Describe the Location, Development and Functions of Paranasal Air Sinuses
Location
Paranasal air sinuses are air-filled spaces present in the bones surrounding the nasal cavity ie. Frontal, ethmoid, sphenoid and maxilla and therefore are named as:
- Frontal air sinuses
- Ethmoidal air sinuses – anterior, middle and posterior
- Sphenoidal air sinuses
- Maxillary air sinuses
All the paranasal air sinuses are in pairs.
Development of Paranasal air sinuses
- develop as diverticula of mucous membrane of nose and therefore, all paranasal air sinuses open in the lateral wall of nasal cavity.
- are rudimentary at birth except frontal air sinuses, which are usually absent at birth.
- maxillary air sinuses are the first to develop.
Functions of Paranasal air sinuses
- Make the inspired air moist and warm
- Reduce the weight of skull.
- Provide resonance to the voice.
- Contribute to facial growth.
Where Do Paranasal Air Sinuses Open?
All the paranasal air sinuses open into the nasal cavity:
- Frontal air sinus (1 on each side) – Hiatus semilunaris (middle meatus)
- Anterior ethmoidal air sinuses (10-11)– Hiatus semilunaris (middle meatus)
- Middle ethmoidal air sinuses (1-5) – Ethmoidal bulla (middle meatus)
- Posterior ethmoidal air sinuses (1-7) – Superior meatus
- Sphenoidal air sinus (1 on each side)– Sphenoethmoidal recess
- Maxillary air sinuses ( 1 on each side)– Hiatus semilunaris (middle meatus)
Describe Briefly Frontal Air Sinus.
Location:They are located in the frontal bone, deep to supercilliary arches.
Dimensions: Vertical- 3cm, Transverse-2.5cm, Antero-posterior- 1.8cm.
Opening: Open into the anterior part of hiatus semilunaris of middle meatus via frontonasal duct.
Relations: Anteriorly- Superciliary arch, Postero-superiorly- Frontal lobe of brain, Inferiorly – Root of nose and roof of orbit ( medial part).
Describe briefly Ethmoidal Air Sinuses
Location: In the labyrinth of ethmoid bone, between the upper part of lateral nasal wall and orbit. They are divided into three groups
- Anterior group having upto 11 air cells.
- Middle group consisting of 1-5 air cells.
- Posterior group having 1-7 air cells.
Opening: Anterior group into hiatus semilunaris of middle meatus. Middle group on bull ehmoidalis of middle meatus and posterior group in superior meatus of nose.
Describe Briefly the Sphenoidal Air Sinuses.
Location: in the body of the sphenoid bone above and behind the nasal cavity.
Dimensions: vertical 2cm, transverse 1.5cm, antero-posterior- 2cm.
Opening: Open into the sphenoethmoidal recess.
Relations:
- Superiorly: optic chiasma & pituitary gland.
- Laterally: cavernous sinus and internal carotid artery.
- Inferiorly: roof of nasopharynx.
- Posteriorly: pons and medulla oblongata.
- Anteriorly: sphenoethmoidal recess.
Describe briefly the Maxillary Air Sinuses.
Maxillary air sinuses are the largest paranasal sinuses.
Location: Are located in the body of maxilla lateral to the nasal cavity and inferior to the floor of orbit.
Dimensions: Capacity-15ml. Height- 3.5cm, Anterior posterior depth – 3.5cm, Width- 2.5cm.
Boundaries and relations: Maxillary air sinuses are pyramidal in shape and have following boundaries:
- Apex: is directed towards zygomatic process of maxilla and
- Base (medial wall): is formed by nasal surface of body of maxilla and is towards the lateral wall of nose. The superior part of the base presents the opening of sinus.
- Anterior wall: is formed by anterior surface of maxilla
- Posterior wall: is related to infratemporal fossa
- Floor: is formed by alveolar and palatine process of maxilla. (roots of upper molars and premolars project into the sinus).
- Roof: is formed by floor of orbit (the infraorbital nerve and vessels pass through the bony canal and groove in the roof of the sinus).
Relations:
- Superiorly– orbit
- Inferiorly – oral cavity
- Posteriorly – pterygopalatine and infratemporal fossa
- Medially – nasal cavity
- Anteriorly – face
Drainage: maxillary air sinus drains into posterior part of hiatus semilunaris of middle meatus.
Nerve supply: maxillary air sinuses are supplied by infraorbital and anterior, middle and posterior superior alveolar nerves.
Blood Supply, Lymphatic Drainage and Nerve Supply of Paranasal Air Sinuses
| Paranasal air sinuses | Arterial Supply | Lymphatic Drainage | Nerve Supply |
|---|---|---|---|
| Frontal | Supraorbital nerve | Submandibular lymph nodes | Supraorbital nerve |
| Ethmoidal | Anterior ethmoidal artery | Submandibular lymph nodes | Anterior ethmoidal nerve |
| Posterior ethmoidal artery | Retropharyngeal lymph nodes | Posterior ethmoidal nerve | |
| Orbital branch of pterygopalatine ganglion | |||
| Sphenoidal | Posterio ethmoidal artery | Retropharyngeal lymph nodes | Posterior ethmoidal nerve |
| Sphenopalatine artery | Orbital branch of pterygopalatine ganglion | ||
| Maxillary | Anterior, middle and posterior superior alveolar arteries | Submandibular lymph nodes | Anterior, middle and posterior superior alveolar nerves |
Applied Aspects
- Pain due to maxillary sinusitis is referred to upper teeth as both are supplied by superior alveolar nerves.
- During extraction of upper premolar or molar – a communication may be accidentally established between oral cavity and sinus (called antro-oral fistula).
- Maxillary air sinus is the most commonly infected air sinus. The infection can occur from the infection of nose and caries of upper molar tooth:
- The high position of the opening of sinus hinders the natural drainage (by gravity) of the sinus. The opening is present in the upper part of the medial wall of sinus, close to is roof.
- The location of opening of frontal (anterosuperiorly) and maxillary air sinus( posteroinferioly) in the hiatus semilunaris favors passage of infection from frontal to maxillary air sinus.
- Maxillary sinus can be surgically evacuated in two ways:
- Antral puncture: Medial wall of the sinus is punctured in the inferior meatus of nose to create an opening of the sinus at a lower level.
- Caldwell Luc operation: An opening is made through the gingivo-labial fold and the sinus is approached via the anterior wall of canine fossa.