If the right and/or left pulmonary arteries are visible, more than a centimetre within the lateral edge of the mediastinal silhouette, then the lesion is not cardiac. It can also be thought of in another way. If the edges of the vessels are appreciated, this implies the cause of the opacity is not in contact with the hilum and is, therefore, either anterior or posterior to it. Most of these opacities are masses in the anterior mediastinum. Causes of these opacities include middle mediastinal tumours, hilar adenopathy, pericardial effusion, vascular enlargement, and cardiac enlargement. If the cause of the opacity arises from the hilum, the silhouette of the normal pulmonary vessels ( interlobar artery, upper lobe arteries, and left lower lobar artery) 2 is obliterated. The sign refers to preserved visualisation of the hilar vessels, excluding abnormalities that localise to the middle mediastinum. The hilum overlay sign is useful in differentiating whether an opacity on a frontal chest radiograph in the region of the lung hilum is located within the hilum versus anterior or posterior to it.
0 Comments
Leave a Reply. |