ct anatomy of para nasal sinuses

CT PNSBy

Dr.K.PRASANNARadiology Resident

RMMCH

CONTENTS

NOSE AND NASAL FOSSA

PARA NASAL SINUSES

OSTEOMEATAL COMPLEX

ANATOMICAL VARIATIONS

IMAGING MODALITIES

CT PROCEDURE & SECTIONS

CONCLUSION

NOSE AND NASAL FOSSA

Bony part & cartilaginous part covered by

muscle & skin

Cartilaginous part – upper & lower lateral

cartilages, lesser alar cartilages & septal

cartilage

Nasal skin

Internal nose divided into the

Right and left by the nasal

septum

NOSE AND THE NASAL FOSSA

NOSE AND THE NASAL FOSSA

NASAL CAVITY PROPER

Roof – Nasal bone,

sphenoid & ethmoid

bone

Floor - Palatine

process of the maxilla

& Palatine bone

Medial wall

Lateral wall

Medial Wall - Nasal Septum•Seperates the nasal cavity into

two.

•Columellar septum

•Membranous septum

•Septum proper

• Perpendicular plate of ethmoid

• Vomer

• Septal cartilage

• Minor contributions – crest of

nasal bone, nasal spine of

frontal bone, rostrum of

sphenoid, crest of maxilla &

palatine bone

Blood supply

Mainly by both Internal &

external carotid, both on

the septum & lateral walls

Anterior & posterior

ethmoidal artery

Sphenopalatine artery

Septal branch of greater

palatine

Septal branch of superior

labial artery

LATERAL WALL

Formed by bony, soft tissue

& cartilage

Bony –

Ethmoid infundibulum &

uncinate

Perpendicular plate of

palatine bone

Medial plate of pterygoid

process of sphenoid bone

Medial surfaces of lacrimal

bones and maxillae

Inferior conchae

Cartilage – In

external nose, the

lateral wall of cavity

is supported by

cartilage (lateral

process of septal

cartilage & major,

minor alar cartilage)

Marked by three bony projections, they extend

medially across the nasal cavity separating the nasal

cavity into for air channels – the turbinates or conchae

Superior ,middle & inferior tubinates or conchae. The

conchae do not extend forwards into the external nose

The air space below and lateral to each turbinate is

called as meatus

Superior, middle & inferior meatus & sphenoethmoidal

recess

Middle Meatus – much significant

LATERAL WALL

Superior Meatus – Limited only to posterior one third of lateral wall. Posterior ethmoidal sinus opens into it.

Middle Meatus

Inferior Meatus – Runs along the whole length of lateral wall. Nasolacrimal duct opens in its anterior part. Largest of all meatus

Sphenoethmoidal recess – Above the superior turbinate. It receives the opening of sphenoid sinus

