HRCT- Technical aspect , normal lung anatomy and HRCT finding of lung disease

1. TECHNICAL ASPECT OF HRCT; NORMAL
LUNG ANATOMY & HRCT FINDINGS OF
LUNG DISEASE
Presenter : Dr. Sarbesh Tiwari
PGT Radiodiagnosis
Assam Medical College
Dibrugarh
1

2. HRCT ------ MEANING
o It is often used for anything and everything to do
with “high resolution”.
o Resolution : Means ability to resolve small object
that are close together ,as separate form.
Actual meaning
o A scan performed using high- spatial frequency
algorithm to accentuate the contrast between
tissue of widely differing densities, eg.,
- air & vessels (lung)
- air & bone (temporal & paranasal sinus)
2

3. INTRODUCTION
• HRCT -- Use of thin section CT images (0.625 to 2 mm slice
thickness) often with a high-spatial-frequency
reconstruction algorithm to detect and characterize
disease affecting the pulmonary parenchyma and airways.
• Superior to chest radiography for detection of lung
disease, points a specific diagnosis and helps in
identification of reversible disease.
3

4. HISTORY
• 1982– The term HRCT was first used by TODO et. Al
• 1985 – Nakata et.al and Naidich et.al published first
report on HRCT
Since then has been an important tool in
pulmonary medicine
• Recent development of MDCT scanner capable of
volumetric high resolution scanning has improved the
investigation
4

5. TECHNICAL ASPECT
Parameters
o Slice thickness
o Kvp
o mAs
o Scan time
o FoV
o Interslice gap (collimation)
o Filming.
5

6. SLICE THICKNESS
• Thin sections 0.5 – 1.5 mm is essential for optimal spatial
resolution
• Thicker slices are prone for volume averaging and reduces
ability to resolve smaller structure
• Better for delineation of bronchi, wall thickness and
diameter
6

7. 7

8. Reconstruction Algorithm
• Denotes the frequency at which the acquired scan data are
recorded when creating the image.
• Using a high-resolution algorithm is critical element in
performing HRCT.
• High spatial frequency or sharp algorithm -- bone algorithm
is used which reduces image smoothing and better depicts
normal and abnormal parenchymal interface.
8

9. 9
High resolution algorithm Standard algorithm

10. Kilovolts (Peak), Milliamperes, and Scan Time
• In HRCT image, noise is more apparent than
standard CT.
• Noise – 1/√ mAs X Kvp X scan time
• As increasing scan time is not feasible, mAs and
Kvp are altered to reduce noise
• Noise decreases with increase in Kvp and mAs.
10

11. • For routine technique –
Kvp -- 120-140
mAs -- 200- 300
• Increased patient and chest wall thickness are associated
with increase image noise, may be reduced by increasing
mAs and Kvp
• Scan Time : As low as possible (1-2 sec) to minimize
motion artifact.
11

12. WINDOW SETTINGS
Lung window
• Window level setting ranging from – 600 to – 700 HU and
window widths of 1000 to 1500 HU are appropriate for a
routine lung window.
Soft tissue window
• Window level/width setting of 40-50/ 350-450 HU are best for
evaluation of the mediastinum, hila, and pleura.
12

13. LOW DOSE HRCT
• Low dose HRCT uses Kvp of 120- 140 and mA of 30-20 at 2
sec scan time.
• Equivalent to conventional HRCT in 97 % of cases
• Disadvantage : Fails to identify GGO in few cases and have
more prominent streak artifact.
• Not recommended for initial evaluation of patients with lung
disease.
• Indicated in following up patients with a known lung
abnormality or in screening large populations at risk for lung
ds.
13

14. Matrix size, Field of View, and Target
reconstruction
• Matrix size : Largest available matrix s/b used – 512 x 512
• Field of view : smallest FOV that will encompass the patient
is used as it will reduce the pixel size. (commonly 35 to 40)
• Retrospectively targeting image reconstruction to a single
lung instead of the entire thorax significantly reduces the
FOV and image pixel size, and thus increases spatial
resolution.
14

15. 15

16. • INTERSLICE GAP – varies from examination to
examination, but is usually 10- 20 mm
• INSPIRATORY LEVEL : Routine HRCT is obtained in
suspended full inspiration, which
 optimizes contrast between normal structures,
various abnormalities and normal aerated lung
parenchyma; and
 reduces transient atelectasis, a finding that may
mimic or obscure significant abnormalities.
• EXPIRATORY SCAN : valuable in obstructive lung disease
or airway abnormality
16

