What does a chest x-ray (CXR) showing a left hilar level lower than the right hilar level indicate?

Chest X-ray Showing Left Hilar Level Lower Than Right Hilar Level

A chest X-ray showing the left hilar level lower than the right hilar level is typically a normal anatomical finding and not indicative of pathology. This asymmetry reflects normal anatomical positioning of the pulmonary vessels and bronchi.

Normal Hilar Anatomy

The hilar regions on a chest X-ray represent the pulmonary vessels, bronchi, and lymph nodes entering and exiting each lung. The normal anatomical arrangement includes:

• The left hilum is normally positioned 1-2 cm lower than the right hilum
• This occurs because:
  • The left main bronchus is longer and has a more horizontal course than the right
  • The left pulmonary artery takes a more horizontal course over the left main bronchus
  • The right main bronchus is shorter and more vertical

Clinical Significance

This finding by itself does not suggest pathology and should be interpreted as a normal variant. However, it's important to evaluate other radiographic features when interpreting hilar positions:

• Abnormal hilar enlargement may suggest:
  • Lymphadenopathy
  • Pulmonary arterial hypertension
  • Hilar masses

When to Be Concerned

While asymmetric hilar levels are normal, certain additional findings warrant further investigation:

• Enlargement of either hilum (>15 mm in women or >16 mm in men at the right descending pulmonary artery) 1
• Abnormal contour or density of the hilar shadows
• Unilateral hilar enlargement
• Associated mediastinal widening
• Rapid change in appearance from previous imaging

Evaluation of Abnormal Hilar Findings

If there are concerns about hilar abnormalities beyond the normal asymmetry:

1. Compare with prior chest X-rays if available
2. Consider CT imaging for better characterization
3. Evaluate for signs of pulmonary hypertension:
   • Enlarged central pulmonary arteries
   • Pruning of peripheral vessels
   • Right heart chamber enlargement 1

Common Pitfalls

• Misinterpreting normal anatomical variation as pathology
• Failing to compare with previous imaging
• Not considering the three-dimensional nature of hilar structures when viewing two-dimensional X-ray images
• Overlooking subtle changes in hilar contour or density that might indicate early pathology

Remember that while the left hilum is normally positioned lower than the right, any significant change in hilar size, shape, or density should prompt further evaluation, particularly if accompanied by clinical symptoms.