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ANATOMY OF PARANASAL SINUSES

MAXILLA:

*Mxilla develops during 6-7wks from 5 ossification centres.

*These ossification centres gives rise to alveolar,palatine,zygomatic& frontal processes of maxilla & floor of the orbit.

*Ossification centre in the medial floor of the pyriform apperture forms the premaxilla.

*Premaxilla gives rise to upper incisors & lower nasal spine.

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ETHMOID:

•Ethmoid ossifies in the cartilagenous nasal capsule from 3 centres.

•One centre for each labyrinth &one for perp.plate of ethmoid.

•These centres appears during 4-5th IUL.

•Perp.plate &crista galli developed from the same centre during 1st yr of life & fuses with labyrinth during 2nd yr.

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FRONTAL:

Develops from 2 centres during 8th wk.

Centres are present in superciliary ridge.

At birth frontal bone – 2halves separated by frontal or metopic suture.

Development complete by 2yrs.

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SPHENOID: Develops from presphenoidal &postsphenoidal portions. These portions fuse during 8th IUM. Central portion- body & lesser wings. Lateral portion- greater wing &pterygoid process. These portions fuse during 1st yr of life. Presphenoid portion: made of 6 ossif.centres.Lies ant. To tuberculm sella. Continous with the lesser wings of sphenoid. Postsphenoidportion: 8 ossif.c Coposed of sella tursica &dorsum sella. Gives rise to greater wings & pterygoid process.

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*Frontal,maxillary and ethmoidal sinuses arise from evagination of lateral nasal wall of nasal capsule.

*Sphenoid sinus arises from a posterior evagination of nasal capsule.

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*At 25-28wks IUG 3 medially projections formed from lateral wall of nose from this PNS are developed.

*Anterior projection;agger nasi.

*Inferior projection (maxillo-terbinal): inf.terbinate & max.sinus.

*Superior projection(ethmo_terbinal): superior terbinate, middile.t, ant. Ethmoidal cells &corresponding drainage channels form.

*Middle meatus invaginates laterally to form infundibulum &UP.

*Infundibulum grows superiorly to form frontal recess.

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Frontal sinus:

*It develops during 4th foetal month as an outpouching, medial to most superior aspect of uncinate process.

*It is very rudimentary at birth, it developes in childhood by upward continuation of embryonic infundibulum & frontal recess.

*Embryologically it can also devlp from ant.ethmoidal air cells.

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Mxillary sinus:

•It develops from primitive ethmoidal infundibulum in to the mass of maxilla.

•It enlarges by absorbtion and expantion.

•At 12yrs pneumatisation reaches under lateral orbital wall at insertion of zygomatic process , inferior to the nasal floor.

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*Ethmoid sinus:

*Develops fromlateral wall of nasal capsule at 9th to10th wk.

*6-7 folds appear,these folds are separated by grooves.

*Folds are fuse to form 3-4 crests with anteriorly ramus ascendus and posteriorly ramus descendus.

*From the main fold middle, superior ,supreme terbinates form.

*From inferior fold inferior terbinate form so called maxillo-turbinal.

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Sphenoid sinus:

It is a evagination from sphenoethmoid recess at 3rd month of gestation.

At 7thyr reaches floor of sella.

Pneumatisation progress rate 0.25mm/yr frm 4yr of age.

In some cases internal carotid artery and optic.n may lie naked with in the sinus cavity.

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Paranasal sinuses:INTRODUCTIONThese are air filled cavities in relation to nasal cavities.

*Classified in 2 groups anterior & posterior.

Four on each side:

They are lined with a mucous membrane continuous with that of the corresponding nasal fossa through their ostia.

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(labyrinth)

(labyrinth)

Anterior group:

I.Frontal sinus.

II.Anterior ethmoidal cells.

III.Maxillary sinus.

Posterior group:

I.Posterior ethmoidal sinuses.

II.Sphenoid sinus.

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Maxillary sinus:*It is the largest of the sinuses,

with an average capacity of about 10-20 ml in the adult.

