This document provides information on chest imaging techniques including CT, MRI, and specific protocols. It discusses the anatomy seen on chest imaging and some common pathologies. Key points include: - CT allows detailed analysis of the small airways, lungs, and interstitium. HRCT and MDCT provide high resolution images. DECT and spiral CT are also discussed. - MRI is limited for lung imaging due to motion artifacts but is useful for vascular structures, cysts, and intraspinal lesions. T1-weighted images show anatomy while T2-weighted images show edema. - The document outlines normal bronchial tree anatomy and variations, pulmonary lobule structure, and common imaging patterns for nodules

1. Chest Imaging
Dr S.V.Srikrishna MS, MCh, FRCS Ed, FIACS
Prof & Sr Consultant Cardiothoracic Surgeon
Narayana Hrudayalaya, Bengaluru

2. 1. SVC Edge
2. Right Paratracheal Line
3. Left Paratracheal Stripe (both
red and white lines)
4. Aortic Arch
5. Descending Aorta (only left
edge seen, and not always)
6. Right Atrium
7. Azygoesophageal edge
8. Left Ventricle
9. Main Pulmonary Artery (also
known as: trunk, middle mogul)

6. • Primary Pulmonary Circulation ⇒ supplies 99% of
blood flow to lungs pulmonary arteries travel along
lobar + segmental bronchi down to subsegmental level
matching caliber of airways
• Large Elastic PAs - Muscular PAs - Arterioles - Capillaries -
Venules - Pulmonary veins course through interlobular fibrous
septa
• Bronchial Circulation ⇒ supplies 1% of blood flow to
lungs = 1% of cardiac output ; systemic high-pressure
system (6 x that of normal pulmonary circulation);
bronchial arteries are resistant to arteriosclerosis.
systemic blood supply to trachea, bronchi, bronchial
branches, visceral pleura, interstitium & esophagus

7. Bronchial Artery Variations

8. Parenchymal patterns
• Mass : Any localized opacity not completely bordered
by fissures/pleura
• Consolidative : Fluffy, cloud-like, coalescent opacities
• Interstitial : Thickening of peribronchial, perivascular,
alveolar wall, and/or subpleural areas; thick-walled
cystic spaces (honeycomb)
• Vascular : Change in diameter of vessels, whether
intrinsically (vascular volume) or extrinsically
(compression such as emphysema)
• Airway : Thick-walled airways (circular on end or tram-
track), segmental or lobar atelectasis, and, lastly,
bronchiectasis Feigin Chest. 1993;103(2):594–600.1993

9. Interstitial Abnormalities
• Linear form ( lines ): Reticulations (lines in all
directions, not just the branching vessels) and
septal lines (Kerley lines).
• Nodular form ( dots ): Small, sharp, numerous,
evenly distributed, uniform (especially uniform in
shape) nodules.
• Destructive form ( holes ): Peripheral, irregular cyst
formation.

11. Consolidation

14. Atelectasis

15. Patterns of atelectasis

19. Nodules

25. Pleural Abnormalities

26. HRCT
• The anatomic detail provided by HRCT imaging
sections allows a more detailed analysis of
pathologic processes affecting the small airways,
airspaces or alveolar walls, and interstitium.
• HRCT plays an important role in detecting early
morphologic changes in patients with suspected
pulmonary disorders such as interstitial lung
disease (ILD), emphysema, asbestosis, and
bronchiectasis.
• Multislice HRCT may be used to acquire high-
resolution images of the lung parenchyma.

27. Spiral CT
• The advantages of spiral CT arise from continuous data
acquisition and short total scanning time. The operator
chooses three basic parameters for spiral CT: section
collimation, table feed per rotation, and reconstruction
interval.
• The section collimation (0.5 mm, 1 mm, 2 mm, 3 mm, 5 mm,
7 mm, or 10 mm) determines the spatial resolution achieved
along the z-axis
• Table speed is set to between 1 and 10 mm/second.
• Pitch is defined as the ratio as the table feed per tube
rotation to the collimation. Pitch is usually best kept
between 1.0 and 2.0.
• Reconstruction of overlapping sections improves the quality
of the 3D images

28. MDCT
• It uses a multiple-row detector with narrow detector
collimation in conjunction with a relatively rapid table
translation to achieve faster scans with thinner slices
than single-detector CT.
• MDCT results in a gapless volumetric acquisition that
eliminates problems of slice misregistration caused by
variations in the depth of inspiration
• An important advance of MDCT scanners is that from
the same data set, thin sections can be reconstructed
to minimize partial volume averaging, and thicker
sections can be reconstructed to decrease image noise
if necessary

29. DECT
• Dual-energy computed tomography (DECT) is very helpful in
the detection and diagnosis of thoracic abnormalities. 325
Selective iodine mapping is made possible by the x-ray
absorption characteristics of iodine, which has a high atomic
number compared with elements that constitute air or soft
tissue.
• A major advantage of dual-energy imaging over
conventional radiography is its superior sensitivity for the
detection of calcification within a pulmonary nodule.
• Other advantages of dual-energy imaging are related to
identification of bone and pleural abnormalities, recognition
of hilar and mediastinal masses, detection of tracheal
narrowing and airway disease, and localization of stents,
catheters, and other indwelling devices

30. DECT
• Pulmonary embolism in a 62-
year-old woman with deep
venous thrombosis,
developing severe dyspnea.
CT image in angiographic
window with superimposed
color-coded DE perfusion
map. Bilateral perfusion
defects in the upper lobes
due to acute PE are depicted
in the color-coded maps by
the lack of color coding
(arrows).
• (Courtesy Marcelo Sanchez, MD, Barcelona, Spain.)

