. If the right cardiac silhouette is obliterated, it means the pathology involves:

Right middle lobe An intra-thoracic radio-opacity, if in anatomic contact with a border of hea, aoa or diaphragm, will obscure that border. This is known as silhouette sign. An intra-thoracic lesion not anatomically contiguous with a border or a normal structure will not obliterate that border. When examining the lung fields of a normal CXR, the silhouettes of the hea borders, the ascending and descending aoa, the aoic knob and the hemidiaphragms should be clear. Obliteration of any of these silhouettes by a radio-opacity can be caused by infection in the lung, blood, pus, etc. All of these silhouettes, or structures, are in contact with a specific poion 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 hea horderlascending aoa Anterior segment of RUL Right hea border RML (medial) Upper left hea border Anterior a sement of LUL ,,, Left hea border Lingula (anterior) Aoic knob Apicoposterior segment of LUL Hemidiaphragms Basal seg.of lower lobes