Even though chest films are the commonest X-ray examinations performed, they are also one of the most difficult plain films to interpret. Therefore it is important to follow a routine to inspect the film and always correlating the images with the patient’s clinical findings. One way of examining the plain chest radiograph is presented below.
The routine chest radiograph comprises a postero-anterior(PA) and a lateral view. Ideally chest radiograph should be exposed on full inspiration with the patient in the upright position and the hands behind the head.
The correctly exposed routine PA chest film is one in which the ribs and espine behind the heart can be identified but the lungs are not over exposed.
A straight film is one where the medial ends of the cavicles are equidistant from the pedicals of thoraxic vertebrae.
The upper surfaces of the diaphragm should be clearly visible from one costophrenic angle to the other except where the heart is in contact with the diaphragm on a food inspiratory film the dome of the right hemidiaphragm being up to 2.5 cm higher than the left.
Normally, the trachea lies midway, or slightly to the right of the midpoint, between the medial ends of the clavicle. The position of the heart is very variable; on average one-third lies to the right of the midline, but anything from one-half to one-fifth of the heart lying tp the right of the midline is within the normal range.
The right superior mediastinal border is usually straight or slightly curved as is passes downward to merge with the right heart border. The left superior mediastinal border is ill defined above the aortic arch. The outline of the mediastinum and heart shouldbe clearly seen except where the heart lines in contact with the diaphragm.
In young children, the normal thymus is cleartly visualised. It may be very large and should not be mistaken for disease.
The only structures that can be identified whithin norma lungs are the blood vessels, the interlobar fissures, and the walls of certain larger bronchi seen end-on. The fissures can only be seen if they lie tangential to the x-ray beam; they are after all composed of just two layers of pleura. Usually, only the horizontal fissure (minor fissure) is visible in the frontal projection, running from the right hilum to the sixth rib in the axilla. There is no equivalent to the horizontal fissure on the left. The oblique fissures (major fissures) are only visible on the lateral view. The fissures form the boundaries of the lobes of the lungs so a knowledge of their position is essential for an appreciation of lobar anatomy.
Look for abnormal pulmonary opacities or translucencies. Do not mistake the pectoral muscles, breasts or plaits of hair for pulmonary shadows. Skin lumps or the nipples may mimic pulmonary nodules. The nipples are usually in the fifth anterior rib space but they are, in practice, rarely misdiagnosed provided one remembers that, in general, if one nipple is visible the other will also be seen.
A good method of finding subtle shadows on the frontal film is to compare one lung with the other, zone by zone. Detecting ill-defined shadows on the lateral view can be difficult. A helpful and reliable feature is that as the eye travels down the thoracic vertebral bodies, each body should appear more lucent than the one above until the diaphragm is reached
In females, check that both breasts are present. Following mastectomy the breast shadow cannot be defined. The reduction in the soft tissue bulk leads to an increased transradiancy of that side of the chest, which should not be confused with pulmonary disease.
Oblique views. Films taken with the patient turned to one or other side are useful for demonstrating the chest wall and, occasionally, for showing intrathoracic shadows to better advantage.
Lateral decubitus views are not, as the same would suggest, lateral views; they are frontal projections taken with the patient lying on one or other side using a horizontal x-ray beam. Their purpose is to demonstrate free pleural fluid which will collect along the dependent chest wall.
Expiration films. A frontal film may be deliberately exposed on expiration in order to demonstrate diaphragmatic movement or the ability of the lung to deflate. A pneumothoraxic may be more obvious on an expiration than an inspiration film.
Go back to RADIOLOGY
Go back to MEDSTUDENTS HOMEPAGE