Chest XRay in Pneumonia

Aka: Chest XRay in Pneumonia, Pneumonia Chest Radiography

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II. Indications: All cases of suspected Community Acquired Pneumonia

  1. Any patient with at least 1 of the following
    1. Temperature >100 F (37.8 C)
    2. Heart Rate >100 beats/min
    3. Respiratory Rate >20 breaths/min
  2. Any patient with at least 2 of the following
    1. Decreased breath sounds
    2. Rales or crackles
    3. No Asthma history to explain findings
  3. Other indications (not included in Ebell protocol)
    1. Hypoxemia
    2. Confusion
    3. Known structural lung disease
    4. Age > 60 years old
    5. Systemic illness signs

III. Technique: Interpretation

  1. See Chest XRay Interpretation
  2. Diffuse, bilateral infiltrates suggests atypical Community Acquired Pneumonia (CAP)
  3. Lobar infiltrate suggests typical Bacterial Community Acquired Pneumonia (CAP)
    1. General findings
      1. Lobar infiltrate
      2. Air Bronchograms (black air filled Bronchi are surrounded by white, infected alveoli)
    2. Right Middle lobe Pneumonia
      1. Obscures the right heart border (Silhouette Sign)
    3. Right lower lobe Pneumonia
      1. May obscure the right hemidiaphragm (PA/AP film)
      2. Right heart border is visible (PA/AP film)
    4. Left Lower Lobe Pneumonia
      1. May obscure the left hemidiaphragm (PA/AP film)
      2. May obscure the lower thoracic Vertebrae on lateral film (spine sign)
    5. Left Lingular Pneumonia
      1. Best seen on lateral film
      2. Heart border may be obscured on PA/AP film (Silhouette Sign)

IV. Precautions

  1. Underlying malignancy
    1. Confirm infiltrate resolution at 6 weeks after management (especially in smokers, or those over age 50)
  2. Low Test Sensitivity in Pneumonia (esp. in early presentation)
    1. Chest XRay Test Sensitivity 43% (Test Specificity 93%) for pulmonary opacities consistent with Pneumonia
      1. Compared with CT Chest as the gold standard
    2. False Negatives are more common in early presentation
      1. However, Pneumonia is a clinical diagnosis, and may be diagnosed despite negative Chest XRay
    3. Serial Chest XRays may be needed, or consider bedside Lung Ultrasound or CT
      1. Repeat XRay during hospital admission is not needed if patient is clinically improving on management
    4. Negative Chest XRay does not exclude Pneumonia in severe illness
      1. Positive in only 40% of acute pneumococcal Community Acquired Pneumonia (CAP)
      2. Treat empirically as Community Acquired Pneumonia if high suspicion despite negative XRay

V. Differential Diagnosis: False Positives - alternative causes of infiltrates

  1. Atelectasis
  2. Acute Respiratory Distress Syndrome (ARDS)
  3. Lung Neoplasm
  4. Diffuse Alveolar Hemorrhage (e.g. immune disorder)
  5. Pulmonary Embolism with Lung Infarction
  6. Right-sided endocarditis with septic emboli
  7. Tuberculosis
  8. Interstitial Lung Disease (e.g. acute Chlorine gas inhalation, Farmer's Lung)

VI. Causes: Pneumonia with effusion (and other non-infectious effusions)

  1. Pneumococcal Pneumonia (most common)
  2. Staphylococcal Pneumonia
  3. Haemophilus Influenzae Pneumonia
  4. Legionella
  5. Tuberculosis (especially consider in comorbid HIV Infection)
  6. Predominately left-sided effusions (e.g. Aortic Dissection, Esophageal Rupture)
  7. Predominately right-sided effusions (e.g. CHF, Pancreatitis, hepatitis)

VII. Causes: Lung Cavitary Lesions

  1. Lung Abscess caused by Anaerobic Bacteria (most common)
  2. Staphylococcal Pneumonia
  3. Pseudomonas Pneumonia
  4. Tuberculosis

VIII. References

  1. Swadron (2019) Pulmonary 1, CCME Emergency Board Review, accessed 5/29/2019
  2. Ebell (2007) Am Fam Physician 76(4): 560-2 [PubMed]

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