Radiological anatomy of frontal sinus

drtbalu's otolaryngology online 1

Radiological anatomy of Frontal sinus

Balasubramanian Thiagarajan


Introduction

Highly complex and variable anatomy Variations – impact on drainage Efficiency of muco-ciliary clearance –

relationship to morphology of frontal sinus


Embryology


Embryology - contd

Continuation of embryonic infundibulum, frontal recess superiorly

Upward migration of anterior ethmoid air cells

Penetration via inferior aspect of frontal bone between the two tables

Pneumatization 2-9 years Complete – 9 years


Frontal sinus drainage

Expands into the diploic space of frontal bone from frontal sinus ostium

Each sinus grows independently of the other

Growth is dependent on ventilation, drainage, growth of surrounding sinuses and skull base

Drainage is hence highly variable


Frontal sinus drainage - contd

Inferomedially into funnel shaped area (frontal sinus ostium)

Anterior wall of drainage channel is bounded by nasal beak

Ostium is oriented perpendicular to the posterior wall of the sinus at the skull base level


Frontal beak


Frontal sinus drainage pathway compartments

Drainage pathway is divided into superior and inferior compartments

Superior compartment is formed by union of adjacent air cells at the antero inferior portion of ethmoid bone

Size and shape of this component varies with the varying anatomy for fronto ethmoidal air cells

Superior compartment communicates with the inferior compartment


Inferior component

This passage is really narrow This compartment is formed by ethmoidal

infundibulum / middle meatus This is dependent on the attachment of

uncinate process


Inferior compartment

Inferior portion - infundibulum Inferior portion - infundibulum


Attachment to lamina papyracea – inferior component formed by middle meatus


Inferior compartment formed by infundibulum



Frontal beak

Frontal beak forms the floor of frontal sinus


Frontal recess

Antero superior portion of ethmoidal air cell system

This is where the frontal bone pneumatization begins

Lateral wall is formed by lamina papyracea Medial wall is formed by vertical

attachment of middle turbinate Posterior wall is variable ? Bulla if it

manages to reach up to skull base


Frontal recess


Agger nasi


Large bulla

Can obstruct frontal sinus outflow This area should be critically studied

during imaging Causes obstruction from behind


Bulla


Uncinate vs frontal sinus drainage

Uncinate – skull base attachment causes frontal sinus to drain into superior portion of ethmoidal infundibulum

Uncinate – attached to middle turbinate causes frontal sinus to drain into ethmoidal infundibulum

Uncinate – attached to lamina papyracea causes frontal to drain into superior aspect of middle meatus. Ethmoidal infundibulum ends in terminal recess


Ethmoidal infundibulum

3 – d space Lateral – LP Anteromedial –

Uncinate Posterior - Bulla

drtbalu's otolaryngology online 22Large agger cell causing narrowing of frontal recess

Frontal recess block



uncinate process attached to skull base. The frontal recess is seen between the agger nasi and uncinate process


Scan showing uncinate process being attached to lamina papyracea. This causes terminal recess to form. Frontal sinus drains directly into middle meatus


scan shows the uncinate process being attached to the middle turbinate. Note the presence of infundibulum between the bulla and the uncinate process. Frontal sinus is seen opening into the infundibulum


Bent's classification of frontal cell variants

Type I: Single frontal recess cell above the agger

Type II: Tier of air cells above agger projecting into the frontal recess

Type III: Single massive air cell above agger expanding in superior direction

Type IV: Single isolated cell within frontal sinus. Difficult to visualize due to thin walls


Type I & II frontal cell


Type III


Type IV


Supraorbital air cells

Pneumatization of orbital plate of frontal bone

Posterior to frontal recess & lateral to frontal sinus

Sometimes can reach high up mimicking frontal sinus


Thank you

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Radiological anatomy of frontal sinus