Radiological anatomy of frontal sinus

This presentation discusses r

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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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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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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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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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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

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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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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Ethmoidal infundibulum
3 – d space
Lateral – LP
Anteromedial –
Uncinate
Posterior - Bulla

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Large agger cell causing narrowing of frontal recess
Frontal recess block

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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

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

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