1. Anatomy and relevant anatomical variants in nasal and paranasal sinuses CT scan
CERTIFICATE OF
MERIT
RSNA 2003
P. Loubeyre1 MD & J.S Lacroix2 MD, PhD
1 Radiology Department,
2 Rhinology-Olfactology Unit
Hôpitaux Universitaires de Genève
CH Genève 14
Switzerland

2. Anatomic variants Anatomy Surgical risks
Sinusitis – Imaging technique (3-10)
Anatomy
Paranasal sinuses (dia 11-12)
Ostiomeatal unit (dia 13-16)
Uncinate process (dia 17-19)
Ethmoid bulla (dia 20-22)
Middle turbinate (dia 23,24)
Ethmoid infundibulum (dia 25)
Frontal recess (dia 26-28)
Sphenoethmoidal recess (dia 29,30)
Posterior nasal fontanel (dia 31)
Posterior choana (dia 32)
Nasal septum (dia 33)
Nasolacrymal duct (dia 34)
Anterior skull base (dia 35-38)
Anatomic variants
Septal deviation (dia 40)
Septal spurs (dia 41)
Middle turbinate (dia 42-44)
Superior turbinate (dia 45)
Uncinate process (dia 46)
Frontal bulla cell (dia 47)
Frontal sinus extension (dia 48)
Agger nasi cell (dia 49)
Maxillary sinus recesses (dia 50)
Sphenoid sinus recesses (dia 51-53)
Intersinus sphenoid septation (dia 54)
Surgical risks
Vulnerability of the carotid canal (dia 55-57)
Vulnerability of the optic nerve (dia 58-61)
Vulnerability of the orbit (dia 62-65)
Vulnerability of the nasolacrymal duct (dia 66)
Vulnerability of anterior skull base (dia 67)
Some articles to read
Mafee MF. Endoscopic sinus surgery: role of the radiologist. AJNR1991;157:855-60
Earwaker J. Anatomic variants in sinonasal CT. Radiographics 1993;13:
Rao VM, El-Noueam KI. Sinonasal imaging. Radiologic Clinics of North America 1998;36(5):921-39
Zeifer B. Update on sinonasal imaging. Neuroimaging Clinics of North America 1998;8(3):607-30

3. Mucociliary clearance impairment increases the risk of infection or
Mucous accumulation
increases the risk of infection or
chronic inflammation

4. Mucociliary transport : anatomy of the drainage pathway of
the paranasal sinuses
Ostio-meatal
complex

5. or Obstruction Normal mucociliary clearance Contact of two opposing
Normal mucosal thickening during
nasal cycle
Contact of two opposing
mucosal surfaces
(ex: anatomic variants)
Mucous accumulation
increases risk of infection

6. CT High spatial resolution
Chronic rhinosinusitis unresponsive to
medical management
The aim of nasal and paranasal sinuses imaging is to provide a surgical road map delineating the anatomy, defining the obstructive lesions, and noting the anatomical factors that may predispose impaired mucociliary clearance and per operative complications
CT High spatial resolution
Minute bony details and adjacent soft tissue structures
Pre-operative investigation for
patients undergoing
endoscopic sinus surgery
Rhinosinusitis is a medical diagnosis,
not a radiologic diagnosis

7. Supine position Confortable position
console
Coronal, sagittal or oblique reformations
Real time image-guided anatomic localization
during endoscopic surgery
1-mm-thick overlapping
axial slices

8. Medical treatment should be performed before CT scan
To reduce transient acute inflammatory or infectious mucosal changes
Nasal lavages
Topical corticosteroids
Antibiotics
Mucolytic agents
CT scan should be scheduled after
completion of medical
treatment

9. Contrast-enhanced CT ? MRI
.Anatomy is adequately assessed without the use
of IV injected iodinated contrast material
.Iodine injection does not allow for discriminating
an inflammatory disease from a tumoral process no
Initial images or clinical symptoms suggest intracranial complications of a chronic inflammatory sinus disease
yes
MRI

10. CT imaging 1. Obstruction of the drainage pathways or anatomic
variants that may compromise already narrow drainage
pathways
2. Identification of critical anatomic areas where anatomic
variants pose special risks during sinus surgery
3. Local extension of disease
4. Complications
1+2 : Preoperative CT scan as a
road map for endoscopic sinus surgery