33. T3/T4 T4 T4/T5 T5

34. T5/T6 T6 T7/T8

35. Normal anatomy of the bronchi on the right side. The first
Boyden’s classification is used with successive1-mm slices.
(A) The arrow shows the division of the apical bronchus of
the right upper lobe.
(B) Right upper lobe bronchus arises from the lateral aspect
of the main bronchus, approximately 2 cm distal to the
carina (large arrow) and courses horizontally for
approximately 1 cm from its origin before dividing in
segmental branches. Subsegmental bronchi of the anterior
bronchus of the right upper lobe are marked by arrows.
(C) The bronchus intermedius divides after 3 to 4 cm into
the middle lobe and lower lobe bronchi.
(D–F) The middle lobe bronchus arises from the
anterolateral wall of the bronchus intermedius and courses
anteriorly and laterally for 1 to 2 cm before dividing into
lateral (B4) and medial (B5) branches. This origin of the
middle lobe is almost at the same level as B6, which is the
first branch of the short right lower lobar bronchus (RLLB).
The superior segmental bronchus B6 and its subsegmental
bronchi arise from the posterior aspect of the RLLB just
beyond its origin and course posteriorly. The truncus basalis
represents a continuation of the lower lobar bronchus
below the origin of B6 and typically appears circular or
ovoid. It extends for approximately 1 cm before dividing in
four basal segmental bronchi. The first basal bronchi is the
medial basilar segmental bronchus (B7) that arises
anteromedially from the TB.
(G–I) Next, there is a successive appearance of the anterior,
lateral (B9), and posterior basilar (B10) bronchi and their
respective subsegmental bronchi. Note that B7 and its
subsegmental bronchus lie typically anterior to the inferior
pulmonary vein. (J) 3D volume rendering.

36. Anatomic variations of the right
bronchial tree.
(A–C) Subsuperior segmental bronchus
B*, accessory superior segmental
bronchus or subapical bronchus, is a
common variation of the right lower
lobe originating below B6 (A) at a
variable level from the truncus basalis
down to the posterior segmental
basilar bronchus. In this case, the
origin is well seen in (B) at the
posterior part of the B8 1 9 1 10 trunk
(curved arrow), B7 lying medially.
Successive origin of B8 and B9 1 10 in
(C).
(D–F) Most common variation of the
subdivision of medial basilar
segmental bronchus B7. In this case,
the medial ramus B7b courses
posterior to the inferior pulmonary
vein, unlike the anterior ramus B7a,
which remains anterior to the vein.

37. Normal anatomy of the bronchi on the left
side. The first Boyden’s classification is used
with successive 1-mm slices.
(A–C) The left upper lobe bronchus bifurcates
in most cases in an upper culminal bronchus
(CB), which almost immediately divides into
an apicoposterior (B113) and anterior (B2)
segmental bronchus and in a lower division,
the lingular bronchus. (A) Subsegmental
divisions of B1, B2, B3 are shown (arrows).
(D–F) The lingular bronchus (arrow inD)
arises from the lower part of the left upper
lobar bronchus (LULB), extends anteriorly and
inferiorly for 2 to 3 cm, and then bifurcates
into the superior (B4) and inferior divisions
(B5). The course of B4 tends to be more
lateral and horizontal than B5. Left lower
lobar bronchus (LLLB) and B6 are similar to
those on the right side. (F) Note that the
rounded lucency corresponds to the medial
subsegmental branch of B6 and that the
lucency at the posterior part of the TB (star)
corresponds to a subapical branch of the
LLLB, more rarely seen on the left side than
onthe right side.
(G–I) The truncus basalis is longer than onthe
right side anddivides into three basal
segmental bronchi, including anteromedial
(B7 1 8), lateral (B9), and posterior (B10).

