3. Thoracic Imaging Terms
By
Gamal Rabie Agmy , MD , FCCP
Professor of Chest Diseases ,Assiut University
ERS National Delegate of Egypt

4. Air Bronchogram
An air bronchogram is a pattern of air-filled
(low-attenuation) bronchi on a background
of opaque (high-attenuation) airless lung . The
sign implies
(a) patency of proximal airways and
(b) evacuation of alveolar air by means of
absorption (atelectasis) or replacement
(eg, pneumonia) or a combination of these
processes.
(c) In rare cases, the displacement of air is
the result of marked interstitial expansion
(eg, lymphoma) .

6. Air Crescent
An air crescent is a collection of air in a
crescentic shape that separates the wall of
a cavity from an inner mass .The air
crescent sign is often considered
characteristic
of
either
Aspergillus
colonization of preexisting cavities or
retraction of infarcted lung in angioinvasive
aspergillosis .However, the air crescent
sign has also been reported in other
conditions,
including
tuberculosis,
Wegener granulomatosis, intracavitary
hemorrhage, and lung cancer.

7. Air Trapping
Air trapping is retention of air in the lung
distal to an obstruction (usually partial). Air
trapping is seen on end-expiration CT
scans as parenchymal areas with less
than normal increase in attenuation and
lack of volume reduction. Comparison
between inspiratory and expiratory CT
scans can be helpful when air trapping is
subtle or diffuse. Differentiation from areas
of decreased attenuation resulting from
hypoperfusion as a consequence of an
occlusive vascular disorder (eg, chronic
thromboembolism) may be problematic ,
but other findings of airways versus
vascular disease are usually present.

9. Where is the pathology ???????
in the areas with increased density
meaning there is ground glass
in the areas with decreased density
meaning there is air trapping

10. Pathology in black areas
Airtrapping: Airway Disease
Bronchiolitis obliterans (constrictive bronchiolitis)
idiopathic, connective tissue diseases, drug reaction,
after transplantation, after infection
Hypersensitivity pneumonitis
granulomatous inflammation of bronchiolar wall
Sarcoidosis
granulomatous inflammation of bronchiolar wall
Asthma / Bronchiectasis / Airway diseases

11. Airway Disease
what you see……
In inspiration
sharply demarcated areas of seemingly increased
density (normal) and decreased density
demarcation by interlobular septa
In expiration
‘black’ areas remain in volume and density
‘white’ areas decrease in volume and increase in
density
INCREASE IN CONTRAST
DIFFERENCES

12. Bronchiolitis
obliterans

13. Aortopulmonary Window
Focal concavity in the left mediastinal
border below the aorta and above the left
pulmonary artery can be seen on a frontal
radiograph . Its appearance may be
modified by tortuosity of the aorta. The
aortopulmonary window is a common site
of lymphadenopathy in a variety of
inflammatory and neoplastic diseases.

14. Lymph
nodes
Enlarged hilar shadow with lobulated outlines
Normal

15. Lymph
nodes
Retrosternal
Prevascular
Retrocaval
Aortic window
Carinal
Subcarinal
Hilar
Z-esophageal
Circm-cardiac
Anatomic Considerations
3
3

16. Lymph
nodes
Anatomic Considerations
5
Retrosternal
Prevascular
Retrocaval
Aortic window
Carinal
Subcarinal
Hilar
Z-esophageal
Circm-cardiac
6

17. Lymph
nodes
Anatomic Considerations
7
Retrosternal
Prevascular
Retrocaval
Aortic window
Carinal
Subcarinal
Hilar
Z-esophageal
Circm-cardiac
7
8
9

19. Apical Cap
The usual appearance is of homogeneous
soft-tissue attenuation capping the extreme lung
apex (uni- or bilaterally), with a sharp or irregular
lower border .Thickness is variable, ranging up to
about 30 mm . An apical cap occasionally mimics
apical consolidation on transverse CT scans.

