The document discusses the anatomy of the paranasal sinuses. There are four main paired sinuses - frontal, maxillary, ethmoidal, and sphenoid. The maxillary sinus is the largest sinus, located in the cheek area below the orbit. It has thin walls that can allow spread of infection. The ethmoidal sinuses are located near the skull base and consist of many thin-walled air cells. The sphenoid sinus is located in the skull base and pneumatizes later in development. Infections of the paranasal sinuses can spread due to their thin bony walls and proximity to adjacent structures like the orbit and skull base.

1. Dr. T. Balasubramanian M.S.
D.L.O.

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

4. 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.

5.  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.  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.  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.  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.  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. o Anterior most ethmoidal air cell is known as agger nasi.
o Large agger nasi air cell can impede frontal sinus drainage due to its close
proximity to the frontal sinus drainage pathway.
o Pneumatized middle turbinate is known as concha bullosa. Inflammed
concha bullosa of middle turbinate may block middle meatus drainage
channels.
o 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.
o 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.  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.  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. 1. The presence of these sinuses lightens the skull
2. They add resonance to speech
3. They play a vital role in conditioning the inspired air