11. Coronal CT
Maxillary sinuses
Ethmoid sinus
Nasal cavity

12. Sagittal CT
Frontal sinuses
Ethmoid sinus
Sphenoid sinus
Nasal cavity

13. Ostio-meatal unit Middle nasal meatus Coronal CT Sagittal CT
(air channel medial to uncinate process
and lateral to the middle turbinate)

14. Ostio-méatal unit Obstruction Sagittal view
Drainage from frontal, maxillary
and anterior ethmoid sinuses
Obstruction
Frontal sinusitis
Maxillary sinusitis
Anterior ethmoid sinusitis
Sagittal view

15. Ostio-meatal unit Coronal CT Orbit Axial CT Ethmoid EB Middle meatus
bulla (EB)
Orbit EB
Middle
turbinate
Middle
meatus
Uncinate
process
Axial CT

16. Ostio-meatal unit Coronal CT Maxillary ostium
Ethmoid infundibulum (posterior)
Hiatus semilunaris
Middle meatus
Coronal CT

17. Uncinate process
Thin-curved bony lamina of variable height from the lateral side of the ethmoid labyrinth, that forms a portion of the lateral nasal wall.
Coronal CT EB
Lamina
papyracea
Supero-anterior
attachment to lamina papyracea in 50%
Inferior attachment to the
neck of the inferior turbinate

18. Uncinate process Coronal CT Sagittal CT
Postero-lateral attachment to the roof of the maxillary sinus

19. Uncinate process Coronal CT Sagittal CT EB Lacrymal bone
Anterior-most ethmoid cell:
agger nasi cell
Lacrymal bone
Anterior attachment
of the uncinate process

20. Ethmoid bulla (EB)
Most posterior of all anterior ethmoid air cells, roof of the
hiatus semilunaris and posterior ethmoid infundibulum
Coronal CT
Sagittal CT EB
Anterior ethmoid drainage
Middle meatus
Anterior ethmoid cells can drain into the middle meatus via the ethmoid bulla

21. Ethmoid bulla Orbit Normal-sized bullae Large bullae Hypoplasic bullae
Uncinate
process
Normal-sized bullae
Large bullae
Hypoplasic bullae
Acording to John Earwaker. Anatomic variants in sinonasal CT.Radiographics 1993;13:

22. Coronal CT
Different
ethmoid
bullae

23. Middle turbinate Coronal CT Coronal CT Basal (ground) lamella
Posterior
ethmoid
cell EB
Bulb
It attaches posteriorly and
laterally to the lamina papyracea:
Basal (ground) lamella
It attaches superiorly to the
cribriform plate:
Medial lamella

24. Middle turbinate Coronal CT Sagittal CT Anterior Posterior ethmoid
air cells
Posterior
ethmoid
air cells
Posterior
ethmoid
Anterior
ethmoid EB
Basal lamella

25. Ethmoid infundibulum Anterior ethmoid cells drainage
Frontal sinus drainage (25%)
Anterior ethmoid cells can directly drain into middle meatus
Coronal CT

26. Frontal recess Communication between frontal sinus and nasal cavity.
It is not strictly a duct but a channel located between
anterior ethmoid cells. Variety of configurations.
Sagittal CT
Coronal CT
Frontal
sinus
Frontal ostium
Agger nasi cell
Anterior middle meatus

27. Coronal CT
Frontal sinus drainage pathways according to supero-anterior attachment
of the uncinate plate
50%
Attachment to the lamina papyracea
Frontal drainage in the medial meatus
25%
Attachment to the skull base
Frontal drainage into the ethmoid infundibulum
25%
Attachment to the neck of the middle turbinate
Frontal drainage into the ethmoid infundibulum or into an anterior ethmoid cell

28. Frontal sinus outflow obstruction
Frontal sinusitis
Sagittal view

29. Sphenoethmoidal recess
Posterior ethmoid and sphenoid sinus drainages
Axial CT
Sagittal CT
Sphenoid
sinus
Sphenoid sinus
ostium
Superior nasal meatus

30. Sphenoethmoidal recess obstruction
Posterior ethmoid sinusitis
Sphenoid sinus sinusitis

31. Posterior nasal fontanel
Coronal CT
coronal
Axial CT
Area of the lateral wall of the nose immediately behind the posterior
attachment of the uncinate plate. Consists of mucous membrane only,
without bony support.
Accessory maxillary ostium is frequently found through the
posterior nasal fontanel (15-40%)