38. Secondary Pulmonary
Nodule
It is the smallest lung unit that is
surrounded by connective tissue
septa
It measures about 1-2 cm and is made
up of 5-15 pulmonary acini, that
contain the alveoli for gas exchange
A, Secondary pulmonary lobule.
Schematic drawing shows the
pulmonary arteriole and airway in the
center of the lobule. Pulmonary veins
lie in the interlobular septum.
B, Photograph of cut surface of
inflated fixed lung. The margin of the
secondary pulmonary lobule is
formed by the interlobular septum,
which is continuous with the pleural
surface (single arrow). The pulmonary
arteriole and airway are seen in the
center of the lobule (three arrows),
the pulmonary veins in the septa (two
arrows). (From Netter FH: Atlas of Human Anatomy)

40. Basic HRCT Patterns
Lines, Nodules, Consolidation, Ground-glass Opacity, and Cysts

42. Nodular Patterns
• Look for the presence of pleural
nodules. These are often easiest to
see along the fissures. If pleural
nodules are absent or few in
number, the distribution is likely
centrilobular.
• If pleural nodules are visible, the
pattern is either random (miliary) or
perilymphatic.
• If there are pleural nodules and
also nodules along the central
bronchovascular interstitium and
along interlobular septa, you are
dealing with a periplymphatic
distribution.
• If the nodules are diffuse and
uniformly distributed, it is likely a
random distribution

44. Low Attenuation pattern

45. Distribution within the lung

47. Additional findings

50. MRI - Basics
RF pulse
Electromagnetic signal emitted to cause resonance of hydrogen nuclei in
the magnetic field. This process leads to the eventual release of RF
energy, which is measured and used to create the MR image.
T1-weighted images
Images obtained using short intervals, or repetition times (TR), between
application of RF pulses. The time to echo (TE), or the time at which the
emitted RF signal caused by relaxation is measured, is also short. Using
short TR and TE produces images in which tissue contrast is produced
primarily by differences in the T1 time constant of various tissues.
T2-weighted images
Images obtained using long intervals, or TR, between application of RF
pulses. The TE, or the time at which the emitted RF signal caused by
relaxation is measured, is also long. Using long TR and TE produces
images in which tissue contrast is produced primarily by differences in
the T2 time constant of different tissues.

51. Basic MRI Scans
• T1-weighted: Differentiate fat from water
• Water is Darker, fat is brighter
• Provide good gray matter/white matter contrast in brain.
• T1-weighted images give information concerning diagnosis of
masses and provide the best information about vascular
anatomy. (Fig.
• T2-weighted: Differentiate fat from water
• Fat shows darker, and water lighter.
• Good for imaging edema
• Abnormal accumulation of fluid beneath the skin or in one or
more cavities of the body
• The T2-weighted images may render fluid collections
distinguishable from solid masses and may help separate
tumor from fibrosis

52. An MRI machine uses a powerful magnetic field to
align the magnetization of some atoms in the body.
Radio frequency fields systematically alter the alignment
of this magnetization
This causes the nuclei to produce a rotating
magnetic field detectable by the scanner
This information is recorded to construct an image of the
body.

53. • Images are constructed when protons in different tissues
return to equilibrium state at different rates.
• Five variables effect these rates
• Spin Density: Concentration of nuclei in tissue processing in a
given region under a magnetic field.
• T1: Longitudinal relaxation time
• T2: Transverse relaxation time
• Flow: Shows blood flow, CSF flow
• Spectral Shifts: Angle/zoom the picture is taken from.

54. MRI
• Despite the fact that magnetic resonance imaging (MRI) has a clear
advantage over other imaging modalities in evaluating cardiac and
vascular disorders of the chest, it continues to play a limited role in
parenchymal lung evaluation.
• Reasons for the limited use of pulmonary MRI include respiratory
motion and magnetic susceptibility effects caused by air-tissue
interfaces.
• MRI, because of its multiplanar capability and high contrast
resolution, is occasionally used to evaluate the location and extent of
disease.
• MRI is the modality of choice for imaging neurogenic tumors,
because it not only demonstrates the number and nature of the
lesions but also depicts intraspinal extension
• Additionally MRI is useful in confirming the cystic nature of
mediastinal lesions that appear solid on CT ( Fig. 38-31 ) and
demonstrating vascular structures

55. Axial T1- and T2-weighted MRIs show the mass to be of homogeneous low signal intensity
on the T1-weighted image ( arrowheads in B ) and high signal intensity on the T2-weighted
image ( C ), consistent with a cyst.

56. • MR to screen for and follow various disease
entities in the thorax without ionizing radiation
exposure, such as endometriosis, chronic
lymphocytic leukemia and lymphoma in young and
pregnant patients ( Fig. 3.1 ), cystic fibrosis,
paragangliomas (e.g., SDHD mutation), teratomas
(NMDA [ N -methyl- d -aspartate] receptor
antibodies), carcinoid tumors (multiple endocrine
neoplasia type 1), and syndromes with high risk for
malignancy (e.g., Li-Fraumeni syndrome).

57. • MRI has superior tissue contrast but it is more
susceptible to cardiac and respiratory motion
artifacts. It is also affected by low proton density,
very short T2* values, and inhomogeneity of the
magnetic field in the lungs. However, recent
advances in MRI techniques and the use of
gadolinium contrast media have enhanced the
diagnostic capability of MRI in detecting and
staging lung cancer.

58. • MRI can be used in cases with questionable CT
findings, given its superior tissue contrast and
multiplanar capabilities.
• ] MRI can delineate infiltration or disruption of the
extrapleural fat planes, which suggests chest wall
invasion. This can be further enhanced by the
administration of intravenous contrast and other
nonemergent techniques such as dynamic cine
MRI.

59. • MRI size criteria are used to identify nodal
involvement, and these are comparable to those
used at CT scanning. However, MRI can be used to
distinguish nodes from vessels without intravenous
contrast enhancement. In addition, direct imaging
in the sagittal and coronal planes is helpful in the
assessment of the subcarinal and aortopulmonary
regions.

60. • With recent advances in MRI, whole body MRI with
DWI is emerging as a single, cost-affective imaging
technique comparable to that PET/CT for staging
patients with metastatic carcinoma
• MRI is superior to CT scanning in detecting brain
metastatic involvement, especially in the depiction
of the posterior fossa and the area adjacent to the
skull base.

61. Indications for Thoracic MRI

62. MRI of mediastinal and hilar anatomy

63. MRI of mediastinal and hilar anatomy

64. MRI vs CT
• No Ionizing Radiation
• Better Soft Tissue Contrast
• Better demonstration of neurovascular, esophageal ,
and chest wall involvement
• Definitive differentiation of cystic from solid lesions
(hyperattenuating hemorrhagic and proteinaceous
cystic lesions can be misperceived as solid on CT)
• More thorough and sensitive depiction of lesion
complexity (heterogeneous composition, small nodules,
septations, wall asymmetries, and irregularities)
Thoracic Imaging: The Requisites, Chapter 3, 61-87

65. MRI vs CT ...
• More thorough and sensitive depiction of lesion
complexity (heterogeneous composition, small
nodules, septations, wall asymmetries, and
irregularities)
• Detection of microscopic fat (in addition to
macroscopic fat), blood products, fibrous tissue,
cartilage, and smooth muscle
• Differentiation of muscles from nerves, tendons,
and ligaments Thoracic Imaging: The Requisites, Chapter 3, 61-87

66. PET / CT
• Increased metabolism of neoplastic cells can be
detected by 2-[18F]fluoro-2-deoxy-d-glucose (FDG)
positron emission tomography (PET) imaging
• PET is routinely used for the evaluation of a single
pulmonary nodule equal to or greater than 1 cm in
diameter and for staging and restaging of
neoplasms, such as lung carcinoma, breast cancer,
lymphoma, and melanoma, which commonly
involve the thorax.
• Lymph nodes are interpreted as abnormal if their
short-axis diameter exceeds 1 cm.

69. (A, B) Distinction between central lung cancer and postobstructive
atelectasis using PET-CT. (A) Axial CT image in a 52-year-old man with a
newly diagnosed right infrahilar squamous cell carcinoma shows near
complete right lower lobe consolidation and collapse due to the central
lesion. The primary tumor is very difficult to visualize on the CT
imaging. (B) Corresponding image from a PET-CT shows nice
delineation between the 4.6-cm mass (white arrow) and the distal
atelectatic lung. Notice some mild uptake in the collapsed right lower
lobe (black arrow).

70. (A, B) Ability of PET-CT to improve detection of areas of invasion.
(A) Coronal PET image shows a large5.4-cm lingular lung cancer (white
arrow) adjacent to the heart (white arrowhead). There is mild FDG
uptake between the heart and mass (black arrow), which is difficult to
localize. (B) Coronal fused PET-CT image at the same level shows that
this area of uptake corresponds to tumor invasion into the epicardial
fat and pericardium (white arrow), which was confirmed on surgery.

71. Increased sensitivity of PET-CT for lymph node staging. (A) Axial CT
image in a 44-year-old woman with newly diagnosed lung cancer
shows an 8-mm right paratracheal lymph node (arrow). (B) Although
less than 1 cm in short-axis diameter, this node demonstrates avid
uptake on FDG-PET imaging consistent with nodal spread of disease
(arrow).

72. (A, B) Occult osseous metastases
on CT.
(A) A 77-year-old man presented to
the emergency department with
shortness of breath and back pain.
A large left effusion was present
with findings suggestive of an
underlying lung mass. (B) Two days
later the patient underwent PET
imaging, and a fusion of the PET
imaging and the CT obtained from
the emergency department
demonstrates numerous bony
metastases, which are
radiologically occult on the CT
images (white arrows). Uptake in
the large lung mass (black arrow) is
also better visualized with the
fusion of the PET and CT images.

73. Pit falls of PET/CT
• Technical artefacts
• Physiologic FDG uptake
• High physiologic uptake of FDG typically occurs in the
brain, kidneys, and urinary tract.
• Low degree of physiologic uptake of FDG is seen in the
thorax, including the heart, great vessels, esophagus,
thymus, and bone marrow.
• Strenuous physical activity before PET imaging can result
in diffuse increased FDG uptake in striated muscles
attributed to replenishment of glycogen stores
• Increased FDG uptake caused by metabolically active
brown fat

74. • False negative PET results may occur with carcinoid tumors and some
adenocarcinomas
• The major causes of false-positive results in PET/CT of
the thorax are infectious and inflammatory etiologies
• Falsepositive lesions have been reported to include
pneumonia, caseating granulomas, sarcoidosis,
amyloidosis, talc pleurodesis rounded atelectasis,
pleural fibrosis, atherosclerosis, and pulmonary
embolism
• FDG uptake can occur in granulation tissue in healing
wounds and focal FDG accumulation can be seen
following invasive procedures
• Talc pleurodesis induces a granulomatous inflammatory
reaction in the pleura that can be FDG avid on PET.