17. Patient Position and the Use of
Prone Scanning
• Supine adequate in most instances.
• Prone for diagnosing subtle lung abnormalities.
e.g., asbestosis, suspected early lung fibrosis
• Prone scan is useful in differentiating dependent
lung atelectasis from early lung fibrosis
17

18. Axial CT image shows opacity in the posterior part of the lung which could represent
dependent opacity or pulmonary inflammation. The prone images shows complete
resolution of the opacity suggesting dependent atelectasis.
18

19. Persistent opacity in the posterior lung in a
patient with pulmonary fibrosis.
19

20. TECHNIQUE OF SCAN ACQUISITION:
1. Spaced axial scans :
• Obtained at 1cm intervals from lung apices to
bases. In this manner, HRCT is intended to
―sample‖ lung anatomy
• It is assumed that the findings seen at the levels
scanned will be representative of what is present
throughout the lungs
• Results in low radiation dose as the individual
scans are widely placed
20

21. 2. Volumetric HRCT -
• MDCT scanner are capable of rapid scanning and thin slice
acquisition.
Advantages :
1. Viewing of contagious slice for better delineation of lung
abnormality
2. Complete imaging of lung and thorax
3. Reconstruction of scan data in any plane using MIPs or
MinIPs.
4. diagnosis of other lung abnormalities
Disadvantage : greater radiation dose. It delivers 3-5 times
greater radiation. 21

22. Multidetector Helical HRCT
• Multidetector CT is equipped with a multiple row detector
array
• Multiple images are acquired due to presence of multiple
detectors
• Advantages : - shorter acquisition times and retrospective
creation of both thinner and thicker sections from the same
raw data
• Acquisition time is so short that whole-lung HRCT can be
performed in one breath-hold.
22

23. Which is better HRCT or MD- HRCT
• Various study shows the image quality of axial HRCT with
multi-detector CT is equal to that with conventional single-
detector CT.
• HRCT performed with spaced axial images results in
low radiation dose as compared with MD-HRCT.
• Increased table speed may increase the volume-
averaging artifact and may result in indistinctness of
subtle pulmonary abnormalities.
• MDCT provides for better reconstruction in Z axis
23

24. Radiation dose
• Annual background radiation ----- --- 2.5 mSv
• PA CHEST Radiograph ----- ----- ----- 0.05 mSv
• Spaced axial HRCT (10mm space) ----- 0.7 mSv ( 14 X ray)
• Spaced axial HRCT (20 mm space) ------ 0.35 mSv ( 7 X ray)
• Low Dose Spaced axial HRCT -------- 0.02 mSV
• MD-HRCT ---- ------- 4 - 7 msv ( 60-80 x ray)
Combining HRCT scan at 20 mm interval with low mAs
scan (40 mAs) would result in radiation comparable to
conventional X ray. 24

25. HRCT ARTIFACT
• Streak Artefacts :
 Fine, linear, or netlike opacities
 Radiate from the edges of sharply
marginated , high-contrast structures
such as bronchial walls, ribs, or vertebral
bodies.
 More evident on low mA
 Mechanisms: beam hardening, photon
starvation, and aliasing.
25

26. Motion-related artifacts
• Pulsation / Star artefacts
• Doubling artefacts.
• Stair-step artefacts in sag/coro
reconstruction.
26

27. MODIFICATION OF SCAN PROTOCOL
 Scan protocol can be modified in relation to disease or
patients comfort.
 If a disease has basal predominance, it may be wise to
begin scanning near the diaphragm and proceed cephalic .
 Caudad for disease with an upper-lobe predominance
(e.g., sarcoidosis)
 An alternative approach - cephalad in all patients.
27

28. 28

29. PART 2
REVIEW OF ANATOMY
29

30. LUNG ANATOMY
• Right lung is divided by
major and minor fissure into
3 lobes and 10 broncho-
pulmonary segments
• Left lung is divided by major
fissure into 2 lobes with a
lingular lobe and 8
bronchopulmonary 1.1 kg
segments
30

31. 31

32. There are approximately 23
generation of dichotomous branching
From trachea to the alveolar sac
HRCT can identify upto 8th order
central bronchioles
32

33. TRACHEAL ANATOMY
• 10-12 cm in length, from C6 level to upper border of D5.
• Extrathoracic (2-4cm) and Intrathoracic(6-9 cm
beyond manubrium)
• In men, tracheal diameter – 25-27 mm
women – 21- 23 mm
• The posterior portion of the tracheal wall is a thin
fibromuscular membrane----- allows for oesophageal
expansion.
33

