Paranasal sinuses By :

Student at faculty of dentistry Ahram Canadian university

• What are paranasal sinuses?

They are air filled spaces in the skull bones surrounding the nose.

They are lined with mucous membrane which is continous with the nose and they open in the lateral wall of the nasal cavity by special foramina.

What are the functions of paranasalsinuses ?

• Decrease the weight of the skull.

• Increase resonance of voice.

• They act as air insulator cusions for the brain, eye and pituitary gland

• The paranasal air sinuses are abscent at birth except the maxillary sinus.

• They show marked growth at the time of eruption of permanent teeth.

Paranasal sinuses

• The paranasal sinuses are:

• 1) frontal sinuses.

• 2) ethmoidal sinuses.

• 3) maxillary sinus

• 4) sphenoid sinus.

• They are 2 asymmetrical sinuses present in the squamous part of frontal bone above and behind supercilliary arches .

• The are separated by a bony septum which is usually deviated to one side .

• Each sinus opens into front nasal duct (ethmoidalinfandibulum ) which opens at the anterior end of hiatus semilunaris in the middle meatus of the nose .

• They are inter communicating spaces lying inside ethmoidal labyrinth between the orbit and the upper part of the nasal cavity.

• They vary in number from 3-18 air cells arranged into 3 groups :

• 1) anterior ethmoidal sinus or cells opens in the ethmidal infandibulum in the middle meatus of the nose.

• 2) middle ethmoidal sinuses or cells produces bulla ethmoidalis on which it opens .

• 3) posterior ethmoidal sinus opens in the superior meatus .

• They are the largest air sinuses and the only present in birth.

• Pyramidal in shape and occupies the whole body of the maxilla .

apex : Laterally directed towards the zygoma

Base: directed medially towards the nasal cavity

roof

floor

• Relations :

• Apex : directed towards zygomatic bone.

• Base : directed medially towards the nasal cavity.

• Roof : it’s the roof of the orbit containing infraorbital groove and canal and infraorbital nerves and vessels.

It separates the sinus from contents of the orbit

Floor : formed by alveolar process of the maxilla .

It lies 1cm below the floor of the nose.

Its lower part lies opposite to the second premolar and first molar teeth so, the extraction of these teeth may damage and perforate the floor leading to oraantral fistula.

• Anterior wall : subcutaneous , containing infraorbital and anterior superior alveolar nerve and vessels .

• Posterior wall : separates the sinus from temporal and pterygopalatine fossae pierced by posterior superior alveolar nerve and vessels .

• Openings of maxillary sinus :

• large rounded opening 2 cm in diameter present in the upper part of the base of the the sinus.

It opens in the middle meatus of the nose at the posterior end of the hiatus semilunaris below the bulla ethmoidalis.

• Acessory small openings are usually present behind the main

opening .

• N.B: the higher position of the opening of the sinus makes the drainage of pus or blood very hard.

Opening of maxillary sinus at the middle meatus

• Nerves and vessels related to maxillary sinuses:

• 1) anterior superior alveolar: from infraorbital nerves and vessels they ascend in the anterior wall supplying it.

• 2) Middle superior alveolar : from infraorbital nerves and vessels. They descend in the lateral wall of the sinus supplying it .

• 3)Posterior superior alveolar : from the maxillary nerve and vessels

They descend and supply the posterior wall of the sinus .

4) infraorbital nerve and vessels : they pass in the infraorbital groove and canal through the roof of the sinus .

5) greater palatine nerve and vessels : they descend behind the sinus supplying its posterior wall .

It occupies the body of the sphenoid and lies behind the upper part of the nasal cavity .

The 2 sphenoid sinuses are separated by a bony septum which lies in the midline and maybe deviated to one side at most of cases .

Relations :

Superiorly : pituitary gland and optic chiasma .

Posteriorly: pons and basilar artery.

Anteriorly: the opening of the sinus lies in the upper part of its anterior wall and it opens in the sphenoethmoidal recess .

Laterally : on both sides there are cavernous sinuses with internal carotid arteries and abducent nerves .

Sphenoid sinuses