20. Architectural Distortion
Lung anatomy has a distorted appearance
and is usually associated with pulmonary
fibrosis and accompanied by volume loss.

21. Atelectasis
Reduced volume is seen, accompanied by
increased opacity (chest radiograph) or
attenuation (CT scan) in the affected
part of the lung . Atelectasis is often
associated with abnormal displacement of
fissures,
bronchi,
vessels,diaphragm,
heart, or mediastinum .The distribution can
be lobar, segmental, or subsegmental.
Atelectasis is often qualified by descriptors
such as linear,discoid, or platelike.

22. Atelectasis
The definition of atelectasis is loss of air in the alveoli;
alveoli devoid of air (not replaced).
A diagnosis of atelectasis requires the following:
1-A density, representing lung devoid of air
2-Signs indicating loss of lung volume

23. Types of Atelectasis:
1-Absorption Atelectasis
When airways are obstructed there is no further
ventilation to the lungs and beyond. In the early
stages, blood flow continues and gradually the
oxygen and nitrogen get absorbed, resulting in
atelectasis.

24. Types of Atelectasis:
2-Relaxation Atelectasis
The lung is held close to the chest wall because of the
negative pressure in the pleural space. Once the
negative pressure is lost the lung tends to recoil due
to elastic properties and becomes atelectatic. This
occurs in patients with pneumothorax and pleural
effusion. In this instance, the loss of negative
pressure in the pleura permits the lung to relax, due
to elastic recoil. There is common misconception that
atelectasis is due to compression.

25. Types of Atelectasis:
3-Adhesive Atelectasis :
Surfactant reduces surface tension and keeps the
alveoli open. In conditions where there is loss of
surfactant, the alveoli collapse and become
atelectatic. In ARDS this occurs diffusely to both
lungs. In pulmonary embolism due to loss of blood
flow and lack of CO2, the integrity of surfactant
gets impaired.

26. Types of Atelectasis:
4-Cicatricial Atelectasis
– Alveoli gets trapped in scar and
becomes atelectatic in fibrotic
disorders

27. Types of Atelectasis:
.
5-Round Atelectasis
An instance where the lung gets trapped by
pleural disease and is devoid of air.
Classically encountered in asbestosis.

28. Types of Atelectasis:
.
6-Compression Atelectasis

29. Signs of Loss of Lung Volume:
Generalized
1-Shift of mediastinum: The trachea and heart gets shifted
towards the atelectatic lung.
2-Elevation of diaphragm: The diaphragm moves up and
the normal relationship between left and right side gets
altered.
3-Drooping of shoulder.
4-Crowding of ribs: The interspace between the ribs is
narrower compared to the opposite side.

30. Signs of Loss of Lung Volume:
Movement of Fissures
You need a lateral view to appreciate the movement of
oblique fissures. Forward movement of oblique fissure in
LUL atelectasis. Backward movement in lower lobe
atelectasis.
Movement of transverse fissure can be recognized in the
PA film.

31. Signs of Loss of Lung Volume:
Movement of Hilum
The right hilum is normally slightly lower than the left.
This relationship will change with lobar atelectasis.

32. Signs of Loss of Lung Volume:
Compensatory Hyperinflation
Compensatory hyperinflation as evidenced by increased
radiolucency and splaying of vessels can be seen with the
normal lobe or opposite lung.

33. Signs of Loss of Lung Volume:
Alterations in Proportion of Left and
Right Lung
The right lung is approximately 55% and left lung 45%. In
atelectasis this apportionment will change and can be a
clue to recognition of atelectasis. .

