This document discusses the anatomy and imaging of the paranasal sinuses. It describes the drainage pathways of each sinus and the structures that make up the osteomeatal complex. It also covers anatomical variations that can occur like concha bullosa, Haller cells, and Onodi cells. Imaging modalities for evaluating the sinuses are described, with CT identified as the gold standard due to its ability to depict bone, soft tissues, and air. Scanning techniques for CT include coronal sections performed with the patient in a prone position and their head hyperextended.

1. IMAGING OF PARANASAL SINUSES
Dr. Archana Koshy

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

4. Nasal Structures
The nasal septum is a midline structure composed of both bone and cartilagenous
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.
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 .
The basal lamella is the portion of the middle turbinate where it attaches to the

5. 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)

6. 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)

7. 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 acute/chronic sinusitis .

8. Frontal sinuses.

9. 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

10. 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.

11. 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.

12. ANATOMICAL VARIANTS

13. 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.

14. 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

15. 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.

16. 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)

17. 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)

18. 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.

19. VARIATIONS OF THE OPTIC NERVE
 The optic nerve, carotid arteries, and vidian nerve develop prior to
the paranasal sinuses, and are responsible for the congenital
variations in the walls of the sphenoid sinus.
 Delano, et al., categorized the various relationships between the
optic nerve and posterior paranasal sinuses into four groups.
 Type I: The most common type, it occurs in 76% of patients. Here,
the nerve courses immediately adjacent to the sphenoid sinus,
without indentation of the wall or contact with the posterior ethmoid
air cell
The nerve is seen to course
immediately adjacent to the
sphenoid sinus, without
contact with the posterior
ethmoid air cell

20.  Type II: The nerve courses adjacent to the sphenoid sinus,
causing an indentation of the sinus wall, but without contact with the
posterior ethmoid air cell

21.  Type III: The nerve courses through the sphenoid
sinus with at least 50% of the nerve being surrounded
by air

22.  Type IV: The nerve course lies immediately adjacent
to the sphenoid and posterior ethmoid sinus

23. KEROS CLASSIFICATION
 Method of classifying the depth of the olfactory fossa.
 In adults, the olfactory recess is a variable depression in the cribriform plate. It
contains olfactory nerves and a small artery.
 The depth of the olfactory fossa is determined by the height of the lateral
lamella of the cribriform plate.
 Keros in 1962, classified the depth into three categories.
 Type 1: 1-3 mm (26.3% of population)
 Type 2: 4-7mm (73.3% of population)
 Type 3: 8-16mm (0.5% of population)
 The type 3 essentially exposes more of the very thin cribriform plate to potential
damage from trauma, tumour erosion, csf erosion (in benign intracranial
hypertension) and local nasal surgery or orbital decompression.
 Thin bone in the skull base, especially the cribriform plate, is susceptible to
erosion, encephalomeningocoele herniation and csf leaks

25. Imaging modalities

26.  X RAY
 CT
 MRI

27.  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.

28. 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.

30. 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.

31. 1

32. PARIETOACANTHIAL TRANSORAL
PROJECTION: OPEN MOUTH WATERS METHOD

33. 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.

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

35. 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 .

36. The ideal scan thickness is 3-5 mm to cover the anterior margin of the
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 kV of
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 .

37. PATHOLOGIES AFFECTING THE
PARANASAL SINUSES

38. 1.INFLAMMATORY SINUS DISEASE
a) ACUTE SINUSITIS
• Often due to secondary bacterial infection following an URTI of viral
origin or a local infection .
• The infection causes swelling of the mucosa which appears as an
opaque rim around the periphery of the sinus .
• Accompanied by an outpouring of the mucus into the sinus cavity ,
causing an opaque sinus on plain X-ray* .
• Non specific sign ,although in most cases,denotes infection , a sinus
filled with blood or new growth can give a similar appearance .
• In any doubts about the presence of fluid , a tilted view should be
obtained – to confirm the presence of a fluid level .

40. Inflammatory sinus disease. Coronal CT image of Inflammatory mucosal disease
demonstrates maxillary (red arrows) and ethmoid (blue arrows) sinus mucosal
thickening, and osteomeatal unit opacification (white arrows).

41. COMPLICATIONS
1. Osteomyelitis –May follow empyema which may rarely lead to bone
involvement
-Results in loss of outline of the sinus wall followed by frank osteolysis and
bone sequestration.
2. Intracranial abscess- Spread of infection from the frontal or sphenoid
sinuses may result in an intracranial abscess
-CT/MRI will show the characteristic ring enhancement .
3. Orbital cellulitis – Commonly follows an ethmoiditis and may result in
abscess formation , situated outside the perioribita adjacent to the
infected sinus .

