The paranasal air sinuses are air filled extensions of the nasal cavities, or Pneumatic areas in the frontal, ethmoid, sphenoid and maxillary bones of the cranium. The sinuses are named according to the bones in which they are located, into frontal, ethmoidal, sphenoidal and maxillary sinuses respectively.

DEVELOPMENT OF THE SINUSES
The skull cap or the calvaria is composed of the superior portions of the frontal, parietal and occipital bones. These bones are constituted by an outer  and inner plate ,or lamina of compact bone, with an intervening layer of spongy  bone called the diploe . After birth the cranium is eventually invaded by veins  which branch and rebranch and unite with adjacent veins . Bone marrow cells  are ' seeded ' into the spaces surrounding these venous channels to form the  diploe.The spongy bone of the diploe may also be invaded by mucus membranes from the nasal cavity and mastoid antrum to form air sinuses.

 Owing to the presence of these air filled cavities, the bones mentioned above are sometimes  referred to as pneumatic bones. The sinuses are paired but asymmetrical. The paranasal sinuses develop from the nasal cavities mainly after birth .  The original openings of the outgrowths persist as orifices in the nasal cavities.  Hence all the sinuses drain directly or indirectly into the nasal cavities.

MASTOID / TEMPORAL BONE AND AIR CELLS.
Mastoid air sinuses are similar to the paranasal sinuses but they drain into the nasal region via the middle ear and auditory tube.It is by the process of  hollowing out of the mastoid/ temporal bone by extension of epithelial sac from  the middle ear, that the mastoid air cells are formed. Each space is air containing  and is in free communication with others. Pneumatisation begins in the 1st year of life and by 6-years the pattern is complete. Depending upon the degree of  pneumatisation, the mastoid process may be pneumatic, sclerotic or mixed.

SUPRA MEATAL TRIANGLE (MAC EWEN'S TRIANGLE)
Formed by the supra meatal crest above, the postero-superior margin of  the bony external auditory canal below, and by an arbitrary line extending tangentially upward from the posterior meatal wall behind. This is the surface  landmark of the mastoid antrum in mastoidectomy. Clinically it is palpated in  the cymba concha of the pinna.

Mastoid infection is secondary to otitis media. The treatment is drainage Of pus through supra meatal triangle. Care should be taken to save the facial  nerve from injury. Spread of mastoid infection may cause thrombosis of sigmoid sinus,  meningitis,cerebellar or cerebral abscess & sometimes a retropharyngeal abscess.

The sinuses enlarge during the period of eruption of permanent teeth & after puberty, there by markedly altering the size and shape of the face.
In short, the sinuses are probably manifestations of unusual growth patterns in the bones in which they occur.
The mucosa of the para nasal air sinuses is continuous with that of the nasal cavity. Mucosa is either
1. columnar
2. Pseudo stratified ciliated epithelium.
Mucus is secreted by the glands of the mucosa and is swept into  the nose through the apertures of the sinuses by the movement of the cilia,  found mainly around the opening of the sinuses.

FUNCTIONS OF THE AIR SINUSES
1. They lighten the skull & help to reduce the amount of cortical bone.
2. Gives resonance to voice.
3. Increases surface area for tooth eruption.
4. Facilitates rapid growth of facial skeleton after birth, mainly the maxillary bone.

Clinically the air sinuses are divided into two groups.
1. Anterior group: Frontal, maxillary and anterior ethmoidal.
2. Posterior group: Sphenoidal, posterior ethmoidal.

This classification is for the purpose of drainage than for actual Anatomical distribution. Anterior group drains to the middle meatus and the posterior group into the sphenoethmoidal recess and the superior meatus of the lateral nasal wall.

