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1. CT Scan
Paranasal Sinus
Dr. Dhwani Shah
Senior Resident

2. Introduction
• A fundamental knowledge of the anatomy of
structures of nose and paranasal sinuses is
essential for the understanding of diseases of
nose and preoperative planning of endoscopic
sinus surgery.
• Computed tomography (CT) has become a
standard diagnostic tool in the evaluation of nose
and paranasal sinuses. Multidetector CT(MDCT)
allows assessment of the patency of sinonasal
passages, shows the effect of anatomic variants,
inflammatory diseases on patency.

3. Need of Imaging
• To confirm Diagnosis
• To facilitate Surgical planning (road map)
• To know extent of disease
• To know character of disease
• Location of surgically relevant anatomic
structures
• Precise identification of critical anatomic
variations

4. Why not Xray PNS?
• Inadequate details
• Overlapping of osseous framework

5. When to be done
• After a course of antibiotics so that acute
inflammation is not mistaken for chronic
mucosal disease
• 4-6 weeks following therapy as radiological
findings may lag behind clinical response(for
follow-up)

6. • A basic paranasal scan includes bony and soft
tissue window of 3-5 mm cuts taken anterior to
posterior coronal plane and axial sections from
inferior to superior.
• A Sagittal reconstruction is done to observe some
particular structures.
• It is extremely important to review the CT images
in all three planes for better understanding of the
anatomy and identification of these anatomic
variations

7. • Proper positioning of the patient’s head is
important.
• For Axial cuts, patient’s hard palate is placed
perpendicular to ct scanner table.
• For coronal cuts, gantry is perpendicular to
patient’s hard palate.
• ask the patient to blow nose and clear out all
loose secretions prior to ct

8. (1) Coronal – easy as we operate in same plane
• Following structures can be assessed going from anterior to
posterior.
 Frontal sinus and nasal bones
 Nasal septum
 Inferior turbinate
 Nasolacrimal duct
 Anterior ethmoidal cells
 Ethmoidal bulla
 Middle turbinate
 Uncinate process and its attachment
 Haller cells
 Maxillary sinus
 Depth olfactory fossa
 Posterior ethmoidal cells
 Sphenoid sinus

9. (2)Axial
– Parallel to hard palate
– Inferior(hard palate) to superior(upper margin of frontal sinus)
• Certain structures are well seen on axial scan.
• Nasolacrimal duct
• Anteroposterior deviation of nasal septum
• Fossa of Rosenmueller
• Ground lamella and its attachment
• Lamina papyracea
• Demarcation between anterior and posterior ethmoid air
cells
• Retrobullar recess
• Pterygopalatine fossa
• Onodi cells

10. (3) Sagittal
• Lateral nasal wall
• Frontal recess area
• Retrobullar and Suprabullar recess
• Sphenoid sinus ostium
• Extent of Onodi cell’s migration

11. What kind of CT PNS should be
ordered?
• CT PNS, coronal cuts, bone window setting,
spaced at 3 mm cuts +/- soft tissue setting +/-
contrast (In case of CSF rhinorrhoea or optic
nerve injury – 1 mm cuts required)

12. • Start from the first cut itself
• Don’t jump
• Read for 2 times

13. Scout/Gantry cut (thickness and
positioning)
Scout film—3 mm slice thickness Scout film—1 mm slice thickness

14. External nose and Nasal bones

15. • The most anterior cut shows frontal sinus and
nasal bones
• Great variations of pneumatization of frontal
sinus
• Interfrontal sinus septum is in midline
inferiorly, but may deviate to any side
posterosuperiorly
• Septadeep lateral recessesclassical
scalloping of frontal sinus

16. Cut showing interfrontal septum, multiple frontal septa show
classical scalloping of frontal sinus  which is lost in mucoceles

17. Nasal septum
Mucosal swellingThe septal tubercle(*)

18. • Septal tubercle consists of erectile tissue, is a
phylogenetic remnant of vomeronasal organ

19. Agger nasi cells (A), nasolacrimal duct
(arrow), middle turbinate not yet visualized

20. The olfactory fossa. Anterior attachment of
middle turbinate seen at the junction of
medial and lateral lamella of cribriform plate

21. Ethmoid sinus and olfactory fossa
• The level of the cribriform plate and the depth
of the olfactory fossa should be assessed and
classified according to the Keros classification.
• The height of the ethmoidal fovea above the
level of the cribriform plate is noted.