42. B) CHRONIC RHINOSINUSITIS
• Chronic inflammatory disease of the paranasal sinuses and nasal cavity
clinically represents recurrent acute sinusitis or a prolonged episode
that has failed to respond to conservative management .
• CT is the investigation of choice as this defines the degree and extent
of involvement of the paranasal sinuses
• Also provides the surgeon with a ‘roadmap’ of the anatomy before
surgery .
• FESS is usually the treatment for patients with chronic rhinosinusitis .

43. OSTEITIS. Axial CT image of chronic sinusitis indicated by left sphenoid
sinus mucosal thickening and debris with adjacent osseous wall
thickening (blue arrow). There is also scattered ethmoid air cell
opacification (white arrow)

44. IMAGING FOR FESS(SSCT)
• Particular attention is paid to the OMC , as most chronic rhinosinusitis is
associated with disease in the middle meatus .
• The CT will show the extent of mucosal thickening and the number of
sinuses affected , and help confirm that the pathology is due to an
inflammatory process .
• CHRONIC DISEASE-will manifest with thickening and sclerosis of the
bones.
• Acute on chronic sinus secretions have a Ct density around 10-25 HU :
watery or mucoid density .
• Once the secretions have chronically thickened and concentrated , the Ct
density will rise to 60-80 HU .
• The MR appearance depends on the protein content of the secretion and
hence can be quite variable .
• MRI is reserved for difficult cases where there is a doubt about the
pathology on SSCT or to assess any intracranial involvement .

45. • SSCT helps the surgeon avoid the known hazards of endoscopic surgery .
• Shows the anatomical landmarks and the anatomical variants .
• FIVE distinct patterns in which chronic rhinosinusitis presents itself :
1. Infundibular pattern – Obstruction of the maxillary infundibulum resulting in
isolated maxillary sinusitis
2. Osteomeatal pattern – Middle meatus obstruction resulting in ipsilateral
sinusitis affecting the frontal , anterior and middle ethmoids and the
maxillary antrum
3. Sphenoethmoidal recess pattern – Obstruction results in posterior
ethmoid and sphenoid sinusitis
4. Sinonasal polyposis – Sinonasal polyps are evident with opacification of
various sinuses .
5. Sporadic pattern- retention cysts,mucoceles and mild mucosal thickening
without mucosal obstruction

46. SINONASAL POLYPOSIS
• Soft tissue pedunculated masses of edematous hyperplastic upper
respiratory mucosa .
• Specific polysaccharide material within the ground substance attracts
excess fluid and electrolytes .
• Commonest site – Ethmoids followed by maxillary antra and then the
sphenoid sinus .
• Plain Xrays and SSCT confirm the presence of a polpoidal mass :
1) Widening of the infundibulum
2) Opacification of the sinuses
3) Thinning of the sinus walls, nasal and ethmoid septa
4) Bulging of the lamina papyracea –Displacement of the eyeballs and
hypertelorism

47. Extensive nasal polyposis
(long white arrow) causing
obstruction of anterior
(short white arrow) and
posterior (black arrow)
drainage pathways causing
pansinusitis

48. Multiple polyps in the maxillary sinus (white arrow) and in the
sphenoid sinus (black arrow)

49. MUCOCELE
 Defined as the end stage of a chronically obstructed sinus – an
obstructed , airless, mucoid filled expanded sinus .
 Most commonly affected is the frontal ( 66%) ; Sphenoid mucocele is
rare .
 On CT- Mucoid attenuation collection with remodelling of the wall
-The bone may be locally thinned or eroded
MRI is the optimum imaging modality – any intracranial or intraorbital
extension can be assessed before surgery .
Post contrast MRI typically shows peripheral enhancement of the
mucosa with no enhancement of the secretions .

50. • FRONTAL SINUS MUCOCELE
-Expansion of the sinus cavity with loss of the scalloped margin of the
normal sinus .
The sinus is more opaque than normal , due to secretions ,but may
appear more radio-dense if bone destruction is marked .
CT will show the full extent of the expansion and is usually enough to make
the diagnosis
MRI may be used to assess intracranial extension.
ETHMOID MUCOCELE
-Majority are found in the anterior ethmoid air cells
-Usually more obvious clinically as most present with a palpable mass at
the medial canthus .
SPHENOID MUCOCELE
-Has to be diagnosed and intervened early before vision is compromised
-Involvement of the optic nerve , cavernous sinus and oculomotor
nerve is common due to the proximity of these structures to the sinus .
CT/MRI –shows partially rounded expansion of the sinus .

51. Mucocele of the ethmoid sinus. Plain X-
ray Water’s view (A) shows an expanded
and opaque left ethmoid sinus.
Coronal non-contrast CT (B) shows the
expanded sinus containing soft tissue
densities. The wall of the sinus are
thickened but are intact

52. A left sided ethmoidal mucocele (A)
encroaching on the left orbit.
Left globe in proptosed.
T2W MR axial and coronal sections (B)
of the same patient showing
hyperintense fluid contents of the
mucocele

53. FUNGAL DISEASE
• Usually diagnosed when an apparent routine infection fails to respond to
normal antibiotic treatment .
• Aspergillus fumigatus – most common
• The ethmoids and the maxilla antra are commonly involved. The frontal
are rarely affected .
• The findings vary from non specific mucosal thickening without bone
involvement to an opacified sinus with a central mycetoma with reactive
new bone formation or even erosions .
• On CT- High density central mass separated by mucoid separations .
-Areas of calcification may be present .
-Calcifcation may be diffuse , nodular or linear
-Accompanied by bone expansion and bone destruction in the invasive
form of the disease .
MRI- Signal hypointensity is the distinctive feature of aspergilloma
Due to the paramagnetic effect of heavy metals present in the fungal ball .

54. CT images coronal and axial showing diffuse nasal and sinus mucosal
thickening with hyperdensities (black arrows) causing expansion and blockage of
the sinuses.
On bone window, the ethmoid lamellae and sinus walls are remodelled and
eroded (white arrow)

55. Invasive fungal sinusitis: Axial T2WI (left) and T1WI (right)
images showing soft tissue in the frontal, ethmoid and
sphenoid
sinuses which is isointense on T1WI and hyperintense on
the T2WI

56. GRANULOMATOUS DISEASE
• Majority are infectious
• Include Tuberculosis , Syphilis, leprosy, rhinoscleroma and
actinomycosis .
• Non specific findings on imaging .
• Most of these start in the nasal cavity with soft tissue masses and
chronic non specific pan sinusitis .
• A diagnosis of granulomatous disease should be considered when
there is evidence of nasal septal mass with septal erosion on
imaging .

57. LEPROSY: DESTRUCTION OF THE NASAL BONES (ARROW) AND A
PERFORATED NASAL SEPTUM ARE CHARACTERISTIC CHANGES OF
LEPROMATOUS LEPROSY

58. RETENTION CYSTS
• Occur as a result of obstruction of the ducts of the mucosal glands .
• Usually small, have a well defined outline
• CT- Smooth , broad based soft tissue mass with a well defined
outline .
• MRI – Low intensity on T1 and bright on T2 but may appear bright on
T1 depending on the concentration of entrapped secretions .

59. TUMOURS OF THE PARANASAL SINUSES
• BENIGN TUMOURS
-OSTEOMA –
• Benign slow growing tumours containing mature compact or
cancellous bone .
• Occur most frequently in the frontal sinus, followed by ethmoid and
maxillary sinuses
• May block the drainage of a sinus resulting in recurrent infection
and/or mucocele .
• Large frontal osteomas can erode the inner table to the frontal bone
which may allow the infection to spread intracranially and
pneumocephalus will be seen .
• Posterior extension may lead to the compromise of the optic nerve .

60. • Plain film and CT – Well defined very dense lesion (if it contains mature
bone)
• Less ossified if it contains cancellous bone
Osteoma of the left frontal sinus.
Axial and coronal CT scans showing a dense bony lesion of the left sinus
occupying much of the sinus cavity leaving only a thin rim of air around it.

61. PAPILLOMA
• The mucosal lining of the nose is derived from ectoderm and is called the
schneiderian membrane .
• Can give rise to three types of papillomas :
(a) FUNGIFORM – Arises from the nasal septum,usually anteriorly .
(b) INVERTED- Commonest usually originate
(c) CYLINDRICAL CELL from the lateral wall .
-Inverted papillomas – Characterestically arises from the lateral nasal wall
near the middle turbinate and extend into the sinuses ,usually involving the
maxillary and ethmoid sinuses .
SYMPTOMS – Nasal obstruction , epistaxis and anosmia .

