Paranasal Sinus(Anatomy)

Paranasal sinuses

Paranasal air sinuses

Air-containing bony-pockets located around the nasal cavity

all lined by mucous membrane (normally respiratory epithelium)

All of them are paired:

(i) Frontal air sinus, (ii) Ethmoidal air sinuses, (iii) Sphenoidal air sinus (iv) Maxillary air sinus.

Functions

(i)Air-conditioning of the inhaled air by adding moisture and temperature regulation.

(ii) Resonating boxes for sound production.

(iii) Making the facial bones lighter.

(iv) Establishing adult contour of face - Teeth and sinus development are responsible for the enlargement of the cranium

Contd..

All the sinuses are rudimentary at birth

 maxillary sinus is the first paranasal sinus to develop

 have two spurts of growth - once at 7-8 years of age (during eruption of permanent teeth)  and again at 14-16 years of age (post-pubertal) Hence a baby's face changes towards adultface during these two phases of growth of the air sinuses.

Frontal sinus

lie between the outer and inner tables of the squamous part of the frontal bone

 behind the medial part of the superciliary arches

are rarely symmetrical

 Each has a triangular shape

Contd..

Dimension : average height, width, and anteroposterior  depth  are each about 2.5 cm.

Sinuses are better developed in males than in female

Blood Supply - From the supraorbital  vessels.

Lymphatics - drain into the submandibular lymph nodes.

Nerve Supply - by supraorbital nerves (hence pain of frontal sinusitis may be referred to the skin of forehead and adjacent scalp).

Contd..

DRAINAGE - into the ethmoidal infundibulum of the middle meatus of nose either directly or via the frontonasal duct

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SURFACE MARKING –

The surface projection of the sinus is triangular.

 angles formed by the nasion,

a point 3cm above the nasion

 a/ point at the junction between medial 1/3^rd and lateral 2/3^rd of supraorbital margin

MAXILLARY AIR SINUS

Largest of all the paranasal sinuses

Lies in the body of maxilla

roughly pyramidal with a base directed towards the lateral wall of nasal cavity and an apex directed laterally into the zygomatic process of the maxilla

DIMENSIONS - 35 mm (vertical) x 35 mm (depth) x 25 mm (transverse)

The size of the sinus is variable

Contd..

ROOF :

formed by the orbital plate of maxilla which is grooved by the infraorbital vessels and nerve.

ANTERIOR WALL- formed by the anterior wall of the body of maxilla.

POSTERIOR WALL –formed by infratemporal surface of maxilla

Contd..

FLOOR : lies about 1.25 cm below the level of the floor of the nose

 Alveolar process of the maxilla lodging the molar and premolar teeth  even canine supports the floor

 In some cases the floor is perforated by the roots of the teeth and extraction of any of them may damage the floor of the sinus.

DRAINAGE -

drains into the middle meatus of the nose just below the bulla ethmoidalis through the floor of hiatus semilunaris due to the elevator –like action of the cillia lining the mucous membrane.

Usually there are two communicating apertures.

Contd..

These apertures being present in the medial wall of the sinus, i.e., much higher from the floor level, there is disadvantage for normal drainage of any collection within the sinus

In the articulated skull the large-sized maxillary hiatus is much reduced in size because ofencroachment by different bones

SURFACE MARKING

The surface projection of the sinus is a bit irregular.

upper limit - represented by a transverse line just below the inferior orbital margin.

lower limit - represented by another transverse line drawn just above the alveolar process of maxilla.

lateral limit - at the zygomatic process of maxilla, and

medial limit -at the lateral wall of the nose.

Arterial supply –facial and greater palatine  arteries

Venous drainage- facial and pterygoid plexus of vein

Lymphatics - They drain into the submandibular group of lymph nodes.

Nerve supply - By the anterior, middle and posterior superior alveolar nerves (CN V2) (hence pain of maxillary sinusitis is often referred to the upper jaw and teeth).

Sphenoidal sinus

Lie within the body of sphenoid bone

Right and left sinuses are separated by a septum

Are usually unequal size

Relation :

Superiorly- optic chaisma, hypophysis cerebri

Inferiorly- nasopharynx

Laterally – internal carotid artery and cavernous sinus

posteriorly – pons and medulla

Contd..

Each sinus opens into sphenoethmoidal recess

BLOOD SUPPLY - By the posterior ethmoidal vessels.

LYMPHATICS - They drain into the retropharyngeal group of lymph nodes.

NERVE SUPPLY - By the posterior ethmoidal branch of nasociliary nerve.

Ethmoidal sinuses

3 to 18 in number on each side

 lie within the labyrinth of ethmoid bone

Lie between the upper part of nasal cavity and orbit

Divided into anterior, middle and posterior groups

}  Anterior ethmoidal air cells

1-7 in number

The most anterior one may encroach upon the frontal sinus

Open into anterior part of hiatus semilunaris

Supplied by anterior ethmoidal nerve and vessels

Lymphatics -drain into submandibular lymphnodes

Middle ethmoidal air cells

less than three in number

 They open into the middle meatus by one or more orifices on or above the ethmoidal bulla

Supplied by anterior ethmoidal nerve and vessels & orbital branches of pterygopalatine ganglia

Lymphatics – submandibular lymphnode

Posterior ethmoidal air cells

1- 7 in number

Open into superior meatus of the nose

Supplied by posterior ethmoidal nerve and vessels and orbital branch of pterygopalatine ganglia

Lymphatics – retropharyngeal lymphnode

Applied anatomy

The maxillary sinus may get infected from a carious tooth.

 As the air sinuses are underdeveloped or rudimentary, one must be skeptical about a diagnosis of sinusitis in a child less than 5 years of age

Secretions draining out of the frontal air sinus flow towards the maxillary hiatus- frontal sinusitis often leads to maxillary sinusitis

Pituitary tumours are commonly approached via the sphenoidal sinus (transnasal approach).

Functional endoscopic sinus surgery (FESS).