CROSS SECTIONAL ANATOMY OF THE PARANASAL SINUSES

PRESENTER --- SARBESH TIWARI

Introduction ….

Paranasal sinuses are air containing cavities in certain bones of skull.

Clinically, Divided into two groups:

1. Anterior group. This includes maxillary, frontal , anterior and middle ethmoidal air cells. They all open in the middle meatus.

2. Posterior groups. This includes posterior ethmoidal sinuses which open in the superior meatus, and the sphenoid sinus which open in sphenoethmoidal recess.

Disease of ear, nose & throat 4th edition – PL Dhingra

Development of paranasal sinuses Paranasal sinuses develop as out-pouchings from the

mucous membrane of lateral wall of nose. At birth, only the maxillary and ethmoidal sinuses are present

and are large enough to be clinically significant. Growth of sinuses continues during childhood and early adult

life. Radiologically, maxillary sinuses can be identified at 4-5

months, ethmoids at 1 year, frontals at 6 years and sphenoids at 4 years of age.

Disease of ear, nose & throat 4th edition – PL Dhingra

Introduction…

They lighten the Facial skeleton

Air-conditioning of the inspired air by providing large surface area over which the air is humidified and warmed.

To provide resonance to voice.

They are lined by Psuedostratified columnar epithelium studded with mucus and serous glands.

Function Histology

MAXILLARY SINUS.. Also known as antrum of Highmore

(1651).

Largest paranasal sinus occupying the maxilla.

Pyramidal in shape with base toward the lateral wall of nose and apex directed laterally into the zygomatic process.

Capacity of 15 ml (average).

Relation of the maxillary sinuses

Anterior wall – facial surface of maxilla and related to the soft tissue of the cheek.

Posterior wall – infratemporal and pterygopalatine fossae.

Medial wall – middle and inferior turbinate

Floor – alevolar and palatine process of maxilla. Related to all the molar tooth and sometimes the premolar teeth.

Roof – Formed by the floor of the orbit. Traversed by infraorbital nerve and vessels.

FRONTAL SINUS ..

Paired sinuses situated deep to the inner and outer table of frontal bone.

It drains through the frontal recess to the middle meatus via the ostiomeatal complex. 

Frontal sinus may be absent on one or both sides or it may be very large extending into orbital plate in the roof of the orbit.

Relation of frontal sinuses

Anterior wall -- The skin over the forehead. Inferior wall -- The orbit and its contents.

Posterior wall -- The meninges and frontal lobe of the brain.

The frontal recess, the drainage pathway of the frontal sinus, is situated at its floor and usually drains into the middle meatus (62%) or into the ethmoid infundibilum (38%).

ETHMOID SINUS .. Ethmoidal sinuses are thin-walled air cavities in the lateral masses of

ethmoid bone.

Clinically, ethmoidal cells are divided into :-

1. Anterior ethmoidal air cells – Up to 11 anterior ethmoidal air cells drain into either the ethmoidal infundibulum or the frontonasal duct.

2. Bullar cells ( middle ethmoidal air cells) -- usually less than three middle ethmoidal air cells. Opens in ethmoidal infundibulum.

3. Posterior group :- Up to seven posterior ethmoidal air cells usually drain by a single orifice into the superior meatus.

Relation of the ethmoid sinus Roof -- Anterior cranial fossa. Meninges of the brain form

important relation here.

Floor – maxillary sinus and hiatus semilunaris.

Lateral wall – lamina papyracea of the orbit.

Medially - nasal cavity & medial plate of ethmoid.

Optic nerve forms close relationship with the posterior ethmoidal cells and is at risk during ethmoid surgery.

SPHENOID SINUS

It occupies the body of sphenoid.

The two, right and left sinuses, are rarely symmetrical and are separated by a thin bony septum.

Ostium of the sphenoid sinus is situated in the upper part of its anterior wall and drains into sphenoethmoidal recess.

Average size – 2 x 2 x 2 cm.

According to Congdon , sphenoid pneumatization can be as follows

A. Conchal – 5 %

B. Presellar – 23 %

C. Post-sellar – 67%

Relation of the sphenoid sinusANTERIOR PART

Roof – related to the olfactory tract, optic chiasma and frontal lobe

Lateral wall -- related to the optic nerve, internal carotid artery and maxillary nerve

POSTERIOR PART

Roof -- Related to pituitary gland in the sella turcica.

Lateral wall -- related to cavernous sinus, internal carotid artery and CN III, IV, VI and all the divisions of V

The Lateral Wall of Nasal Cavity Marked by 3 projections:

Superior concha

Middle concha

Inferior concha

The space below each concha is called a meatus.

The Lateral Wall of Nasal Cavity 1. Inferior meatus:

nasolacrimal duct2. Middle meatus:

• Maxillary sinus• Frontal sinus• Anterior ethmoid

sinuses3. Superior meatus:

posterior ethmoid sinuses4. Sphenoethmoidal

recess: sphenoid sinus

Osteomeatal complex The ostiomeatal complex (or unit) is a common channel that

links the frontal sinus, anterior and middle ethmoid sinuses and the maxillary sinus to the middle meatus.

