The document discusses the anatomy and patterns seen on HRCT in interstitial lung disease. It describes the three subdivisions of the lung interstitium: bronchovascular, parenchymal, and subpleural. Common patterns seen on HRCT are then summarized, including linear and reticular opacities, nodules, increased lung opacity, and abnormalities associated with decreased lung opacity such as cysts and emphysema. Differential diagnoses are provided for each pattern.

1. K Mohamed Rafi

3. The interstitium of the lung is not normally visible radiographic-
ally; it becomes visible only when disease (e.g., edema, fibrosis,
tumor) increases its volume and attenuation.
The interstitial space is defined as continuum of loose
connective tissue throughout the lung composed of three
subdivisions:
(i) the bronchovascular (axial), surrounding the bronchi,
arteries, and veins from the lung root to the level of the
respiratory bronchiole
(ii) the parenchymal (acinar), situated between the alveolar and
capillary basement membranes
(iii) the subpleural, situated beneath the pleura, as well as in the
interlobular septae.
The Lung Interstitium

5. Secondary lobule
 For the purposes of the interpretation of HRCT, the
secondary lobule is most appropriately conceptualized
as having three principal parts or components:
 Interlobular septa and contiguous subpleural
interstitium
 Centrilobular structures
 Lobular parenchyma and acini

12. Lobular Anatomy and the Concept of Cortical &
Medullary Lung

14. Patterns of Interstitial Lung Disease
 Generally, HRCT findings of lung disease can be
classified into four large categories based on their
appearances. These are
 (i) linear and reticular opacities,
 (ii) nodules and nodular opacities,
 (iii) increased lung opacity, and
 (iv) abnormalities associated with decreased lung
opacity, including cystic lesions, emphysema, and
airway abnormalities.

15. Linear and reticular opacities,
Thickening of the interstitial fiber
network of the lung by fluid or fibrous
tissue, or because of interstitial
infiltration by cells or other material,
primarily results in an increase in linear
or reticular lung opacities as seen on
HRCT

16. Linear and reticular opacities,
Linear or reticular opacities may be manifested by the
 interface sign,
 peribronchovascular interstitial thickening,
 interlobular septal thickening,
 parenchymal bands,
 subpleural interstitial thickening,
 intralobular interstitial thickening,
 honeycombing,
 irregular linear opacities, &
 subpleural lines

18. Interface sign
 The presence of irregular interfaces between the
aerated lung parenchyma and bronchi, vessels, or
visceral pleural surfaces has been termed the interface
sign. The interface sign is nonspecific, and is
commonly seen in patients with an interstitial
abnormality, regardless of its cause. In the original
description of the interface sign, this finding was
visible in 89% of patients with interstitial lung disease

20. Peribronchovascular Interstitial
Thickening
 Central bronchi and pulmonary arteries are
surrounded and enveloped by a strong connective
tissue sheath, termed the peribronchovascular
interstitium, extending from the level of the
pulmonary hila into the peripheral lung. In the lung
periphery, the peribronchovascular interstitium
surrounds centrilobular arteries and bronchioles, and,
more distally, supports the alveolar ducts and alveoli
 The peribronchovascular interstitium is also termed
the axial interstitium by Weibel.

21. • Lymphangitic carcinomatosis,
lymphoma, leukemia
• Lymphoproliferative disease (e.g.,
lymphocytic interstitial pneumonia)
• sarcoid
nodular
• Pulmonary edema
• Lymphangitic
carcinomatosis
smooth
• Sarcoidosis
• Silicosis/coal worker’s
pneumoconiosis, talcosis
conglomerate
masses

23. SMOOTH

24. NODULAR

25. Peribronchovascular interstitial
thickening /bronchiectasis

26. Peribronchovascular interstitial
thickening /bronchiectasis

27. Interlobular Septal Thickening
 Thickened septa 1 to 2 cm in length may outline part
of or an entire lobule and are usually seen extending to
the pleural surface, being roughly perpendicular to the
pleura
 Lobules at the pleural surface may have a variety of
appearances, but they are often longer than they are
wide, resembling a cone or truncated cone.
 Within the central lung, thickened septa outline
lobules that are 1 to 2.5 cm in diameter and appear
polygonal, or sometimes hexagonal, in shape

29. Smooth
• Pulmonary edema
• Lymphangitic carcinomatosis, lymphoma, leukemia
irregular
• Silicosis/coal worker’s pneumoconiosis; talcosis
• Asbestos
• Hypersensitivity pneumonitis
Nodular
“beaded
• Sarcoidosis

30. SMOOTH

31. Nodular

32. Irregular

34. Differential diagnosis of intralobular
interstitial thickening

35. Crazy pavement appearance

38. Subpleural Interstitial
Thickening
 Thickening of the interlobular septa within the
peripheral lung is associated with thickening of the
subpleural interstitium
 differential diagnosis of subpleural interstitial
thickening is the same as that of interlobular septal
thickening, although subpleural interstitial thickening
is more common than septal thickening in patients
with IPF or UIP of any cause

