1. Anatomy of Para nasal sinuses
Dr. T. Balasubramanian M.S. D.L.O.

2. Introduction
Para nasal sinuses are air filled sacs found in the skull bone
These sacs surround the nasal cavity
They are paired
Four in number
They include frontal, maxillary, ethmoidal and sphenoid sinuses
Ethmoidal sinuses can be divided into anterior, middle and posterior groups

3. Maxillary sinus Also known as Antrum of Highmore
This is the largest of all paranasal sinuses
Lie just under the cheek area
It is shaped like a pyramid
Its capacity is roughly one fluid ounce (30ml)

4. Maxillary sinus - Boundaries
Medial wall – This is the base of the pyramidal shaped maxillary sinus. This corresponds to the lateral wall of the nasal cavity. This wall has its convexity towards the maxillary sinus. The central portion of this wall is very thin and could even be membranous in places. The natural ostium is present in this wall. The natural ostium is present closer to the roof of the sinus.
Anterior wall – Corresponds to the cheek area of the face. This portion also constitutes the lateral wall of the maxilla. Hence it would be appropriate to call it as antero lateral wall. The most important feature of this wall is the canine fossa.
Roof – Forms the floor of the orbit. This wall is thin. It is through this wall the infraorbital vessels and nerve traverses.
Floor – Is formed by the alveolar process of maxilla and the hard palate. The roots of the first and second molars may reach up to the floor of the sinus.
Posterior wall – Formed by temporal surface of maxilla and is very thick

5. Canine fossa Thinnest portion of the anterior wall of maxillary sinus.
Inferiorly – Bounded by alveolar ridge
Laterally – Bounded by canine eminence
Superiorly – Infraorbital foramen
Medially – Pyriform aperture
Caldwell Luc surgery is performed through this area

6. Applied anatomy of maxillary sinus
Canine fossa is used as an entry point in Caldwell luc surgery. It is just 2mm thick.
Roof of maxillary sinus is weakened by the presence of infraorbital canal and infraorbital foramen
In children the floor of the maxillary sinus lie at the same level as that of the nasal cavity, in adults it lies about 5 – 10 mm below the level of nasal cavity
Dental infections involving the first and second molars may involve the maxillary sinus, because the bone is thin in this area.
Maxillary sinus shows biphasic growth. The first growth phase during the first three years of life, and the next growth phase occur between 7 – 18 years.

7. Frontal sinus This sinus shows the maximum variation
It is shaped more or less shaped like L
Posterior wall – Related to the anterior cranial fossa
Floor – Is formed by the upper part of orbit
Drains into the anterior part of middle meatus via the frontonasal duct
Develops very later in life – fully developed only by the age of 9

8. Ethmoidal sinus Situated close to the anterior skull base
It is composed of complex bony labyrinth with thin walls
There may be 6 – 10 ethmoid cells present in adults
Common sinus infections in children involve Ethmoidal sinuses
Because of its close proximity to orbit and skull base infection involving this group of sinus is more prone for complications.
Ethmoidal sinus anatomically have been divided into anterior, middle and posterior groups according to their drainage pattern. Anterior and middle group drain into the middle meatus while the posterior group drain into the superior meatus
With the advent of FESS the study of Ethmoidal sinuses have gained importance.
The size of Ethmoidal air cells increases from above downwards and from before backwards.

9. Ethmoidal sinus - Boundaries
Lateral wall – Is formed by the orbital plate of ethmoid. It is paper thin and is known as lamina papyracea. It separates the ethmoid air cells from the orbit. Infections involving the Ethmoidal air cells may spread to the orbit via this thin plate of bone.
Roof – It is formed by the frontal bone anteriorly, by the face of sphenoid and orbital process of palatine bone posteriorly.

10. Ethmoidal sinus – Applied anatomy
Anterior most ethmoidal air cell is known as agger nasi.
Large agger nasi air cell can impede frontal sinus drainage due to its close proximity to the frontal sinus drainage pathway.
Pneumatized middle turbinate is known as concha bullosa. Inflammed concha bullosa of middle turbinate may block middle meatus drainage channels.
Haller cells belong to the anterior ethmoidal group of air cells. These cells are also known as infra orbital cells. Enlargement of this cell may block drainage of the maxillary sinus.
Extension of posterior ethmoidal cells supero lateral to the sphenoid sinus is known as onodi cell. This cell lies in close proximity to optic nerve. Inflammation of this cell may cause blindness. This anatomy is also crucial in endoscopic sinus surgical procedures.

11. Sphenoid sinus
This sinus is located in the skull base at the junction of anterior and middle cranial fossa.
Pneumatization of this sinus begins during the 4th year of childhood and gets completed by the 17th year of life.
It varies in size and may be asymmetric.
Drains into the superior meatus.

12. Sphenoid sinus - Relations
Superiorly – Pituitary gland
Lateral wall – Optic nerve and internal carotid artery
Floor – Nerve of pterygoid canal
Infections of sphenoid sinus may involve optic nerve if the nerve is dehiscent.

13. Functions of paranasal sinuses
The presence of these sinuses lightens the skull
They add resonance to speech
They play a vital role in conditioning the inspired air