75. Loculated empyema vs Lung
abscess

76. Pneumothorax vs Bulla

77. Bronchogenic Carcinoma

78. Bronchogenic Carcinoma

79. Sir, may I be excused ?
My brain is full

80. Air Bronchogram Sign
Branching, linear, tubular lucency
representing a bronchus or
bronchiole passing through airless
lung parenchyma .
This sign indicates that the
underlying opacity must be
parenchymal rather than pleural or
mediastinal in location.
DD:
Pneumonia
Lymphoma
Bronchoalveolar cell carcinoma.

81. Silouhette sign
•This classic roentgenographic sign first
described by Felson in 1950 states that
"an intrathoracic lesion touching a
border of the heart, aorta, or
diaphragm will obliterate that border
on the roentgenogram
• An intra-thoracic lesion not
anatomically contiguous with a border
or anormal structure will not obliterate
that border

82. Split Pleura Sign
Split pleura sign is seen in CT scan in
cases of empyema which most
commonly occurs due to bacterial
pneumonia. There occurs fluid
accumulation in the pleural space,
which causes fibrin coating of the
inner visceral and outer parietal
layers of pleura. This results in
separation, thickening, and
increased enhancement of pleural
layers, producing split pleura sign .
Empyema causes extrapleural fat
stranding and thickening of
extrapleural soft tissues. Even
though these pleural changes are
commonly seen in empyema,
similar changes can also be
visualized in conditions like
mesothelioma, hemothorax, and
post lobectomy.

83. Split Pleura Sign
• Seen on contrast enhanced CT of
chest
• Separation and enhancement of the
visceral and parietal pleural layers on CT
is considered strong evidence of
empyema
• Normally, individual pleural layers are
not discernable as discrete structures
• Empyemic fluid fills the pleural space,
resulting in thickening and
enhancement of the pleura with a
denotable separation
• It can also be seen with exudative
effusion
• Causes:
- bacterial pneumonia
- cancer
- viral infection

84. Tram – Track Sign
• Parallel line opacities (tram
tracks) caused by thickened dilated
bronchi
• Seen on chest CT
• Bronchiectasis- defined as
localized irreversible dilatation of
part of the bronchial tree
• Causes:
- infection
- bronchial obstruction
(endobronchial tumors,
encroachment of hilar lymph
nodes, foreign body aspiration)
- cystic fibrosis

85. Monod’s Sign
Crescent sign
• Air surrounding fungus ball or
mycetoma in preexisting air cavity
(old tuberculosis, histoplasmosis,
sarcoidosis, neoplasm)
• It should not be confused with
the air crescent sign which is seen
in recovering angioinvasive
aspergillosis and heralds
improvement in the condition
• The air around the mycetoma is
often crescent shaped and hence,
the term air crescent sign is often
used interchangeably by many to
refer to both pathological
processes

86. Tree – in Bud Sign
• Commonly seen at thin-section
CT. This sign appears as small,
peripheral, centrilobular soft
tissue nodules connected to
multiple contiguous, linear
branching opacities. This
radiologic term represents the
mucous plugging, bronchial
dilatation, and wall thickening of
bronchiolitis. The
histopathological correlate
demonstrates small airway
plugging with mucus, pus, or
fluid, with dilated bronchioles,
peribronchiolar inflammation,
and wall thickening
Initially described in
endobronchial spread of
tuberculosis
Causes:
- infection (bacterial, fungal, viral)
- congenital disorders (cystic

87. Miliary Shadowing
• The term miliary derives from the
radiograqphic picture of diffuse, discrete
nodular shadows about the size of a millet seed
• Innumerable, small (1-4mm) pulmonary
nodules are seen scattered throughout the lungs
• It can be seen in:
- tuberculosis
- histoplasmosis
- sarcoidosis
- rheumatoid arthritis
- pneumoconiosis
- COPD
- pulmonary siderosis
- bronchoalveolar carcinoma
- metastasis (thyroid, kidney, trophoblast and
some sarcomas)

88. Signet Ring Sign
• Seen on CT/HRCT scans of chest
• CT finding in patients with
bronchiectasis
• Ring shadow representing dilated
thick-walled bronchus associated
with a nodular opacity representing
pulmonary artery

89. Fallen lung Sign
• This sign refers to the appearance
of the collapsed lung occurring
with a fractured bronchus
• It refers to the collapsed lung in a
dependent position, hanging on the
hilum only by its vascular
attachments and was first
described by Oh et al in 1969 and
by Kumpe et al in 1970
• The bronchial fracture results in
the lung to fall away from the
hilum, either inferiorly and laterally
in an upright patient or posteriorly,
as seen on CT in a supine patient