34. Signs of Loss of Lung Volume:
Hemithorax Asymmetry
In normals, the right and left hemithorax are equal in size.
The size of the hemithorax will be asymmetrical and
smaller on the side of atelectasis

35. Signs of Loss of Lung Volume:
Generalized
Shift of mediastinum: The trachea and heart gets shifted towards the atelectatic lung.
Elevation of diaphragm: The diaphragm moves up and the normal relationship between left
and right side gets altered.
Drooping of shoulder.
Crowding of ribs: The interspace between the ribs is narrower compared to the opposite side.
Movement of Fissures
You need a lateral view to appreciate the movement of oblique fissures. Forward movement of
oblique fissure in LUL atelectasis. Backward movement in lower lobe atelectasis.
Movement of transverse fissure can be recognized in the PA film.
Movement of Hilum
The right hilum is normally slightly lower than the left. This relationship will change with lobar
atelectasis.
Compensatory Hyperinflation
Compensatory hyperinflation as evidenced by increased radiolucency and splaying of vessels
can be seen with the normal lobe or opposite lung.
Alterations in Proportion of Left and Right Lung
The right lung is approximately 55% and left lung 45%. In atelectasis this apportionment will
change and can be a clue to recognition of atelectasis.
Hemithorax Asymmetry
In normals, the right and left hemithorax are equal in size. The size of the hemithorax will be
asymmetrical and smaller on the side of atelectasis

36. Atelectasis Right Lung
Homogenous density right hemithorax
Mediastinal shift to right
Right hemithorax smaller
Right heart and diaphragmatic silhouette are not identifiable

37. Atelectasis Left Lung
Homogenous density left hemithorax
Mediastinal shift to left
Left hemithorax smaller
Diaphragm and heart silhouette are not identifiable

38. Left Lower Lobe Atelectasis
•
•
•
•
Inhomogeneous cardiac density
Left hilum pulled down
Non-visualization of left diaphragm
Triangular retrocardiac atelectatic LLL

39. Atelectasis Left Lower Lobe
Double density over heart
Inhomogenous cardiac density
 Triangular retrocardiac density
Left hilum pulled down
Other findings include:
Pneumomediastinum

40. Atelectasis Left
Upper Lobe
Mediastinal shift to left
Density left upper lung field
Loss of aortic knob and left hilar
silhouettes
Herniation of right lung
Atelectatic left upper lobe
Forward movement of left
oblique fissure "Bowing sign"

41. Atelectasis Left Upper
Lobe
Hazy density over left
upper lung field
Loss of left heart
silhouette
Tracheal shift to left
Lateral
A: Forward movement of
oblique fissure
B: Herniated right lung
C: Atelectatic LUL

42. Atelectasis Right Upper Lobe
Homogenous density right upper lung
field
Mediastinal shift to right
Loss of silhouette of ascending aorta
Lateral
Movement of oblique and transverse
fissures

43. Atelectasis Right Upper Lobe
Homogenous density right upper lung field
Mediastinal shift to right
Loss of silhouette of ascending aorta
Lateral
Movement of oblique and transverse
fissures

44. RML Atelectasis
Vague density in right lower lung field, almost normal
RML atelectasis in lateral view, not evident in PA view

45. Vague density in right lower lung field (almost a normal film).
Dramatic RML atelectasis in lateral view, not evident in PA view. Movement of
transverse fissure.
Other findings include: Azygous lobe

46. Atelectasis Right Lower Lobe
Density in right lower lung field
Indistinct right diaphragm
Right heart silhouette retained
Transverse fissure moved down
Right hilum moved down

47. Adhesive Atelectasis
Alveoli are kept open by the integrity of surfactant. When there is loss
of surfactant, alveoli collapse. ARDS is an example of diffuse alveolar
atelectasis.
Plate-like atelectasis is an example of focal loss of surfactant.

48. Relaxation Atelectasis
The lung is held in apposition to the chest wall because of negative pressure
in the pleura. When the negative pressure is lost, as in pneumothorax or
pleural effusion, the lung relaxes to its atelectatic position. The atelectasis is
a secondary event. The pleural problem is primary and dictates other
radiological findings.