FRONTAL SINUS
Develops by invading the frontal bone above the superior margins of the orbits. It is triangular in outline, formed out of three points, the nasion, a point 3cm above the nasion and a point intersecting the medial 1/3 of the supra ciliary arch. The sinus might sometimes extend across the midline to the opposite side.
Blood supply - Supra orbital artery
Anterior ethmoidal arteries.
Venous return - Anastomotic veins in supra orbital notch, connecting supra orbital and supra ophthalmic veins.
Lymphatic drainage - Submandibular nodes.
Nerve supply - Supra orbital nerve traversing the floor of the sinus.

THE ETHMOIDAL SINUSES
Composed by several small cavities called ethmoidal cells, within the *ethmoidal labyrinth of the lateral mass of ethmoid bone. The ethmoid cells are divided into ,
1. Anterior
2. Middle
3. Posterior groups according to the area of drainage.
*Ethmoidal labyrinth constituted by Facial
Maxillary
Lachrymal
Sphenoidal &
Palatine bones.
The ethmoidal sinus lies between the upper part of nasal cavity and orbits and is separated from the orbit only by a paper thin orbital plate of ethmoid laterally.
Below the ethmoidal sinus is the part of maxillary air sinus and superiorly is the anterior part of frontal sinus.
Blood supply : Sphenopalatine artery
Anterior and posterior ethmoidal artery.
Lymphatic drainage : Submandibular nodes
Retropharyngeal nodes.
Nerves : Anterior and posterior ethmoidal nerves.
Orbital branches of pterygopalatine ganglion..

MAXILLARY SINUS.
Largest air sinus. Pyramidal in shape. Base is constituted by the lateral nasal wall and the apex by the zygomatic process of maxilla. Floor of the orbit forms the roof and the alveolar process of maxilla forms the floor of the sinus. Conical elevations corresponding to roots of 1st or 2nd molar tooth projects into the floor of the sinus. Sometimes the premolar, 3rd molar and canines are also found protruding into the sinus. The infra orbital nerve is found at the roof of the sinus & the supra alveolar nerve in the floor of the sinus.

Blood supply : Facial, infra orbital, greater palatine arteries.
Lymphatic drainage : Submandibular nodes.
Nerve supply : Infra orbital, anterior, middle and post superior alveolar nerves.

SPHENOIDAL SINUSES
Sphenoidal sinuses are derived from a posterior ethmoidal cell. The sinus lies posterior to the upper part of the nasal cavity with in the body of the sphenoid bones. The sinus is related to
Above - Optic chiasma and pituitary.
Sides - Internal carotid artery and cavernous sinus.
Maxillary nerve, pterygoid nerve.
Floor carries the nerve of pterygoid canal (vidian nerve).
Blood supply : Posterior ethmoidal artery.
Lymphatic drainage : Retropharyngeal nodes.
Nerve supply : Posterior ethmoidal nerve.

STRUCTURES IN THE LATERAL NASAL WALL

DRAINAGE OF THE SINUSES
Sphenoidal - Spheno ethmoidal recess.
Ethmoidal
Posterior- Superior nasal meatus.
Middle - Ethmoidal bulla.
Anterior - Middle meatus.
Frontal - Hiatus semilunaris of middle meatus, by the infundibulam.
Maxillary - Middle meatus.

RADIOLOGICAL ANATOMY OF THE SINUSES
Normal sinuses : Radiolucent.
Diseased sinuses : Varying degrees of opacity.
Almost all sinuses are visible in the antero posterior view.

ANTERO POSTERIOR VIEW
Frontal : Asymmetry , vertical extend, position of septa.
Ethmoidal : superimposed and on the sphenoidal.
Sphenoidal : obscured.

LATERAL VIEW
1. Extend of frontal sinuses upto the frontal bone & back into
the orbital roof.
2. Ethmoid extending back from frontal process of maxilla
upto sphenoid sinus.
3. Both sphenoids are superimposed.
4. Maxilla : relation to tooth is obvious.
Maxillary and frontal sinuses can be trans illuminated in a dark room.
Maxillary : Light in the mouth.
Frontal : Against superomedial angle of orbital opening.
Red glow usually appears.

