmoidal cell pneumatizing into the floor of the orbit, just above the maxillary ostium.

Also known as Infraorbital Ethmoid Cell.

What is the clinical significance of Haller cell?

🔍 Supraorbital Ethmoid Cell

An anterior ethmoidal cell extending superiorly and laterally over the orbital roof.

⭐ On a coronal view, it gives the appearance of a septated frontal sinus.

What is the clinical significance of Supraorbital Ethmoid cell?

Two Openings in the Frontal Recess

When a supraorbital cell is present, the frontal recess shows two openings:

🔍 Onodi Cell (Sphenoethmoidal Cell)

A posterior ethmoidal cell pneumatizing superior and lateral to the sphenoid sinus.

⭐ Unlike the other cells discussed, the Onodi cell is a posterior ethmoidal cell.

What is the location of Sphenoid sinus in relation to Onodi cell?

What is the clinical significance of Onodi cell?

Radiological Identification

👉 On the coronal view of a CT scan, the Onodi cell gives the appearance of a horizontal septation.

⚠️ It may be mistaken for the true sphenoid sinus, leading to an incomplete dissection.

🔍 Frontal Recess

🔍 Definition

A narrow, funnel shaped space forming the drainage pathway connecting the frontal sinus to the middle meatus.

⭐ Hourglass Configuration

On a sagittal section, three structures form an hourglass configuration:

⭐ The frontal ostium lies posteriorly, at the medial end of the floor of the frontal sinus.

What are the Boundaries of the Frontal Recess?

🔍 Frontal Cells

⭐ The presence of frontal cells can impact the drainage of the frontal recess.

Classifications

What is Kuhn's Classification of frontal cells?

What is Modified Kuhn's Classification of frontal cells?

What is the IFAC classification of frontal recess cells?

🔍 Maxillary Sinus Ostium

Two ostia are described:

1️⃣ Natural ostium

• Drains into the inferior part of the ethmoidal infundibulum, at a 45 degree angle
• Lies just below the orbital floor, in the medial wall of the sinus
• Lies halfway between the anterior and posterior walls of the sinus

⭐ Maxillary sinus mucociliary flow is always towards the natural ostium.

What is the position of natural maxillary ostium within the Ethmoidal Infundibulum?

What are the Relations of the natural maxillary ostium? What is the clinical importance of knowing the relations?

2️⃣ Accessory ostium

👉 Accessory ostia lie in the anterior and posterior fontanelles.

What are fontanelles? Where do the anterior and posterior fontanelles lie?

How will you differentiate between Natural maxillary Ostium and Accessory maxillary Ostium?

⚠️ An ostium seen before uncinectomy is most likely an accessory ostium, and must not be mistaken for the natural ostium.

What is Mucus Recirculation Phenomenon?

🔍 Sphenoid Ostium

• Drains into the sphenoethmoidal recess
• The sphenoethmoidal recess lies medial to the inferior third of the superior turbinate
• The ostium lies medial and posterior to the superior turbinate
• Located about halfway to two-thirds up the anterior wall of the sphenoid sinus

What are the Landmarks to locate the Sphenoid Ostium?

🧠 Viva Pearls

• The middle turbinate is boomerang shaped and has three parts in three different planes.
• The first part lies in the sagittal plane and attaches to the cribriform plate.
• The second part lies in the coronal plane and attaches to the lamina papyracea; it is the basal or ground lamella.
• The basal lamella separates the anterior from the posterior ethmoidal cells.
• The third part lies in the horizontal plane and attaches to the lamina papyracea and the perpendicular plate of the palatine bone.
• The osteomeatal complex consists of the uncinate process, bulla ethmoidalis, hiatus semilunaris and ethmoidal infundibulum.
• Bulla ethmoidalis is the largest and most constant anterior ethmoidal cell.
• Hiatus semilunaris is a two dimensional space; the infundibulum is a three dimensional space.
• Maxillary sinus drains into the inferior aspect and frontal sinus into the superior aspect of the infundibulum.
• The uncinate process is sickle shaped, running anterosuperiorly to posteroinferiorly.
• Anterior ethmoidal cells drain into the middle meatus; posterior ethmoidal cells into the superior meatus.
• Suprabullar and retrobullar recesses together form the sinus lateralis of Grunwald.
• Agger nasi is a bony mound at the attachment of the middle turbinate to the lateral nasal wall.
• Agger nasi cell is the most anterior ethmoidal cell and the first landmark in frontal sinus surgery.
• Haller cell is an infraorbital ethmoid cell.
• Onodi cell is a posterior ethmoidal cell.
• Onodi cell appears as a horizontal septation on the coronal CT.
• Frontal infundibulum, frontal ostium and frontal recess form an hourglass configuration.
• An ostium visible before uncinectomy is most likely an accessory ostium.

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