* Is pyramidal in shape and

occupies the body of the maxilla.

* The base lies medially,

the apex is in the zygomatic portion of the maxilla.

* Medial wall is the wall

between the sinus and the nasal fossa. * Dimensions :

height)3.3cm(

width)2-3cm(

ant.post)3-4cm(

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* Floor :is formed by the alveolar

process and hard palate:

Œ- In children the floor lies

at, or above, the level of

the floor of the nasal

fossa.

Œ- In adults it lies about

1.25cm below the floor of

the fossa.

Œ- The roots of several teeth

may project into, or even

perforate, the floor.

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1,25cm

The ostia of maxillary sinus:

*Main ostium is situated high up between the medial wall and roof of the cavity. It opens into the hiatus semilunaris.*Accessory ostia are sometimes present, behind the main one. Both main and accessory ostia are surrounded by a wide area of mucous membrane unsupported by bone.

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Relations of maxillary sinus:1*Orbit: is separated from

the antrum by the thin

roof of the sinus which

contains the infraorbital

nerve.

2*Teeth: may produce

elevations in the floor of

the sinus and the number

of related teeth depends

on the size of the antrum.

The second premolar and

first molar are usually

related.

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3* Middle meatus of nose: is related to the upper

part of the antrum.

4* Inferior meatus of nose: is separated from the middle part of its medial wall by bone, which is usually thick in front and below,but thinner above and behind.

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5* maxillary artery : : is related to the posterior

wall, where it occupies the pterygopalatine fossa. It may be approached through the antrum for ligature.

6* Maxillary division of the Vth cranial nerve: also traverses the pterygo- palatine fossa.

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7* Nasolacrimal duct: passes downwards,

medial to the antrum,

to open into the inferior

meatus.

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maxillary sinus

ARTERIAL:

oBy facial artery branch of ECA.

oBy infra orbital & greater palatine arteries branch of max. art which is branch of ECA.

VENOUS:

oTo anterior facial vein& pterygoid plexus.

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Infraorbital artery

superior dental arteries

o Maxillary division of trigeminal.n gives sensory supply via.

o Infraorbital.n ,sup.alveolar.n , greater palatine.n.

o Ant superior alveolar.n- ant. Wall of antrum passing through canalis sinosus.

o Also supply-pulps of canine, incisors teeth, ant.inf.quadrant of lat.wall of nose,floor of nose,ant. Part of nasal septum.

o Middle sup. Alveolar.n-

o Lateral wall of sinus, upper pre molar teeth.

o Posterior.sup.alveolar.n

o Through pterygo palatine fossa supply posterior sinus wall.

o Adjacent mucosa,molar teeth.

o Greater palatine.n – posterio medial wall of sinus.

o Perforating branches of infra orbital.n –roof of sinus.

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Ethmoid means sieve like

Ethmoid is trapezoid box

narrow/taller anteriorly

wide posteriorly.

Multiple air containing cells situated

in ethmoidal labyrinth(3-18)

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Anterior group-(drains –middle meatus)Middle group(drains-middle meatus)Posterior group(drains-superior meatus)

Haller cell..ant ethmoidal cells seen anteriorly & below the orbit

Onadi cells… posterior ethmoidal cells seen just in front of sphenoid

Type I: depth of olfactory fossa 1-3mm (26.3%)

Type II: 4-7mm(73.3%).

TypeIII:8-16MM(0.5%).

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Anterior ethmoidal artery(ophthalmic artery)

Post. Ethmoidal arterySphenoidal artery(maxillary artery)

Venous drainageVenous drainageNasal veins

Ant. Ethmoidal vein

Post. Ethmoidal vein

Anterior ethmoid artery posterior ethmoidal

artery

Ethmoidal aircells recieves innervation from anterior &posterior ethmoidal.n & orbital branches of pterygopalatine ganglion.

Postganglionic parasympathetic fibres for mucous secreton from facial .n

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Frontal sinus:*Should be regarded as an

upward extension of an

anterior ethmoidal cell.

*It occupies a very variable

extent of the frontal bone

and may be partly loculated.