34. BRONCHIAL ANATOMY
• Approximately 23 generations of branches from the
trachea to the alveoli.
• Bronchi with a wall thickness of less than 300 um is not
visible on CT or HRCT.
• As a consequence, normal bronchi less than 2 mm in
diameter or closer than 2 cm from pleural surfaces
equivalent to seventh to ninth order airways are generally
below the resolution even of high-resolution CT
34

35. BRONCHUS
BLOOD SUPPLY Bronchial Arteries—
2 on left side i.e. superior and inferior
1 on right side
Left arises from thoracic aorta
Right from either thoracic aorta, sup. left bronchial or right 3rd
intercostal artery
VENOUS DRAINAGE
on right- azygous vein
on left- left superior intercostal or accessory
hemiazygous vein
• NERVE SUPPLY Pulmonary plexus at hilum (vagus and
sympathetic)
35

36. BRONCHOARTERIAL RATIO (B/A)
• Internal diameter of both bronchus and accompanying
arterial diameter calculated and ratio measured.
• Normal ratio is 0.65-0.70
• B/A ratio >1 indicates bronchiectasis.
NB:: B/A ratio increases with age and may exceed 1 in
normal patients > 40 years.
36

37. SECONDARY PULMONARY
LOBULE
• Smallest lung unit that is
surrounded by
connective tissue septa
(Miller)
• The basic anatomic unit
• Irregular polyhedral in
shape.
• Measures 1 to 2.5 cm
37

38. Anatomy of the Secondary Lobule and Its
Components
1. Interlobular septa
and contiguous
subpleural
interstitium,
2. Centrilobular
structures, and
3. Lobular parenchyma
and acini.
38

39. Interlobular septa and contiguous subpleural interstitium
The secondary pulmonary lobule is marginated by septa which
extends from the pleural surface.
They measure 0.1 mm in thickness.
They are less well defined in central lung
Lobular core :
The secondary lobule is supplied by arteries and bronchioles that
measures approximately 1 mm in diameter.
It consists of functioning lung parenchyma namely the alveoli,
alveolar duct and vessels. The parenchyma is supported by
network of central and peripheral fibers of interstitium.
39

40. PULMONARY ACINUS
 Portion of lung parenchyma
supplied by a single respiratory
Bronchiole.
 Size is 7 to 8 mm in adults
 3 to 24 acini = Sec Pul. Lobule
Primary Lobule: Lung
parenchyma associated with a
single Alveolar duct.
4-5 Primary Lobules  Acinus
40

42. A group of terminal bronchioles

43. Accompanying pulmonary arterioles

44. Surrounded by lymph vessels

45. Pulmonary veins

46. Pulmonary lymphatics

47. Connective Tissue Stroma

48. LUNG INTERSTITUM
Lung
interstitium
Axiel fiber Peripheral fiber
system sysem
Peribronchovascular Centrilobular Subpleural Interlobular
interstitium interstitium interstitium septa
48

49. • The peribronchovascular interstitum invests the bronchi
and pulmonary artery in the perihilar region.
• The centrilobular interstitium are associated with small
centrilobular bronchioles and arteries
• The subpleural interstitium is located beneath the visceral
pleura; envelops the lung into fibrous sac and sends
connective tissue septa into lung parenchyma.
• Interlobular septa constitute the septas arising from the
subpleural interstitium.
49

50. The normal pulmonary vein
branches are seen marginating
pulmonary lobules. The centrilobular
artery branches are visible as a
rounded dot
50

51. Anatomy of pleural surfaces and chest wall.
51

52. NORMAL LUNG
ATTENUATION
• Normal lung attenuation : –700 to – 900 HU
• Attenuation gradient : densest at dependent region of
lung as a result of regional difference in blood and gas
density due to gravity
Difference in attenuation of anterior and posterior lung
ranges from 50 – 100 HU
• In children, lung attenuation is greater than adults.
52

53. NORMAL EXPIRATORY HRCT
• Performed to detect air trapping in small airway obstruction
• Attenuation increases with expiration (ranges from 100 to
130 HU)
• 60 % of normal individual shows air trapping in the superior
segment of lower lobe and involving single lobule, normal
variant.
53

54. PART 3
PATTERN OF LUNG DISEASE
IN HRCT
54

55. STRUCTURED APPROACH
Q.1. What is the dominant HR-pattern ?
Q.2. Where is it located within the secondary lobule
(centrilobular, Perilymphatic or random) ?
Q.3. Is there an upper versus lower zone or a central
versus peripheral predominance ?
Q.4. Are there additional findings (pleural
fluid, lymphadenopathy, traction bronchiectasis) ?
55