62. INVERTED PAPILLOMA of
the right antrum and
ethmoids. Noncontrast CT
scan shows a hyperdense
soft tissue lesion in the
right
ethmoid and nasal cavity
extending into the right
antrum.
The middle turbinate is
destroyed and the septum
shows focal erosion.
The floor and medial wall of
the orbit is eroded at places

63.  Imaging appearance can vary from a small nasal polypoid mass to
an expansile mass with remodelling of the nasal cavity
 May extend into the sinuses with secondary obstructive sinusitis .
 The nasal septum usually remains intact but may be remodelled with
bowing of the septum .
 INVERTED PAPILLOMAS – usually multicentric .
 ADENOMAS – may simulate a nasal polyp but are locally invasive
and local recurrence occurs if they re not completely excised .

64.  NASAOPHARYNGEAL ANGIOFIBROMA
-Rare histologically benign but locally aggressive tumour .
-Highly vascular polypoid mass-usually in males (10-18)
-Almost all tumours originate from the posterior choanal tissue near the
pterygopalatine fossa and the sphenopalatine foramen .
-They fill the entire nasopharynx and frequently extend into the
pterygolpalatine fossa causing widening of the fossa and anterior bowing
of the posterior ipsilateral antral wall .
-Intracranial extension occurs uncommonly in 5-20%-----Superior orbital
fissure widening is seen as an indication .

65. ANGIOFIBROMA LATERAL X-RAY OF SKULL - showing anterior bowing
(small arrow) of the posterolateral wall of the maxillary sinus due to the
angiofibroma (open arrow)

66. Angiofibroma: Contrast enhanced axial CT sections show a well-defined
mass in the nasal cavity and in the pterygomaxillary fissure which is wide.
Posterolateral wall of the antrum is pushed anteriorly (Arrow).
Coronal sections shows widening of the pterygomaxillary fissure

67. • In addition , a soft tissue nasopharyngeal mass and opacification of the
sphenoid sinus may be seen .
• Cross sectional imaging may demonstrate an avidly enhancing mass .
• Multiple flow voids will be seen within the tumour on T1 and T2
weighted spin – echo sequences .
• The internal maxillary artery and the ascending pharyngeal artery are
the major feeding vessels which will be demonstrated on angiography
• Pre operative embolisation may be used to aid subsequent surgery .

68. ANGIOMATOUS POLYP
- Located in the nasal fossa and NOT the NASOPHARYNX , unlike the
nasopharyngeal angiofibroma .
- Does not extend into the pterygopalatine fossa or intracranially .
- The vascular supply of these lesions is less extensive than
angiofibromas .
- Does not enhance avidly following intravenous contrast and vascular
flow voids are not seen on MRI .

69. LYMPHOMAS
 Forty-seven percent of non-Hodgkin’s lymphomas are found in the head
and neck; 90 percent of these are in the cervical lymph nodes.
 Though the nasopharyngeal region surrounded by the Waldeyer’s ring is a
potential site of lymphoma, actual involvementof the sinonasal cavity is
rare.
 Lymphomas arising in the nose and PNS are of the non-Hodgkin’s type and
are seen in cases of disseminated lymphoma.
 Lesions may be mistaken for sinusitis, polyposis and granulomatous
processes.
 On CT and MR - bulky masses which show moderate enhancement.
 The osseous changes include remodeling, expansion, erosion and
infiltration of the sinus walls.
 Primary lymphoma of the paranasal sinus is uncommon.

70. MALIGNANT TUMOURS
 Plain radiographs are no longer recommended for screening for sinonasal
malignancy
 Cross-sectional imaging is required to stage these tumours in order to visualise
the extent of tumour beyond the sinuses.
 The areas of particular concern are the intraorbital cavity, pterygomaxillary
fossa, pterygopalatine fossa, infratemporal region and intracranial extension
 CT acquisition is much faster with helical and multislice scanners , is sensitive
to bone destruction and is more readily available.
 Gadolinium-enhanced MRI is better than CT for the detection of intracranial and
perineural tumour extension.
 Nodal disease may be assessed by either CT or MRI.
 Intravenous contrast enhancement allows identification of rim enhancement
and central necrosis, which is often seen in squamous cell carcinoma.
 Extracapsular spread of nodal disease is better assessed by CT than MRI.

