The Basics Of Chest X Ray Interpretation

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Chest X Ray is probably the most common imaging test.  Few providers (including MDs) are comfortable interpreting their own films. Clinical decisions are too often made based on reports from non-clinicians. Having a systematic and repetitive approach is the key.

By the end of this lecture, the learner will be able to:

  • Develop an understanding of the normal CXR appearance
  • Assess the technical quality of a CXR
  • Utilize a systematic and reliable approach in CXR evaluation
  • Identify common CXR findings
  • Correlate basic CXR findings with clinical evaluation in order to reach a diagnosis

Understand the normal Chest X Ray

  • Develop confidence with the normal appearance.
  • Type of CXR will have an impact on what is considered “normal”
  • Know which structures should be present or absent

Different Types of CXR

Postero-anterior (PA; standard):

Patient is usually standing with anterior chest against the x-ray plate. X-ray beam originates from 5-6 feet behind the patient. The beam penetrates from posterior to anterior chest


Antero-posterior (AP; portable):

Patient is usually in bed and leaning with back against the x-ray plate. X-ray beam originates from 2-4 feet in front of the patient. The beam penetrates from anterior to posterior chest.





Utilize a Systematic Approach


Assessing Technical Quality

  • R – rotation
  • I – inspiration
  • P – penetration


Ideally CXR beam should be transmitted perpendicular to the chest. Abnormal angles will distort the image by creating an oblique view. Clavicular heads should be equidistant from vertebral spinous processes.




Assessment of inspiratory effort and lung volumes. Ideally 7-9 ribs should be visible. Less than 7 suggests poor effort by the patient and/or low lung volumes as in restrictive lung disease, atelectasis, etc. 10 or more ribs typically suggests hyperinflation as in COPD, asthma, bronchiectasis.





Exposure quality of the film. Over-penetration will make structures more radiolucent which could lessen significance of opacities. Under-penetration will make structures more radioopaque, which may lead to “over-calling” certain findings




 Evaluation of Structures

  • A – airway
  • B – bones (and soft tissues)
  • C – cardiac silhouette
  • D – diaphragm
  • E – everything else (hardware)



  • Deviation
  • Caliber


  • Typical angle
  • Splaying

Mainstem and lobar bronchi

  • Right mainstem is more straightly aligned with trachea


 Bones (and soft tissues)

Scan all bony structures

  • Fractures
  • Pins/rods/staples/wires
  • Thoracic cage deformities (scoliosis, etc.)


Evaluate the size and shape of the cardiac silhouette. Look for following:

  • Cardiomegaly – width of the silhouette is greater than 1⁄2 the thoracic cage width. Can be exaggerated or “over-called” on AP (portable) films.
  • Aortic knob
  • Left atrium
  • Pulmonary arteries
  • Shift of mediastinal structures
  • Cardiac borders
  • Pericardial effusion



  • Diaphragmatic line should be clearly demarcated
  • Evaluate costophrenic and cardiophrenic angles
  • Retrocardiac space
  • Elevation or flattening of the hemidiaphragms
  • Also look at structures immediately beneath diaphragm (liver, gastric bubble,

free air in the abdomen)

  • Things that obscure the diaphragm:

Pleural effusion

○ Atelectasis

○ Lower lobe infiltrates or mass


Everything Else (Hardware)

  • Endotracheal tube

○ Tip should be 2-4 cm from the carina

  • Central line

○ Tip of catheter should lie in the cavo-atrial junction

  • Pacemaker or defibrillator

○ Know how to tell the difference

○ Leads can be placed in the atria or ventricles

  • Chest tubes

○ Always identify the “sentinel” hole to make sure it is within the pleural space




  • Make a conscious effort to evaluate the lung parenchyma last!!
  • Look at each side independently and then compare the two sides
  • Point out features that seem abnormal
  • Always describe before diagnosing!


