CT IMAGING OF THE PARANASAL SINUSES BASIC ANATOMY AND ...
Transcript of CT IMAGING OF THE PARANASAL SINUSES BASIC ANATOMY AND ...
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CT IMAGING OF THE
PARANASAL SINUSES –
BASIC ANATOMY AND
IMAGE INTERPRETATION
Benjamin Y. Huang, MD, MPH
University of North Carolina
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OVERVIEW
• Indications for imaging chronic sinusitis
• Scan technique
• Basic anatomy of the paranasal sinuses
• Anatomic variants which predispose to
sinusitis and surgical complications
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WHY DO WE CARE ABOUT THE
PARANASAL SINUSES?
• Rhinosinusitis affects 14-16% of adults
• Accounts for 11.6 million outpt office visits annually
• Estimated direct costs of sinusitis $5.8 billion
• 5th most common diagnosis leading to antibiotic prescriptions
• Over 200,000 FESS procedures performed annually
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INDICATIONS FOR CT
**THE DIAGNOSIS OF SINUSITIS IS MADE
CLINICALLY!!!
• Sinusitis refractory to maximal medical therapy
• Surgical planning and operative guidance
• Evaluation of operative failure or complications
• Suspected complications of sinusitis (invasive
fungal dz, mucocele, orbital cellulitis/abscess,
intracranial spread)
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SCAN TECHNIQUE
• Standard coronal CT is INADEQUATE to understand 3D sinus anatomy, particularly in the frontal recess
• Axial thin section (<1mm) helical CT
• Axial, coronal, and sagittal reconstruction (3 mm thick or less)
• Bone and soft tissue windows
• Patients should only be scanned after a trial of maximal medical therapy (3-6 wks)
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ANATOMIC “TIGHT SPOTS”
• Areas which are predisposed to
obstruction
1) Ostiomeatal complex
2) Frontal recess
3) Sphenoethmoidal recess
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Name the structure
indicated by the arrow.
A) Middle turbinate
B) Ethmoid bulla
C) Uncinate process
D) Ethmoidal
infundibulum
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Name the structure
indicated by the arrow.
A) Middle turbinate
B) Ethmoid bulla
C) Agger nasi
D) Ethmoidal
infundibulum
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ETHMOID BULLA
• Bulge on the lateral
nasal cavity wall above
the hiatus semilunaris
• Forms the roof the of
ethmoidal infundibulum
• Usually a single large
ethmoid air cell
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OSTIOMEATAL COMPLEX
Common channel
draining the maxillary,
anterior ethmoid & frontal
sinuses:
• Maxillary sinus ostium
• Ethmoid infundibulum
• Uncinate process
• Ethmoid bulla
• Hiatus semilunaris
• Middle turbinate
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FRONTAL RECESS
Structures involved in drainage pathway for the frontal sinus
• Frontal sinus ostium
• Nasofrontal process
• Frontal recess
• Agger nasi
• Frontal recess cells
• Uncinate process
• Middle meatus
• Lamina papyracea
Frontal sinus
Frontal recess
Middle
meatus
Frontal sinus
Frontal sinus ostium
Frontal recess
Nasofrontal
process
Ethmoid bulla
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FRONTAL SINUS DRAINAGE
Frontal sinus
↓
Frontal ostium
↓
Frontal recess
↓
[Infundibulum]
↓
[Hiatus semilunaris]
↓
Middle meatus
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*
Name the structure
indicated by the
asterisk.
