1. Radiological anatomy of Frontal sinus
Balasubramanian Thiagarajan
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Introduction
Highly complex and variable anatomy
Variations – impact on drainage
Efficiency of muco-ciliary clearance – relationship to morphology of frontal sinus
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Embryology
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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
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5. 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
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6. 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
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Frontal beak
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8. 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
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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
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Inferior compartment
Inferior portion - infundibulum
Inferior portion - infundibulum
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Attachment to lamina papyracea – inferior component formed by middle meatus
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12. Inferior compartment formed by infundibulum
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14. Frontal beak Frontal beak forms the floor of frontal sinus
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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
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Frontal recess
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Agger nasi
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Large bulla
Can obstruct frontal sinus outflow
This area should be critically studied during imaging
Causes obstruction from behind
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Bulla
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20. 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
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21. Ethmoidal infundibulum
3 – d space
Lateral – LP
Anteromedial – Uncinate
Posterior - Bulla
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Frontal recess block
Large agger cell causing narrowing of frontal recess
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uncinate process attached to skull base. The frontal recess is seen between the agger nasi and uncinate process
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Scan showing uncinate process being attached to lamina papyracea. This causes terminal recess to form. Frontal sinus drains directly into middle meatus
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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
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27. 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
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Type I & II frontal cell
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Type III
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Type IV
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31. 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
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Thank you
drtbalu's otolaryngology online