CROSS SECTIONAL ANATOMY OF THE PARANASAL SINUSES

CROSS SECTIONAL ANATOMY OF THE PARANASAL SINUSESPRESENTER --- 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).

Nathaniel highmore.. Trinity college oxford. 6

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.

The PPF is a pyramidal space located inferior to the orbital apex and posterior to the maxillary sinus. Laterally, it communicates with the infratemporal fossa via the pterygomaxillary ssure. It also connects with the nasal cavity medially via the sphenopalatine foramen, the orbit via the inferior orbital ssure, and intracranial space via the foramen rotundum.8

FRONTAL SINUS ..Paired sinuses situated deep to the inner and outer table of frontal bone. It drains through the frontal recess to themiddle meatusvia theostiomeatal 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 sinusesAnterior 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

Conchal 5 %

Presellar 23 %

Post-sellar 67%

Relation of the sphenoid sinusAnterior partRoof related to the olfactory tract, optic chiasma and frontal lobe Lateral wall -- related to the optic nerve, internal carotid artery and maxillary nervePosterior partRoof -- 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 conchaMiddle conchaInferior conchaThe space below each concha is called a meatus.

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The Lateral Wall of Nasal Cavity Inferior meatus: nasolacrimal ductMiddle meatus:Maxillary sinusFrontal sinusAnterior ethmoid sinusesSuperior meatus: posterior ethmoid sinusesSphenoethmoidal recess: sphenoid sinus

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Osteomeatal complex Theostiomeatal complex(orunit) is a common channel that links thefrontal sinus, anterior and middleethmoid sinusesand themaxillary sinusto themiddle meatus. The ostiometal complex is composed of five structures:Maxillary ostium- drainage channel of the maxillary sinusInfundibilum- 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 semilunarisUncinate process- hook-like process that arises from the posteromedial aspect of thenasolacrimal ductand forms the anterior boundary of the hiatus semilunarisHiatus semilunaris- final drainage passage; a region between the ethmoidal bulla superiorly and free-edge of the uncinate process

Figure 1 (A, B): (A) Coronal CT scan shows the osteomeatal complex which comprises of - infundibulum (dotted line), hiatus semilunaris (asterisk), maxillary ostium (arrow) and Ethmoidal bulla (EB). MT-middle turbinate, LP-lamina papyracea. (B) Coronal CT images reveals a prominent agger nasi cell (A) inferior and lateral to the nasofrontal recess (solid curved line). The medial relationship of the recess is formed by the middle turbinate (MT)22

Overview of sinus drainage

CROSS SECTIONAL ANATOMY AXIALS

Intersinus septum. 25

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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.

Closeness to frontal recess make them excellent surgical landmarks often opened to view nasofrontal duct48

Haller cells ..Also called infraorbital ethmoid cells. Extramuralethmoidal air cellsthat extend into the inferomedialorbital floor. Present in approx. 20 % pateints. Clinical significance Become infected , with potential extension into orbit. Narrows the maxillary ostium.

Can cause recurrent maxillary sinusitis. 49

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.

Bilateral aerated cavities lateral to the optic canal, extending into the anterior clinoid processes.50

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: