The paranasal sinuses drain into specific areas of the nasal cavity. The frontal sinuses drain into the frontoethmoidal recess. The anterior ethmoid air cells drain into the anterior aspects of the hiatus semilunaris. The middle ethmoid air cells drain through the ethmoid bulla into the superior meatus. The maxillary sinus drains via the infundibulum into the maxillary ostium. The sphenoid sinus drains into the sphenoethmoid recess posterior to the superior meatus. Coronal CT is the preferred imaging modality to evaluate the paranasal sinuses and displays important anatomical landmarks like the maxillary sinus, turbinates, nasal septum, and unc

1. PARANASAL SINUSES
Radiological Anatomy
Islah Raoof
DNB Resident

2. The normal secretions produced by the sinuses are cleared by the cilia lining the
mucosa.
These drain the secretions towards the natural sinus ostia
1. FRONTAL SINUSES – drain into the frontoethmoidal recess through the
anterior ethmoid air cells into the anterior frontal recess of the middle meatus.
2. ANTERIOR ETHMOID – drain into the anterior aspects of the hiatus
semilunaris
3. MIDDLE ETHMOID – Through the ethmoid bulla , the posterior ethmoids
drain into the superior meatus
4. MAXILLARY SINUS – drains via the infundibulum into the ostium
5. SPHENOID SINUS – into the sphenoethmoid recess posterior to the superior
meatus
SINONASAL PHYSIOLOGY

4. Nasal Structures
The nasal septum is a midline structure composed of both bone
and cartilaginous tissue. Its deviation can cause partial obstruction
in the nasal cavities unilaterally or on both sides depending on its
shape.
The lateral nasal wall has three projections superior,
middle and inferior turbinates.
These structures divide the nasal cavity into three air
passages the superior, middle and inferior meatus.

5. Nasal Structures
The inferior turbinate is the lower most projections arising
from the lateral nasal bone and extending into the nasal
cavity and running posteriorly toward the nasopharynx.
The middle turbinate lies above the inferior turbinates.
Anterosuperiorly, the middle turbinate attaches to the skull
base just lateral to the cribriform plate. In its middle third it
turns coronally and laterally to insert on the lamina papyracea
and posteriorly to the roof of ethmoidal complex

6. Coronal CT image showing nasal
structure. Middle turbinate (white
arrow) and lamina papyracea (black
arrow)
Coronal CT at the level of OMC showing
uncinate process
(black arrow), agar nasi cells (short
white arrow) and frontal recess(white
long arrow)

7. Coronal section showing anterior draining pathway including frontal
recess (white arrow), maxillary ostium (thin black arrow), infundibulum
(thick black arrow), middle meatus (short black arrow) and maxillary
sinus (star)

8. Nasal septum
The nasal septum and the inferior turbinate are the first
structures encountered on entering the nasal cavity.
The nasal septum forms the medial border of the nasal
cavity. It consists of the quadrangular cartilage
anteriorly, extending to the perpendicular plate of the
ethmoid bone postero superiorly and the vomer postero
inferiorly

10. THE OSTEOMEATAL COMPLEX
• Region where the frontal ,anterior and middle ethmoid and maxillary sinuses drain
• Includes the fronto ethmoidal recess , uncinate process , hiatus semilunaris ,
ethmoid bulla , the maxillary infundibulum and ostium and the ethmoid
infundibulum .
• Disease at the OMC is the major cause of recurrent chronic sinusitis

11. Osteomeatal Unit

12. Osteomeatal Unit
An area of superomedial
maxillary sinus + middle meatus
as the common mucociliary
drainage pathway of frontal
maxillary, and anterior + middle
ethmoid air cells into the nose

13. Components of Osteomeatal Unit
1. Maxillary osteum
2. Infundibulum : the flattened cone like
passage
3. Uncinate process: Key bony structure in
lateral nasal wall
4. Hiatus semilunaris:Final segment for
drainage of maxillary sinus
5. Ostea :
• multiple ostea from ant. and middle
ethmoidal cells at ant. Aspect
• Maxillary osteum at posterior aspect

14. Frontal sinuses

15. FRONTAL RECESS
The frontal recess is an
hourglass like narrowing
between the frontal sinus and the
anterior middle meatus through
which the frontal sinus drains
The frontal recesses are the
narrowest anterior air channels
and are common sites of
inflammation. Their obstruction
subsequently results in loss of
ventilation and mucociliary
clearance of the frontal sinus

