Abstract Id: IRIA-1173
Anatomy:
* Maxillary sinus
* Frontal sinus
* Ethmoid sinus
* Sphenoid sinus
Sphenoid sinus:
It spreads laterally to invade the greater and lesser wings
and medial & lateral pterygoid plates of sphenoid. A foramen
in the center of each turbinate allows the sinus of each side
to communicate with the nasal cavity at the sphenoethmoidal recess.
Recently transsphenoidal hypophysectomy is done and has
significant advantages over open craniotomy.
Types of sphenoid sinus - 1.Conchal 2.Pre sellar 3. Sellar.
Conchal
Pre sellar
Relationship of important structures:
Optic nerve- superior – lateral
Carotid canal / cavernous sinus- mid- lateral
Vidian nerve / maxillary nerve – inferior - lateral
Sellar
Frontal recess:
It is the bordering anatomical
structure forming the walls of the
passage from frontal sinus to the
middle meatus.
Boundaries- Anteriorly by the agger
nasi cells, laterally by orbit, medially
by middle turbinate and posteriorly by
bulla lamella.
* 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 in to frontal recess.
Type III- Single massive air cell above agger expanding into frontal sinus.
Type IV- single isolated cell within frontal sinus.
* Middle turbinate:
It lies inferomedial to the anterior ethmoidal air cells.Middle
turbinate also serves as a important surgical landmark for skull
base, frontal sinus and orbit.
• Anterior- oriented in sagittal plane and it is vertically attached
to the cribriform plate.
• Middle- oriented in frontal plane and it is attached to the
lamina papyracea or basal lamella laterally. It separates anterior
and posterior ethmoids.
• Posterior-oreinted in horizontal plane and it is attched to the
perpendicular plate of palate.
* Anterior osteomeatal unit:
It is a complex anatomic region at
crossroads of mucociliary drainage from
frontal, anterior and maxillary sinuses.
Components of anterior osteomeatal unit are:
• Maxillary
ostiummaxillary sinus.
drainage
channel
of
• Infundibulum-
common channel that drains
the ostia of maxillary & ethmid sinuses to the
hiatus semilunaris.
• Uncinate
process- hook like process that
arises
from
posteromedial
aspect
of
nasolacrimal duct and froms the anterior
boundary for hiatus semilunaris.
• Ethmoid
bulla- usually a single air that
projects
inferomedially
over
hiatus
semilunaris.
• Hiatus
semilunaris -final drainage passage;
region that between ethmoid bulla superiorly
and free edge of uncinate process. It can be
demonstrated in saggital section of CT.
*Posterior osteomeatal unit:
It comprises of postero superior concha(sphenoethmoid recess), which is
draining site for sphenoid sinus through sphenoid ostium. Inferior to
superior concha in the superior meatus, there are two opening for
posterior ethmoidal air cells.
Sagittal CT image showing sphenoid
ostium & sphenoethmoid recess
* UNCINATE PROCESS:
• The uncinate process is a superior extension of the lateral
nasal wall that is anatomically relevant for draining frontal
recess.
• Variations such as hypertrophy, deviation and pneumatization
may affect the drainage, generating abnormalities in
osteomeatal complex.
Horizontal uncinate
Pneumatisation of uncinate
Vertical uncinate
Hypertrophy of uncinate
* OLFACTORY FOSSA:
It is a variable depression seen in cribriform plate that medially
bounded by perpendicular plate and laterally by lateral lamella.
KEROS CLASSICIFICATION:
The depth of olfactory fossa is determined by the height of the
lateral lamella of cribriform plate by Keros in 1962 in to three
catergories. Type III essentially expose the thin cribriform plate to
potential damage from trauma, tumour erosion, local nasal
surgeries and orbital decompression.
Type I- 1-3mm. Type II- 4-7mm. Type III- 8-16mm.
Type I
Type II
Type III
Anterior ethmoid foramen:
It as a small opening in the ethmoid
bone and transmits the anterior
ethmoid artery and nerve.
Importance- It is the anatomical
border for anterior and posterior
ethmoid air cells in coronal plane.