22. (1) Horizontal lamella
(2) Lateral lamella (0.2 mm)
(3) Orbital plate of frontal bone(0.5 mm)
(4) Anterior ethmoidal artery

23. • Fovea ethmoidalis:
– Makes up the roof of ethmoid bone labyrinth
– Is a part of frontal bone that separates the
ethmoidal cells from the anterior cranial fossa

25. The ethmoidal bulla

26. Osteomeatal unit

27. • Components of OMC:
– Uncinate process
– Hiatus semilunaris
– Bulla ethmoidalis

28. • Any septal spur impinging or compromising
OMC
• Turbinate hypertrophy or concha bullosa
• Mode of attachment or deviations of Uncinate
• Large bulla ethmoidalis
• Presence of haller cells
Factors affecting OMC patency

29. Maxillary sinus
• The maxillary sinus changes shape from
triangular to ovoid, in more posterior cuts.
• CT in the coronal plane demonstrates the
maxillary sinus to be narrow anteriorly, widest
in mid portion and narrow again posteriorly.

30. Maxillary sinus appears triangular in
anterior cuts (arrow: infraorbital nerve)

31. Accessory ostium in the left posterior fontanelle

32. Anterior ethmoidal artery. Beaking of lamina papyracea
seen on left. Orbitocranial canal seen on the right

33. • 2-3 mm behind bulla, Anterior Ethmoidal
artery is seen as a classical “beaking” of
medial orbital wall
• The artery may lie close to the skull base or
may cross low within the anterior ethmoids in
which case the orbitocranial canal with its
bony mesentery is clearly seen

35. The ground lamella (arrow). Intermediate
attachment of middle turbinate

36. Posterior attachment of middle turbinate

37. • The middle turbinate is attached to the lamina
papyracea by its ground lamella separating
the anterior ethmoid cells from the posterior
ethmoid cells
• superior turbinate is visualized in the more
posterior cuts and any variations in it, e.g.
pneumatization, paradoxical curvature should
be looked for

38. Posterior ethmoidal cells (asterix).
Inferior orbital fissure (arrow)-> opens laterally into Infra
Temporal Fossa

39. Orbit
• The orbit changes from a circular outline to a
triangular or pyramidal shape

40. Fat intervening between lamina
papyracea and medial rectus anteriorly

41. Medial rectus in direct contact with lamina
papyracea posteriorly

42. • It is important to know that the medial rectus
is separated from the lamina papyracea by a
pad of fat anteriorly. However, more
posteriorly in the orbit this pad of fat is absent
and the medial rectus is in direct relation to
the lamina papyracea and therefore more
prone to injury

43. Bilateral sphenoid ostia

44. • In the more anterior cuts both the posterior
ethmoid cells and the sphenoid sinus are
seen. The superolateral cell is the posterior
ethmoid cell whereas the inferomedial cell is
the sphenoid sinus.
• The more subsequent cuts show the sphenoid
anatomy more clearly.

45. Orbital apex (arrow), sphenoid dominance
(left), pterygoid processes (P)

46. • The retort-shaped orbital apex is seen on
either side of the sphenoid sinus in the
anterior cuts
• The pterygoid processes extend downwards
and are perforated by two canals. The first is
the foramen rotundum, which is seen just
below the orbital apex. Inferomedial to this
foramen is the opening of the vidian canal

47. Vidian canal (thin arrow), foramen rotundum
(thick arrow), and optic nerve (curved arrow)

48. Sphenopalatine foramen ( arrow)

49. • A canal may be seen below the sphenoid sinus
between the pterygopalatine fossa and the
posterior choana
• This is the sphenopalatine foramen, which
opens above the posterior end of the middle
turbinate.

50. Torus tubaris (T), fossa of Rosenmueller
(arrow), adenoids (A)

51. • Coronal sections of the nasopharynx show the
eustachian tube opening, the torus tubaris,
the fossa of Rosenmueller and the adenoids, if
present

52. Foramen ovale

53. • The foramen ovale is seen laterally in the
greater wing of sphenoid
• Widening or destruction of the foramen
should be looked for in a case of
nasopharyngeal angiofibroma or a carcinoma
of nasopharynx respectively.

