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.
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.