32. Posterior choana
Coronal CT
Sagittal CT
Nasopharynx

33. Nasal septum Coronal CT Sagittal view Septal vomer cartilage post ant
Perpendicular plate
of the ethmoid
post
ant
Septal
cartilage
vomer
Chondrovomeral
junction

34. Nasolacrymal duct 2
Axial CT 1 3 4
Coronal CT
Inferior
meatus

35. Anterior skull base Crista galli
Coronal CT
Axial CT
Crista galli
Cribriform plates (floor of the olfactive fossa)
Ethmoid roof (fovea ethmoidalis)

36. Ethmoid roof
Axial CT
Sagittal CT

37. Lateral lamella Coronal CT 1-16 mm length
(point of structural weakness in
the anterior skull base)
Point of structural
weakness during
turbinectomy
Coronal CT
Ethmoid roof
Medial
lamella
Cribriform plate
Middle
turbinate
1-16 mm length
Dehiscent in 15% of specimens
Anterior ethmoidal artery

38. Anterior ethmoidal artery
Coronal CT
Coronal CT
Olfactory
fossa
Lateral lamella
Medial lamella of
Middle turbinate
The anterior ethmoidal artery - branch of the ophtalmic artery - exits the
orbit through the anterior ethmoidal foramen and enters the olfactory
fossa at the point of attachment of the middle turbinate to the cribriform
plate

39. Anatomic variants Very frequently noted
The presence of anatomic variants, singly or in
combination, does not represent a disease state per se
Equal prevalence of patients with and without sinus
disease in the presence of the same anatomic variant

40. Septal deviation Coronal CT Coronal CT Middle meatus Inferior meatus
Hypoplasic
middle
turbinate
Large
middle
turbinate
Middle meatus
Inferior meatus

41. Septal spurs Axial CT Coronal CT Coronal CT
Bridging spur
Frequently encountered at the junction of the perpendicular plate of the ethmoid and the vomer
May impige on and invaginate the middle or inferior turbinates. When the turbinate mucosa swells with the normal nasal cycle or inflammation, it is impaled on the spur, setting up a cycle of facial pain or headache. A septal spur occasionally produces a complete bridge.

42. Size variations of middle turbinate
Coronal CT
Coronal CT
Ostio-méatal complex compromise?
Turbinate septal contact when the turbinate mucosa swells with the normal nasal cycle or inflammation

43. Pneumatized middle turbinate
Axial CT
Coronal CT
Air cell in the vertical lamella: concha neck air cell
Air cell in the bulbous segment:
concha bullosa cell

44. Paradoxical middle turbinate
Coronal CT
Usually
Convex configuration medially
Concave configuration laterally
Paradoxical turbinate
Concave configuration medially
Convexe configuration laterally

45. Pneumatized superior turbinate
Coronal CT
A cause of migraine headache?
Enlargement of the superior turbinate due to pneumatization,
with accompanying mucosal contact, acts as a mechanical
stimulus initiating an axon reflex with resultant referred pain?

46. Uncinate process Medially rotated uncinate Pneumatized Height : 1-4 mm
Length : mm
Coronal CT
Coronal CT
Medially rotated uncinate
Pneumatized

47. Frontal bulla cell (suprabullar cell)
Anterior ethmoid air cell extending upwards (intramural ethmoid air cell)
sagittal
axial
coronal
Frontal recess
May be small and impiges only on the floor of the frontal sinus.
May elevate and narrows the frontal recess
May be prominent and bulges into the frontal sinus

48. Frontal sinus extension
Pneumatization of the orbital plate of the frontal bone
ant
post
Coronal CT
Frontal sinus
No frontal sinus drainage compromise

49. Agger nasi (AN) cell Frontal recess Coronal CT Sagittal CT AN
Lacrymal
fossa
Frontal recess
The most anterior of the ethmoid cells. Forms the floor of the frontal
recess. It reaches the lacrimal fossa inferiolaterally, and is
anterolaterally arched by the nasal bone. A large agger nasi can impige on
and distort the frontal recess.
Its posterior-medial wall usually gives rise to the anterior uncinate process

50. Maxillary sinus recesses
Coronal CT
Palatine recess
Axial CT
Infraorbital recess of
The maxillary sinus
Coronal CT
Axial CT
Sagittal CT
Alveolar recesses
(roots of the premolar
and molar teeth)
Zygomatic recess

