Paranasal
PARANASAL SINUSES
Definition
Functions
Development
Frontal Sinus
Maxillary Sinus
Sphenoidal Sinus
Ethmoidal Sinuses
Clinical Anatomy
01
Definition
- Paranasal sinuses are air-filled spaces present within some bones around the nasal cavities.
The Sinuses Are
1. Frontal
2. Maxillary
3. Sphenoidal
4. Ethmoidal
- All of them open into the nasal cavity through its lateral wall.
02
Functions
- Make the skull lighter.
- Warm up and humidify inspired air.
- Add resonance to the voice.
- In infection of the sinuses (sinusitis), the voice is altered.
03
Development
- Sinuses are rudimentary or even absent at birth.
- They enlarge rapidly during 6–7 years of age, i.e. at the time of eruption of permanent teeth, and then after puberty.
- From birth to adult life → growth of sinuses occurs due to enlargement of the bones.
- In old age → growth is due to resorption of the surrounding cancellous bone.
04
Frontal Sinus
Location and Extent
- Frontal sinus lies in the frontal bone, deep to the superciliary arch.
- Extends upwards above the medial end of the eyebrow.
- Extends backwards into the medial part of the roof of the orbit.
Opening
- Opens into the middle meatus of the nose at the anterior end of the hiatus semilunaris:
- Either through the infundibulum
- Or through the frontonasal duct.
Size and Development
Size
- Right and left sinuses are usually unequal in size.
- Rarely, one or both may be absent.
- Average height, width and anteroposterior depth → each about 2.5 cm.
- Better developed in males than in females.
Development
- They are rudimentary or absent at birth.
- Well developed between 7–8 years.
- Reach full size only after puberty.
Blood Supply and Drainage
| Component | Supply / Drainage |
|---|---|
| Arterial supply | Supraorbital artery |
| Venous drainage | Supraorbital and superior ophthalmic veins |
| Lymphatic drainage | Submandibular nodes |
| Nerve supply | Supraorbital nerve |
05
Maxillary Sinus
Location and Shape
- Maxillary sinus lies in the body of maxilla.
- It is the largest of all paranasal sinuses.
- Pyramidal in shape.
- Base → directed medially towards the lateral wall of the nose.
- Apex → directed laterally into the zygomatic process of maxilla.
Opening
- Opens into the middle meatus of the nose in the lower part of the hiatus semilunaris.
- The opening/hiatus is nearer the roof.
Size and Opening in the Skull
- In an isolated maxilla, the opening/hiatus of the maxillary sinus is large.
- In the intact skull, the opening is reduced to 3–4 mm because it is overlapped by:
From Above
- Uncinate process of ethmoid
- Descending part of lacrimal bone
From Below
- Lacrimal and ethmoidal processes of inferior nasal concha
From Behind
- Perpendicular plate of palatine bone
- Ethmoidal process of inferior nasal concha
- The opening is further reduced by the thick mucosa of the nose.
Size of Sinus
Height
3.5 cm
Width
2.5 cm
Anteroposterior Depth
3.5 cm
Development
Maxillary sinus is the first paranasal sinus to develop.
Roof
- Formed by the floor of orbit.
- Traversed by the infraorbital nerve.
Floor
- Formed by the alveolar process of maxilla.
- Lies about 1 cm below the level of floor of the nose.
- Its level corresponds to the lower border of the ala of nose.
- Marked by several conical elevations produced by the roots of upper molar and premolar teeth.
- Roots may even penetrate the bony floor and lie beneath the mucous lining.
- Canine tooth may project into the anterolateral wall.
Blood Supply and Drainage
| Component | Supply / Drainage |
|---|---|
| Arterial supply | Facial, infraorbital and greater palatine arteries |
| Venous drainage | Facial vein and pterygoid plexus of veins |
| Lymphatic drainage | Submandibular nodes |
| Nerve supply |
Posterior superior alveolar branches from maxillary nerve. Anterior and middle superior alveolar branches from infraorbital nerve. |
06
Sphenoidal Sinus
- Right and left sphenoidal sinuses lie within the body of sphenoid bone.
