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The maxillary sinus, the largest of the sinuses, is within the body of the maxilla. It is shaped like a pyramid; its base is usually medial, with its apex in the zygomatic process of the maxilla. Its roof is the floor of the orbit, and its floor is the alveolar process of the maxilla. The maxillary sinus drains into the middle meatus by means of the semilunar hiatus. The floor of the maxillary sinus is slightly below the level of the nasal cavity, and it is related to the upper teeth
If present, a Haller cell can cause narrowing of the infundibulum and maxillary sinus ostuim potentially causing obstruction
Roof of ethmoid
olfactory fossae are deeper and the lateral lamellae are longer
olfactory fossae are very deep
Normal frontal recess anatomy. Coronal (a) and sagittal (b) CT images show the right frontal recess (dotted red line), which is bounded anteriorly and laterally by an agger nasi cell (white arrow) and a type 1 frontal cell (black arrow), medially by the middle turbinate, and posteriorly by the ethmoid bulla and bulla lamella. The nasofrontal process (arrowhead in b) forms the floor of the frontal sinus and demarcates the level of the frontal sinus ostium.
Sagittal image shows frontal sinus ostium (*) and arrow pointing to the superior compartment of the FSDP. (FS: frontal sinus, AG: agger nasi, PE: posterior ethmoid, SpS: sphenoid sinus, MT: middle turbinate, IT: inferior turbinate)
Type 2 frontal cells. (a, b) Coronal (a) and parasagittal (b) drawings show a tier of type 2 frontal cells (blue areas) sitting atop an agger nasi cell. (c, d) Coronal (c) and sagittal (d) CT images show a tier of two type 2 frontal cells (arrows) sitting directly atop an agger nasi cell (*).
Type 3 frontal cell. Coronal (a) and parasagittal (b) drawings show a type 3 frontal cell (blue area) sitting atop an agger nasi cell. The type 3 cell extends superiorly from the frontal recess through the frontal ostium and into the frontal sinus.
Type 4 frontal cell. (a, b) Coronal (a) and parasagittal (b) drawings show a type 4 frontal cell (blue area) situated entirely within the right frontal sinus and bordered by the anterior frontal sinus wall. The type 4 cell does not abut the agger nasi cell. (c, d) Coronal (c) and sagittal (d) CT images show an opacified type 4 frontal cell (arrow) in the frontal sinus.
Axial CT image shows the supraorbital ethmoid cell (arrow), which is clearly differentiated from the frontal sinus (*) by a discrete bony septum.
pneumatized crista galli. Pneumatized crista galli may communicate with the frontal recess and can potentially obstruct the frontal sinus ostium
which arises from the frontal sinus septum
Axial image shows sphenoid sinus (SpS) and the sphenoethmoidal recess marked by the (*). (AE: anterior ethmoid, PE: posterior ethmoid, CC: carotid canal, NS: nasal septum)
Coronal image of the sphenoid sinus (SpS) and neighboring structures. (FR: foramen rotundum, VC: vidian canal, OC: optic canal, AC: anterior clinoid, PtP: pterygoid plate)
Sinus anatomy and variants
Paranasal Sinuses Anatomy &
A Systematic Approach To
Imaging Before FESS
Dr Priyanka Vishwakarma
Four Paired Sinuses –
• The sinuses develop as outgrowths from
the nasal cavity; hence they all drain
directly or indirectly into the nose
• superior meatus drains the posterior ethmoid
air cells and the sphenoid sinus via the
• middle meatus drains the frontal sinus via the
nasofrontal duct/frontal recess, the maxillary
sinus via the maxillary ostium, and the anterior
ethmoid air cells via the ethmoid cell ostia.
• The nasolacrimal duct drains into the inferior
• spheno-ethmoidal recess, above and posterior
to the superior concha, receives the opening of
the sphenoidal sinus
Common Drainage Pathway Of The Ant.
Group of Sinuses.-Coronal scan
The osteomeatal unit (OMU) includes the
• uncinate process
• Ethmoid infundibulum
• Ethmoid Bulla
• Middle Meatus
• Hiatus Semilunaris
Most common site of inflammatory disease
• Largest and most constant pns.
• Pyramidal in shape- base is usually
medial, with its apex in the zygomatic
process of the maxilla
• Base -lat nasal wall-ostium
• Posterior wall/Temporal- pterygomaxillary
• Roof -Formed by roof of the orbit- infra
orbital foramen containing the infra orbital
vessels and nerves
• Ant-maxilla facial surface
Variants Related To the maxillary Sinus
Paradoxical curvature of MT
the bulbous portion
of the middle
concha bullosa may
from the middle
• Ethmoidal air cells belonging to the
anterior ethmoidal group.
• Also known as the infra orbital cells
• Adhere to roof of maxillary sinus forming
the lat wall of infundibulum
• Enlargement of these cells can impede
the maxillary sinus drainage
Paradoxical curvature- can potentially narrow or
obstruct the infundibulum or middle meatus.