51. Sphenoid sinus recesses
Sagittal view
Coronal anterior view
ant
post
Sphenoid
sinus
Sphenoid sinus
Temporal
bone
Orbital
wall
Maxillary
bone
Rostrum
Septum, vomer
Sup or inf clivus
Lesser wing
Greater wing
Pterygoid process

52. Sphenoid sinus recesses
Sagittal CT
Sagittal CT
Septal recess
Inferior clival recess

53. Sphenoid sinus recesses
Coronal CT
Lesser wing
Greater wing
Ptérygoid process
Anterior clinoid process
Coronal CT
Foramen rotundum
(maxillairy nerve)
Optic nerve

54. Intersinus septation of sphenoid
Axial CT
Coronal CT
Presellar segment of the internal carotid artery

55. Vulnerability of the carotid canal
Internal carotid artery bulges into sphenoid sinus
Axial CT
Axial CT
Sphenoid
sinus
surgery
septum

56. Vulnerability of the carotid canal
Dehiscent carotid canal
Sphenoid
sinus
surgery
Axial CT
Axial CT

57. Vulnerability of the carotid canal
Normal
sphenoid
sinus
Hypoplasia or aplasia
of the sphenoid sinus
Carotid canal impiges on or bulges into posterior ethmoid
Axial CT
Posterior
ethmoid
surgery
Ethmoid
ETHMOIDE
POST
Normal
sphenoid
sinus

58. Vulnerability of the optic nerve
1 Onodi cell (bulging of the optic canal into the posterior ethmoid)
2 Pneumatization of the lesser wing of the sphenoid bone
3 Pneumatization of the anterior clinoid process of the sphenoid bone
Coronal CT 2
Coronal CT 3
Sagittal CT 1
Posterior
ethmoid
surgery
Sphenoid
sinus
surgery
Sphenoid
sinus
surgery
Encasement of the optic nerve
Within the sphenoid sinus
Optic nerves

59. Onodi cell Vulnerability of the optic nerve Sagittal CT Axial CT
Sinus
sphénoide
Posterior
ethmoid
surgery
Coronal CT
Posterior ethmoid cell, with prominent superior or lateral pneumatization to the sphenoid sinus, and a bulge of the optic canal into it.

60. Vulnerability of the optic nerve
Axial CT
Sphenoid
sinus
surgery 1 2
Coronal CT 2
1. Bulging of the optic nerve
into the sphenoid sinus
2. Dehiscent optic canal
Sphenoid
sinus
surgery

61. Vulnerability of the optic nerve
Hypoplasia or aplasia of the sphenoid sinus
(Optic nerves impinge on or bulge into the posterior ethmoid)
Posterior
ethmoid
surgery
Post
ethmoid
Normal-sized
sphenoid sinus mt mt mt
Sagittal view
mt: middle turbinate
Optic nerve

62. Vulnerability of the orbit
Haller cells
Coronal CT
Anterior
ethmoid
endoscopy
Anterior ethmoid air cells that extend along
the medial floor of the orbit

63. Vulnerability of the orbit
Coronal CT
Axial CT
orbite
orbit
Uncinectomy
Uncinate process is very close to infero-medial orbit wall.
They can be merged.

64. Vulnerability of the orbit
Lamina papyracea localized medial to
the maxillary sinus ostium
Coronal CT
Coronal CT
orbit
Fusion of the uncinate process to the
medial orbital wall
(usually associated with ipsilateral hypoplastic maxillary sinus)
(Ex :maxillary sinus hypoplasia;reduced
ethmoid transverse diameter;children)

65. Vulnerability of the orbit
Coronal CT
Axial CT
Axial CT
Anterior
ethmoid
endoscopy
coronal
Dehiscent lamina
papyracea
Dehiscent lamina
papyracea
Thin medial orbital wall
(lamina papyracea)

66. Vulnerability of the nasolacrymal duct
Agger nasi cell can invade the lacrymal bone
and impinge on or encircle the nasolacrymal duct
Coronal CT
Anterior
ethmoid
endoscopy
Axial CT

67. Vulnerability of the anterior skull base
Low cribriform plate: below the upper third of the vertical
orbital plate
Coronal CT
orbit
Risk of penetration into the
anterior cranial fossa during
ethmoid endoscopic surgery
Usually associated with
hypoplastic middle turbinate(s)