56. LINEAR AND
RETICULAR
OPACITIES
INCREASED NODULES AND
LUNG NODULAR
OPACITIES
ATTENUATION
PARENCHYMAL consolidation
OPACIFICATION
Ground glass
HRCT
PATTERN CYSTIC LESIONS,
EMPHYSEMA, AND
BRONCHIEACTASIS
MOSAIC
ATTENUATION AND
PERFUSION
DECREASED
LUNG
ATTENUATION AIR TRAPPING ON
EXPIRATORY
SCANS
56

57. LINEAR AND RETICULAR OPACITIES
• Represents
thickening of
interstitial fibers of
lung by
- fluid or
- fibrous tissue or
- infiltration by cells
57

58. Interface sign
Irregular interfaces between the
aerated lung parenchyma and
bronchi, vessels, or visceral
pleural surfaces.
Represent thickened interlobular
septa, intralobular lines, or
irregular scars.
Nonspecific.
Common in patients with an interstitial abnormality, fibrotic
lung disease.
58

59. Peribronchovascular Interstitial Thickening
PBIT
Irregular
Smooth
Nodular
Venous, lymphatic
or infiltrative lymphatic or
disease infiltrative
diseases
Pulmonary
edema/ Due to
hemorrhage adjacent
lung fibrosis
Sarcoidosis
Lymphoma /
leukemia
Lymphangitic Sarcoidosis,
Lymphangitic spread of silicosis, TB
spread of carcinoma and talcosis 59
carcinoma

60. sarcoidosis
UNILATERAL LYMPHANGITIC SPREAD
OF CARCINOMA
60

61. INTERLOBULAR SEPTAL THICKENING
• Normally, only a few septa seen
• On HRCT, if numerous
interlobular septas are seen, it
almost always indicate
abnormality.
• Septal thickening d/t -interstitial
fluid, cellular infiltration or fibrosis.
• The thickened interstitium outline
the secondary pulmonary lobules
and are perpendicular to the
pleura.
• D/D are similar to that of PBIT. 61

62. Smooth Septal thickening
Septal thickening and ground-glass opacity with a
gravitational distribution in a patient with cardiogenic
pulmonary edema.
62

63. Nodular Septal thickening
Lymphangitic carcinomatosis :
show diffuse smooth and nodular
septal thickening. Sarcoidosis :
right lung base shows interlobular
septal thickening associated with
several septal nodules giving
beaded appearance
Focal septal thickening in
lymphangitic carcinomatosis 63

64. Intralobular interstitial thickening (Intralobular lines)
• Results in a fine reticular
pattern on HRCT, with the
visible lines separated by a
few millimeters
• Fine lace- or netlike
appearance
• Causes : Pulmonary fibrosis
Asbestosis
Chronic Eosinophilic
pneumonitis.
64

65. PARENCHYMAL BANDS
• Non tapering , reticular opacity usually
1 to 3 mm in thickness and from 2 to 5
cm in length.
• Is often peripheral and generally
contracts the pleural surface
• D/D : 1. Asbestosis
2. Sarcoidosis
3. Silicosis/ coal worker
pneumoconiosis
4. Tuberculosis with associated
scarring.
65

66. Subpleural Interstitial Thickening
• Mimic thickening of fissure.
• DD similar to that of interlobular
septal thickening.
• more common than septal
thickening in IPF or UIP of any
cause.
66

67. HONEYCOMBING
• Defined as - small cystic spaces with irregularly thickened
walls composed of fibrous tissue.
• Predominate in the peripheral and subpleural lung regions
• Subpleural honeycomb cysts typically occur in several
contiguous layers. D/D- paraseptal emphysema in which
subpleural cysts usually occur in a single layer.
• Indicates the presence of ―END stage‖ disease regardless of
the cause.
67

68. Causes
Lower lobe predominance :
1. UIP or interstitial fibrosis
2. Connective tissue disorders
3. Hypersensitivity pneumonitis
4. Asbestosis
5. NSIP (rare)
Upper lobe predominance :
1. End stage sarcodosis
2. Radiation
3. Hypersensitivity Pneumonitis
4. End stage ARDS
68