LATERAL WALL

MIDDLE MEATUS

Bulla ethmoidalis – Bulge

produced by the middle

ethmoidal cells

Uncinate process – Superior

extension of lateral nasal wall

(medial wall of maxillary

sinus). Medial and inferior to

bulla ethmoidalis

MIDDLE MEATUS

Infundibulum – Air passage

connecting the maxillary

sinus ostium to middle

meatus

Hiatus Semilunaris – Gap

between the uncinate

process and bulla

ethmoidalis. Medially it

communicates with middle

meatus. Laterally & inf it

communicates with

infundibulum

MIDDLE MEATUS

Frontal sinus – Opens

into the anterior part of

hiatus semilunaris

Maxillary sinus – Opens

into the posterior part

of hiatus semilunaris

Anterior and middle

ethmoidal cells – Opens

into the upper margin

bulla ethmoidalis

ETHMOID BONE

SINUSES

SINUSES

Air containing cavity in certain skull bones

Develop as a diverticula/outpouching from the

lat wall of nose & extend into Maxilla, Ethmoid,

sphenoid and frontal bones

Four sinuses – Maxillary, Frontal, Ethmoid (Ant

& Post) & Sphenoid

Some sinuses are well developed &

asymmetrical

Sinuses

Each sinuses have orifices that open into the meatus, covered by turbinates

Clinically - two

groupsAnterior – Frontal,

Maxillary, Ant.Ethmoida

l

Posterior – Post

Ethmoidal, Sphenoid

Sinuses

Middle meatus

Sup. Meatus & sphenoethmoidal recess

Significance

Lighten the skull & facial bones

Contributes to vocal resonance

Collapsible framework that helps the brain to

protect from blunt trauma

EPITHELIUM

They are lined by mucosa similar to that of the nasal

cavity – pseudo stratified ciliated columnar epithelium

Epithelium contains – Mucinous & serous glands

Mucoperiosteum

SINUSES

Physiology

•Approx 1.5 - 2

lit/day

•Mucous produced

from the glands are

removed by two

mechanisms

• Ciliary action

• Slime trails

Sinuses Status at Birth

First Radiologi

cal evidence

Reaches Adult size by

Maxillary sinus

Present at birth

4-5 months after birth

15 years

Ethmoid sinus

Present at birth

1 year 12 years

Sphenoid sinus

Not Present 4 years 15 years – adult age

Frontal Sinus

Not Present 6 years Size increases

until teens

Maxillary Sinus - (Antrum of Highmore )

Largest paranasal sinus

Pyramidal in shape

Base - towards lateral wall of nose

Apex – towards zygomatic process of maxilla


Present at birth as a rudimentary sinus

First radiological evidence is at 4-5 months

after birth

Reaches adult size by 15 years

On average,

it has capacity

of 14.75 ml (14-15)

• Facial surface of maxilla and cheekAnt wall

• Infra temporal & pterygopalatine fossaPost wall

• Middle & inferior meatuses (this wall is thin & membranous)

Med wall• Floor of orbits

Roof• Alveolar part of maxilla

Floor



DRAINAGE – OSTIUM

Seen high up in the medial wall

Does not open directly into the nasal cavity, but

opens into post. part of ethmoidal infundibulum, via

hiatus semilunaris into middle meatus.

The infundibulum is the air passage that connects

the maxillary sinus ostium to the middle meatus.

Unfavourable for natural sinus drinage

Accessory ostium – 30 % cases


Arterial supply – Maxillary

artery, infra orbital, facial

& greater palatine

Venous supply – anteriorly

by facial vein & post.by

maxillary vein

Nerve supply – infra orbital,

anterior, middle & posterior

superior alveolar nerves

Lymph nodes – cervical nodes

& submandibular nodes

Situated between the outer & inner table of frontal

bone

Funnel shaped

Two sinuses on either side

Asymmetrical

Intervening bony septum which may be thin or

deficiency

FRONTAL SINUS

Not present at birth

First radiological evidence is at 6 years

Reaches adult size after puberty

The natural frontal sinus ostium is usually located in the

posteromedial floor of the sinus (most dependent part).

It opens into the middle meatus

The ethmoidal infundibulum can act as a channel for

carrying the secretions (and infection) from the frontal

sinus to anterior ethmoid cells and the maxillary sinus or

vice versa.

Frontal Sinus

Frontal Sinus

They develop from a variable site, their drainage

will be either via an ostium into the frontal

recess or via a nasofrontal duct into the anterior

infundibulum. The opening or duct can be

distorted by expansion of adjacent ethmoid cells

Boundaries

Ant wall – Skin over the forehead

Post wall - Meninges & the frontal lobe of brain

Inferior wall - orbit & its contents

Frontal Sinus

FRONTAL RECESS

The frontal recess is an

hourglass like narrowing

between the frontal

sinus and the anterior

middle meatus through

which the frontal sinus

drains. It is not a tubular

structure, as the term

nasofrontal duct might

imply, and therefore the

term recess is preferred.

The frontal recesses are

the narrowest anterior

air channels and are

common sites of

inflammation. Their

obstruction

subsequently results in

loss of ventilation and

mucociliary clearance of

the frontal sinus

AGGER NASI CELL

Anterior, lateral, and inferior to the frontal

recess is the agger nasi cell. It is aerated and

represents the most anterior ethmoid air cell,

usually lying deep to the lacrimal bone.