49. Round Atelectasis
Mass like density
Pleural based
Base of lungs
Blunting of costophrenic angle
Pleural thickening
Pulmonary vasculature curving
into the density
Esophageal surgical clips

50. Round Atelectasis
Mass like density
Pleural based
Base of lungs
Blunting of costophrenic angle, pleural thickening
Pulmonary vasculature curving into the density

51. RML Lateral Segment Atelectasis

52. Sub-segmental Atelectasis

53. Atelectasis
Segmental
Anterior sub-segment of RUL
"Bronchial wedge"

54. Azygoesophageal Recess
The azygoesophageal recess on a frontal
chest radiograph, is seen as a vertically
oriented interface between the right lower
lobe and the adjacent mediastinum (the
medial limit of the recess). Superiorly, the
interface is seen as a smooth arc with
convexity to the left. Disappearance or
distortion of part of the interface suggests
disease (eg, subcarinal lymphadenopathy).
On CT scans, the recess merits
attentionbecause small lesions located in
the recess will often be invisible on chest
radiographs

55. Acute interstitial pneumonia, or AIP
In the acute phase, patchy bilateral
groundglass opacities are seen , often with
some sparing of individual lobules,
producing a geographic appearance;
dense opacification is seen in the
dependent lung .
In the organizing phase, architectural
distortion, traction bronchiectasis, cysts,
and reticular opacities are seen .

56. Azygos Fissure

57. Beaded Septum Sign
This sign consists of irregular and nodular
thickening of interlobular septa reminiscent
of a row of beads . It is frequently seen in
lymphangitic spread of cancer and less
often in sarcoidosis .

58. Bleb
Anatomy.—A bleb is a small gas-containing space
within the visceral pleura or in the subpleural lung,
not larger than 1 cm in diameter . CT scans.—A
bleb appears as a thin-walled cystic air space
contiguous with the pleura. Because the arbitrary
(size) distinction between a bleb andbulla is of little
clinical importance, the use of this term by
radiologists is discouraged.

59. Cavitary lesions of lung
Bulla
<1mm wall
>1cm size
Pneumatocele Honey combing
<1mm wall
staph. infection
<1cm size
multiple equal
Cyst
Cavity
1-3mm wall
1-10 cm size
>3mm wall
Any size

60. Bulla
Definition
•Thin-walled–less than 1 mm
•Air-filled space
•In the lung> 1 cm in size and up to 75% of lung
•Walls may be formed by pleura, septa,
or compressed lung tissue.
•Results from destruction, dilatation and
confluence of airspaces distal to terminal
bronchioles.

61. •Bullous disease may be primary or associated
with emphysema or interstitial lung disease.
• Primary bullous lung disease may be familial
and has been associated with Marfan's, Ehler's
Danlos, IV drug users, HIV infection, and
vanishing lung syndrome.
•Bullae may occasionally become very large
and compromise respiratory function. Thus
has been referred as vanishing lung syndrome,
and may be seen in young men.

62. Upper lobe Bulla

63. Lower lobe Bulla

64. A: Xray shows bilateral bulla.
B: CT shows bilateral bulla.
C: CT after bullectomy.

66. Pneumatocele is a benign air containing cyst of lung, with
thin wall < 1mm as bulla but with different mechanism 
Infection with staph aureus is the commonest cause ( less
common causes are, trauma, barotrauma) lead to necrosis
and liquefaction followed by air leak and subpleural
dissection forming a thin walled cyst.

67. •Honeycombing is defined as multiple cysts < 1cm in diameter,with
well defined walls, in a background of fibrosis, tend to form
clusters and is considered as end stage lung .
•It is formed by extensive interstitial fibrosis of lung with residual
cystic areas.

69. A cyst is a ring
shadow > 1 cm in
diameter and up to
10 cm with wall
thickness from 1-3
mm.

71. Thin walled cysts of LAM

72. A cavity is > 1cm
in diameter, and its
wall thickness is
more than 3 mm.

73. Mechanism
•A central portion  necrosis and communicate to bronchus.
•The draining bronchus is visible (arrow). CT (2 mm slice thickness)
shows discrete air bronchograms in the consolidated area.