69. Nodules and Nodular Opacities
Size, Distribution, Appearance
Small Nodules: <10 mm Miliary - <3 mm
Size
Large Nodules: >10 mm Masses - >3 cms
Interstitial opacity:
 Well-defined, homogenous,
Soft-tissue density
Obscures the edges of vessels or adjacent structure
Appearance
Air space:
Ill-defined, inhomogeneous.
Less dense than adjacent vessel – GGO
small nodule is difficult to identify 69

70. Interstitial nodules Air space opacity
Miliary tuberculosis
in a lung transplant patient with
bronchopneumonia
70
sarcoidosis

71. RANDOM: no consistent relationship to any structures
Distribution CENTRILOBULAR: related to centrilobular structures
PERILYMPHATIC: corresponds to distribution of lymphatics
71

72. Perilymphatic distribution
Nodules in relation to pulmonary lymphatics at
# perihilar peribronchovascular interstitium,
# interlobular septa,
# subpleural regions, and
# centrilobular interstitium.
72

73. Perilymphatic nodules: D/D
 Sarcoidosis
 Lymphangitic carcinomatosis
 Lymphocytic interstitial
pneumonia (LIP)
 Lymphoproliferative disorders
 Amyloidosis
73

74. Centrilobular nodules
• Distributed primarily within the
centre of the secondary
pulmonary lobule
• Reflect the presence of either
interstitial or airspace
abnormalities
• Dense or ground-glass opacity
• Subpleural lung is typically
spared- distinguishes from
diffuse random nodules.
74

75. Tree-in-bud
 Centrilobular nodules m/b further characterized by presence
or absence of ‗‗tree-in-bud.‘‘
 Tree-in-bud -- Impaction of centrilobular bronchus with
mucous, pus, or fluid, resulting in dilation of the
bronchus, with associated peribronchiolar inflammation .
 Dilated, impacted bronchi produce Y- or V-shaped structures
 This finding is almost always seen with pulmonary infections.
75

76. 76

77. Centrilobular nodules with or without tree-in-bud opacity: D/D :
With tree-in-bud opacity Without tree-in-bud opacity
 Bacterial pneumonia  All causes of centrilobular
 Typical and atypical nodules with tree-in-bud
mycobacteria infections opacity
 Bronchiolitis  Hypersensitivity
 Diffuse panbronchiolitis pneumonitis
 Aspiration  Respiratory bronchiolitis
 Allergic bronchopulmonary  Cryptogenic organizing
aspergillosis pneumonia
 Cystic fibrosis  Pneumoconioses
 Endobronchial-neoplasms  Langerhans’ cell
(particularly histiocytosis
 Bronchioloalveolar  Pulmonary edema
carcinoma)  Vasculitis
 Pulmonary hypertension 77

78. Random nodules
 Random nodules – No definable distribution
 Are usually distributed uniformly throughout the lung parenchyma
in a bilaterally symmetric distribution.
Random nodules: Miliary
tuberculosis.
Axial HRCT image shows
multiple nodules scattered uniformly
throughout the lung parenchyma.
78

79. Random nodules: D/D
1. Haematogenous metastases
2. Miliary tuberculosis
3. Miliary fungal infection
4. Disseminated viral infection
5. Silicosis or coal-worker‘s pneumoconiosis
6. Langerhans‘ cell histiocytosis
79

80. 80

81. Parenchymal Opacification
Ground-glass
opacity
Consolidation
Lung calcification &
high attenuation
opacities.
81

82. GROUND GLASS OPACITIES
• Hazy increased attenuation of lung,
with preservation of bronchial and
vascular margins
• Pathology : it is caused by
# partial filling of air spaces,
# interstitial thickening,
# partial collapse of alveoli,
# normal expiration, or
# increased capillary blood
volume
• D/t volume averaging of morphological
abnormality too small to be resolved
82
by HRCT

83. IMPORTANCE OF GGO
• Can represent - microscopic interstitial disease
(alveolar interstitium)
- microscopic alveolar space disease
- combination of both
 In the absence of fibrosis, mostly indicates the presence of
an ongoing, active, potentially treatable process
 NB :: Ground Glass opacity should be diagnosed only on
scans obtained with thin sections : with thicker sections
volume averaging is more - leading to spurious
GGO, regardless of the nature of abnormality
83

84. DIFFERNTIAL DIAGNOSIS : GGO
84

85. The location of the abnormalities in ground glass pattern
can be helpful:
• Upper zone predominance:
Respiratory bronchiolitis
PCP.
• Lower zone predominance: UIP, NSIP, DIP.
• Centrilobular distribution:
Hypersensitivity pneumonitis,
Respiratory bronchiolitis
85

