Anatomy of Paranasal Sinuses

Anatomy of the Paranasal Sinuses

In this post, we'll cover the paranasal sinuses — their anatomy, drainage, relations, variations, and clinical significance.

🌬 What Are Paranasal Sinuses?

Paranasal sinuses are air-filled cavities located within the bones of the skull.

There are four paired sinuses:

• Maxillary Sinus
• Frontal Sinus
• Ethmoidal Sinuses
• Sphenoidal Sinus

🔺 Maxillary Sinus (Antrum of Highmore)

• Largest of all sinuses

• Shape: Pyramidal

• Location: Occupies the body of the maxilla

• Capacity: ~15 ml

📍 Orientation:

• Base: Faces the lateral nasal wall
• Apex: Directed towards the zygomatic process

📤 Drainage: Drains into the middle meatus via its ostium

🔄 Maxillary Ostia:

There are 2 maxillary Ostium - Natural Ostium and Accessory Ostium.

What are the differences between Natural Ostium and Accessory Ostium?

🧭 Relations of Maxillary Sinus:

• Anterior Wall: Facial surface of maxilla, cheek soft tissue

• Posterior Wall: Infratemporal and pterygopalatine fossa

• Medial Wall (Base): Middle and inferior meatus; often thin

• Floor: Alveolar & palatine processes; related to roots of 2nd premolar and 1st molar

• Roof: Orbital floor — traversed by infraorbital nerve and vessels

🔺 Frontal Sinus

• Located in between inner and outer tables of frontal bone

• Often asymmetrical

• Divided by a thin or absent bony septum

📤 Drainage: Via frontal ostium into frontal recess, then into middle meatus

🧭 Relations of Frontal Sinus:

• Anterior Wall: Skin of forehead

• Inferior Wall: Orbit and its contents

• Posterior Wall: Meninges and frontal lobe

🔺 Ethmoidal Sinuses

• Numerous thin-walled air cells (3–18)

• Located in the lateral masses of the ethmoid bone

• Separated into:

  • Anterior group → Middle meatus
  • Posterior group → Superior meatus
  • Divided by ground lamella (basal lamella of middle turbinate)

What are the relations of Ethmoidal sinuses?

Anterior Ethmoid Cells

• Agger Nasi Cell: Anterior-most cell; affects uncinate process position

• Ethmoidal Bulla: Most constant anterior cell

• Supraorbital Cell: Lies over orbit → can mimic frontal sinus

What is the surgical importance of Supraorbital cells?

• Suprabulla or Frontal Bulla Cells

• Frontoethmoidal Cells - situated in area of Frontal Recess and may encroach Frontal sinus.

What is Kuhn's Classification of Frontoethmoidal Cells?

• Haller Cells: Infraorbital; can obstruct maxillary drainage

What is the surgical importance of Haller cells?

Posterior Ethmoid Cells

• Drain into superior meatus

• Onodi Cell:

  • Most posterior cell
  • May be confused with sphenoid sinus
  • Lies close to optic nerve and carotid artery

What is the surgical importance of Onodi cell?

🔺 Sphenoid Sinus

• Located in the body of sphenoid bone
• Rarely symmetrical; separated by a thin septum

📤 Drainage: - Into sphenoethmoidal recess

What is the location of sphenoid ostium in relation to Posterior Choana?

What are the different types of pneumatization patterns of Sphenoid sinus?

🧭 Relations of Sphenoid Sinus:

• Lateral Wall:

  • Optic nerve, carotid artery, opticocarotid recess
  • Maxillary nerve (lower lateral wall)

• Roof:

  • Olfactory tract, optic chiasma, frontal lobe (anterior)
  • Pituitary gland, cavernous sinus (posterior)

• Floor: Vidian nerve

• Posterior Wall: Contributes to clivus

�� Drainage Summary

🔬 Mucosal Lining of Sinuses

• Thinner and less vascular than nasal mucosa

• Epithelium: Ciliated columnar with goblet cells

• Cilia are denser near the ostia → assist mucus drainage

📌 Clinical Points to Remember

• Accessory ostia can hinder natural drainage
• ONODI cells pose a risk during endoscopic surgery due to proximity to optic nerve
• Supraorbital cells may obstruct frontal recess and confuse surgical orientation
• Frontal cell classification prevents incomplete dissection during FESS
• Sphenoid sinus relations are vital during skull base or pituitary surgeries