Radiological analysis of chest lesions detected on chest radiographs or CT scans begins with their classification into parenchymal, pleural, or extrapleural lesions according to their presumed origin. The mediastinum is divided anatomically into the anterior, middle, and posterior mediastinal compartments, and localizing a mediastinal mass to one of these divisions can locationfacilitate their differential diagnosis. A differential diagnosis of a mediastinal mass is usually based on a number of findings, including its ; the structure from which it is arising; whether it is single, multifocal (involving several different areas or lymph node groups), or diffuse; its size and shape; its attenuation (fatty, fluid, soft-tissue, or a combination of these); the presence of calcification along with its characteristics and amount; and its opacification following the administration of contrast agents.