Kerley Lines: Radiographic Signs of Interstitial Lung Disease
Overview and Definition
Kerley lines are radiographic manifestations of interstitial thickening on chest X-ray, representing three distinct patterns (A, B, and C lines) that indicate fluid accumulation or pathologic processes in the pulmonary interstitium. These lines are most commonly seen in pulmonary edema from cardiac or renal insufficiency, lymphangitic carcinomatosis, and pulmonary veno-occlusive disease 1, 2, 3.
Kerley A Lines
Anatomic Basis and Appearance
- Kerley A lines represent thickened septal plates between lung segments and subsegments 4
- They appear as dense, fine lines (<1 mm thick) that are ≥2 cm in length, radiating from the hilum toward the periphery without bifurcation 4
- These lines primarily correspond to thickened and continued interlobular septal lines between lung segments (76% of cases) and subsegments 4
- In some cases (8%), they may represent thickened fissures, or occasionally bronchial walls/arteries (12%) or veins (4%) 4
Clinical Associations
- Kerley A lines are generally apparent in patients with pulmonary edema or lymphangitic carcinomatosis 4
- They indicate more central interstitial involvement compared to Kerley B lines 3
Kerley B Lines
Anatomic Basis and Appearance
- Kerley B lines are short (1-2 cm), thin, horizontal lines perpendicular to the pleural surface, representing thickened interlobular septa 2, 3
- They are most commonly visible at the lung bases and periphery on chest X-ray 2, 3
- These lines indicate increased lymphatic pressures from chronic fluid accumulation 2
Distribution Patterns for Differential Diagnosis
Pulmonary Congestion (Cardiac/Renal Insufficiency):
- Kerley B lines in the lung apex are present in 81% of cardiac insufficiency and 76% of renal insufficiency cases, which is highly specific for pulmonary congestion 5
- Distribution is homogenous throughout all lung zones (upper, middle, and lower lobes) 5
- The septal lines appear thicker than in interstitial lung disease 5
- When combined with peribronchial cuffing (present in 67% of cardiac cases) and increased cardiothoracic ratio, this pattern reliably differentiates congestion from ILD 5
Interstitial Lung Disease:
- Kerley B lines in the apex are present in only 26% of ILD cases 5
- Distribution shows a basilar predominance, increasing from 32% in upper lobes to 90% in lower lobes 5
- The septal lines appear thinner than in pulmonary congestion 5
- Ground-glass opacities are more prominent in lower lobes (87% of ILD cases vs. 42% in insufficiency) 5
Clinical Associations
- Kerley B lines are particularly associated with mitral stenosis or chronic heart failure 2
- They appear on chest X-ray in pulmonary veno-occlusive disease along with peripheral interstitial infiltrates 1
- In lymphangitic carcinomatosis, they represent tumor infiltration of the lymphatic system 4
Kerley C Lines
Anatomic Basis and Appearance
- Kerley C lines represent a reticular pattern created by the superimposition of multiple Kerley B lines 3
- They appear as a fine reticular or net-like pattern in the lung parenchyma 3
- These lines are less commonly described and represent more diffuse interstitial involvement 3
Kerley D Lines
Anatomic Basis and Appearance
- Kerley D lines are reticular opacities seen in the retrosternal clear space on lateral chest radiographs 6
- They were initially described in interstitial edema but are more commonly associated with pulmonary fibrosis 6
- These lines may be more easily identified in the retrosternal clear space than elsewhere on the chest radiograph 6
Clinical Significance
- Kerley D lines should prompt further evaluation with chest CT to assess for pulmonary fibrosis 6
- They represent a third type of pathology (after anterior mediastinal masses and emphysema) that can be identified in the retrosternal clear space 6
Clinical Context and Diagnostic Approach
When Kerley Lines Indicate Pulmonary Edema
The European Society of Cardiology recommends that chest X-ray findings of Kerley B lines, combined with pulmonary venous congestion, interstitial edema, and pleural effusions, confirm pulmonary congestion from elevated left ventricular filling pressures 2.
Key diagnostic steps:
- Measure plasma natriuretic peptides (BNP or NT-proBNP) using point-of-care assay to differentiate acute heart failure from non-cardiac causes 2
- Perform bedside lung ultrasound if expertise is available, as it has superior sensitivity to chest X-ray for detecting interstitial syndrome 1, 2
- Obtain ECG to exclude ST-elevation myocardial infarction 2
- Assess troponin, BUN/creatinine, electrolytes, and complete blood count 2
Lung Ultrasound as Superior Alternative
Lung ultrasound should be used as the first-line diagnostic approach for suspected interstitial syndrome, as it may lead to better patient outcomes compared to conventional chest radiography 1, 2.
- B-lines on ultrasound are the sonographic equivalent of Kerley lines, representing interstitial thickening 1, 7
- Three or more B-lines in a longitudinal plane between two ribs defines a positive region for interstitial syndrome 7
- The eight-region technique (four per hemithorax: anterior superior, anterior inferior, lateral superior, lateral inferior) is the standard protocol 1, 7
- Quantification of B-lines is directly proportional to the severity of pulmonary congestion 1, 2
- Chest X-ray is normal in nearly 20% of acute heart failure patients, limiting its sensitivity 2
Common Pitfalls and Clinical Caveats
Diagnostic Errors to Avoid
- A normal chest X-ray does not rule out heart failure, especially in early or well-compensated cases 2
- Interstitial edema can be confused with other interstitial lung diseases; always confirm heart failure with clinical context and biomarkers 2
- The absence of Kerley lines does not exclude pulmonary congestion, as some patients may have predominantly peripheral edema with minimal lung findings 2
Special Clinical Scenarios
- In pulmonary veno-occlusive disease, Kerley B lines appear with subpleural thickened septal lines, centrilobular ground-glass opacities, and mediastinal lymphadenopathy on high-resolution CT 1
- Vasodilators and prostanoids must be used with great caution in pulmonary veno-occlusive disease due to high risk of acute pulmonary edema 1
- Stage 1 near-drowning pulmonary edema manifests as Kerley lines with peribronchial cuffing and patchy perihilar consolidation 3
- High-altitude pulmonary edema usually demonstrates central interstitial edema with peribronchial cuffing and patchy airspace consolidation 3
Treatment Implications
When Kerley lines indicate acute pulmonary congestion:
- Administer intravenous loop diuretics (furosemide) as first-line treatment 2
- Provide oxygen therapy if SpO₂ <90% 2
- Consider intravenous nitroglycerin if systolic BP >100 mmHg to reduce preload and afterload 2
- Use non-invasive ventilation (CPAP/BiPAP) for patients with respiratory distress 2
- Monitor response with serial lung examinations and B-line quantification on ultrasound 2
- A decrease in natriuretic peptides >30% by day 5 and discharge NT-proBNP <1500 pg/mL indicates good prognosis 2