39. Parenchymal Bands
 The term parenchymal band has been used to describe
a nontapering, reticular opacity, usually several
millimeters in thickness and from 2 to 5 cm in length,
seen in patients with atelectasis, pulmonary fibrosis,
or other causes of interstitial thickening

42. Honeycombing
 Honeycombing is defined by the presence of small air-
containing cystic spaces, generally lined by
bronchiolar epithelium and having thickened walls
composed of dense fibrous tissue. Honeycombing
indicates the presence of end-stage lung and can be
seen in many diseases leading to end-stage pulmonary
fibrosis

43. Honeycombing

45. This 50-year-old man presented with end-stage lung fibrosis
PA chest radiograph shows medium to coarse reticular
B: CT scan shows multiple small cysts (honeycombing) involving
predominantly the subpleural peripheral regions of lung. Traction
bronchiectasis, another sign of end-stage lung fibrosis.

46. Subpleural Lines
 curvilinear opacity a few millimeters or less in
thickness, less than 1 cm from the pleural surface and
paralleling the pleura, is termed a subpleural line .
 It is a nonspecific indicator of atelectasis, fibrosis, or
inflammation. It was first described in patients with
asbestosis , it was termed a subpleural curvilinear
shadow.

48. Nodular pattern
 The term nodule is defined as a rounded opacity, at
least moderately well-defined, and no more than 3 cm
in diameter
 The term small nodule is used to define a rounded
opacity smaller than 1 cm in diameter,
 whereas large nodule is used to refer to nodules 1 cm or
larger in diameter.
 Some authors have used micronodule to describe
nodules smaller than 7 mm in diameter.

49. 1.Perilymphatic Distribution
For small nodules

51. 3.Random Distribution
 Small nodules that appear randomly distributed in
relation to structures of the secondary lobule and lung
are often seen in patients with miliary tuberculosis
miliary fungal infections, and hematogenous
metastases

52. Random

53. 2.Centrilobular Distribution
 Centrilobular nodules can reflect the presence of
either interstitial or airspace abnormalities, and the
histologic correlations reported to occur in association
with centrilobular nodules vary with the disease entity
 Centrilobular nodules may be dense and of
homogeneous opacity, or of ground-glass opacity and
may range from a few millimeters to a centimeter in
size.

59. Tree in bud appearance

66. 3.Random Distribution

67. Hematogenous metastases and nodular ILD. This 45-year-old
woman presented with metastatic gastric carcinoma. The PA
chest radiograph shows a diffuse pattern of nodules, 6 to 10
mm in diameter.

68. Differential diagnosis of a nodular pattern of
interstitial lung disease
SHRIMP
Sarcoidosis
Histiocytosis (Langerhan cell
histiocytosis)
Hypersensitivity pneumonitis
Rheumatoid nodules
Infection (mycobacterial, fungal, viral)
Metastases
Microlithiasis, alveolar
Pneumoconioses (silicosis, coal
worker's, berylliosis)

69. Reticulonodular pattern
A reticulonodular pattern results from a combination
of reticular and nodular opacities.
This pattern is often difficult to distinguish from a
purely reticular or nodular pattern, and in such a case a
differential diagnosis should be developed based on
the predominant pattern.
If there is no predominant pattern, causes of both
nodular and reticular patterns should be considered.
most commonly in silicosis,sarcoidosis.

70. Increased lung opacity

72. Decreased Lung Opacity
A variety of abnormalities result in decreased lung
attenuation or air-filled cystic lesions on HRCT. These
include
 honeycombing,
 lung cysts,
 emphysema, bullae,
 pneumatoceles,
 cavitary nodules,
 bronchiectasis,
 mosaic perfusion,
 air-trapping due to airways disease

74. Honeycombing/cyst
 Honeycombing is defined by the presence of small air-
containing cystic spaces, generally lined by
bronchiolar epithelium and having thickened walls
composed of dense fibrous tissue. Honeycombing
indicates the presence of end-stage lung and can be
seen in many diseases leading to end-stage pulmonary
fibrosis

75. UIP

76. UIP

77. UIP

78. Cyst

79. Bullae
 Emphysematous bullae are well seen using HRCT. A
bulla has been defined as a
 sharply demarcated area of emphysema measuring 1
cm or more in diameter and possessing a thin
epithelialized wall that is usually no thicker than 1 mm

80. Blebs
 The term bleb is used pathologically to refer to a gas-
containing space within the visceral pleura
 Radiographically, this term is sometimes used to
describe a focal thin-walled lucency contiguous with
the pleura, usually at the lung apex.
 However, the distinction between bleb and bulla is of
little practical significance and is seldom justified. The
term bulla is preferred

87. How To Approach
a Practical
Diagnosis?

88. An acute appearance suggests pulmonary edema or
pneumonia
Rule no. 1

89. Pulmonary edema
sparing of the apices and extreme lung bases
characteristic ‘butterfly’ or ‘bat's wing’ distribution

90. Pulmonary edema
There is diffuse ground-glass opacification,
smooth thickening of multiple interlobular
septa and peribronchovascular cuffing.
Bilateral pleural effusions are also seen.

