The hilum of the lung: Two classical radiological signs to decipher it.

Assessing the hilum of the lung is a common challenge in daily practice because various structures converge in this complex anatomic region. Because chest X-rays are widely available and deliver relatively low doses of radiation, they continue to be the most common imaging test, although new imaging modalities have decreased the use of chest X-rays for differentiating between true abnormalities and superimposed lung opacities. This article reviews the literature and describes the principal anatomic relations of the lung hilum through illustrative cases to enable the two most important radiologic signs to be identified: "hilum overlay" and "hilum convergence". In the initial imaging evaluation of patients with cardiothoracic disease, knowledge of these basic principles facilitates the three-dimensional location of lesions in a single-plane image, optimizing time and resources.