90. Popcorn Calcification
• A cluster of sharply
defined, irregularly
lobulated, calcifications,
usually in a pulmonary
nodule
• Popcorn calcifications
within a well circumscribed
pulmonary nodule are
highly suggestive of
pulmonary chondroid
hamartoma

91. Bat Wing Appearance
• Bat's wing or butterfly pulmonary opacities
refer to a pattern of bilateral perihilar
shadowing .
• It is classically described on a frontal chest
radiograph but can also refer to appearances on
chest CT
• Causes:
- pulmonary edema (especially cardiogenic)
- pneumonia (aspiration pneumonia, PCP, viral,
lipoid)
- inhalation injury (noxious gas, liquid)
- pulmonary alveolar proteinosis
- pulmonary hemorrhage (e.g. Goodpasture
syndrome)
- lymphoma

92. CT Angiogram Sign
• Consists of enhancing branching
pulmonary vessels in homogeneous
low-attenuating consolidation
• Low-attenuating component can be
caused by production of mucin within
air spaces
• Initially described as a specific sign
(92%) of lobar bronchoalveolar
carcinoma
• Also seen in:
- pneumonia
- pulmonary edema
- obstructive pneumonitis central
tumor
- metastasis from GI carcinomas
- lymphoma

93. Finger in glove Sign
• Indicates mucoid impaction
within an obstructed bronchus.
Characterized by branching
tubular or fingerlike opacities .
Originate from the hilum and are
directed peripherally. Also seen in
cases of dilated bronchi with
secretions. Visualization of the
gloved fingers is made possible by
collateral air drift through the
interalveolar pores of Kohn and
canals of Lambert aerating lung
distal to the point of mucoid
impaction (distal lung remains
aerated)
There are two broad etiologic
categories: non-obstructive and
obstructive
Non-Obstructive:
- allergic bronchopulmonary
aspergillosis (ABPA)

94. Halo Sign
• Ground glass attenuation
surrounding a pulmonary
nodule/mass on CT images
• Described by Kuhlman in 1985
in patients with invasive
aspergillosis
• In febrile neutropenic patients,
the sign suggests angioinvasive
fungal infection, (which is
associated with a high mortality
rate in the immunocompromised
host) the zone of attenuation
represents alveolar hemorrhage
whereas the nodules represent
areas of infarction and necrosis
caused by thrombosis of small to
medium sized vessels Associated
with hemorrhagic nodules and
may be caused by neoplasms or
inflammatory conditions
• Familiarity with adequate
clinical setting helps to narrow

95. Reverse Halo Sign
•Central ground-glass opacity surrounded by
denser consolidation of crescentic or ring
shape, at least 2 mm thick
• First described by Voloudaki in 1996
• Kim in 2003 used the term reverse halo
• Found to be relatively specific for
cryptogenic organizing pneumonia
(COP)
• Seen in other conditions:
- Wegener's and lymphomatoid
granulomatosis
- paracoccidiodomycosis
- neoplastic (metastasis)
- invasive aspergillosis
- lipoid pneumonia
- schistosomiasis

96. Coin lesion
• The term coin lesion was defined by
Thornton et al in 1944 as a solitary lesion, 1
to 5 cm in size, round or oval with well
defined margins
• Solitary, round, circumscribed shadows
found in the lungs in x-ray or CT
examinations
• Smaller than 3 centimeters in diameter
• Common causes:
- tuberculosis
- coccidioidomycosis
- histoplasmosis
- neoplasms (primary bronchogenic
carcinoma, metastatic tumors, bronchial
adenomas etc)
- cysts
- vascular anomalies

97. Bulging Fisure Sign
• The bulging fissure sign refers to
lobar consolidation causing lobar
expansion and bulging of the adjacent
fissure inferiorly
• Historically Klebsiella pneumoniae
involving the RUP- Friedlander
pneumonia
• Although previously reported in up
to 30% of patients with Klebsiella
pneumonia, the finding is identified
less commonly today, most likely due
to rapid prophylactic implementation
of antibiotics.
• The most common infective
causative agents are:
- Klebsiella pneumoniae
- Streptococcus pneumoniae
- Pseudomonas aeruginosa

98. Golden S Sign
• Described by Ross Golden in 1925
• Resembles a reverse S shape
• It can be seen on PA/lateral views
and CT
• This sign is typically seen with right
upper lobe collapse
• The medial portion of minor fissure
is convex inferiorly due to a central
mass and the lateral portion of the
fissure is concave inferiorly .
• It can be observed in cases of
bronchial carcinoma, primary
mediastinal tumor, metastasis and
enlarged lymph nodes

99. Continuous
Diaphragm Sign
This sign is seen in
pneumomediastinum in which air
accumulates between the lower
border of the heart and the
superior part of the diaphragm,
which results in complete
visualization of the diaphragm in
chest X-ray . Hence named
continuous diaphragm sign.
Normally, the central part of the
diaphragm is obscured by the
heart, and hence is not seen on
chest radiographs.
Pneumopericardium can have a
similar appearance but will show
air circumferentially outlining the
heart.