91. Reticulonodular lower lung predominant
distribution with decreased lung volumes
suggests: (APC)
1. Asbestosis
2. Aspiration (chronic)
3. Pulmonary fibrosis (idiopathic)
4.Collagen vascular disease
Rule no. 2

92. Asbestos-related
pleural disease and
asbestosis

93. Pulmonary fibrosis and rheumatoid arthritis.

94. Systemic sclerosis.
A: PA chest radiograph shows a bibasilar and subpleural distribution of fine
reticular ILD. The presence of a dilated esophagus (arrows) provides a clue to
the correct diagnosis.
B: CT scan shows peripheral ILD and a dilated esophagus (arrow).

95. A middle or upper lung predominant distribution
suggests: (Mycobacterium Settle Superiorly in
Lung)
1. Mycobacterial or fungal disease
2. Silicosis
3. Sarcoidosis
4. Langerhans Cell Histiocytosis
Rule no. 3

96. Complicated silicosis. PA chest radiograph shows multiple nodules
involving the upper and middle lungs, with coalescence of nodules
in the left upper lobe resulting in early progressive massive fibrosis

97. Sarcoidosis. CT scan shows nodular thickening of the bronchovascular bundles
(solid arrow) and subpleural nodules (dashed arrow), illustrating the typical
perilymphatic distribution of sarcoidosis.

98. Langerhan cell histiocytosis.
This 50-year-old man had a
30 pack-year history of
cigarette smoking.
A: PA chest radiograph shows
hyperinflation of the lungs
and fine bilateral reticular
ILD.
B: CT scan shows multiple
cysts (solid arrow) and
nodules (dashed arrow).

99. Associated lymphadenopathy suggests :
1.Sarcoidosis
2.neoplasm (lymphangitic carcinomatosis,
lymphoma, metastases)
3. infection (viral, mycobacterial, or fungal)
4. silicosis
Rule no. 4

100. Simple silicosis.
A: CT scan with lung windowing shows numerous circumscribed
pulmonary nodules, 2 to 3 mm in diameter (arrows).
B: CT scan with mediastinal windowing shows densely calcified
hilar (solid arrows) and subcarinal (dashed arrow) nodes.

101. Associated pleural thickening and/or
calcification suggest asbestosis.
Rule no. 5

102. Associated pleural effusion suggests :
1.pulmonary edema
2.lymphangitic carcinomatosis
3.lymphoma
4.collagen vascular disease
Rule no. 6

103. Cardiogenic pulmonary edema.
PA chest radiograph shows enlargement of the cardiac
silhouette, bilateral ILD, enlargement of the azygos vein (solid
arrow), and peribronchial cuffing (dashed arrow).

104. Lymphangitic carcinomatosis. This 53-year-old man presented
with chronic obstructive pulmonary disease and large-cell
bronchogenic carcinoma of the right lung.
CT scan shows unilateral nodular thickening (arrows) and a
malignant right pleural effusion.

105. Associated pneumothorax suggests
lymphangioleiomyomatosis or LCH.
Rule no. 7

106. Lymphangioleiomyomatosis
(LAM).
A: PA chest radiograph shows a
right basilar pneumothorax and
two right pleural drainage
catheters. The lung volumes are
increased, which is characteristic
of LAM, and there is diffuse
reticular ILD.
B: CT scan shows bilateral thin-
walled cysts and a loculated right
pneumothorax (P).

107. Associated with increased lung volume
* cystic fibrosis (CF)
* eosinophilic granuloma (EG)
* lymphangioleiomyomatosis (LAM)
Rule no. 8

108. Tell me the rules
again?

109. 1. Acute
•P.Edema
•Pneumonia
2. Pleural effusion
•1.pulmonary edema
•2.lymphangitic carcinomatosis
•3.lymphoma
•4.collagen vascular disease
3.Pneumothorax
•lymphangioleiomyom
atosis
•LCH
4.Predominantly Below with
reduced volume
1.Asbestosis
2. Aspiration (chronic)
3. Pulmonary fibrosis (idiopathic)
4.Collagen vascular disease

110. 5. A middle or upper lung predominant
1. Mycobacterial or fungal disease
2. Silicosis
3. Sarcoidosis
4. Langerhans Cell Histiocytosis
6. Associated lymphadenopathy
1.Sarcoidosis
2.neoplasm (lymphangitic
carcinomatosis, lymphoma,
metastases)
3. infection (viral, mycobacterial, or
fungal)
4. silicosis
7. Pleural Thickening
and or Calcification
•Asbestosis
Associated with increased lung
volume
* cystic fibrosis (CF)
* eosinophilic granuloma (EG)
* lymphangioleiomyomatosis
(LAM)

111. Summary

112. Thank You
for this
opportunity
REF- HRCT-WEB