- Separated by a septum.
- Usually unequal in size.
- Each sinus opens into the sphenoethmoidal recess of the corresponding half of the nasal cavity.
Relations
Superiorly
Optic chiasma and hypophysis cerebri.
Laterally
Internal carotid artery and cavernous sinus.
Blood Supply and Drainage
| Component | Supply / Drainage |
|---|---|
| Arterial supply | Posterior ethmoidal and internal carotid arteries |
| Venous drainage | Pterygoid venous plexus and cavernous sinus |
| Lymphatic drainage | Retropharyngeal nodes |
| Nerve supply | Posterior ethmoidal nerve and orbital branches of pterygopalatine ganglion |
07
Ethmoidal Sinuses
- Ethmoidal sinuses are numerous small, intercommunicating spaces.
- They lie within the labyrinth of ethmoid bone.
- They are completed:
- From above → by orbital plate of frontal bone.
- From behind → by sphenoidal conchae and orbital process of palatine bone.
- Anteriorly → by lacrimal bone.
- Divided into:
- Anterior
- Middle
- Posterior groups.
A. Anterior Ethmoidal Sinus
- Made up of 1–11 air cells.
- Opens into the anterior part of the hiatus semilunaris of the nose.
- Supplied by anterior ethmoidal nerve and vessels.
- Lymphatics drain into submandibular nodes.
B. Middle Ethmoidal Sinus
- Consists of 1–7 air cells.
- Opens into the middle meatus of the nose.
- Supplied by:
- Anterior ethmoidal nerve and vessels.
- Orbital branches of pterygopalatine ganglion.
- Lymphatics drain into submandibular nodes.
C. Posterior Ethmoidal Sinus
- Consists of 1–7 air cells.
- Opens into the superior meatus of the nose.
- Supplied by the posterior ethmoidal nerve.
08
Clinical Anatomy
1. Sinusitis
- Infection of a sinus is known as sinusitis.
- It causes:
- Headache
- Persistent, thick, purulent discharge from the nose.
- Diagnosis is assisted by:
- Transillumination
- Radiography
- A diseased sinus is opaque.
2. Ostiomeatal Complex
- Openings of the anterior ethmoidal, frontal and maxillary sinuses in the middle meatus are known as the ostiomeatal complex.
3. Anterior Ethmoiditis
- Anterior ethmoiditis narrows the ostiomeatal complex.
- This prevents proper drainage from the sinuses.
- Hence, anterior ethmoiditis is also a common cause of chronic sinusitis.
4. Frontal Sinusitis and Ethmoiditis
- Frontal sinusitis and ethmoiditis can cause oedema of the lids secondary to infection of the sinuses.
5. Referred Pain from Ethmoid Sinus
- Pain from the ethmoid air sinus may be referred to the forehead.
- Both are supplied by the ophthalmic division of trigeminal nerve.
6. Maxillary Sinusitis
- Opening of maxillary air sinus is near the roof of the sinus.
- It cannot drain properly.
- Therefore, maxillary sinusitis is the commonest cause of chronic sinusitis.
7. Infection of Maxillary Sinus
- Maxillary sinus may be infected:
- From the nose
- From a caries tooth
- Drainage of the sinus is difficult because its ostium lies at a higher level than its floor.
Surgical Drainage
- Antrum puncture can be done by:
- Breaking the lateral wall of the inferior meatus.
- Pushing in fluid.
- Letting it drain through the natural orifice.
- Head is kept in a dependent position.
8. Carcinoma of Maxillary Sinus
- Carcinoma of the maxillary sinus arises from the mucosal lining.
9. Referred Pain in Maxillary Sinusitis
- Pain of maxillary sinusitis may be referred to:
- Upper teeth
- Infraorbital skin
- All these are supplied by the maxillary nerve.