What is the significance of Kerley A and B lines on a chest X-ray and how are they managed?

Kerley A and B Lines: Clinical Significance and Management

Definition and Radiographic Appearance

Kerley B lines are short (1-2 cm), horizontal, thin lines perpendicular to the pleura at the lung bases, representing thickened interlobular septa, while Kerley A lines are longer (2-6 cm), diagonal lines radiating from the hilum toward the periphery, representing thickened septal plates between lung segments. 1, 2

• Kerley B lines appear as thin horizontal opacities at the lung periphery, most commonly at the costophrenic angles 1
• Kerley A lines are defined as dense, fine (<1 mm thick), ≥2 cm in length lines radiating from the hilum with no bifurcation and not adjacent to the pleura 2
• Kerley A lines primarily represent thickened and continued interlobular septal lines corresponding to septa between lung segments and subsegments 2

Clinical Significance

The presence of Kerley B lines on chest X-ray indicates interstitial pulmonary edema from elevated left ventricular filling pressures and is associated with worse prognosis in heart failure patients. 1, 3

Primary Etiologies:

• Cardiogenic pulmonary edema (most common): Elevated left ventricular filling pressure exceeding oncotic pressure forces fluid across the alveolar-capillary membrane 1
• Lymphangitic carcinomatosis: Tumor infiltration of pulmonary lymphatics 2
• Chronic heart failure/mitral stenosis: Increased lymphatic pressures from chronic fluid accumulation 1
• Renal insufficiency: Fluid overload states 4

Prognostic Value:

• Kerley B lines were present in 71% of patients hospitalized with acute heart failure 3
• A chest X-ray score incorporating Kerley B lines, pulmonary venous congestion, pleural effusions, and alveolar edema was independently associated with all-cause mortality (HR 1.10,95% CI 1.07-1.13, p<0.001) 3

Diagnostic Approach

When Kerley lines are identified on chest X-ray, immediately assess for heart failure using clinical examination, natriuretic peptides (BNP/NT-proBNP), and echocardiography to guide urgent treatment. 5, 1

Initial Evaluation:

• Measure plasma natriuretic peptides (BNP, NT-proBNP, or MR-proANP) using point-of-care assay to differentiate acute heart failure from non-cardiac causes of dyspnea 5
• Perform bedside lung ultrasound if expertise available—this modality has superior sensitivity compared to chest X-ray for detecting interstitial syndrome 5
• Obtain ECG to exclude ST-elevation myocardial infarction 5
• Laboratory assessment: troponin, BUN/urea, creatinine, electrolytes, glucose, complete blood count 5

Distinguishing Features on Imaging:

Kerley B lines in the lung apex are highly specific (81% sensitivity) for pulmonary congestion from cardiac or renal insufficiency rather than interstitial lung disease. 4

• In cardiac/renal insufficiency: Kerley B lines distributed homogeneously throughout lungs, including apices 4
• In interstitial lung disease: Kerley B lines increase from upper (32%) to lower lobes (90%), with thinner septal lines 4
• Peribronchial cuffing is significantly more frequent in cardiac insufficiency (67%) versus interstitial lung disease (0%, p<0.0001) 4

Management Strategy

Immediate treatment with intravenous loop diuretics and vasodilators (if systolic BP ≥90 mmHg) is mandatory when Kerley lines indicate acute cardiogenic pulmonary edema. 1

Acute Management Protocol:

1. Oxygen therapy: Administer immediately to maintain SpO2 >90% 1
2. Intravenous loop diuretics (e.g., furosemide): Cornerstone therapy, dose titrated to resolve clinical congestion 1
3. Vasodilators (intravenous nitroglycerin): First-line unless systolic BP <90 mmHg 1
4. Address underlying cardiac dysfunction: Identify and treat precipitating factors 1

Monitoring Response to Therapy:

Serial lung examinations and lung ultrasound quantification of B-lines provide objective assessment of treatment response. 5, 1

• B-line quantification on ultrasound is directly proportional to severity of pulmonary congestion 5
• Decreasing number of B-lines on serial ultrasound indicates successful diuresis 5
• Target natriuretic peptide reduction >30% by day 5, with discharge NT-proBNP <1500 pg/mL indicating good prognosis 1
• Serial lung examinations to assess resolution of rales 1

Ultrasound Superiority Over Chest X-Ray:

Lung ultrasound should be used as first-line diagnostic approach for suspected interstitial syndrome, as it has superior sensitivity compared to conventional chest X-ray and may lead to better patient outcomes. 5

• Chest X-ray is normal in nearly 20% of acute heart failure patients, limiting sensitivity 5
• Lung ultrasound allows direct visualization of interstitial edema with higher sensitivity 5
• Three or more B-lines in a longitudinal plane between two ribs defines positive interstitial syndrome 6
• Eight-region scanning technique (four per hemithorax) is the standard protocol 6

Critical Pitfalls to Avoid

• Do not assume normal chest X-ray excludes heart failure: Nearly 20% of acute heart failure patients have normal initial radiographs 5, 1
• Not all heart failure presents with Kerley lines: Some patients have predominantly peripheral edema with minimal lung findings 1
• Absence of rales does not rule out heart failure: Patients may have exercise intolerance without fluid retention 1
• Consider alternative diagnoses: Acute eosinophilic pneumonia can rarely present with Kerley A and B lines mimicking interstitial edema 7
• Kerley D lines (retrosternal reticular opacities on lateral chest X-ray) suggest pulmonary fibrosis and require chest CT evaluation 8