Physiological approach to reading chest radiography. Clinical implications

Interpretation of chest X-ray relies not only on morphological criterion bu t also on physiological bases. vascular opacities represent 80% of visible structures in the lung area; the contour of the heart and large vessels are well recognized. In the first part we review the current knowledge about t he physiology of the pulmonary circulation and its factors of regulation. I n the second part we present the reading principals of a chest X-ray obtain ed in an erect patient at the end of inspiration. A check list should be ve rify in every patient: pulmonary flow distribution (ratio apex/basis); size of small vessels in the periphery of both lungs; Simon's line; shape of ve ssels; ratio of the artery/bronchus diameter; size and shape of the heart; diameters of aorta, right pulmonary artery, and azygos vein. in the last pa rt, we present the main pathological patterns: diffuse increase of pulmonar y flow; pulmonary venous hypertension; pulmonary arterial hypertension; loc alized changes of the pulmonary blood flow in which the role of expiratory X-ray is emphasized. Many pitfalls are identified: egalisation of the ratio apex/basis; enlargement of the vascular pedicle; enlargement of the azygos vein.