• basal lamellae of the middle turbinate
separates the ethmoid into anterior and
posterior groups with different drainage
• Ant cells form 1st followed by the posterior
cells.They are not seen on radiographs
until age one
• Lateral wall-Formed by the orbital plate of
the ethmoid,known as the lamina
papyracea.this wall could be dehiscent-
route of spread of infection
. The transition of thick fovea to the thin
portion of roof of ethmoid medially is very
weak-injuries during surgery leading on to
vertical attachment of basal
lamellae to anterior skull base
• A cell above the orbit is called a
supraorbital cell.found in 15% of pt
• Invasion of an ethmoid cell into the floor of
the frontal sinus is called a frontal cell(type
Agger Nasi Cell
term Agger in Latin - Mound/Eminence.
• anterior to the antero superior attachment
of the middle turbinate and borders the
• its size may directly influence the patency
of the frontal recess. These agger nasi
cells are commonly involved in the
pathogenesis of the formation of frontal
• It is the 1st prominent anatomical
landmark encountered in FESS
• superior to uncinate processes.
• Ethmoid bulla air cells are part of the
anterior ethmoid sinuses and make up the
superior border of the hiatus semilunaris.
• variable pneumatization.
• posterior ethmoidal cells extending supero
lateral to the sphenoid sinus & can either
abut 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
• It is also a potential cause of incomplete
• The depth of the olfactory fossa is determined by
the height of the lateral lamella of the cribriform
plate, which is part of the ethmoid bone. In 1962,
Keros had classified the depth of the olfactory
fossa into three types, that is,
• Keros type I: <3 mm,
• type II: 4-7 mm , and
• type III: 8-16 mm.-Kero type III is most
vulnerable to iatrogenic injury.
• different sizes, are separated by a bony
septum that is usually deviated to one side
• Asymmetry btw the two sinuses frequent
• It may be absent in 5% of cases
• Best seen on Saggital images
• Among the para nasal sinuses this sinus
shows the maximum variations.
• The post wall separates the frontal sinus
from the anterior cranial fossa and is
• Floor is formed by the upper part of the
• Frontal sinus appear very late in life. Infact
they are not seen in skull films before the
age of 6.
• Nasofrontal duct-misnomer
• Frontal Recess
• the frontal recess can be conceptualized as an
inverted funnel within the anterior ethmoid complex
through which the frontal sinus drains.
• The tip or apex of the funnel lies at the frontal sinus
ostium, -sagittal CT images as a “waist” located at
the level of the nasofrontal process.
• The frontal recess typically flares out inferiorly and
posteriorly to form the wider opening of the funnel.
• inferior portion of the frontal sinus (commonly
referred to as the frontal infundibulum)
the frontal ostium
frontal recess = frontal sinus outflow tract
the right frontal
red line), which is
laterally by an
agger nasi cell
(white arrow) and
a type 1 frontal
by the middle
posteriorly by the
(arrowhead in b)
forms the floor of
the frontal sinus
the level of the
Frontal outflow tract shows conglomeratization of
Types of frontal sinus air cells include:
• I – Type I frontal cell (a single air cell above
• II – Type II frontal cell (a series of air cells above
agger nasi but below the orbital roof)
• III – Type III frontal cell (this cell extends into the
frontal sinus but is contiguous with agger nasi
• IV – Type IV frontal cell lies completely within
the frontal sinus
• The uncinate process may be attached to:
• Lamina papyracea or agger nasi (lamina
terminalis). The frontal recess opens
directly into middle meatus,medial to UP
The lamina terminalis is the blind pouch
between the UP and lamina papyracea
• Skull base or middle turbinate. The frontal
recess drains into the ethmoid
infundibulum lateral to UP
• Orbital floor or inferior aspect of the lamina
papyracea (silent sinus syndrome,
atelectatic uncinate process). This variant
is associated with hypoplastic, ipsilateral
• They remain undeveloped until age
three.By age seven the pneumatisation
has reached the sell turcica.By age 18 the
sinuses have reached full size
• Optic nerve and internal carotid arteries
traverse its lateral wall.
• Pneumatisation can extend as far as the
clivus,the sphenoid wings and the foramen
(SpS) and the
recess marked by
•(AE: anterior ethmoid, PE:
posterior ethmoid, CC: carotid
canal, NS: nasal septum)
variations of intersinus septum
• 1.A single midline intersinus septum
extending on to the anterior wall of sella.
• 2. Multiple incomplete septae may be
• 3. Accessory septa may be present.
These could be seen terminating on to the
carotid canal or optic
FESS-a roadmap to the otorhinolaryngologist prior to
There are two main questions that the radiologist should
1. Are there anatomic features on the computed
tomography (CT) scan that predispose the patient to
impaired mucociliary clearance?
2. Are there anatomic features that pose a surgical
• the extent of sinus opacification,
• patency of sinus drainage pathways,
• anatomic variants(obstruct drainage
pathways &limit Surgical access),
• critical variants, (CP,LP,SphS
• condition of soft tissues of the brain, neck,
and orbits.-extrasinus extent of the