Description
Radiological practice includes classification of illnesses with similar
characteristics through recognizable signs. Knowledge of and ability
to recognize these signs can aid the physician in shortening
the differential diagnosis list and deciding on the ultimate diagnosis for
a patient. In this report, 23 important and frequently seen radiological
signs are presented and described using chest X-rays, computed tomography
(CT) images, illustrations and photographs.
Plain films
Air bronchogram sign
Bronchi, which are not normally seen, become visible as a result of
opacification of the lung parenchyma. Branching, tubular lucencies of
bronchi are seen in an opacified lung . This sign shows that
the pathology is in the lung parenchyma itself . This sign is most
frequently encountered in pneumonia and pulmonary edema. Its generalized
form can be seen in respiratory distress syndrome . The air
bronchogram sign shows that the central bronchi are not obstructed;
however, it can also be seen when a mass causes half-obstruction. Bronchioalveolar
carcinoma, lymphoma, interstitial fibrosis, alveolar hemorrhage,
fibrosis due to radiation and sarcoidosis can also present with this
sign (1–3). This sign can also be seen on CT images (Fig. 1b).
Silhouette sign
In a chest x-ray, non-visualization of the border of an anatomical
structure that is normally visualized shows that the area neighboring
this margin is filled with tissue or material of the same density (Fig. 2).
The silhouette sign is an important sign indicating the localization of a
lesion (4). A well-known example is obliteration of the right heart border
due to middle lobe atelectasis. This rule can also be applied to the arch of
the aorta, the hemidiaphragms and the left border of the heart.
A silhouette sign of the hila is called the “hilum overlay sign”. It is
used to determine the localization of a lesion in the hilar region in chest
X-rays. If hilar vessels can clearly be seen inside the lesion, the lesion
is either anterior or posterior to the hilus. If the hilar vessels cannot be
discriminated from the lesion, the lesion is at the hilus.
Deep sulcus sign
The deep sulcus sign describes the radiolucency extending from
the lateral costophrenic angle to the hypochondrium . It is an
important clue indicating possible pneumothorax in chest x-rays obtained
in the supine position. When plain films are taken with the subject
in an upright position, the free air in the pleural space gathers at
the apicolateral space.