A) Ethmoid bulla
B) Agger nasi
C) Type I frontal cell
D) Type IV frontal cell
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FRONTAL RECESS CELLS
• Agger nasi cell (ANC)
• Frontal cell (FC)
• Supraorbital ethmoid cell (SOC)
• Frontal bullar cell (FBC)
• Suprabullar cell (SBC)
• Interfrontal sinus septal cell (ISSC)
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AGGER NASI CELL
• “Anterior-most ethmoid
cell”
• Found in nearly all
patients normally
• Pneumatized intranasal
portion of the frontal
process of the maxilla
• Forms the anterior
boundary of the FR
• Best seen on coronal
and sagittal images
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AGGER NASI CELL
*
*
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FRONTAL CELLS
• 4 types of frontal cells (I-IV)
• Found in 20%-41% of sinus specimens
• Can obstruct outflow at the FR or ostium
• Frontal cells are well seen on coronal and
sagittal images
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TYPE I FRONTAL CELL
• Most common of the
frontal cells, seen in
14%-37% of frontal
recess sides
• Single anterior
ethmoid cell above
the agger nasi cell
• Posterior wall makes
up the anterior FR
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TYPE II FRONTAL CELLS
• Tier of 2 or more
anterior ethmoid cells
above the agger nasi
cell
• Posterior wall makes
up the anterior frontal
recess
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TYPE III FRONTAL CELL
• Single large anterior ethmoid cell, above the agger nasi, extends from frontal recess into the true frontal sinus
• Posterior wall makes up the anterior frontal recess wall
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TYPE IV FRONTAL CELL
• Isolated anterior cell
completely within the
frontal sinus, above
the agger nasi cell
• “Sinus within a sinus”
• Should not extend to
posterior frontal sinus
table
• Rarest form of frontal
cell seen
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FRONTAL CELLS
Type 1 Type 2 Type 3 Type 4
*
*
*
*
Arrow = frontal cell(s)
Asterisk = agger nasi cell
*
*
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FRONTAL RECESS CELLS
• Agger nasi cell (ANC)
• Frontal cell (FC)
• Supraorbital ethmoid cell (SOC)
• Frontal bullar cell (FBC)
• Suprabullar cell (SBC)
• Interfrontal sinus septal cell (ISSC)
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SUPRAORBITAL ETHMOID CELL
• Ethmoid cell extending over the orbit from
the frontal recess
• Opens into the lateral aspect of frontal
recess (posterior to true frontal sinus
ostium)
• Single or multiple
• Mimics a septated frontal sinus
• Seen best on axial and coronal images
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SUPRAORBITAL ETHMOID
CELL
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FRONTAL BULLAR CELL
• Posteriorly positioned cell above the ethmoid bulla
• Anterior border extends into frontal sinus
• Posterior wall is anterior cranial fossa skull base
• Seen best on sagittal images
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SUPRABULLAR CELL
• Posteriorly positioned cell above the ethmoid bulla
• Anterior border does not extend into the frontal sinus
• Superior wall is anterior cranial fossa skull base
• Seen best on sagittal images
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FRONTAL BULLAR AND
SUPRABULLAR CELLS
Frontal Bullar Cell
Suprabullar Cell
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FRONTAL RECESS CELLS
• Agger nasi cell (ANC)
• Frontal cell (FC)
• Supraorbital ethmoid cell (SOC)
• Frontal bullar cell (FBC)
• Suprabullar cell (SBC)
• Interfrontal sinus septal cell (ISSC)
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INTERFRONTAL SINUS SEPTAL
CELL
• Pneumatization of the frontal sinus septum
• May pneumatize the crista galli
• Drains into frontal recess
• Best characterized on axial and coronalimages
Interfrontal
sinus septal
cell
Interfrontal
sinus septal
cell
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ANATOMIC “TIGHT SPOTS”
SPHENOETHMOIDAL
RECESS
• Drains sphenoid (via
sphenoid ostium) and
posterior ethmoids
• Empties into superior
meatus
– Superior & middle
turbinates
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PRIMARY FESS
• Commonly performed
procedures for initial
treatment include:– Uncinectomy/Maxillary (middle
meatal) antrostomy (red)
– Anterior ethmoidectomy (blue)
– Partial middle turbinectomy (green)
• Refractory or more
complicated disease in the
FR may require a Draf type
drill out
Anterior
ethmoids
Uncinate
process
Middle
turbinate
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FESS
PREOPERATIVE EVALUATION