It usually borders the primary ostium or floor

of the frontal sinus, and thus its size may

directly influence the patency of the frontal

recess and the anterior middle meatus.

The frontal sinus can pneumatize both the

vertical and the horizontal (orbital) plates of

the frontal bone. The deepest area of the

vertical portion of the sinus is near the midline

at the level of the supraorbital ridge, and the

medial sinus floor and the caudal anterior sinus

wall are thinnest in this area. As a result, the

sinus is best approached for a trephination at

this level

Frontal Sinus

There is a rich sinus venous plexus (Breschet’s

canals) that communicates with both the

diploic veins and the dural spaces.

Arterial supply – supra orbital & supra

trochlear

Venous supply – superior opthalmic vein

Lymph – Submandibular lymph node

Sensory innervation – supra orbital & supra

trochlear

Frontal Sinus

Sphenoid sinus

Occupies the body of

sphenoid

Right & left, seperated by a

thin strip of bony septum

(like frontal sinus)

Ostium opens into spheno

ethmoidal recess

Relations of the sinus are

very important, esp during

the surgical approach of

pituitary gland

Sphenoid sinus

Relations –

Anterior part –

Roof – olfactory tract, optic chiasma

& frontal lobe

Lateral – optic nerve, internal

carotid artery & maxillary nerve

Posterior part

Roof – Pituitary gland in sella

turcica

Lateral – Cavernous sinus,ICA &

Cranial nerves III, IV, VI & all

divisions of V

Sphenoid sinus

Thin strips of bone separate the

sphenoidal sinuses from the

nasal cavities below and

hypophyseal fossa above

The pituitary gland can be

surgically approached through

the roof of the nasal cavities by

passing first through the

anteroinferior aspect of the

sphenoid bone and into the

sphenoidal sinuses and then

through the top of the sphenoid

bone into the hypophyseal

fossa

Sphenoid sinus

ETHMOID SINUS

Thin walled air cavities in the lateral masses of

the ethmoid bone

Varies from 3 – 18

Occupy the space between the upper third of the

lateral nasal wall and the medial wall of orbit

Clinically divided into anterior ethmoidal air cells

& posterior ethmoidal air cells, by basal lamella

(lateral attachment of middle turbinate to

lamina papyracea)

ETHMOID SINUS

DRAINAGE:

Anterior - a recess of hiatus

semilunaris & middle meatus

via ehmoid bulla

Post- sup.meatus &

spenethmoidal recess.

Present at birth

Reaches adult size by 12 years

First radiological evidence

seen at 1 year

ETHMOID SINUS

Relations

Roof – formed by the anterior cranial fossa

Lateral wall - orbit

Medial wall – nasal cavity

Thin paper like bony part of the ethmoid separating

the air cells from the orbit, called lamina

papyracea, can be easily destroyed leading to

spread of ethmoidal infections into the orbit

Optic nerve forms a close relationship with the

posterior ethmoidal cells & is at risk during

ethmoidal surgery

ETHMOID SINUS

OSTEOMEATAL COMPLEX

OSTEO MEATAL COMPLEX

The osteomeatal complex is the key anatomic

area addressed by endoscopic sinus surgeons.

Blockage of the osteomeatal complex prevents

effective mucociliary clearance, thus leading to

a stagnation of secretions and therefore leading

to recurrent or chronic sinusitis.


The OMC is bounded

medially by the middle

turbinate,

posteriorly and

superiorly by the basal

lamella, and

laterally by the lamina

papyracea.

Inferiorly and anteriorly

the OMC is open.

This anatomic region

therefore includes

Maxillary sinus ostium

ethmoid bulla

frontal recess

uncinate process

infundibulum

hiatus semilunaris

middle meatus.

ANATOMICAL VARIANTS

Variations of Middle turbinate

Paradoxic Curvature Normally, the convexity of the middle

turbinate bone is directed medially,

toward the nasal septum.

When paradoxically curved, the

convexity of the bone is directed

laterally toward the lateral sinus wall.

The inferior edge of the middle

turbinate may assume various shapes,

which may narrow and/or obstruct the

nasal cavity, infundibulum, and middle

meatus.