16. The frontal recess, or the frontal outflow tract
leads from the frontal sinus into the nasal cavity.
Anteriorly, the frontal sinus outflow tract is
bordered by the uncinate process or agger nasi
cells.If any of them are diseased,frontal sinusitis,
may occur.
The lateral wall of the frontal recess is bounded by
the lamina papyracea. The medial boundary is the
middle turbinate. Posteriorly, the frontal recess is
bordered by the anterior wall of the ethmoid bulla.
Frontal Recess

17. SPHENOID SINUS
Sphenoid sinus develops in the
body of the sphenoid sinus and
drains via a sinus ostium into
spheno ethmoid recess.
The degree of pneumatisation is
variable and may extend into
greater and lesser wing of
sphenoid and pterygoid plates.
There are many important structures
in relation to sphenoid sinus like
vidian canal, optic nerve and
foramen rotundum.

18. Ethmoid air cells
Thin walled air cavities in the lateral masses of the ethmoid
bone. Varies from 3 – 18 in number.
Clinically divided into anterior ethmoidal air cells & posterior
ethmoidal air cells, by basal lamella (lateral attachment of
middle turbinate to lamina papyracea)
Anterior drain into- Middle meatus.
Posterior- sup.meatus & spenethmoidal recess.

19. ANATOMICALVARIANTS

22. INTERFRONTAL SINUS SEPTAL CELL

23. AGGER NASI AIR CELL
Its an ethmoturbinal
remnant present in nearly all
patients.
Located anterior to the
vertical attachment of the
middle turbinate to the skull
base.
The degree of ANC
pneumatization varies and
has a significant effect on
both the size of the frontal
sinus ostium and the shape
of the recess.

24. FRONTAL RECESS CELLS
•The frontal cells are anterior ethmoidal cells that are
located anterior and superiorly to the ANC.
•The frontal cells are classified according to KUHN
CRITERIA into four types (I, II, III and IV)
•They are important in the frontal sinuses drainage and
are related with sinonasal inflammatory process.
•The frontal cells are better seen coronal and sagittal
views

25. FRONTAL CELLS TYPE I

26. FRONTAL CELLS TYPE II

27. FRONTAL CELLS TYPE III

28. FRONTAL CELLS TYPE IV

29. SUPRA ORBITAL ETHMOIDAL CELLS

30. SUPRA ORBITAL ETHMOIDAL CELLS

31. HALLER CELL
These are ethmoid air cells located
anterior to the ethmoid bulla, along the
orbital floor, adjacent to the natural
ostium of the maxillary sinus, which
may cause mucociliary drainage
obstruction, predisposing to the
development of sinusitis.
Coronal CT image showing Haller cells
(white arrows) along the roof of the
maxillary sinus medially, causing
narrowing of the infundibulum (black
arrow)

33. Sphenoethmoid cell (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 / or carotid artery would
be exposed in the pneumatized cell.
Coronal CT at the level of sphenoid
sinus (asterix), showing Onodi cells
lying superior to the sphenoid sinuses
and in close relation to optic nerves
(black arrows)

34. PARADOXIC CURVATURE
Normally, the convexity of the
middle turbinate bone is
directed medially, toward the
nasal septum.
When paradoxically curved, the
convexity of the bone is
directed laterally toward the
lateral sinus wall.
The inferior edge of the middle
turbinate may assume various
shapes, which may narrow
and/or obstruct the nasal cavity,
infundibulum, and middle
meatus.

35. Concha Bullosa
It is an aerated turbinate, most often the
middle turbinate.
When the pneumatization involves the
bulbous segment of the middle turbinate, the
term concha bullosa applies.
If only the attachment portion of the middle
turbinate is pneumatized, and the
pneumatisation does not extend into the
bulbous segment, it is known as a lamellar
concha.
Concha bullosa (arrow) causing partial
obstruction of the middle meatus. Note le
DNS

36. Concha bullosa ( Pneumatized middle turbinate)

37. Accessory maxillary ostia
Accessory maxillary ostia are
generally solitary, but
occasionally may be multiple.
Such variation may be congenital
or secondary to sinusal diseases.
Possible mechanisms involved in
the development of such variation
include:
main ostium obstruction,
maxillary sinusitis or
anatomical/pathological factors in
the middle meatus, resulting in
rupture of membranous areas.

38. ETHMOIDAL BULLA
•Most constant anterior ethmoidal air cells.
•It is just beyond the natural ostium of the
maxillary sinus and forms the posterior border of
the hiatus semilunaris.
•The lateral extent of the bulla is the lamina
papyracea.
•Superiorly, the ethmoid bulla may extend all the
way to the ethmoid roof (the skull base).