100. Flat Waist Sign
• Indicates left lower lobe collapse
• Visualized on frontal views
• Hilar structures shift downward
and rotation of heart produces
flattening of cardiac waist

101. Honeycomb Lung
• The term "honeycomb lung" first appeared
in the English literature in 1949 (Oswald and
Parkinson)
• Radiologically, in the latest version from the
Fleischner Society, it is defined as "clustered
cystic air spaces, typically of comparable
diameters on the order of 3-10 mm but
occasionally as large as 2.5 cm... usually
subpleural and characterized by well-defined
walls"
• Recent understanding indicates that
"honeycombing is often considered specific
for pulmonary fibrosis and is an important
criterion in the diagnosis of usual interstitial
pneumonia (UIP)"
• Causes:
- idiopathic interstitial pneumonia
- diffuse alveolar damage
- asbestosis
- interstitial granulomatous diseases
- eosinophilic granuloma

102. Cervicothoracic Sign
• Used to determine location of
mediastinal lesion in the upper
chest
• Uppermost border of the anterior
mediastinum ends at level of
clavicles, so when the cephalic
border of a mass is obscured at or
below the level of the clavicles, it is
deemed to be a "cervicothoracic
lesion" involving the anterior
mediastinum
• Middle and posterior
mediastinum extends above the
clavicles . Mediastinal mass
projected superior the level of
clavicles must be located either
within middle or posterior
mediastinum
• More cephalad the mass extends
the more posterior the location

103. Deep Sulcus Sign
• The presence of radiolucency in a
deep costophrenic sulcus on a supine
thoracic radiograph is characteristic of
a pneumothorax in a supine patient
• Seen on X-rays in supine position
• Intrapleural air rises to the highest
portion of the hemithorax leading to
the presence of a lucency in the
anteromedial, subpulmonic, and lateral
basilar space adjacent to the
diaphragm

104. Westermark Sign
• Described by Neil Westermark in
1938
• Chest radiograph and CT show
increased lucency or
hypoattenuation
• Typically signifies either
occlusion of a larger
lobar/segmental artery or
widespread small vessel occlusion
• Represents oligemia distal to PE;
seen only in 2% of patients
• Sign results from combination of
dilatation pulmonary arteries
proximal embolus and collapse of
distal vasculature
• Low sensitivity 11%, high
specificity 92%

105. Westermark Sign
Westermark sign is defined as a
focal area of oligemia distal to an
occluded pulmonary artery. This
area appears hypoattenuated
compared to the normal lung and
can be seen on both X-ray and CT
scan. This sign was first described
by Neil Westermark in the year
1938. This sign is quite rare and
seen in 2% of patients with
pulmonary thromboembolism. It
occurs due to a combination of
obstruction of pulmonary artery by
embolus and vasoconstriction
occurring in the hypoxic lung.

106. Ground Glass Pattern
• Ground glass opacity is a hazy,
increased attenuation of lung with
preservation of bronchial and
vascular margins .
• It is a nonspecific radiologic
finding
• It is caused by partial filling of air
spaces, interstitial thickening,
partial collapse of alveoli, normal
expiration, or increased capillary
blood volume
• It can be seen with alveolar wall
inflammation or thickening, with
partial air-space filling, or with
some combination of the two

107. Crazy Paving Sign
• Scattered or diffuse ground glass
attenuation with superimposed intralobular
and interlobular septa thickening .
Commonly seen at thin-section CT. Initially
described in pulmonary alveolar proteinosis.
Recognized in diverse entities
• Causes:
- infection (Pneumocystis jiroveci pneumonia,
organizing pneumonia, usual interstitial
pneumonia, non-specific interstitial
pneumonia, and exogenous lipoid
pneumonia)
- neoplasm (bronchioloalveolar carcinoma)
- pulmonary alveolar proteinosis
- sarcoidosis
- respiratory bronchiolitis with interstitial
lung disease
- sanguineous (pulmonary hemorrhage
syndromes, ARDS)

108. Mosaic Pattern
• Patchy ground glass opacicities,
resulting in a mosaic pattern of
lung attenuation .
• Such a pattern can be seen in
infiltrative lung disease, airway
abnormalities (e.g., asthma,
bronchiolitis obliterans), and
chronic pulmonary vascular
disease (e.g., chronic
thromboembolic disease)
• The distinction between these
three entities can be made by
observing the size of the
pulmonary vessels in the area of
increased lung attenuation
(increased in both airway disease
and vascular disease, but not in
infiltrative disease), and by
examining air trapping on
expiratory scans (indicating
airway disease)