74. 1. Site

75. A cavity in apicoposterior segment of left upper lobe

76. 2.Number
Multiple cavities:
1. Aspiration.
2. TB
3. Fungal.
4. Metastatic.
5. Septic emboli.
6.Wegners granulomatosis

77. Multiple thick wall cavities from
adenocarcinoma of right lung
Multiple cysts of metastasis
from
squamous
cell
carcinoma.

80. 3. Thickness and
irregularity
Irregular , nodular inner lining of thick wall abscess
Malignant cavity.

81. 4. eccentric
Malignant

82. 5. Relation to lymph
node enlargement

83. 6. Contents

84. •Arrow head  Crescent sign.
•Black arrows  Fibrotic bands surrounding cavity
(Fibrocavitary TB).

86. Bronchiectasis
Morphologic criteria on thin-section CT
scans include bronchial dilatation with
respect to the accompanying pulmonary
artery (signet ring sign), lack of tapering
of bronchi, and identification of bronchi
within 1 cm of the pleural surface (27)
(Fig 11). Bronchiectasis may be classified
as cylindric, varicose, or cystic, depending
on the appearance of the affected bronchi.
It is often accompanied by bronchial wall
thickening, mucoid impaction, and smallairways abnormalities

87. Bronchiolectasis
When dilated bronchioles are filled with
exudate and are thick walled, they are
visible as a tree-in-bud pattern or as
centrilobular
nodules.
In
traction
bronchiolectasis, the dilated bronchioles
are seen as small, cystic, tubular
airspaces, associated with CT findings of
fibrosis

88. Bronchocele
bronchocele is a tubular or branching Yor
V-shaped structure that may resemble a
gloved finger (Fig 13). The CT attenuation
of the mucus is generally that of soft tissue
but may be modified by its composition
(eg, high-attenuation material in allergic
bronchopulmonary aspergillosis). In the
case of bronchial atresia, the surrounding
lung may be of decreased attenuation
because of reduced ventilation and, thus,
perfusion.

89. Bronchiolitis
This direct sign of bronchiolar inflammation
(eg, infectious cause) is most often seen
as the tree-inbud pattern, centrilobular
nodules, and bronchiolar wall thickening .

90. Bronchocentric
This descriptor is applied to disease that is
conspicuously centered on macroscopic
bronchovascular bundles . Examples of
diseases with a bronchocentric distribution
include sarcoidosis , Kaposi sarcoma , and
organizing pneumonia

91. Broncholith
The imaging appearance is of a small
calcific focus in or immediately adjacent to
anairway (Fig 15), most frequently the right
middle lobe bronchus. Broncholiths are
readily identified on CT scans . Distal
obstructive
changes
may
include
atelectasis,
mucoid
impaction,
and
bronchiectasis.

92. Bulla
An airspace measuring more than 1 cm—
usually several centimeters in diameter,
sharply demarcated by a thin wall that is no
greater than 1 mm in thickness. A bulla is
usually accompanied by emphysematous
changes in the adjacent lung.
Radiographs and CT scans.—
A bulla appears as a rounded focal lucency
or area of decreased attenuation, 1 cm or
more in diameter, bounded by a thin wall .
Multiple bullae are often present and are
associated with other signs of pulmonary
emphysema (centrilobular and paraseptal).

93. Cavity
A cavity is a gas-filled space, seen as a
lucency or low-attenuation area, within
pulmonary consolidation, a mass, or a
nodule . In the case of cavitating
consolidation, the original consolidation
may resolve and leave only a thin wall. A
cavity is usually produced by the expulsion
or drainage of a necrotic part of the lesion
via the bronchial tree. It sometimes
contains a fluid level. Cavity is not a
synonym for abscess.

94. Cavitary Lung Lesions

95. Number:
Multiple bilateral cavities would raise
suspicion for either bronchiogenous or
hematogenous process. You should consider:
Aspiration lung abscess
Septic emboli
Metastatic lesions
Vasculitis (Wegener's)
Coccidioidomycosis, tuberculosis

96. Location:
• Classical locations for aspiration lung abscess
are superior segment of the lower lobes
posterior segments of upper lobes.
• Tuberculous cavities are common in superior
segments of upper and lower lobes or posterior
segments of upper lobes.
• When a cavity in anterior segment is
encountered, a strong suspicion for lung cancer
should be raised. TB and aspiration lung
abscess are rare in anterior segments. Cancer
lung can occur in any segment.

