1 Department of Respiratory Medicine, Bristol Royal Infirmary, Bristol BS2 8HW Find articles by Khalid A Gaber 2 Department of Respiratory Medicine, Derriford Hospital, Plymouth PL6 8DH, UK Find articles by Clive R McGavin 3 Department of Radiology, Derriford Hospital, Plymouth PL6 8DH, UK Find articles by Irving P Wells Despite advances in radiology, the chest X-ray (CXR) has survived as the most frequently requested examination. About 6.7 million are performed each year in the UK.1 The radiation dose of a frontal CXR is equivalent to only three days' exposure to natural background radiation (effective dose 0.02 mSv.2 The lateral CXR is less frequently requested and more difficult to interpret. Nevertheless it contains much information on the thoracic cage, pleura, lungs, pericardium, heart, mediastinum and upper abdomen. Many junior doctors, at ease with the frontal CXR, seem intimidated by the lateral film. Uncertain when to request or how to interpret, they may retreat expensively and unnecessarily into computerized tomography. The lateral CXR is performed with the side of interest closer to the X-ray film, giving an effective dose of 0.05 mSv. If the side is not specified, a left lateral is usually taken. In this paper we offer a brief guide to demystify and clarify this cheap and useful investigation. Essentially there are four indications and four main abnormalities to interpret. When a lateral film is desired, the reasons should be stated on the request form. The four indications are to localize a lesion seen on frontal CXR, to clarify lobar collapse/consolidation, to explore a retrosternal or retrocardiac shadow or to confirm the presence of encysted fluid in the oblique fissure (pseudotumour). The fissures are important landmarks on a lateral CXR, becoming visible when the X-ray beam passes parallel to them. The oblique fissure begins posteriorly at T4/5 level, passing through the hilum. The left is steeper and finishes 5 cm behind the costophrenic angle whereas the right ends just behind the angle. The horizontal fissure runs anteriorly from the hilum separating the right upper lobe from the middle lobe. On the left there is no horizontal fissure. Both hemidiaphragms should be visible, silhouetted by the lung air against the fluid-density of the abdominal contents. The anterior end of the left hemidiaphragm may be lost against the heart. The diaphragms can be distinguished from each other if there is clearly gastric air under one, or if one can be seen to be inserted into the magnified ribs further from the X-ray plate. Vertebral bodies become darker as they proceed caudally (Figure 1) until they reach the diaphragm—because there is more soft tissue and less lung tissue at the apex but more lung tissue and less soft tissue at the bases.  Normal lateral chest X-ray The retrocardiac and retrosternal spaces are normally seen as dark areas about equal in size and lucency. The fissures will be displaced in the direction of a collapsing lobe (Figure 2). With simple consolidation there will be opacification up to the straight edge of a non-displaced fissure (Figure 3); displacement of a fissure results from collapse. The bi-convex shadow of fluid in a fissure will clarify a pseudotumour seen on the frontal view. The diaphragms: when only one diaphragm is visible the silhouette of the other must have been lost. That is to say, there is fluid density as opposed to air density above the diaphragm—usually indicating effusion or consolidation. If no other border is seen higher up, this suggests complete opacification of that hemithorax. Vertebral bodies: if these remain white as they proceed caudally, this indicates increased radiodensity as opposed to radiolucency at the lung base, caused by pleural disease, consolidation or a mass lesion (Figure 4). The retrosternal space is enlarged in pulmonary over-inflation (emphysema) and opacified by anterior mediastinal disease such as thymoma or lymphoma. The retrocardiac space will appear opaque where there is effusion, consolidation or a mass. Other abnormalities may be evident such as pectus excavatum, pericardial calcification and hiatus hernia. The lateral CXR is seldom indicated for examining the hilum in an adult but in children it can be helpful in investigation of lymphadenopathy, for example in primary tuberculosis. 1. National Radiological Protection Board. Frequency of Medical and Dental X-Ray Examination in the UK 1997-1998. London: NRPB, 2000 2. Royal College of Radiologists. Making the Best Use of a Department of Clinical Radiology: Guidelines for Doctors, 3rd edn. London: RCR, 1995: 12 Articles from Journal of the Royal Society of Medicine are provided here courtesy of Royal Society of Medicine Press Begin by reviewing the systematic approach to the left lateral chest radiograph in Fig. 10.1 These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.
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The lateral chest view examines the lungs, bony thoracic cavity, mediastinum, and great vessels. This orthogonal view to a frontal chest radiograph may be performed as an adjunct in cases where there is diagnostic uncertainty. The lateral chest view can be particularly useful in assessing the retrosternal and retrocardiac airspaces. If locating a specific pulmonary opacity within the chest cavity, it would be useful for requesting doctors to ensure that the side of the opacity is mentioned in their clinical notes. This will allow radiographers/imaging technologists to image with the side of interest against the image receptor, hence reducing any magnification from an increased SID. Otherwise, a left lateral view is the default and preferred side as it demonstrates better anatomical detail of the heart.
The entire lung fields should be visible superior from the apices inferior to the posterior costophrenic angle
The same principle of positioning can be applied to patients in a chair. Before exposing ensure your patient is not leaning forward or backwards too much, this will result in anatomy being cut off. Patients with a longstanding history of emphysema or COPD will have abnormally long lungs compared to the general population, remember this when collimating superior to inferior. Side marker placement is imperative; patients can have congenital conditions that mimic a mirrored image 2. Patients with scoliosis may not demonstrate the traditional indicators of a correctly positioned lateral radiograph; it is important to note that patients with this condition particularly in the thoracic region will appear rotated by conventional evaluation, yet this is not the case. Remember to explain to your patient what you are about to do; that is, ask them to take a breath in and hold it. Many times this gives the patient time to prepare and results in better breath-hold and therefore a higher quality radiograph. Always remember to tell your patient to breathe again! |
Why is the left lateral chest position the most commonly used for lateral radiographs of the chest?
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