From svuhradiology.ie

1. How to Interpret a Chest X-Ray:
(Almost) everything a med student
needs to know
Dr Eric Heffernan
St Vincent’s University Hospital

2. Outline
• Introduction
• Normal CXR- technical aspects
• Normal Anatomy
• Approach to Interpretation
• Patterns of Abnormality

3. Introduction
• The CXR is the most commonly performed
imaging procedure in general Radiology
departments
• Comprises 30 – 50% of studies
• One of the most difficult films to interpret
– For Radiologists
– For you… on-call… at night… on your own!

4. Technical Aspects

5. The Normal CXR
• Standard CXR is taken:
– PA – minimal magnification of the heart
– Patient standing
– Full inspiration
• In ill patients, the CXR is usually taken:
– AP – magnifies cardiac shadow
– Often supine – diaphragms higher, lung volumes
lower, pathology often obscured

6. PA
AP
Effect of projection on apparent heart size
X-ray tube

7. PA
AP
Effect of projection on apparent heart size
X-ray tube

8. The Lateral CXR
• Purpose:
– To pinpoint location of a lesion seen on PA
– To identify lesions hidden behind the heart on PA
• Left lateral = left side of patient is against
digital plate = standard lateral projection
• Right lateral = performed to assess a lesion in
the right lung (decreases magnification of
lesion)

9. The Lateral CXR
• In practice, lateral radiographs are not routinely
performed any more so you will rarely have to
interpret one
• We occasionally request one ourselves when
reporting a PA chest radiograph, to clarify an
apparent abnormality rather than going straight
to CT
• When there is a definite abnormality on a PA
radiograph that requires further investigation, we
tend to go directly to CT nowadays

10. Additional CXR Views
• Lordotic
– Direction of x-ray beam relative to patient is angled
upwards at 45 degrees
– This projects clavicles above lung apices
– Useful if suspect an apical mass but is obscured by
clavicle
– Also useful if suspect an apparent apical lesion is
actually in a rib or clavicle
• Decubitus
– To confirm the presence of fluid suspected on upright
film (e.g. subpulmonic effusion)

11. Subpulmonic effusion on decubitus film
• The PA film shows an apparently elevated right diaphragm
• On the decubitus view, the effusion flows up along the side of the lung

12. Expiratory CXR
• Makes a pneumothorax appear relatively larger
than on an inspiratory film
• PTx may only visible on expiration film
• When you see the word ‘expiration’ on a CXR you
are almost certainly looking for a pneumothorax
(especially in an exam!)
• Expiratory film is also useful in kids when looking
for air trapping due to an obstructing foreign
body – lung on obstructed side remains expanded

13. Inspiration - 500mls air in
pleural space,
2500mls in lung
= 17% pneumothorax

14. Expiration - 500mls air in
pleural space,
1500mls in lung
= 25% pneumothorax
• Pleural line displaced
further inferiorly

15. Pneumothorax on inspiration

16. Same patient on expiration –
Pleural line is pushed lower and there is now evidence of tensio

17. Densities Displayed on CXR
• Air
• Fat
• Water/soft tissue
• Calcium
• Bone
• Metal
Black
White

18. Normal CXR Anatomy

19. Normal PA CXR

20. Assessing for Rotation
Spinous process should be equidistant
from medial ends of both clavicles

22. Trachea

23. Left main bronchus

24. Right main bronchus

25. Carinal Angle (40-75 degrees)

26. Right pulmonary artery

27. Left pulmonary artery

28. Aortic Arch

29. Descending Aorta

30. Aortopulmonary Window

31. Right Heart Border = Right atrium

32. Left Heart Border = Left Ventricle

33. Left Atrium

34. Cardiothoracic Ratio (<50%)

35. Anterior Ribs - full inspiration
1
2
3
4
5
6

36. Gastric air bubble

37. Normal lateral CXR

38. Trachea

39. Scapulae

40. 2 hemidiaphragms

41. Gastric air bubble

42. Aortic Arch

43. Left pulmonary artery

44. Left upper lobe bronchus

45. Right pulmonary artery

46. Left atrium

47. Left ventricle

48. IVC

49. Oblique Fissures

50. Fissures
Horizontal

51. Thoracic Vertebrae getting darker inferiorly
(if the lower vertebrae appear denser, it suggests pathology in a lower lobe e.g. consolidation)

52. Interpreting the CXR

53. Rule #1 – Don’t panic!

54. Rule #1 – Don’t panic!

55. Before you start…
1. Check patient label – name, DOB, gender
2. Orientation
– R or L marker (?dextrocardia)
– PA or AP (if not labeled, assume PA)
– Inspiratory or expiratory (if not labeled = insp)
– Erect or supine (again, if not labeled assume
erect)
– Rotated? (clavicles relative to spinous process!)

56. Rotated ED film
One lung field appears whiter,
Difficult to assess cardiac silhouette
Same patient,
better centred CXR
Traumatic diaphragmatic hernia

57. Don’t get caught out by markers!

58. Same image shown the correct way around –
Patient had Kartagener’s Syndrome with situs inversus

59. Before you start…
3. Adequate exposure?
– Should just about be able to see thoracic
vertebrae through heart
• Can’t see them at all? – underexposed, everything too
white
• Vertebrae and disk spaces very clear? – overexposed,
everything too dark
• In over- and under-exposed CXRs, lung pathology is
easily obscured
• This is less of a problem now that we have digital
radiography and automatic exposure control

60. Before you start…
4. Adequate inspiration?
– Count ribs – choose one of these methods
• 9 or 10 ribs posteriorly
• 6 ribs anteriorly (I prefer this one)
– If inspiration is suboptimal, basal lung pathology
may be obscured

61. Interpretation of Findings
ABCDEs

62. Interpretation of Findings
A – airway
B – breasts and bones
C – cardiovascular
D – diaphragm
E – examine the lungs
s – soft tissues

63. Airway
• Trachea, carina and main bronchi

64. Airway
• Trachea
– Central?
• Can be pulled by
– lobar collapse
– fibrosis (e.g. old TB)
– lobectomy
• Can be pushed by
– mediastinal mass
– tension pneumothorax
– large pleural effusion

65. Airway
• Trachea
– Narrowed?
• Retrosternal goitre, other mediastinal masses
• Carina
– Splayed?
• Normal carinal angle is ~60 degrees (range 40-75)
• Angle increased by subcarinal lymphadenopathy, left
atrial enlargement

66. Airway
• Bronchi
– Narrowed?
– Elevated or depressed?
• Lobar collapse, lobectomy, fibrosis

67. Retrosternal goitre
Goitre
Trachea
Goitre on CT

68. Splayed carina due to left atrial
enlargement (cardiomyopathy)

69. Breasts
• Mastectomy?
– Makes underlying lung look relatively dark
– Look for:
• Lung mets
• Pleural effusion
• Interstitial disease (lymphangiitis)
• Lymphadenopathy
• Bone mets

70. Right mastectomy – arrow pointing at left breast shadow
Note how relatively lucent the right lung appears.

71. Left mastectomy
Beware of remaining nipple mimicking a nodule!

72. Right mastectomy - rib met and pathological fracture left humerus

73. Bones
• Destructive lesions – metastases
• Erosion by adjacent tumour, e.g. Pancoast
• Rib fractures
– Sensitivity of CXR is less than 20%
– However, when you see one look carefully for
pneumothorax, haemothorax, lung contusion
• Shoulder dislocation

74. Rib met

75. Pancoast tumour – eroding second rib

76. Dislocated humeral head

77. Forequarter amputation – left clavicle and scapula missing

78. Cardiovascular system
• Heart size <50% of cardiothoracic ration on PA
film
• Generalize cardiomegaly or specific chamber?
• Valve replacement?
• Sternotomy wires?
• Pacemaker? – check for complications if
recently inserted (pneumothorax)

79. Left atrial enlargement in mitral stenosis -
double right heart border, splayed carina

80. Sternotomy wires and aortic valve replacement

81. Cardiovascular
• Abnormal calcifications
– Valves
– Coronary arteries
– Old infarct
– Atrial myxoma
– Previous pericarditis e.g. old TB

82. Cardiovascular
• Thoracic aorta – aneurysm?
• Aortopulmonary window – nodes?
• Hila - ?enlarged – nodes or vessels

83. Ascending thoracic aortic aneurysm

84. Cardiovascular
• Pulmonary vasculature
– Generalized increase in vascular markings
• Left to right shunt
– Focal or unilateral decrease in lung markings
• Westermark’s sign (PE)
– Large central pulmonary arteries with sudden
tapering
• Pulmonary hypertension, e.g. chronic lung disease, PPH

