Читать книгу Respiratory Medicine - Stephen J. Bourke - Страница 107

The chest X‐ray has a key role in the investigation of respiratory disease. The standard view is the erect, postero‐anterior (PA) chest X‐ray taken at full inspiration with the X‐ray beam passing from back to front. A lateral X‐ray gives a better view of lesions lying behind the heart or diaphragm, which may not be visible on a PA view, and allows abnormalities to be viewed in a further dimension. Supine and antero‐posterior (AP) views are usually taken at the bedside using mobile equipment in patients who are too ill to be brought to the X‐ray department. AP films are less satisfactory in defining many abnormalities, producing magnification of the cardiac outline, for example.

The main landmarks of the normal chest X‐ray are shown in Figs 4.1 and 4.2. X‐rays should be examined both close up and from a short distance from the computer screen in an area with reduced background lighting. It is important to confirm the name and date on the X‐ray and to check the technical quality of the film. Symmetry between the medial end of both clavicles and the thoracic spine confirms that the film has been taken without any rotation artefact. If the film has been taken in full inspiration, the right hemidiaphragm is normally intersected by the anterior part of the sixth rib. The vertebral bodies are usually visible through the cardiac shadow if the X‐ray exposure is satisfactory.

It is helpful to examine the film systematically to avoid missing useful information. The shape and bony structures of the chest wall should be surveyed and the position of the hemidiaphragms and trachea noted. The shape and size of the heart and the appearances of the mediastinum and hilar shadows are examined. The size, shape and disposition of the vascular shadows are noted and the pattern of the lung markings in different zones is carefully compared. It is advisable to focus attention on areas of the chest X‐ray where lesions are commonly missed, such as the lung apices, hila and the area behind the heart. Any abnormality detected should be analysed in detail and interpreted in the context of all clinical information. It is often helpful to obtain previous X‐rays or to monitor the evolution of abnormalities over time on follow‐up X‐rays. Some of the radiological features of the major lung diseases are shown in individual chapters. In some circumstances chest X‐ray abnormalities follow a specific pattern that allows a differential diagnosis to be outlined.