<prompt> Which among the following are a cause of posterior mediastinal opacity on Posterior-Anterior PA and lateral view of chest radiograph?Tortuous innominate arteryBochdaleks HerniaEnlarged pulmonary arteryThymoma  <response>: Amongst the given options Bochdalek hernia is the posterior mediastinal mass.Tortuous innominate artery and enlarged pulmonary artery e.g. aneurysm are middle mediastinal mass, and thymoma is anterior mediastinal mass. 