85. Cardiovascular
• Pulmonary vasculature
– Increased size of upper lobe pulmonary veins in
CCF – subtle early CXR sign
• Finally, look BEHIND the heart
– Lung nodule/mass
– Hiatus hernia
– Oesophageal dilatation (tumour, achalasia)

86. Upper lobe venous diversion
- patient with mitral stenosis
Left atrial enlargement
Kerley B lines

87. Magnified Kerley B lines in same patient

88. Large hiatus hernia

89. Diaphragms
• Right higher than left by no more than 2.5 cm
• Larger difference, or L higher than R
– Phrenic nerve palsy e.g. tumour, surgery
– Volume loss in lung e.g. lobar collapse, lobectomy,
pneumonectomy
– Diaphragmatic hernia
– Subpulmonic effusion

90. Diaphragms
• Depressed, flattened diaphragms
– Hyperinflation (asthma, COPD, cystic fibrosis)
• GAS BELOW DIAPHRAGM (erect film)
– Need to be sitting up for at least 20 minutes
• NO gas below diaphragm (no gastric air
bubble)
– Sign of achalasia
• Costophrenic angles - blunted?
– pleural effusion

91. Pneumoperitoneum

92. Achalasia -
no gastric air bubble
Same patient –
Barium swallow

93. Examine the Lungs
• Are the lungs equal in density?
• One lung too dark
– Rotation
– Mastectomy
– Pneumothorax
– Large bulla
– PE

94. Left lung slightly dark-
small pneumothorax

95. Examine the Lungs
• Are the lungs equal in density?
• One lung too white
– Solitary breast
– Pleural effusion
– Pleural mass (mesothelioma, mets)
– Lobar collapse
– Consolidation
– Pulmonary mass

96. Large effusion with mediastinal shift

97. Effusion with absent meniscus -
hydropneumothorax

98. Examine the Lungs
• Are the lungs equal in density?
• Both lungs too dark
– Overexposed film – check if vertebral bodies too
clearly seen
– COPD
• Count ribs (8 or more anteriorly)
• Flattened diaphragms
• Bullae

99. Emphysema
• Flattened diaphragms
• Too many ribs
8
1

100. Examine the Lungs
• Are the lungs equal in density?
• Both lungs too white
– Underexposed film
– Pulmonary oedema
– Pulmonary fibrosis (what zones??)
– Miliary shadowing – TB, mets

101. Pulmonary oedema - cardiomegaly

102. Examine the Lungs
• Are the hemithoraces equal in volume?
– Increased volume
• Tension pneumothorax
• Large effusion
• Expanded lobe (e.g. Klebsiella pneumonia)

103. Examine the Lungs
• Are the hemithoraces equal in volume?
– Decreased volume
• Lobar collapse
• Lobectomy, pneumonectomy
• Fibrothorax (restrictive, thickened pleura secondary to
old TB or empyema)
• Diaphragmatic paralysis or rupture

104. Tension pneumothorax

105. Soft Tissues
• Surgical emphysema – neck and chest
– Trauma
– Surgery
– Chest drain
– Asthma
• When you see surgical emphysema, search
very carefully for a pneumothorax and/or
pneumomediastinum

106. Surgical emphysema – pneumothorax (arrow)

107. Patterns of Abnormality on CXR

108. CXR Patterns
• Having identified that the lungs are abnormal,
you now need to decide what the problem is
• Which of the following patterns does the
abnormality fit into?
– Alveolar consolidation
– Interstitial lung disease
– Atelectasis (collapse)
– Nodules and masses
– Cavities and cysts
– Calcification/ossification

109. Alveolar Consolidation
• Signs
– May be localized or diffuse
– Homogeneous, amorphous increased density
– Ill-defined margins
– Air bronchograms
– No volume loss

110. Air bronchograms in left lower lobe and lingular pneumonia

111. Alveolar Consolidation
• Causes
– Water (oedema)
– Pus (pneumonia)
– Blood (contusion, vasculitis, Goodpasture’s,
anticoagulation)
– Chronic infiltrative lung disease (BOOP, alveolar
proteinosis, eosinophilic pneumonias)
– Neoplasm (adenocarcinoma)
– Aspiration (gastric contents, near-drowning)