109. Sandstorm
Appearance
• Seen on CT or chest X-ray
• The appearance is given by the
presence of diffuse, scattered,
bilateral areas of micronodular
calcifications (sandstorm
appearance)
• Pulmonary alveolar microlithiasis
(PAM) should be considered
• PAM is an uncommon chronic
disease characterized by
calcifications within the alveoli
which occurs in the absence of any
known disorder of calcium
metabolism

110. Feeding Vessel Sign
This sign consists of a pulmonary
artery leading to the center of the
nodule signifying the
hematogenous origin of the nodule
. It is seen in CT scan of the chest,
and is a strong indication of septic
embolism and is seen in
approximately 67–100% of septic
embolus cases. This can also be
seen in secondaries to the lung,
hemorrhagic nodules, pulmonary
vasculitis, pulmonary infarct, and
pulmonary arteriovenous
malformation. The feeding vessel
may even rotate around the nodule
instead of entering the center of
the nodule, which is seen clearly on
multiplanar images or may even
represent a pulmonary vein

111. Hampton Hump Sign
Pulmonary infarction secondary to pulmonary embolism produces an abnormal area of
opacification on the chest radiograph, which is always in contact with the pleural surface.

112. Wave Sign
• Sign produced by lateral
indentation of thymus by adjacent
anterior ribs resembling a wave
• This sign in seen in the pediatric
population and represents a
normal thymus

113. Tapered Margins Sign
• Lesions in the chest wall, pleura
or mediastinum have smooth
tapered borders and obtuse angles
• While parenchymal lesions
usually form acute angles

114. 1-2-3 Sign
• Characterized by bilateral
hilar and right paratracheal
lymphadenopathy so-called
Garland triad or 1-2-3 sign
• Suggestive of sarcoidosis
• Separation between nodes
and heart which is not seen
in lymphoma

115. Hilum Overlay Sign
• Described by Benjamin Felson
• If hilar vessels are sharply
delineated it can be assumed that
the overlying mass is anterior or
posterior
• If mass is inseparable from
pulmonary arteries, structures are
adjacent to one another

116. Hilum
Covergence Sign
• Used to distinguish between a
prominent hilum and an enlarged
pulmonary artery
• If branches of PA converge
toward central mass, is an enlarged
PA
• If branches of PA converge
toward heart rather than mass, is a
mediastinal tumor

117. Thoracoabdominal
Sign
• Posterior costophrenic sulcus extends
more caudally than anterior basilar lung
• Lesion extending below the dome of
diaphragm must be in posterior chest
whereas lesion terminating at dome
must be anterior
• Thoracoabdominal signs were
described by Felson

118. Water Bottle
Configuration
• Seen in pericardial effusion
• Causes:
- inflammatory
- infectious
- malignant
- autoimmune processes within the
pericardium
• Chest radiography shows an
enlarged cardiac silhouette

119. Double Density Sign
• On frontal chest radiographs,
this sign presents as a curvilinear
density projecting over the right
retrocardiac region, indicating
left atrial enlargement
• The curvilinear line represents
the inferolateral margin of the
left atrium
• The double density sign may be
observed in patients without
cardiac disease; however, there
is a semiquantitative
measurement to estimate the
left atrial diameter and better
estimate whether it is a real
finding

120. Juxtaphrenic Peak
Sign
This sign refers to a small triangular
shadow that obscures the dome of
the diaphragm secondary to upper
lobe atelectasis . The shadow is
caused by traction on the lower
end of the major fissure, the
inferior accessory fissure, or the
inferior pulmonary ligament.

121. Juxtaphrenic Sign
Also known as the Katten's sign.It is
seen on chest radiograph and
appears as a peak arising from the
medial part of the diaphragm . This
peak is caused most commonly by
traction from the inferior accessory
fissure, but can also be caused by
major fissure or inferior pulmonary
ligament. It is seen in upper lobe
collapse, middle lobe collapse, and
in cases of post upper lobectomy.

122. Luftsischel Sign
In left upper lobe collapse, the
superior segment of the left lower
lobe, which is positioned between
the aortic arch and the collapsed
left upper lobe, is hyperinflated.
This aerated segment of left lower
lobe is hyperlucent and shaped like
a sickle, where it outlines the aortic
arch on the frontal chest
radiograph.
This peri-aortic lucency has been
termed the luftsichel sign, derived
from the German words luft (air)
and sichel (sickle).

123. Naclerio's V Sign
This sign is a common presentation
in pneumomediastinum in which
there occurs a lucency in the shape
of “V” which is caused by air
outlining the medial part of the left
hemidiaphragm and lower
mediastinal border, and can be
seen both on X-ray and CT scan.
Although this sign was first
described by Naclerio in cases of
spontaneous esophageal rupture,
this sign is not specific for
esophageal rupture.

124. Polo Mint Sign
This sign is seen in a blood vessel in
a contrast-enhanced CT scan in
which the central filling defects
represent the thrombus while the
peripheral rim appears as a
hyperattenuating area due to
contrast which mimics the polo
mint. This could be seen in any
vessel with thrombus, such as
pulmonary artery, superior vena
cava, or portal vein.