APPLIED ANATOMY
The sinuses are lined by respiratory epithelium continuous with that of the nasal mucosa. Hence this invites infecion into the sinuses, where by a common cold or rhinitis can progress into a state of sinusitis. The growth of paranasal sinuses is important in altering the size and shape of face during infancy and childhood, and in addingresonance to voice in adolescence.

Once there is infection, inflammation and collection of exudates follows.This produces blockage of the opening of the sinus.The maxillary  sinus drains into the middle meatus through hiatus semilunaris.As the ostium is highly positioned, this sinus is prone to drainage disorders, particularly if the cilia are destroyed as in chronic sinusitis.Maxillary sinus  is drained better when the patient lies on the unaffected side. Pus from anterior ethmoidal sinus or frontal sinus may enter the maxillary sinus, through the hiatus semilunaris. The maxillary sinus is also prone to get  infected from an infected tooth in its close vicinity.

Infection of the ethmoid sinus may erode through the lamina papyraceae into the orbit. If the drainage is blocked, infections may break through the fragile wall of the orbit, producing orbital cellulitis. Severe infections may cause blindness due to compression on the optic canal.  Infection spreading to the dural sheath of the optic nerve can cause optic  neuritis.

Proximity of the maxillary tooth to the sinuses produces problems  during tooth extraction. Broken pieces of the root may be driven into the sinus, introducing oral bacteria into the sinus creating maxillary sinusitis.  A communication is created between the oral cavity and the sinus, which interferes with the nasal-oral seal, necessary for sucking and blowing.  Infection can also spread from an abscessed maxillary molar tooth. As the superior alveolar nerve, which is the branch of maxillary nerve, supply both the maxillary teeth and the mucus membrane of maxillary sinus, inflammation of the mucosa of the sinus is frequently  accompanied by the sensation of toothache.

Patients with fractures of the frontal ethmoid, maxillary or nasal bones should be warned against blowing their noses because of the possibility of expelling air from the sinuses into the cranium, subcutaneous tissue or orbit. CSF rhinorrhoea might occur.
Congenital deformities of the nose might occur. For example,complete absence of the external nose. Only the aperture is present.There can be suppression of development or malformation of one side. The nasal septum may be displaced by injury or congenital defect.When the deviation of the nasal septum is exaggerated the septum comes into contact with the lateral wall.

The pituitary lies just above the sphenoidal sinus.Hence the gland is reached easily through the nose and sphenoidal sinus.Trans-sphenoidal approach follows the septum of the nose through the body of sphenoids. Since the sphenoid is in close vicinity of the cavernous sinus, care is to be  employed to prevent venous ooze or catastrophic arterial haemorrhage during surgical operations. When the sphenoidal sinus becomes infected the infection may  spread upwards in front of the pituitary to affect the optic chiasma, giving  rise to disturbance of vision. Collection of pus in the sphenoidal sinus can be cleared out properly only by removing the anterior wall. This is reached through the posterior ethmoidal sinus by removal of middle and superior conchae.

DIAGNOSTIC METHODS IN DISEASES OF THE SINUSES.

1 .ELICITING SINUS TENDERNESS: Frontal sinuses are palpated by pressing the finger superiorly at the medial end of the superior orbital margin. Ethmoidal sinuses are palpated with the thumb in the inner canthus of one eye and the index finger in the other and pushing posteriorly, posterior to the lachrymal bone and squeezing.
2. TRANSILLUMINATION: In maxillary and frontal sinusitis.
3. RADIOLOGICAL EXAMINATION.
4. DIAGNOSTIC PROOF PUNCTURE.
5. SINOSCOPY: Using a fibre optic sinoscope. Detects early pathology, particularly malignancy. Done through intranasal anterostomy.
6. ECHOSINOGRAPHY : Detects sinus pathology by ultrasound.
7. CT SCAN : Confirmatory.