The ostiometal complex is composed of five structures:

1. Maxillary ostium - drainage channel of the maxillary sinus

2. Infundibilum - common channel that drains the ostia of the maxillary and ethmoid sinuses to the hiatus semilunaris

Ethmoidal bulla - usually a single air cell that projects inferomedially over the hiatus semilunaris

Uncinate process - hook-like process that arises from the posteromedial aspect of the nasolacrimal duct and forms the anterior boundary of the hiatus semilunaris

Hiatus semilunaris - final drainage passage; a region between the ethmoidal bulla superiorly and free-edge of the uncinate process

Overview of sinus drainage

CROSS SECTIONAL ANATOMY – AXIALS

CORONAL ANATOMY

SAGITTAL ANATOMY

Variation of the Paranasal sinus …Middle turbinate variations --

Paradoxical curvature:

Normally the convexity of the middle turbinate is directed medially toward the nasal septum.

When the convexity is directed laterally, it is termed a paradoxical middle turbinate .

Most authors agree that the paradoxical middle turbinate can be a contributing factor to sinusitis.

Middle turbinate variations --

Concha bullosa:

This is an aerated turbinate, most often the middle turbinate.

When pneumatization involves the bulbous portion of the middle turbinate, it is termed concha bullosa.

If only the attachment portion of the middle turbinate is pneumatized, it is termed lamellar concha .

A concha bullosa may obstruct the ethmoid infundibulum.

Variations of uncinate process..

The uncinate process may be medialized, lateralized, or pneumatized/bent.

Medialization occurs with giant bulla ethmoidalis.

Lateralization of the uncinate process may obstruct the infundibulum.

Pneumatization of the uncinate process (uncinate bulla)  can rarely cause obstruction of the infundibulum. 

Agar nasi cells .. They are the most anterior

ethmoidal air cells.

It lies anterior, lateral, and inferior to the frontal recess.

Its size may directly influence the patency of the frontal recess and the anterior middle meatus.

Haller cells .. Also called infraorbital ethmoid

cells.

Extramural ethmoidal air cells that extend into the inferomedial orbital floor.

Present in approx. 20 % pateints.

Clinical significance – Become infected , with potential

extension into orbit.

Narrows the maxillary ostium.

Onodi cells.. These are posterior ethmoidal cells

extending into the sphenoid bone ,either adjacent to or impinging upon the optic nerve. 

 When these Onodi cells abut or surround the optic nerve, the nerve is at risk when surgical excision of these cells is performed.

It is also a potential cause of incomplete sphenoidectomy.

Variation of the ethmoidal roof anatomy ..

The ethmoid roof is of critical importance for two reasons.

First, it is most vulnerable to iatrogenic cerebrospinal fluid leaks. Second, the anterior ethmoid artery is vulnerable to injury.

The depth of the olfactory fossa is determined by the height of the lateral lamella of the cribriform plate.

In 1962, Keros had classified the depth of the olfactory fossa into three types, that is,

Keros type I: <3 mm  , type II: 4-7 mm ,and type III: 8-16 mm 

Kero type III is most vulnerable to iatrogenic injury.

Coronal CT scan shows that the ethmoid roofs are almost in the same plane as the cribriform plate (double arrow) - Keros type I

Coronal CT reveals the olfactory fossae are deeper and the lateral lamellae are longer (double arrow) - Keros type II

Coronal CT shows that the olfactory fossae are very deep (double arrow) - Keros type III

Variations of sphenoid sinus …

Agenesis of sphenoid sinus

 Pneumatization of the anterior clinoid process (bent up arrow) and bilateral pterygoid processes (star), with protrusion and partial dehiscence of bilateral vidian nerves (arrow).

Pneumatized bilateral greater wing of sphenoid (star), with protrusion of maxillary nerve bilaterally (arrow). The left maxillary nerve is dehiscent. Note also the protuberant vidian nerves bilaterally (downward curved arrow)

Bullae ethmoidalis..

The bulla ethmoidalis is a prominent anterior ethmoid air cell.

A degree of pneumatisation may vary, and failure to pneumatise is termed torus ethmoidalis.

 A 'giant bulla' may fill the entire middle meatus and force its way between the uncinate process and the middle turbinate.

Pneumatization of the crista galli…

The crista galli is normally bony.

When aerated, it may communicate with the frontal recess, causing obstruction of the ostium and thus lead to chronic sinusitis and mucocele formation. 

FESS & Post-FESS Anatomy

References …1. Uma Devi Murali Appavoo Reddy, Bhawna Dev. Pictorial essay: Anatomical variations of

paranasal sinuses on multidetector computed tomography-How does it help FESS surgeons? Indian journal of radiology & imaging 2012, vol -22 pg 317- 324.

2. Ashok K Gupta et.al. Anatomy and its variation for endoscopy sinus surgery . Clin rhinol An Int J 2012; 5(2)55-62.

3. Multiplanar Sinus CT: A Systematic Approach to Imaging Before Functional Endoscopic Sinus Surgery Jenny K. Hoang, James D. Eastwood, Christopher L. Tebbit, and Christine M. Glastonbury American Journal of Roentgenology 2010 194:6, W527-W536 

4. Laurie A. Loevner et al. Imaging of neoplasms of the paranasal sinuses, Neuroimag Clin N Am 14 (2004) 625 – 646

5. David L. Daniels et.al. The Frontal Sinus Drainage Pathway and Related Structures, AJNR: 24, August 2003.

6. Disease of Ear, Nose & Throat . P.L Dhingra 4th edition.

7. Interactive Atlas. http://uwmsk.org/sinusanatomy2/axial/axial.html.

Thank you..