86. GGO with few cystic and reticular
lesion in HIV + ve patient -- PCP
Combination of GGO with
fibrosis and tractional
bronchiectasis-- NSIP
86

87. CRAZY PAVING PATTERN
• It is scattered or diffuse ground-glass attenuation with
superimposed interlobular septal thickening and intralobular
lines.
• Causes:
87

88. Combination of ground glass
opacity and septal thickening
: Alveolar proteinosis.
88

89. CONSOLIDATION
• Consolidation is defined as increased attenuation, which results in
obscuration of the underlying vasculature, usually producing air
bronchogram.
• The presence of consolidation implies that the air within affected
alveoli has been replaced by another substance, such as
blood, pus, oedema, or cells.
• When consolidation is evident on a chest radiograph, HRCT does
not usually provide additional diagnostically useful information.
89

90. D/D on the basis of presentation
Acute consolidation is seen in:
- Pneumonias (bacterial, mycoplasma , PCP)
- Pulmonary edema due to heart failure or ARDS
- Hemorrhage
- Acute eosinophilic pneumonia
Chronic consolidation is seen in:
- Organizing Pneumonia
- Chronic eosinophilic pneumonia
- Fibrosis in UIP and NSIP
- Bronchoalveolar carcinoma or lymphoma
90

91. Patchy ground-glass opacity,
Peripheral consolidations with
consolidation, and nodule mainly with
upper lobe predominance (photo
peribronchovascular distribution with
negative of pulmonary edema)
reversed halo signs (central ground-
glass opacity and surrounding air-space
consolidation)
91

92. Lung calcification & high attenuation opacities
Multifocal lung calcification
• Infectious granulomatous ds - TB, histoplasmosis, and
varicella, pneumonia;
• Sarcoidosis , silicosis, Amyloidosis
• Fat embolism associated with ARDS
Diffuse & dense lung calcification
• Metastatic calcification,
• Disseminated pulmonary ossification, or
• Alveolar microlithiasis
92

93. High attenuation opacity
• Talcosis asso with fibrotic mass,
• inhalation of metals (tin/barium)
Small focal areas of increased attenuation
• injection and embolized radiodense materials such as
mercury or acrylic cement
Diffuse, increased lung attn in absence of calcification
• amiodarone lung toxicity or
• embolization of iodinated oil after chemoembolization
93

94. 94

95. HRCT findings manifesting as decreased lung
opacity
Lung Cysts,
Emphysema,
and
Bronchiectasis
95

96. Lung cysts
• Thin walled (less than 3mm) , well defined and
circumscribed air containing lesions
• They are lined by cellular epithelium, usually fibrous or
epithelial in nature.
• Common cause are : 1. Lymphangiomyomatosis
2. Langerhans Histiocytosis
3. Lymphoid interstitial pneumonia
They need to be differentiated from emphysematous bullae,
blebs and pneumatocele.
96

97. Axial HRCT image through the
upper lobes shows multiple bilateral
uniform, thin-walled cysts.
Axial HRCT image through the upper
lobes shows multiple bilateral bizarre-
shaped cysts and small centrilobular
nodules in a smoker with Langerhans’
cell histiocytosis. 97

98. BRONCHIEACTASIS
Bronchiectasis is defined as localized, irreversible dilation of
the bronchial tree.
HRCT findings of the bronchiectasis include
# Bronchial dilatation
# Lack of bronchial tapering
# Visualization of peripheral airways.
98

99.  BRONCHIAL DILATATION
# The broncho-arterial ratio (internal diameter of the
bronchus /pulmonary artery) exceeds 1.
# In cross section it appears as ―Signet Ring
appearance‖
 LACK OF BRONCHIAL TAPERING
# The earliest sign of cylindrical bronchiectasis
# One indication is lack of change in the size of an airway
over 2 cm after branching.
 VISUALIZATION OF PERIPHERAL AIRWAYS
# Visualization of an airway within 1 cm of the costal
pleura is abnormal and indicates potential bronchiectasis
99

100. Coned axial HRCT image shows bronchial
dilation with lack of tapering . Bronchial
morphology is consistent with varicose
bronchiectasis. 100

101. A NUMBER OF ANCILLARY FINDINGS ARE ALSO
RECOGNIZED:
# Bronchial wall thickening : normally wall of bronchus
should be less than half the width of the accompanying
pulmonary artery branch.
# Mucoid impaction
# Air trapping and mosaic perfusion
Extensive, bilateral mucoid impaction
Mosaic perfusion caused by large and small
airway obstruction.
Small centrilobular nodules are visible in the
right lower lobe
101