39. ETHMOIDAL BULLA

40. ETHMOIDAL BULLA

41. FRONTAL BULLAR CELLS

42. SUPRA BULLAR CELLS

43. LAMINA PAPIRACEA DEFECTS

44. Sinus Hypoplasias

45. DEHISCENCE OF THE OPTIC NERVES AND ICA

46. CRISTA GALLI PNEUMATIZATION

47. NASAL SEPTUM PNEUMATIZATION

48. PTERYGOID PLATE PNEUMATIZATION

49. CLINOID PROCESS PNEUMATIZATION

50. Paradoxical middle turbinate
means the major curvature of the middle turbinate projects
laterally, leading to narrowing of the middle meatus.

51. Paradoxical middle turbinate

52. Bony spurs at the floor of the maxillary sinuses
During FESS a large spur can be mistaken for lateral sinus wall.

53. The uncinate process is a hook shaped bone of the lateral nasal wall and
forms the anterior border of the ethmoid infundibulum of hiatus
semilunaris, which is the location of the osteomeatal complex,
where the natural ostium of the maxillary sinus opens.
For patients with sinus disease, a patent
osteomeatal complex is critical for an improvement of symptoms.
Anteriorly, the uncinate process attaches to the lacrimal bone, and
inferiorly to the the ethmoidal process of the inferior turbinate.
The posterior edge lies in the hiatus semilunaris inferioris.
Superiorly the uncinate process may attach to the middle turbinate,
the lamina papyracea, and/or the skull base.
Uncinate Process Insertion

54. Uncinate Process Insertion – Type I

55. Uncinate Process Insertion – Type II

56. Uncinate Process Insertion – Type III

57. Uncinate Process Insertion – Type IV

58. Uncinate Process Insertion – Type V

59. Uncinate Process Insertion – Type VI

60. Imaging modalities

61. X RAY
CT
MRI

62. X ray – Water’s view & caldwell view.
CT – gold standard. Coronal & axial sections.
MRI is predominantly used for pre and post operative
management of naso sinus malignancy.
The chief disadvantage of MRI is its inability to show the bony
details of the sinuses, as both air and bone give no signal.

63. PARIETOACANTHIAL PROJECTION:
WATERS VIEW
Extend neck, placing chin and nose
against table/upright Bucky surface.
Head is adjusted so as to bring the
orbito meatal line to a 45 degree angle
to the casette holder.
Position the median saggital plane is
perpendicular to the midline of grid or
table/upright bucky surface.
Ensure that no rotation or tilt exists.
Centering is done at acanthion.

65. CALDWELL
Place patient's nose and forehead
against upright Bucky or table with
neck extended to elevate the OML
15° from horizontal. A radiolucent
support between forehead and
upright Bucky or table may be used
to maintain this position.(alternate
method if Bucky can be tilted 15°.)
Align MSP perpendicular to midline
of grid or upright Bucky surface.
Centering is done at nasion, ensuring
no rotation.

66. 1

67. CT procedures and techniques
CT is currently the modality of choice in the evaluation of
the paranasal sinuses and adjacent structures.
Its ability to optimally display bone, soft tissue, and air
provides an accurate depiction of both the anatomy and
the extent of disease in and around the paranasal sinuses.
In contrast to standard radiographs, CT clearly shows the
fine bony anatomy of the osteomeatal channels.

68. SCAN LIMITS :
From the ant margin of
frontal sinus to post
margin of sphenoid sinus

69. Coronal section procedure
Coronal scans are performed by hyperextension of the patients head and
angulation of the gantry
The patient should preferably be in the prone position with the chin resting on a
pad -KEEPS THE FREE FLUID OUT OF THE INFUNDIBULUM .
In patients unable to do the above, the HEAD HANGING position should be
acceptable .

70. The ideal scan thickness is 3-5 mm to cover the anterior margin ofthe
frontal sinus to the posterior margin of the sphenoid sinus.
The radiation dose is kept to the minimu by use of low mA with peak kVof
120.
Images should be obtained at an intermediate setting of 2000-2500 HU
window width and 200-350 HU window level as this provides details of
bone and soft tissues on a single set of films .

71. CORONAL CT OF PNS
Important anatomical
landmarks seen on coronal
images.
1 - maxillary sinus
2 - inferior turbinate
3 - middle turbinate
4 - nasal septum
5 - uncinate process
6 - semilunate hiatus
7 - orbit

72. THANK YOU