97. Wall Thickness:
• Thick walls are seen in:
– Lung abscess
– Necrotizing squamous cell lung cancer
– Wegener's granulomatosis
– Blastomycosis

98. Wall Thickness:
• Thin walled cavities are seen in:
• Coccidioidomycosis
• Metastatic cavitating squamous cell
carcinoma from the cervix
• M. Kansasii infection
• Congenital or acquired bullae
• Post-traumatic cysts
• Open negative TB

99. Contents:
• The most common cause for air fluid level is
lung abscess. Air fluid levels can rarely be
seen in malignancy and in tuberculous
cavities from rupture of Rasmussen's
aneurysm.
• A fungous ball should make you consider
aspergillosis. A blood clot and fibrin ball will
have the same appearance.
• Floating Water Lily: The collapsed membrane
of a ruptured echinococcal cyst, floats giving
this appearance.

100. Lining of Wall:
The wall lining is irregular and nodular in
lung cancer or shaggy in lung abscess

101. Evolution of Lesion:
Many times review of old films to assess the
evolution of the radiological appearance of
the lesion extremely helpful. Examples
• Infected bullae
• Aspergilloma
• Sub acute necrotizing aspergillosis
• Bleeding from Rasmussen's aneurysm in a
tuberculous cavity

102. Associated Features:
Ipsilateral lymph nodes or lytic
lesions of the bone is seen
with malignancy

103. Centrilobular
A small dotlike or linear opacity in the center of a normal secondary
pulmonary lobule, most obvious within 1 cm of a pleural surface,
represents the intralobular artery (approximately1 mm in diameter) .
Centrilobular abnormalities include
(a) nodules,
(b) a tree-in-bud pattern indicating small-airways disease,
(c) increased vis-ibility of centrilobular structures due to thickening
or infiltration of the adjacent interstitium, or
(d) abnormal areas of low attenuation caused by centrilobular
emphysema

104. Centrilobular Emphysema
CT findings are centrilobular areas of
decreased attenuation, usually without visible
walls, of nonuniform distribution and
predominantly located in upper lung zones .
The term centriacinar emphysema is
synonymous.

105. Consolidation
Consolidation appears as a homogeneous
increase in pulmonary parenchymal
attenuation that obscures the margins of
vessels and airway walls .An air
bronchogram may be present. The
attenuation characteristics of consolidated
lung are only rarely helpful in differential
diagnosis (eg, decreased attenuation in
lipoid pneumonia and increased in
amiodarone toxicity

106. Crazy-paving Pattern
This pattern appears as thickened
interlobular septa and intralobular lines
superimposed on a background of groundglass opacity , resembling irregularly
shaped paving stones. The crazy-paving
pattern is often sharply demarcated from
more normal lung and may have a
geographic outline. It was originally
reported in patients with alveolar
proteinosis and is also encountered in
other diffuse lung diseases that affect both
the interstitial and airspace compartments,
such as lipoid pneumonia

107. Cyst
A cyst appears as a round parenchymal
lucency or low-attenuating area with a
well-defined interface with normal lung.
Cysts have variable wall thickness but
are usually thin-walled (2 mm) and
occur without associated pulmonary
emphysema . Cysts in the lung
usually contain air but occasionally contain
fluid or solid material. The term is
often used to describe enlarged thinwalled
airspaces
in
patients
with
lymphangioleiomyomatosis or Langerhans
cell
histiocytosis
;
thickerwalled
honeycomb cysts are seen in patients with
end-stage fibrosis .

108. Desquamative Interstitial Pneumonia
or DIP
Ground-glass opacity is the dominant
abnormality and tends to have a basal and
peripheral distribution . Microcystic or
honeycomb changes in the area of groundglass opacity are seen in some cases .