Concha Bullosa

It is an aerated turbinate, most often the

middle turbinate.

Less frequently, superior & inferior

turbinate aeration can occur.

When the pneumatization involves the

bulbous segment of the middle turbinate,

the term concha bullosa applies.

If only the attachment portion of the

middle turbinate is pneumatized, and the

pneumatization does not extend into the

bulbous segment, it is known as a

lamellar concha.

Other Variations Additional variations of the middle turbinate can

occur, including medial & lateral displacement, lateral

bending, L shape, and sagittal transverse clefts

Medial displacement – due to other middle meatal

structures (i.e., polypoid disease, pneumatized

uncinate process) encroaching upon the middle

turbinate.

Lateral displacement - due to the compression of the

turbinate toward the lateral nasal wall by a septal

spur or septal deviation.


Nasal septal deviation

The nasal septum

deviation may compress

the middle turbinate

laterally, narrowing the

middle meatus and the

presence of associated

bony spurs may further

compromise the OMU.

Obstruction, secondary

inflammation, swollen

membranes, and

infection can occur

VARIATIONS OF UNCINATE PROCESS

DEVIATION

The course of the free edge of the uncinate

process may either extend slightly obliquely

toward the nasal septum, with the free edge

surrounding the inferoanterior surface of the

ethmoid bulla, or it extends more medially to

the medial surface of the ethmoid bulla. If the

free edge of the uncinate is deviated in a more

lateral direction, it may cause narrowing or

obstruction of the hiatus semilunaris and

infundibulum.

Attachment

Attachment to the lamina papyracea, the lateral

surface of the middle turbinate, or the fovea

ethmoidalis in the floor of the anterior cranial fossa

may occur.

If the uncinate process attaches to the ethmoidal

roof or middle turbinate, during uncinatectomy,

traction could inadvertently damage the ethmoid

roof and result in CSF rhinorrhea or other

intracranial complications.

Sometimes the free

edge of the uncinate

process adheres to

the orbital floor, or

inferior aspect of the

lamina papyracea.

This is referred to as

an atelectatic

uncinate process

Pneumatization

The pneumatization of the

uncinate process is believed

to be due to extension of the

agger nasi cell within the

anterosuperior portion of the

uncinate process.

Functionally, the pneumatized

uncinate process resembles a

concha bullosa or an enlarged

ethmoid bulla.

Infraorbital Ethmoid Cells (Haller’s Cells)

Infraorbital ethmoid cells

are pneumatized ethmoid

air cells that project

along the medial roof of

the maxillary sinus and

the most inferior portion

of the lamina papyracea,

below the ethmoid bulla

and lateral to the

uncinate process

Onodi Cells

Two definitions of Onodi cells.

The first defines them as the most

posterior ethmoid cells, being

superolateral to the sphenoid sinus

and closely associated with the optic

nerve.

Another, more general description

defines Onodi cells as posterior

ethmoid cells extending into the

sphenoid bone, situated either

adjacent to or impinging upon the

optic nerve

Ethmoid Bulla Variations

Its appearance varies considerably, based on

the extent of pneumatization.

Extensive pneumatization may obstruct the

ostiomeatal complex.

Elongated ethmoid bullae are usually in a

superior to inferior direction rather than in an

anterior to posterior direction.

So, Relatively unlikely to obstruct the

ostiomeatal complex.

Extensive Pneumatization of the SphenoidSinus

Encountered rarely

extends into the

lesser wing and the

anterior and

posterior clinoid

processes

Can lead to

distortion of optic

cannal configuration

Medial Deviation or Dehiscence of theLamina Papyracea

May be either congenital

or the result of prior

facial trauma.

It occur most often at the

site of the insertion of the

basal lamella into the

lamina papyracea, thus

rendering this portion of

the lamina papyracea

most delicate

Orbit at risk

Aerated Crista Galli

When aeration of the normally bony crista galli

occurs the aerated cells may communicate with

the frontal recess, and obstruction of this

ostium.

To avoid unnecessary surgical extension into

the anterior cranial vault, it is important to

recognize an aerated crista galli and

differentiate it from an ethmoid air cell.