SINUSITIS

AETIOLOGY
Extension from nasal infection.
Arrest of drainage and aeration of the sinuses.
Narrow air passage, By DNS, growths, foreign bodies.
Extreme temperature variations improper air conditioning.
Infection from carious tooth.
Excessive blowing of nose, driving infection into the sinus. Nasal
douching should not be done in early stages of inflammation.
Sudden rush of infection in driving or underwater swimming.

PATHOLOGY
Mucus membrane passes through all the stages of infection and inflammation.
Outpouring of secretion which soon becomes purulent.
Initially there is increased ciliary activity, later ciliary activity becomes
ineffective leading to ciliary destruction.
Thickening of membranes of the sinuses leading to polyp formation.
Whole cavity becomes infiltrated with polyps.
Infection spreads to submucus layer, even to bone.
Proliferation of mucus membranes.
Fibrous tissue formation and new bone formation.
All the sinuses get affected - leading to pansinusitis.

CLINICAL FEATURES.
HEADACHE , FEVER , PULSE RATE

Vacuum headache: In blocks of the fronto nasal duct, the air in the sinuses get absorbed, resulting in hyperaemia, causing headache of vascular type . Pain is felt above the eye and is maximum in morning hours on waking up, in frontal sinusitis.
Ethmoidal headache is deep seated behind the eyes . In maxillary sinusitis, pain is localised to upper teeth.In sphenoidal headache, deep seated central pain is observed.In maxillary sinusitis, pain is reduced in the morning but more towards noon.
Mucus membranes of the nose is reddened and oedematous.
Pus comes out through the corresponding outlets.
Frontal sinusitis is associated with swelling of upper eyelid.
Maxillary sinusitis is associated with swelling of lower eyelid.
Ethmoidal sinusitis is associated with swelling in the medial canthus.
Hoarseness.
Halitosis.
Postnasal discharge
Nasal obstruction.

COMPLICATIONS
Orbital cellulitis and abscess.
Meningitis - Due to spreading thrombophlebitis.
Brain abscess
Headache Persists.
Defects in memory, behaviour, personality.
Osteomyelitis
Cavernous sinus thrombosis
Mucocoele
Cutaneous fistula.

MISCELLANEOUS DISEASES AFFECTING THE SINUSES
Mucocoele
Cysts
Oro antral fistula
Tumours of the sinuses
Malignancies in the sinuses
Barotrauma
Fractures

MUCOCOELE: Either a retension cyst of mucous gland of sinus or thinning and expansion of sinus wall due to blockage of the sinuses. Frontal sinuses are usually involved.Dull headache and swelling of the corresponding region of the sinus. Mucocoele of the frontal sinus is associated with downward displacement of the eye

ORO ANTRAL FISTULA:Patient complains of air from the fistula and also escape of fluid from nose while drinking. Diagnosis is confirmed by radio  opaque dye introduced into the antrum showing the fistula.

TUMOURS OF THE SINUSES: 1. BENIGN.2. MALIGNANT

BENIGN TUMOURS.
(a). TRANSITIONAL CELL PAPILLOMA: There is thickening of epithelial surface leading to infolding and paplloma formation. Can become malignant. Treatment is by excision and exenteration of the mass.
(b). LOCALISED IVORY OSTEOMA: Occurs in the frontal sinus, is ivory hard in consistency.
( c) . CANCELLOUS OSTEOMA: Occurs in maxillary and ethmoid sinuses. Clinically may remain silent. Pain and headache result from pressure and obstruction.

MALIGNANT TUMOURS.
Commonly affect the maxillary and ethmoid sinuses.
Common variety is Squamous cell carcinoma (80%)
Carcinoma of the maxillary sinus may be primary within the sinus or secondary by extension from alveolus, palate or ethmoid. Early symptoms are nasal obstruction, blood stained nasal discharge and lachrymation. Dull pain over the face is observed. Toothache may be found.