102. Types
1. CYLINDRICAL BRONCHIECTASIS
# mildest form of this disease,
# thick-walled bronchi that extend
into the lung periphery and fail to
show normal tapering
2. VARICOSE BRONCHIECTASIS
# beaded appearance of bronchial
walls - dilated bronchi with areas of
relative narrowing
# string of pearls.
# Traction bronchiectasis often
appears varicose. 102

103. 3. CYSTIC BRONCHIECTASIS :
# Group or cluster of air-filled
cysts,
# cysts can also be fluid
filled, giving the appearance of a
cluster of grapes.
4.TRACTION BRONCHIECTASIS :
# Defined as dilatation of
intralobular bronchioles because
of surrounding fibrosis
# due to fibrotic lung diseases
103

104. Differential diagnosis
1. Infective causes : specially childhood pneumonia,
pertusis, measles, tuberculosis
2. Non- infective causes : Bronchopulmonary
aspergillosis, inhalation of toxic fumes
3. Connective tissue disorder : Ehlers-Danlos Synd,
Marfan synd , tracheobronchomeglay
4. Ciliary diskinesia : Cystic fibrosis, Kartangener
synd, agammaglobulinemia .
5. Tractional bronchiectasis in interstitial fibrosis.
104

105. EMPHYSEMA
• Permanent, abnormal enlargement of air spaces distal
to the terminal bronchiole and accompanied by the
destruction of the walls of the involved air spaces.
105

106. Centrilobular (proximal or centriacinar)
emphysema
• Found most commonly in the upper lobes
• Manifests as multiple small areas of low attenuation without a
perceptible wall, producing a punched-out appearance.
• Often the centrilobular artery is visible within the centre of these
lucencies.
106

107. PANLOBULAR EMPHYSEMA
• Affects the entire secondary pulmonary lobule and is more
pronounced in the lower zones
• Complete destruction of the entire pulmonary lobule.
• Results in an overall decrease in lung attenuation and a
reduction in size of pulmonary vessels
107

108. Paraseptal (distal acinar) emphysema
• Affects the peripheral parts of the secondary pulmonary
lobule
• Produces subpleural lucencies.
108

109. Cicatricial Emphysema/ irregular air space
enlargement
• previously known as irregular or cicatricial emphysema
• can be seen in association with fibrosis
• with silicosis and progressive massive fibrosis or
sarcoidosis
BULLOUS EMPHYSEMA :
• Does not represent a specific histological abnormality
• Emphysema characterized by large bullae
• Often associated with centrilobular and paraseptal
emphysema
109

110. Paraseptal Emphysema vs Honeycombing
Paraseptal emphysema Honeycomb cysts
occur in a single layer at the may occur in several layers in
pleural surface the subpleural lung
predominate in the upper lobes predominate at the lung bases
unassociated with significant Asso with other findings of
fibrosis fibrosis.
Associated with other findings of Absent
emphysema
110

111. Bullae
 A sharply demarcated area of emphysema ≥ 1 cm in
diameter
 a thin epithelialized wall ≤ 1 mm.
 uncommon as isolated findings, except in the lung apices
 Usually asso with evidence of extensive centrilobular or
paraseptal emphysema
 When emphysema is associated with predominant
bullae, it may be termed bullous emphysema
111

112. Pneumatocele
• Defined as a thin-walled, gas-filled space within the lung,
• Associated with acute pneumonia or hydrocarbon
aspiration.
• Often transient.
• believed to arise from lung necrosis and bronchiolar
obstruction.
• Mimics a lung cyst or bulla on HRCT and cannot be
distinguished on the basis of HRCT findings.
112

113. CAVITARY NODULE
• Thicker and more irregular walls
than lung cysts
• In diffuse lung diseases -
LCH, TB, fungal infections, and Cavitary nodules or cysts in
sarcoidosis. tracheobronchial papillomatosis.
• Also seen in rheumatoid lung
disease, septic
embolism, pneumonia, metastati
c tumor, tracheobronchial
papillomatosis, and Wegener
granulomatosis
113
fungal pneumonia

114. Mosaic attenuation & perfusion
• Lung density and attenuation depends partially on amount of
blood in lung tissue.
• The term 'mosaic attenuation' is used to describe density
differences between affected and non-affected lung areas.
• It is seen as inhomogeneous attenuation of lung parenchyma
with focal region of lucency which show smaller size of
vessels
• May be due to vascular obstruction, abnormal ventilation or
airway disease/
114

