MEDIASTINAL MASSES Whenever you see a mass on a chest x-ray that is possibly located within the mediastinum, your goal is to determine the following: Is it a mediastinal mass? Is it in the anterior, middle or posterior mediastinum? Are you able to characterize the lesion by determining whether it has any fatty, fluid or vascular components?

Statistically, it is important to remember the following Most masses (> 60%) are: Thymomas Neurogenic Tumors Benign Cysts Lymphadenopathy (LAD) In children the most common (> 80%) are: Neurogenic tumors Germ cell tumors Foregut cysts In adults the most common are: Lymphomas LAD Thyroid masses

Localize to the mediastinum Unlike lung lesions, a mediastinal mass will not contain air bronchograms. A lung mass abuts the mediastinal surface and creates acute angles with the lung, while a mediastinal mass will sit under the surface creating obtuse angles with the lung. There can be associated spinal, costal or sternal abnormalities.

The four T's make up the mnemonic for anterior mediastinal masses:: Thymus Teratoma (germ cell) Thyroid Terrible Lymphoma

Hilum Overlay Sign When there is a mediastinal mass and you still can see the hilar vessels through this mass, then you know the mass does not arise from the hilum.  This is known as the hilum overlay sign.

Cervicothoracic sign The anterior mediastinum stops at the level of the superior clavicle. Therefore, when a mass extends above the superior clavicle, it is located either in the neck or in the posterior mediastinum. When lung tissue comes between the mass and the neck, the mass is probably in the posterior mediastinum.  This is known as the Cervicothoracic Sign.

Silhouette Sign When two radio opaque densities comes in anatomical contact with each other the line of demarcation between them is lost. When examining the lung fields of a normal CXR, the silhouettes of the heart borders, the ascending and descending aorta, the aortic knob and the hemidiaphragms should be clear.

 Obliteration of any of these silhouettes by a water density can be caused by infection in the lung, blood, pus, etc.  All of these silhouettes, or structures, are in contact with a specific portion of the lung.  Therefore, by determining exactly which structure is obliterated, you can determine where the lung pathology is located.

Silhouette/Structure Contact with Lung Upper right heart border/ascending aorta Anterior segment of RUL Right heart border RML (medial) Upper left heart border Anterior segment of LUL Left heart border Lingula (anterior) Aortic knob Apical portion of LUL (posterior) Anterior hemidiaphragms Lower lobes (anterior)

D.Y.P.H Pulmonary Medicine Department. @ Face Book