Posterior Nasal Septal Air Cell

Air cells are commonly found within the

posterosuperior portion of the nasal septum

and, when present, communicate with the

sphenoid sinus.

As a result, any inflammatory disease that

occurs within the paranasal sinuses may also

affect these cells

Asymmetry in Ethmoid Roof Height

It is important to note any asymmetry in

the height of the ethmoid roof.

Intracranial penetration during surgery is

more likely to occur on the side where the

position of the roof is lower

IMAGING MODALITIES

X RAY

CT

MRI

X ray – Water’s view & caldwell view

Ct – gold standard. Coronal & axial sections

MRI is predominantly used for pre and post

operative management of naso sinus malignancy

The chief disadvantage of MRI is its inability to

show the bony details of the sinuses, as both air

and bone give no signal


CT is currently the modality of choice in the

evaluation of the paranasal sinuses and adjacent

structures.

Its ability to optimally display bone, soft tissue, and

air provides an accurate depiction of both the

anatomy and the extent of disease in and around

the paranasal sinuses.

In contrast to standard radiographs, CT clearly

shows the fine bony anatomy of the osteomeatal

channels.

There are few pre requisites in few situations

a course of adequate medical therapy to eliminate

or diminish reversible mucosal inflammation.

pretreatment with a sympathomimetic nasal spray

15 minutes prior to scanning in order to reduce

nasal congestion (mucosal edema) and thus

improve the display of the fine bony architecture

and any irreversible mucosal disease


Coronal & axial views

The coronal plane best shows the ostiomeatal

unit (OMU), shows the relationship of the brain

to the ethmoid roof.

Coronal plane should be the primary imaging

orientation for evaluation of the sinonasal tract

in all patients with inflammatory sinus disease

who are endoscopic surgical candidates


Coronal section - procedure

Prone with chin

hyperextended

Gantry anglutaion-

perpendicular to hard palate

Section thickness-3mm

contigous

Table increment- 3-4

mmeach step

Kvp-125

Mas-80

Hanging head technique

Coronal section - procedure

SCAN LIMITS :

• From the ant

margin of frontal

sinus to post

margin of sphenoid

sinus

Coronal section - procedure HEAD HANGING METHOD

Performed in the prone

position, so that any

remaining sinus secretions

do not obscure the OMU

In patients who cannot

tolerate prone positioning

(children, patients of

advanced age, etc.), the

hanging head technique

can sometimes be utilized.

In this technique, the patient is

placed in the supine position and

the neck is maximally extended.

A pillow placed under the patient’s

shoulders facilitates positioning.

The CT gantry is then angled to be

perpendicular to the hard palate.

It is not always possible to obtain

true direct coronal images with this

technique

Axial image

Axial images complement the coronal study,

particularly when there is severe disease

(opacification) of any of the paranasal sinuses

and surgical treatment is contemplated.

The axial studies provide the best CT evaluation

of the anterior and posterior sinus walls

Axial images are particularly important in

visualizing the frontoethmoid junction and the

sphenoethmoid recess.

CT axial section of PNS - image

Whenever there is total opacification of the

frontal, maxillary, or sphenoid sinuses, a

complete axial and coronal CT examination

should be performed.

And also, if the patient has a suspected

neoplasm, a complete axial and coronal

examination need to be performed to provide the

most detailed analysis of the sinonasal cavities

and the adjacent skull base

Axial image

IMAGING PLANE :

REIDS’S LINE – runs b/w infraorbital margin

(IOM line)

& EAM. (parallel - axial)

ALEXANDER’S LINE – perpendicular to reids

line. (perpendicular - coronal)

Contrast in CT PNS

Contrast is not required for all cases of CT

paranasal sinus

Used in cases such as vascular lesion,

malignancy, mass extending intra cranially,

acute infections

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ct anatomy of para nasal sinuses

Education

lateral wall of cavity

yearssphenoid sinus

rudimentary sinus

meatus superior

middle meatusinferior

opening of sphenoid

natural frontal sinus

posterior ethmoidal