Chest Imaging: Basics

The presentation will provide a reading guide for the frontal and lateral chest radiograph. The most useful signs in chest radiology will be introduced, using side-by-side plain film and CT imaging to help understand the imaging features. Although the clinical value of the chest X-ray remains undiminished, errors of interpretation of the chest X-ray remain one of the most frequent causes of malpractice issues. The skills required for accurate interpretation of the chest radiograph will be explored. The objective is to help you improve your performance in plain film interpretation of the chest.

Many acute or chronic diseases of the lung may manifest at imaging with the appearance of an alveolar, interstitial or nodular syndrome. All of these imaging syndromes are well known to thoracic radiologists and can be detected at chest radiography. Especially when interpreted in the correct clinical setting, alveolar, interstitial or nodular opacities can provide hints to the diagnosis. In this presentation, the typical imaging signs that allow to make a diagnosis of an alveolar or interstitial disease or suspect the presence of pulmonary nodules will be reviewed by using anatomic and imaging correlation between chest radiograph and CT.

Lobar collapse or closure of a pulmonary lobe is associated with a loss of volume and results in reduced or absent gas exchange, a condition where the alveoli are deflated down to little or no volume. This presentation aims to review the radiographic and CT signs of lobar collapse, or loss of volume, and associated abnormalities when for example the cause of the collapse is a bronchial obstruction of a mass. Differentiation of lobar collapse and consolidation will be discussed. Distinct entities will be imaged such as aerated lobar collapse and chronic lobar collapse without mass-like consolidation.

Chest radiographs are particularly useful to diagnose pneumothorax, albeit smaller ones may be missed on radiographs. Pneumothorax is commonly seen as an area of hyperlucency with lack of vessels in the apical and the lateral regions on the photograph performed standing or sitting. Pneumothorax in the supine position is best seen as the deep sulcus sign as the air moves anteromedially and subpulmonic. Pneumothorax can be spontaneous (either primary or secondary) or iatrogenic. It is important to recognise the “do-not-miss” state of tension pneumothorax, which can be fatal if left untreated. A partial pneumothorax is seen when part of the lung is still adherent to the chest wall. It is, however, important to differentiate it from bullous lung disease, which sometimes may be difficult on radiographs, and may require a CT for a definite diagnosis.

Chest radiography has been traditionally used to evaluate the chest, including lung parenchyma, airways, and mediastinum. Despite the wide use of computed tomography imaging, chest radiography still plays a fundamental role in the detection and characterisation of mediastinal lesions through the use of mediastinal lines, stripes, and interfaces. Lines and stripes are formed by air outlining thin or thick intervening tissue on both sides, respectively. Interfaces are formed when structures of different densities contact with one another, such as in the azygoesophageal recess. The recognition and understanding of the anatomic basis of these mediastinal lines, stripes, and interfaces along with their normal and abnormal appearances allow radiologists to develop an appropriate differential diagnosis of mediastinal lesions before obtaining additional information by using chest computed tomography or magnetic resonance imaging.