Uncategorized

• • What is it:
    • Oligemia refers to:
      • Decreased blood volume within a region
        • of the lung,
        • or the entire lung.
    • It represents:
      • Reduced vascularity, often
      • seen on imaging as an:
        • Area of diminished pulmonary vascular markings.
    • Oligemia is typically associated with conditions causing:
      • Vascular obstruction,
      • Hypoperfusion, or
      • Increased pulmonary vascular resistance.
  • Etymology:
    • Derived from the Greek words oligos (few) and haima (blood), meaning “reduced blood.”
  • AKA:
    • Hypovascular lung.
  • How does it appear on each relevant imaging modality:
    • Chest X-ray:
      • Localized or diffuse areas of decreased pulmonary vascular markings.
      • Hyperlucency in the affected region due to reduced blood flow.
      • May demonstrate the Westermark sign:
        • A focal area of hyperlucency caused by a reduction in pulmonary blood flow, commonly seen in acute pulmonary embolism.
    • Chest CT (CT angiography):
      • Parts: Affected lung regions show a reduction in visible pulmonary vessels.
      • Size: The hypovascular area may involve a segment, lobe, or the entire lung.
      • Shape: Typically corresponds to vascular territories.
      • Position: Often peripheral or segmental in conditions like pulmonary embolism.
      • Character:
        • Decreased vascularity with potential accompanying findings like thrombus in pulmonary arteries or signs of overinflation.
      • Time:
        • May resolve with treatment (e.g., thrombolysis) or persist in chronic conditions (e.g., chronic thromboembolic pulmonary hypertension).
      • Utility of dual-energy CT angiography (CTa):
        • Provides enhanced visualization of perfusion abnormalities through iodine maps, highlighting regions of hypoperfusion caused by vascular obstruction or other pathologies.
    • MRI:
      • Can demonstrate reduced perfusion in affected areas using contrast-enhanced sequences.
    • Nuclear medicine (V/Q scan):
      • Shows areas of ventilation-perfusion mismatch, with normal ventilation but reduced perfusion (classically seen in pulmonary embolism).
    • Angiography:
      • Direct visualization of vascular obstruction or hypoperfusion in the affected regions.
  • These findings reflect:
    • Vascular obstruction or hypoperfusion:
      • Pulmonary embolism (most common cause).
      • Pulmonary arterial stenosis (congenital or acquired).
      • Tumor invasion causing vascular obstruction.
    • Hyperinflation or air trapping:
      • Asthma or COPD (regional oligemia due to localized hyperinflation).
      • Foreign body obstruction with regional hypoperfusion.
    • Increased vascular resistance:
      • Pulmonary hypertension (primary or secondary).
      • Chronic thromboembolic pulmonary hypertension (CTEPH).
  • Differential diagnosis:
    • Vascular causes:
      • Acute pulmonary embolism.
      • Pulmonary arterial stenosis or vasculitis.
      • Tumor embolism or vascular compression.
    • Pulmonary causes:
      • Severe COPD with regional hypoperfusion.
      • Asthma with lobar or segmental air trapping.
      • Foreign body causing localized air trapping and oligemia.
    • Congenital causes:
      • Congenital pulmonary arterial hypoplasia or stenosis.
    • Cardiac causes:
      • Eisenmenger syndrome with right-to-left shunting.
  • Recommendations:
    • Perform CT pulmonary angiography (CTPA) to evaluate for vascular obstruction such as pulmonary embolism.
    • Use dual-energy CTa with iodine mapping to assess regional perfusion abnormalities.
    • Obtain V/Q scan for functional assessment in cases where CTPA is contraindicated (e.g., in renal failure or pregnancy).
      • V/Q scan is often preferred in pregnancy due to its lower radiation dose to breast tissue compared to CTPA, especially when using a perfusion-only protocol when there is no other clinical suspicion of lung disease.
    • Consider echocardiography to assess for elevated pulmonary pressures or right-sided heart strain.
    • MRI or invasive angiography may be required for suspected vascular malformations or tumors.
  • Key points and pearls:
    • Oligemia is most commonly associated with pulmonary embolism, and its detection should prompt immediate evaluation for thromboembolic disease.
    • Areas of oligemia in hyperlucent lungs may indicate air trapping (e.g., in asthma or COPD).
    • The Westermark sign is a key radiographic finding for oligemia in acute pulmonary embolism.
    • Dual-energy CTa with iodine maps provides advanced evaluation of perfusion abnormalities, improving diagnostic accuracy for vascular causes of oligemia.