112. Alveolar Consolidation
• Which lobe is involved?
• Look for absent silhouette:
– Right hemidiaphragm = RLL
– Right heart border = RML
– Left hemidiaphragm = LLL
– Left heart border = lingula (of LUL)
– None – could be upper lobes or apical segments
of lower lobes

113. RUL (above horizontal fissure) and
lingular (obscuring left heart border) pneumonia
Horizontal fissure

114. RLL pneumonia LLL pneumonia (apical segment)
Small effusion
(meniscus sign)

115. LLL pneumonia obscuring left hemidiaphragm

116. Interstitial Lung Disease
• Signs
– Opacities
• Linear (reticular – fine or coarse)
• Nodular
• Mixed (reticulonodular)
– Septal lines e.g. Kerley B
– Honeycombing

117. Interstitial Lung Disease
• Examples
– Reticular pattern
• Fibrotic lung diseases
– UIP/CFA/IPF
– Collagen vascular disease
– Asbestosis

118. Interstitial Lung Disease
• Examples
– Nodular pattern
• Silicosis
• Coal workers’ pneumoconiosis
• Sarcoidosis
• Miliary TB

119. Fine reticular pattern -
Idiopathic pulmonary fibrosis

120. Nodular pattern - miliary TB

121. Atelectasis
• Signs
– Opacification of a lobe
– Volume loss
• Displacement of fissures
• Elevated hemidiaphragm
• Mediastinal displacement
• Tracheal displacement
• Compensatory hyperinflation of opposite lung

122. Atelectasis
• Right upper lobe atelectasis
– Collapses superiorly and medially
– Wedge shaped opacity in right upper zone
– Horizontal fissure displaced upwards
– Oblique fissure displaced anteriorly on lateral CXR

123. Atelectasis
• Left upper lobe atelectasis
– ‘veil’-like opacity in left hemithorax
– Often obliterates left heart border silhouette (as
lingula is in LUL)
– Elevated left hilum
– Oblique fissure displaced anteriorly

124. LUL collapse -
trachea displaced to left
left hilum elevated
left hemidiaphragm elevated

125. Atelectasis
• Right middle lobe atelectasis
– Collapses medially obliterating right heart border
– On lateral, see wedge-shaped opacity anteriorly
– Pulls horizontal fissure downwards

126. RML collapse

127. Atelectasis
• Lower lobe atelectasis
– Similar appearance on both sides
– Obliterates normal silhouette of hemidiaphragm
– On lateral CXR, see triangular density posteriorly
with increasing opacity of lower thoracic
vertebrae

128. LLL collapse – ‘sail’ sign

129. LLL collapse – lateral

130. Nodules and Masses
• Nodule is <3cm, mass is >/= 3cm
• Solitary or multiple?
• Solitary – long differential diagnosis e.g.
– Bronchogenic ca, granuloma, hamartoma, met
• Multiple – also long ddx
– Mets, granulomas, rheumatoid nodules,
sarcoidosis

131. Bronchogenic carcinoma -
background COPD and thoracic aortic aneurysm

132. Cannonball metastases

133. Cavities and Cysts
• Cyst = thin wall (< 3mm)
– Fluid or air-filled, or both (air/fluid level)
• Cavity = thicker wall (> 3mm)
– Always contain air +/- air/fluid level
– Usually in an area of consolidation, a mass or a
nodule

134. Cavities or Cysts
• Types
– Congenital
• Bronchogenic cyst
• Cystic adenomatoid malformation
– Acquired
• Infection – abscess, TB, fungal, septic infarct
• Rheumatoid nodules
• Wegener’s
• Neoplasms - primary (SCC), mets
• Bullae
• Bronchiectasis

135. Cavitating pneumonia

136. Calcification and Ossification
• Nodules
– TB, histoplasmosis, mets from osteosarcoma
• Diffuse
– Alveolar microlithiasis
– Silicosis
– End-stage mitral stenosis
– Healed infections – miliary TB, chickenpox

137. Multiple very dense lung masses –
Metastatic osteosarcoma

138. Final Comments
• Before diving into a CXR, take a step back and
look at the age/gender, any labels on the
image (L/R, erect, AP, expiration), technical
quality
• If you remember your ABCDEs you’re unlikely
to miss any findings

139. svuhradiology.ie
Dr Eric Heffernan
St Vincent’s University Hospital