109. Ground-Glass Opacity or GGO
it appears as hazy increased opacity of
lung, with preservation of bronchial and
vascular margins .It is caused by partial
filling of airspaces, interstitial thickening
(due to fluid, cells, and/or fibrosis), partial
collapse of alveoli, increased capillary
blood volume, or a combination of these,
the common factor being the partial
displacement of air .Ground-glass opacity
is less opaque than consolidation, in which
bronchovascular margins are obscured.

110. Halo Sign
The halo sign is a CT finding
of ground-glass opacity surrounding a
nodule or mass .It was first
d e s c r i b e d a s a si g n o f h e mo r r h a g e
a r o u n d f o ci o f i n va si ve a sp er g ill o si s
. The halo sign is nonspecific and
ma y a l so b e ca u se d b y h e mo r r h a g e
associated with other types of nodules
o r b y l ocal pul monar y infiltr ation
b y n e o p l a s m ( e g , a d e n o c a r ci n o ma ) .

111. Honeycombing
On chest radiographs, honeycombing appears as
closely approximated ring shadows, typically 3–10
mm in diameter with walls 1–3 mm in thickness, that
resemble a honeycomb; the finding implies endstage lung disease. On CT scans, the appearance is
of clustered cystic air spaces, typically of
comparable diameters on the order of 3–10 mm but
occasionally as large as 2.5 cm . Honeycombing is
usually subpleural and is characterized by welldefined walls . It is a CT feature of established
pulmonary fibrosis . Because honeycombing is often
considered specific for pulmonary fibrosis and is an
important criterion in the diagnosis of usual
interstitial pneumonia (63), the term should be used
with care, as it may directly impact patient care.

112. Idiopathic pulmonary fibrosis
The typical imaging findings are reticular
opacities and honeycombing, with a
predominantly peripheral and basal
distribution . Ground-glass opacity, if
present, is less extensive than reticular and
honeycombing patterns. The typical
radiologic findings are also encountered in
usual interstitial pneumonia secondary to
specific causes, such as asbestos-induced
pulmonary fibrosis (asbestosis), and the
diagnosis is usually one of exclusion.

113. Infarction
A pulmonary infarct is typically triangular or
dome-shaped, with the base abutting the
pleura and the apex directed toward the
hilum.The
opacity
represents
local
hemorrhage with or without central tissue
necrosis

114. Interlobular septal thickening
This finding is seen on chest radiographs as thin linear
opacities at right angles to and in contact with the lateral
pleural surfaces near the lung bases (Kerley B lines); it is
seen most frequently in lymphangitic spread of cancer or
pulmonary edema. Kerley A lines are predominantly
situated in the upper lobes, are 2–6 cm long, and can be
seen as fine lines radially oriented toward the hila. In recent
years, the anatomically descriptive terms septal lines and
septal thickening have gained favor over Kerley lines. On
CT scans, disease affecting one of the components of the
septa (see interlobular septum) may be responsible for
thickening and so render septa visible. On thin-section CT
scans, septal thickening may be smooth or nodular , which
may help refine the differential diagnosis.

115. Interlobular septum
Interlobular septa appear as thin linear
opacities between lobules ; these septa are
to be distinguished from centrilobular
structures. They are not usually seen in the
healthy
lung
(normal
septa
are
approximately 0.1 mm thick) but are clearly
visible when thickened (eg, by pulmonary
edema).

116. Interstitial emphysema
Interstitial emphysema is rarely recognized
radiographically
in
adults
and
is
infrequently seen on CT scans . It appears
as perivascular lucent or lowattenuating
halos and small cysts

117. Intralobular lines
Intralobular lines are visible as fine linear
opacities in a lobule when the intralobular
interstitial tissue is abnormally thickened .
When numerous, they may appear as a
fine reticular pattern. Intralobular lines may
be seen in various conditions, including
interstitial fibrosis and alveolar proteinosis