Coronal CT image showing anterior ethmoid foramen
* STRUCTURES DEMONSTRATED BETTER IN SAGITTAL
SECTION CT:
• Hiatus semilunaris
• Frontal recess
• Spheno ethmoid recess
• Type of sphenoid sinus
• Agger nasi cells
Computed tomography(CT):
It is the imaging modality of choice for
assessment of paranasal sinus. A complete coronal and axial
sections CT scan series provides an excellent and comprehensive
evaluation of PNS. CT excels over MRI at evaluating fine bone
details, assessment of fibro-osseous lesions of PNS and sino facial
lesions.
CT plays an important role in the pre-operative evaluation of
patients and provides a “ROAD MAP” to guide the surgeons during
surgery.
PIT FALLS IN CT:
• Due
to its complex projections, artefacts induced by very high
density structures around PNS, by the patient movement, limited
soft tissue resolution and even radiation exposure in CT
examinations limits frequent usage in children and pregnant
women.
• For
these reasons, MRI is considered as imaging modality in
conditions.
• Anatomical
variations are which impairs the normal
functional drainage pathways and increase the risk of
surgeries.
• Identification of these anatomic variants of paranasal sinus
helps the surgeons to access sites of diseases which are
extremely difficult.
* Agger nasi cells (ANC):
It is the most constant and anterior of ethmoid air cells. It
is located anterior to the vertical attachment of middle
turbinate to the skull base.
Agger nasi cells seen in axial and coronal CT
Spheno ethmoid cells (Onodi cell):
This is formed by lateral and posterior pneumatization of
the most posterior ethmoid cells over the sphenoid sinus . The presence
of Onodi cells increases the chance that the optic nerve and carotid
artery would be exposed in the pneumatized cell.
Infra orbital air cells(Haller Cells):
These are centered inferior to the ethmoidal bulla and grow
into the floor of the orbit. They may narrow the maxillary sinus
ostium, especially if infected.
Axial and Coronal sections
CT images showing Haller
cells
Ethmoidal Bulla:
The Ethmoidal bulla is an anterior
ethmoidal air cell of variable size located
just posterior to the free edge of the
uncinate process. An enlarged ethmoidal
bulla may compromise the outflow of both
the maxillary antrum and the frontal sinus
by distorting the ethmoid infundibulum or
hiatussemilunaris and the frontal recess.
Deviated nasal septum (DNS):
The nasal septum may be focally
deviated inferiorly at the chondrovomeral junction or have a more broad
based curvature . Septal spurs may be
associated with septal deviation, which
makes surgical access difficult and
narrow the middle meatus or Ethmoid
infundibulum.
Coronal section CT image showing nasal septum
deviation towards right side
Concha Bullosa:
It is the pneumatization of the inferior
bulbous portion of the turbinate. A large
concha bullosa, which usually present with
septal deviation may obstruct the drainage
pathway of the antrum by distorting the
uncinate process and narrowing the
infundibulum.
Paradoxical middle turbinate turn:
The middle turbinate may have a
lateral convexity ( a paradoxical
turn). If large, it is associated with
septal deviation and may impair
access to the osteo- meatal unit.
Coronal CT image showing paradoxical turn of middle turbinate
Maxillary sinus septations:
The maxillary sinus septum may be
fibrous or bony and often extends from
the infra orbital canal to the lateral
wall. If not recognised, it may lead to
inadequate drainage of the antrum.
SPHENOID SINUS SEPTATION:
It is the presence of multiple
septation within the sphenoid than the
main septa. It is percepted that multiple
accessory septs are seen more commonly
on the right side of main septa. It makes
the access difficult for the surgeons while
performing surgeries invloving transsphenoidal approach.
axial section CT showing multiple septa sphenoid sinus
CLOSE Technique:
C- Cribriform
• Assess the keros type.
• Look for assymmetry.
L- Lamina Papyracea
• Check for dehiscence or pathologic fractures.
O- Orbit, Optic nerve, Onodi cells
• Check for dehiscence .
• Assess for onodi cells (superior-lateral to sphenoid).
• Orbital slope.
S – Sphenoid, Skull base
• Assess for carotid dehiscence and aeration patterns.
• Conchal, Pre-sellar & Sellar(thickness of clivus).
• Assess slope of skull base.
• Assess if roof of sphenoid is level with skull base.
E- Ethmoid arteries.
• CT is a sensitive technique for evaluating para nasal
sinus.
• Identification of anatomical variants are important
because, it helps surgeons during sinonasal surgeries.
• CT helps in staging the PNS diseases by its extension and
involvement of surrounding structure.
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4.
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