Radiological anatomy of
Frontal sinus
Balasubramanian Thiagarajan
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Introduction
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Highly complex and variable anatomy
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Variations – impact on drainage
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Efficiency of muco-ciliary clearance –
relationship to morphology of frontal sinus
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Embryology
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Embryology - contd
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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
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Pneumatization 2-9 years

Complete – 9 years
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Frontal sinus drainage
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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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Frontal sinus drainage - contd
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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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Frontal sinus drainage
pathway compartments
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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
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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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Inferior compartment formed by infundibulum
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Frontal beak
Frontal beak forms the floor of frontal sinus
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Frontal recess
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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
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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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Uncinate vs frontal sinus
drainage
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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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Ethmoidal infundibulum
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3 – d space
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Lateral – LP
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Anteromedial –
Uncinate
Posterior - Bulla
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Frontal recess block
Large agger cell causing
narrowingonline
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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Bent's classification of frontal
cell variants
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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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Supraorbital air cells
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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
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