Increase in cardio-thoracic ratio is a relatively specific indicator of left ventricular end-diastolic volume. Left atrial enlargement is seen as double density shadow, lifting up of the left main bronchus and left atrial appendage enlargement.
When pulmonary venous pressure rises to 12 to 18 mmHg, pulmonary blood flow is redirected to upper lobes in the erect position. Thus prominent upper lobar veins indicate pulmonary venous hypertension ("cephalisation").
With pressure above 18 mmHg, interstitial edema develops. Kerley B lines are seen in interstitial pulmonary edema. Kerley B lines are interlobular septal lines and are seen as thin horizontal lines at both lung bases perpendicular to the lateral pleural surface.
When the pulmonary venous pressure exceeds 25 mmHg, alveolar edema occurs. Acute pulmonary edema produces "butterfly" or "bat wing" pattern in the chest X-ray seen in the inner two thirds of the lung. The outer third of the lung has better ventilation, better pumping action during respiration, better compliance and better lymphatic drainage.
Onset of pulmonary arterial hypertension leads to prominent central vessels with peripheral pruning ("Centralisation").