115. Mosaic attenuation due to small airway disease
# Air trapping and bronchial dilatation commonly seen.
# Areas of increased attenuation have relatively large
vessels, while areas of decreased attenuation have small
vessels.
# Causes include: Bronchiectasis, cystic fibrosis and
bronchiolitis obliterans.
Mosaic attenuation due to vascular disease
# common in patients with acute or chronic pulmonary
embolism (CPE), and
# decreased vessel size in less opaque regions is often
visible
115

116. MOSIAC PATTERN
DEPENDENT LUNG ONLY NONDEPENDENT LUNG
EXPIRATION
PRONE
POSITION
NO AIR
TRAPPING
AIR
NOT TRAPPING
RESOLVE
RESOLVE
VESSEL SIZE
PLATE GROUND
ATELECTASIS GLASS
AIRWAYS
DECREASED NORMAL DISEASE
GROUND
VASCULAR GLASS
116

117. Inhomogeneous lung
opacity: mosaic
perfusion in a patient
with bronchiectasis.
central bronchiectasis with
multifocal, bilateral
inhomogeneous lung opacity.
The vessels within the areas of
abnormally low attenuation are
smaller than their counterparts
in areas of normal lung
attenuation.
117

118. Air trapping on expiration
• Most patients with air trapping seen on expiratory scans
have inspiratory scan abnormalities, such as
bronchiectasis, mosaic perfusion, airway thickening, or
nodules suggest the proper differential diagnosis.
• Occasionally, air trapping may be the sole abnormal finding
on an HRCT study.
• The differential diagnosis include ---
bronchiolitis obliterans; asthma; chronic
bronchitis; and hypersensitivity pneumonitis
118

119. Air trapping on expiratory imaging
in the absence of inspiratory scan
findings in a patient with
bronchiolitis obliterans.
(A) Axial inspiratory image through
the lower lobes shows no clear
evidence of inhomogeneous lung
opacity.
(B) Axial expiratory image shows
abnormal low attenuation
(arrows) caused by air trapping,
representing failure of the
expected increase in lung
attenuation that should normally
occur with expiratory imaging.
119

120. Head cheese sign
• It refers to mixed densities which includes presence of-
# consolidation
# ground glass opacities
# normal lung
# Mosaic perfusion
• Signifies mixed infiltrative and obstructive disease
• Common cause are : Hypersensitive pneumonitis
Sarcoidosis
DIP
120

121. Axial HRCT image in a patient with
hypersensitivity pneumonitis shows a
combination of ground-glass opacity, normal
lung, and mosaic perfusion (arrow) on the same
inspiratory image.
121

122. Distribution within the lung
Upper lung zone preference is seen in:
1.Inhaled particles: pneumoconiosis (silica or
coal)
2.Smoking related diseases (centrilobular
emphysema
3. Respiratory bronchiolitis (RB-ILD)
4.Langerhans cell histiocytosis
5.Hypersensitivity pneumonitis
6.Sarcoidosis
Lower zone preference is seen in:
1. UIP
2. Aspiration
3. Pulmonary edema 122

123. Central vs peripheral zone
• Central Zone Peripheral zone
1. Sarcoidosis 1. COP
2. Cardiogenic pulmonary 2. Ch Eosinophilic Pneumonia
edema 3. UIP
3. Bronchitis 4. Hematogenous mets
123

124. Additional findings
Pleural effusion is seen in:
• Pulmonary edema
• Lymphangitic spread of carcinoma - often unilateral
• Tuberculosis
• Lymphangiomyomatosis (LAM)
• Asbestosis
124

125. Hilar and mediastinal lymphadenopathy
# In sarcoidosis the common pattern is right paratracheal
and bilateral hilar adenopathy ('1-2-3-sign').
# In lung carcinoma and lymphangitic carcinomatosis
adenopathy is usually unilateral.
#'Eggshell calcification' in lymph nodes occurs in ----
Silicosis and coal-worker's pneumoconiosis and is
sometimes seen in sarcoidosis, post irradiation Hodgkin
disease, blastomycosis and scleroderma .
125

126. Conclusion
 • A thorough knowledge of the basic anatomy is of utmost
importance.
 When attempting to reach a diagnosis or differential
diagnosis of lung disease using HRCT, the overall
distribution of pulmonary abnormalities should be
considered along with their morphology, HRCT appearance,
and distribution relative to lobular structures.
 Correlation of the radiological findings with patients clinical
and laboratory findings to reach a likely diagnosis
126

127. 127