54. Axial Cuts

55. Nasolacrimal duct (arrow)

56. Fossa of Rosenmueller (arrow),
EO—eustachian tube opening

57. The ground lamella (arrow)

58. G: ground lamella, B: bulla,
R: retrobullar recess, U: uncinate process

59. The orbit in axial section

60. Lamina papyracea in lower section of the orbit

62. Crista galli (thick arrow),
foramen cecum (thin arrow)

63. Sagittal cuts

65. FS-frontal sinus, B-ethmoidal bulla, A- agger
nasi, PE-post. Ethmoidal cells, SB-suprabullar cells

66. (1) uncinate process (blue), (2) anterior wall of bulla (green), (3) ground
lamella (yellow), (4) anterior wall of sphenoid (black)

67. • The four lamellae that the endoscopic surgeon
has to cross in an anteroposterior direction
are well seen in a single cut on the sagittal
section.
– Uncinate Process
– Ant wall of bulla
– Post wall of bulla
– Ant wall of sphenoid

68. Anatomical Variations

69. Septal deviations
• Can present as a spur at the junction of
cartilage with vomer or along the length of
the septum
• Compromised Osteomeatal complex(OMC)

70. Septal deviations
Septal spur with hypertrophied
Inferior turbinate

71. Pneumatization of the septum

72. Agger nasi

73. • 1-3 in no.
• Pneumatises lacrimal bone and frontonasal
process of maxilla
• Displaces anterior attachment of Middle
turbinate postero-superiorly if prominent

74. Various attachments of Uncinate
Process
Attaching laterally to lamina papyracea

75. Attaching to cribriform plate

76. Attaching medially to middle turbinate

77. Lying free in middle meatus

78. Pneumatized uncinate process

79. Drainage of frontal recess—medial to infundibulum on the
right and into the infundibulum on the left

80. Middle turbinate variations
Concha bullosa
Interlamellar cell of Grunwald (when
superior meatus pneumatizes
vertical lamella of MT)

81. Paradoxically curved middle turbinate The turbinate sinus

82. Bulla Ethmoidalis
• Most consistent and prominent anterior
ethmoid cell
• Shows variations in pneumatization
(hypoplastic, rarely non-pneumatized,
extensively pneumatized)

83. • Suprabullar recess: space between the upper
margin of the bulla and skull base
– Opens into the frontal recess
• Retrobullar space: space between ground
lamella and bulla
• Sinus lateralis
• Hiatus semilunaris superioris
• Hiatus semilunaris inferioris

86. Ethmoid air cells classification
according to their migration

87. Patterns of migration of ethmoidal air cells into: (1) lacrimal bone (agger nasi), (2) inferior to
orbit (Haller’s cell), (3) frontal bone (frontal cells), (4) supraorbital cell, (5) middle turbinate
(concha bullosa), (6) crista galli, (7) above sphenoid (Onodi)

88. • Anteriorly—into the lacrimal bone and frontonasal
process of maxilla as the agger nasi cells.
• Inferolaterally—into the roof of maxillary sinus as
Haller cell
• Anterosuperiorly—into the frontal bone to form
the frontal sinus.
• Superiorly—above the ethmoidal bulla over the
orbit and behind frontal sinus to form supraorbital
cell.
• Into the middle turbinate—concha bullosa
• Pneumatized crista galli
• Posteriorly—above sphenoid sinus as Onodi cell.
• Superiorly—into the frontal recess to form the
different types of frontal cells.

89. `
Haller’s cell

90. Supraorbital cell

91. Pneumatization of crista galli

92. Onodi cell with dehiscent optic nerve

93. • Frontal cells classification

94. Type I: A single cell above the agger nasi cell.

95. Type II: Two or more cells above the agger nasi cell.

96. Type III: (Frontal bulla) A cell which extends well into the
frontal sinus and simulates the frontal sinus itself on
endoscopy

97. Type IV: An isolated “loner cell” within the frontal sinus.

98. Ground lamella
Ground lamella spliting into septae

99. Missed” ground lamella

100. Superior turbinate
Pneumatized superior turbinate
Paradoxically curved superior
turbinate

101. The olfactory fossa

102. Keros classification
Type I — 1-3 mm

103. Type II — 4-7 mm

104. Type III — 8-17 mm

105. Patterns of sphenoid pneumatization

106. Intersphenoid septum attaching
to optic nerve
Intersphenoid septum attaching to
internal carotid artery

107. Delano classification

110. Pneumatized anterior clinoid process

111. Lateral recesses of the sphenoid

112. Pneumatized interfrontal septum

113. Septa within maxillary sinus Dehiscent infraorbital nerve

114. Some pathological diseases
of PNS

115. ANTROCHOANAL POLYP

116. SINONASAL POLYPOSIS

117. INVERTED PAPILLOMA

118. AFRS

119. JUVENILE NASOPHARYNGEAL
ANGIOFIBROMA

120. LEFT MAXILLARY CARCINOMA