• Surgical planning is initiated only after
maximal medical treatment has failed or in
patients with chronic or recurrent episodes
of sinusitis
• Preoperative evaluation includes– Diagnostic nasal endoscopy
– Multiplanar sinus CT • performed after maximal medical treatment
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PREOPERATIVE CT IMAGING IN
CHRONIC SINUSITIS
• To assess the extent and severity of
disease
• To identify anatomic causes of sinus
outflow obstruction
• To search for potential surgical pitfalls
• To elucidate sinus anatomy
• Intraoperative guidance
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LUND-MACKAY CT SCORING
SYSTEM
Score range: 0-24
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IGS SYSTEMS
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ANATOMIC VARIANTS
• Haller cell
• Concha bullosa
• Paradoxical middle turbinate
• Lateralized middle turbinate
• Atelectatic uncinate
• Pneumatized uncinate
• Nasal septum deviation
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HALLER CELL
• AKA infraorbital ethmoid cell
• Incidence ~20%
• Air cell extending along the medial floor of the orbit
• Can become infected
• Can narrow infundibulum or maxillary sinus ostium
• May lead to inadvertent entry into the orbit
*
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CONCHA BULLOSA
• Pneumatized
turbinate (usually MT)
• Incidence ~35%
• May obstruct middle
meatus when large
– Can interfere with
FESS
• Can also become
infected
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PARADOXICAL MIDDLE
TURBINATE
• Normal MT convexity
directed medially
• Controversy exists as
to whether
paradoxical MT
increases likelihood
of sinusitis
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LATERALIZED MT
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LATERALIZED MT AND
ATELECTATIC UNCINATE
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What is the diagnosis?
A) Maxillary sinus
mucocele
B) Antrochoanal polyp
C) Silent sinus
syndrome
D) Orbital blowout
fracture
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SILENT SINUS SYNDROME
• “Imploding antrum”
• Chronic maxillary outflow tract obstruction
• Negative pressure causes shrinking of maxillary sinus
• UP is atelectatic
• Causes painless enophthalmos
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ANTROCHOANAL POLYP
• Solitary polyp arising in
maxillary sinus and
passing through maxillary
ostium or accessory
ostium
• Extends into nasal cavity
and nasopharynx
• Mucin density
• Widens maxillary ostium
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Name the structure
indicated by the
asterisk:
A) Sphenoid sinus
B) Onodi cell
C) Ethmoid bulla
D) Suprabullar cell
*
*
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ONODI CELL
• AKA sphenoethmoidal
air cell
• Ethmoidal cell lying
superior or posterior to
the sphenoid sinus
• Incidence ~10%
• May be located close
to the ON or ICA
– Potential for injury to
either during FESS
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SPHENOID REGION VARIANTS
• Onodi cell
• Large lateral recess
• Anterior clinoid
pneumatization
• Dehiscent nerves or
ICA
• Septal insertion on
the ICA or ON canal
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MEDIALIZED CAROTID
ARTERIESSPHENOETHMOIDAL
RECESS
• Superior turbinate
• Posterior ethmoids
• Sphenoid ostium
• Optic nerve
• Foramen rotundum
• Vidian canal
• Carotid canal
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OTHER FINDINGS PREDISPOSING
TO SURGICAL COMPLICATIONS
Medialized carotid arteries & septal insertion on the carotid canal
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OTHER FINDINGS PREDISPOSING
TO SURGICAL COMPLICATIONS
Lamina papyracea dehiscence Asymmetry in ethmoid roof height
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OTHER FINDINGS PREDISPOSING
TO SURGICAL COMPLICATIONS
Low lying anterior ethmoidal artery canal
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CONCLUSION
• Normal drainage pathways
– OMC – Maxillary & anterior ethmoids
– Frontal recess – Frontal sinus
– Sphenoethmoidal recess – Sphenoid &
posterior ethmoids
• Anatomic factors that may alter sinus
drainage or affect surgical procedure
• Potential surgical pitfalls
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CONCLUSION
What to include in your reports:
• Prior surgeries
• Status of individual sinuses and their drainage
pathways
• Potential causes of obstruction including variant
anatomy
• Bony changes (osteoneogenesis, dehiscence)
• Anatomic factors which might influence surgery
• Complications and other findings