*Its average capacity is about

5-10ML in the adult.

* The right and left sinuses

are often asymmetrical.

*Dimensions…height)28-32mm(

width)24-26mm(

depth)18-20mm(

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*They are separated by a thin

bony septum, which may be

deficient in part.

* The sinus may invade the

orbital plate of the frontal

bone and occasionally it

extends to the optic foramen.

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Relations of frontal sinuses:Anterior cranial fossa: separated from the sinus by the compact bone of its posterior wall.

Orbit: lies below the floor of the sinus. This is also compact bone which may rarely be deficient.

Skin and periosteum of forehead: cover the anterior wall, which is of diploic bone and is related To supratrochlear andsupraorbitalnerves.

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*Type1…single frontal recess cell above the agger nasi cell, but below the frontal sinus*Type11…A tire of more than one cell in frontal recess above the agger nasi cell, but below the frontal sinus*Type111…large single cell pneumatizing cephaloid into frontal sinus*Type1V…single isolated cell within the frontal sinus

The frontonasal duct:*It passes through the anterior

part of the ethmoidal labyrinth.

* Its length and curvature vary

considerably.

* Its lower end )ostium( usually

opens in to the infundibulum,

less often independently above

this level.

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*Drainage into frontal recess anterior to the infundibulum(55%)*Drainage above but not into the

infundibulum(30%)*Drainage into

infundibulum(15%)*Drainage above the bulla(1%)

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Blood supply of frontal sinus*Supraorbital artery*Supratrochlear arteryVenous drainage*Small vein that unites the Supraorbital and

Superior ophthalmic veins.Nerve supply*Supraorbital nerve(ophthalmic nerve)*Supratrochlear nerve(ophthalmic nerve)Lymphatic drainage*Submandibular nodes

Sphenoidal sinus:*Lies behind the upper part of the nasal fossa.* It occupies the body, and some times the wings and pterygoid processes, of the sphenoid bone. * The average capacity is about 7 ml in the adult. * The right and left sinuses are rarely symmetrical.* They are separated by a septum which may be deficient in part and is often oblique.

* Dimensions … )L..4-44mm( W)25-34mm(h)5-33(

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1. conchal…(3%)

2. Presellar(11%)

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The ostium of sphenoid sinus:

*situated in the upper part of

the anterior wall of the sinus.

*It communicates with the

superior meatus indirectly

through the sphenoethmoidal

recess.

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Relations:*Cavernous sinus lies laterally containing the:

IIIrd,

IVth,

Vth )ophthalmic

and maxillary-

divisions( and

VIth cranial nerves,

internal carotid artery

optic nerve39

*Above the sinus there are:

Pituitary gland,

optic chiasm,

frontal lobe of brain

olfactory tract

The pituitary gland may be approached surgically through the sinus.

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*Posterior ethmoidal artery(roof of sinus)*Sphenopalatine artery(floor of sinus)

Nerve supplyNerve supply*Trigeminal (I/II div)

LymphaticsLymphatics

*Retropharyngeal nodes to upper deep cervical nodes.

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*Lined by mucus membrane

*Ciliated columnar epithelium

* goblet cells secretes mucus

*Cilia are more marked near ostia.

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*Plain sinus radiography

*Computed tomography

*Magnetic resonance imaging

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*Radiographic positions to study the paranasal sinuses are standardised around three positions: *1. Two anatomical - namely coronal and sagittal *2. One radiographic - termed as radiographic base

line.. *The various radiographic positions used to study

paranasal sinuses are: 1. Occipito-mental view (Water's view) 2. Occipital-frontal view (Caldwell view) 3. Submento-vertical position (Hirtz position/jug

handle) 4. Lateral view 5. Oblique view 39 Degrees oblique (Rhese

position)

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Infra orbital

margin

orbit

Max.sinus

ns

Fronta.s

ethmoids

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Frontal.s

Sphenoid.b

nsMax.s

Inferior.t

Hard palate

orbit

mandible

Ethmoid air.c

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MAXILLARY.S

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