Common terms

  • Opacities

○ Something which appears relatively radio-opaque compared to normal lung

○ Alveolar opacity

○ Interstitial opacity

  • Mass/Nodule

○ Discrete appearance with apparent borders

○ Nodule < 3 cm

○ Can be pleural-based or parenchymal

  • Consolidation

○ Focal confluence of alveolar opacities

○ Air bronchograms

○ Obliteration of vessels

  • Atelectasis vs. Effusion

○ Look for discrete lines or lobar distribution for atelectasis

○ Effusions are usually dependent which causes gradation from base upwards

  • Edema

○ Alveolar vs. Interstitial patterns

  • Fibrosis

○ Septal thickening

○ Honeycombing


Clinical Correlations

A Common Radiology Report “The lung fields demonstrate non-specific hazy, discrete interstitial and alveolar infiltrates or opacities that could represent any of the following: consolidation, effusion, atelectasis, or mass. These findings could suggest pneumonia, lung malignancy, or absolutely nothing. Please correlate clinically.”

Case #1

60 y/o M with recent pneumonia, returns with severe shortness of breath and cough. Also complains of L-sided chest pain when taking a breath.

T 101.3 HR 115 BP 120/70 RR 30 O2Sat 87%

Exam: tachypneic, diminished breath sounds in L hemithorax

Labs: WBC 21.2 BUN 28 Cr 1.4


What is the most likely diagnosis?

A) Recurrent pneumonia

B) Mucus plugging leading to atelectasis

C) Parapneumonic pleural effusion

D) Hemothorax

E) Tension pneumothorax


C) Parapneumonic pleural effusion

 Case #2

68 y/o male with history of smoking presents with intermittent night sweats, weight loss, and hemoptysis.

T 99.0 HR 96 BP 118/80 RR 18 O2Sat 98%

Exam: no distress; breath sounds clear bilaterally

Labs: WBC 11.5 Hgb 9.5


What is the most likely diagnosis?

A) Aspergilloma

B) Tuberculosis

C) Lung adenocarcinoma

D) Sarcoidosis


C) Lung adenocarcinoma

 Case #3

42 y/o male with history of CAD presents with sudden onset of chest pain and severe shortness of breath. The pain radiates to the back and he finds it hard to take a deep breath. He also was in a car accident 2 days ago and has been under a lot of stress.

T 98.0 HR 130 BP 85/50 RR 35 O2Sat 80%

Exam: severe resp distress, diminished breath sounds, mild tracheal deviation

Labs: WBC 14.5

EKG: sinus tachycardia, T wave inversions


What is the most likely diagnosis?

A) Aspiration pneumonia

B) Myocardial infarction

C) Aortic dissection

D) Hemothorax

E) Tension pneumothorax


E) Tension pneumothorax

 Case #4

What do you think of this CXR?

A) Lobar pneumonia

B) Atelectasis

C) Pleural effusion

D) Cardiomegaly



B) Atelectasis

 Case #5

40 y/o male with recent influenza infection presenting with shortness of breath, recurrent fever, cough, and yellow-green sputum production.

T 102.3 HR 110 BP 105/65 RR 24 O2Sat 93%

Exam: diminished breath sounds and some scattered crackles/rhonchi

Labs: WBC 22.5 BUN 30 Cr 1.6 BNP 45


What is the most likely diagnosis?

A) Pleural effusion

B) Pulmonary edema

C) Multifocal pneumonia

D) Atelectasis due to mucus plugging

E) Interstitial lung disease


C) Multifocal pneumonia

 Case #6

70 y/o male with history of ETOH abuse is admitted with acute pancreatitis. He is admitted to the hospital for aggressive IV fluid resuscitation and pain control. Over the next 24 hours he develops worsening respiratory distress?

T 100.2 HR 120 BP 160/95 RR 35 O2Sat 86%

Exam: diaphoretic, tachypneic, inspiratory crackles in lower lung fields


What is the most likely diagnosis?

A) Hospital-acquired pneumonia


C) Myocardial infarction leading to pulmonary edema

D) Aspiration pneumonitis




  • Look at all your films – even the “normal” ones
  • Use a repetitive & reliable system to avoid missing details
  • Describe findings first before considering a diagnosis
  • Clinical correlation is ALWAYS necessary to arrive at a diagnosis


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