71.  Ideally scans should include the first and second oral draining
nodes.
 Tumours involving the maxillary antrum drain initially to the
retropharyngeal nodes but level 2 (upper internal jugular) and
level I (submandibular) groups may be involved and these
should therefore be included within the scan.
 Collimation should be 5 mm or less.
 Direct coronal and axial scans should be obtained with both
bone and soft-tissue algorithm.
 On MRI a slice thickness of 4 mm or less should be used.
 Sagittal T1-weighted fatsaturated scans after gadolinium
enhancement may also be useful in assessing perineural and
intracranial extension.

74.  Squamous cell carcinomas show little contrast enhancement.
 However, contrast administration is necessitated in CT evaluation of
these tumors because it can help to differentiate
(1) Fluid from areas of necrosis
(2) involvement of normal structures from tumors especially in the orbit
(3) and to delineate intracranial extent of the tumor
 Limitations of CT scan include:
1. Inability to distinguish between inspissated and retained secretions
from tumors
2. Detect involvement of the periorbital structures especially the lamina
papyracea and the adjacent structures
3. To differentiate soft tissues involvement by tumors versus swelling
due to edema.
 On MRI inflammatory tissue and retained secretions can be
differentiated with some degree of confidence from tumors as the latter
have a higher water content and thus appear to be of high intensity
on T2WI and low intensity on T1WI

75. Coronal MRI images showing mass to be isointense on T2WI which enhances on post
contrast images (black arrow).
MR show extensive lesion with aggressive behavior infiltrating into the right
orbit, frontal sinuses and frontal bone diploe.
Also seen are intensely bright maxillary sinuses (short white arrow) on T2WI which
does not enhance suggestive of postobstructive changes.
Note normal thin mucosal enhancement of maxillary sinuses (long white arrow)

76.  These tumours often present at an advanced stage.
 The commonest tumour is squamous cell carcinoma, which accounts for
80% of all sinus malignancies.
 Approximately 50-65% arise in the maxillary sinuses,10-25% in the
ethmoid sinuses and 15-30% in the nasal cavity.
 Small tumours will mimic the appearances of chronic sinusitis and nasal
polyposis, thus many patients will be diagnosed at a late stage of their
disease.

 The Primary tumour shows little if any enhancement on CT following
intravenous contrast.
 On MRI, the tumours are of intermediate T, signal intensity and slightly
higher signal intensity on T,-weighted images.
 Larger tumours may have areas of necrosis and haemorrhage
altering the signal intensities within them.
 They also enhance slightly following intravenous gadolinium.

77. SQUAMOUS CELL CARCINOMA OF THE RIGHT MAXILLARY SINUS.
Noncontrast CT scan shows soft tissue mass of intermediate attenuation with
central necrosis filling the right antrum.
The lesion extends beyond the bony walls of the sinus, bone window setting show
extensive lytic destruction of the walls

78.  Intestinal-type adenocarcinomas of the sinonasal cavities are
especially common in individuals with a previous exposure to
hardwood dust
 The histology of the high-grade tumours resemble colonic and gastric
carcinomas.
 In these patients metastatic disease from gastrointestinal primaries
should be ruled out before making the diagnosis, but this is a rare
occurrence.

79. MALIGNANT MELANOMAS
 Occur more commonly in the sinonasal cavities.
 When they do occur, involvement of the nose is more common than the
sinus.
 Local recurrence or metastatic disease within the first year is seen in up
to 65% of patients, metastases affecting the lungs, nodes, brain,
adrenal glands, liver and skin.
 These tumours enhance more avidly than squamous cell carcinomas
on postcontrast scans.
 Some lesions willexhibit high signal intensities on T,-weighted
sequences owing to the presence of haemorrhage and/or melanin.

80. OLFACTORY NEUROBLASTOMA
 Arises from the olfactory epithelium of the nasal cavity and is a tumour of
neural crest origin.
 Epistaxis and nasal obstruction
 The prognosis is related to the extent of disease at presentation.
 These lesions are hypointense to brain on T,-weighted images and
 hypertense to brain on T2 -weighted images.
 Coronal and sagittal scans are usual to determine the relationship of the
tumour to the cribriform plate and intracranial extension.
 The tumours enhance with intravenous contrast on both CT and MRI.
 Metastatic disease is seen in up to 38% of patients, with involvement of
cervical lymph nodes, parotid glands, skin, lung, liver, eye, spinal cord
and spinal

81. Olfactory neuroblastoma: Axial and coronal contrast enhanced CT section
showing a uniformly enhanced mass in the right nasal cavity extending from
the superior nasal fossa upto the inferior turbinate, the thinned out nasal
septum bulges to the left. There is erosion of the right fovea ethmoidalis and
the cribriform plate