What does it mean if the left hilum is higher than the right on a chest X-ray?

Left Hilar Elevation on Chest X-Ray: Significance and Implications

A left hilum higher than the right on a chest X-ray is typically a normal anatomical variant and is not usually a cause for concern. 1

Normal Anatomical Variation vs. Pathological Finding

The position of the pulmonary hila on chest radiographs follows a general pattern:

• Normal finding: The left hilum is typically positioned 0.5-1.0 cm higher than the right hilum due to:

  • The normal anatomical course of the left pulmonary artery
  • The heart's leftward position in the chest
  • The asymmetrical branching of the bronchial tree

• Abnormal finding: The right hilum being higher than the left is more concerning and may indicate pathology

Radiographic Assessment of Hilar Position

When evaluating hilar position on chest X-ray, consider:

• Measurement technique: The right descending pulmonary artery should measure ≤16 mm in men and ≤15 mm in women at the hilum on a PA view 1
• Left descending pulmonary artery: Should measure ≤18 mm on the lateral view (though this has lower specificity at 67%) 1
• Additional views: Both anteroposterior and lateral chest X-rays are recommended for proper assessment 1

When to Consider Pathology

While left hilar elevation is usually normal, certain accompanying findings warrant further investigation:

• Enlargement of the hilar shadow (>35 mm from midline to left lateral border of pulmonary artery)
• Rapid tapering or "pruning" of pulmonary vessels
• Right heart chamber enlargement
• Abnormal lucency or soft tissue opacity
• Deviation of the mediastinum
• Abnormal bowel gas pattern within the chest

Differential Diagnosis When Hilar Elevation is Concerning

If hilar elevation is accompanied by concerning features, consider:

1. Pulmonary hypertension: May show enlarged central pulmonary arteries with rapid tapering 1
2. Diaphragmatic hernia: May present with abnormal bowel gas pattern or air-fluid levels in the chest 1
3. Hilar mass: Including primary lung cancer, metastasis, or benign conditions like sarcoidosis 2
4. Bronchial rupture: Complete rupture can cause the "fallen lung sign" with the lung hanging on the hilum 3

Next Steps for Concerning Findings

If the hilar elevation is accompanied by concerning features:

1. CT scan with contrast: Gold standard for further evaluation of hilar abnormalities, with sensitivity and specificity of 14-82% and 87%, respectively 1
2. Echocardiography: If pulmonary hypertension is suspected 1
3. Diagnostic procedures: May include bronchoscopy, mediastinoscopy, or biopsy depending on the suspected pathology 2

Common Pitfalls in Interpretation

• Perceptual errors: Chest X-rays are prone to interpretation errors, with hilar abnormalities being commonly missed 4
• Technical factors: Patient positioning, degree of inspiration, and rotation can affect the apparent position of the hila
• Overlooking subtle signs: Small changes in hilar size or density may be the only indication of early pathology
• Satisfaction of search: Finding one abnormality (like hilar elevation) may lead to missing other important findings

Remember that while isolated left hilar elevation is typically normal, any accompanying concerning features should prompt further investigation with more advanced imaging.