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Chest X-Ray Basic Interpretation. Dr. Shujauddin S Rahimi Senior Registrar Department of Radio-Diagnosis.
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Chest X-Ray Basic Interpretation Dr. Shujauddin S Rahimi Senior Registrar Department of Radio-Diagnosis
Evaluation of a chest X-ray may appear to be simple, but is in fact a more complex task, requiring careful observation, sound understanding of chest anatomy and the principles of physiology and pathology. A systematic approach to chest X-ray review is essential to gain the optimum diagnostic information available from the film and to avoid potential errors in the interpretation.
Normal and Variants The chest x-ray is the most frequently requested radiologic examination. The interpretation of a chest film requires the understanding of basic principles. In this presentation we will focus on: • Normal anatomy and variants. • Systematic approach to the chest film using an inside-out approach. • Pathology of the heart, mediastinum, lungs and pleura.
The film should be analyzed using a light box with low ambient lighting to optimize viewing conditions. Identification Label Verify the patient's identity: name, date of birth, hospital number, and sex. Ensure that you are looking at the correct film: check the date and time it was taken. Side Marker Ensure that the orientation is correct. A misplaced marker is much more common than dextrocardia or situsinversus. There have been reports of chest drain insertion on the opposite side to a pneumothorax because of mislabelling.
Projection Most departmental films are from posterior to anterior (PA). Where there is difficulty in positioning the patient because of acute illness or general immobility, the film may be taken anterior to posterior (AP),which should be noted on the radiograph. If in doubt, look at the scapulae: in a PA view, the scapulae should be clear of the lungs. Due to divergence of the X-ray beam, the heart and mediastinal structures appear magnified on an AP view, making heart size difficult to assess.
PA view On the PA chest-film it is important to examine all the areas where the lung borders the diaphragm, the heart and other mediastinal structures. At these borders lung-soft tissue interfaces are seen resulting in a: Line or stripe - for instance the right para tracheal stripe. Silhouette - for instance the normal silhouette of the aortic knob or left ventricle These lines and silhouettes are useful localizers of disease, because they can be displaced or obscured with loss of the normal silhouette.
The azygoesophageal recess is the region inferior to the level of the azygos vein arch in which the right lung forms an interface with the mediastinum between the heart anteriorly and vertebral column posteriorly. It is bordered on the left by the esophagus. • Deviation of the azygoesophageal line is caused by • Hiatalhernia • Esophageal disease • Left atrial enlargement • Subcarinallymphadenopathy • Bronchogeniccyst
Venaazygoslobe A common normal variant is the azygos lobe. The azygos lobe is created when a laterally displaced azygos vein makes a deep fissure in the upper part of the lung. On a chest film it is seen as a fine line that crosses the apex of the right lung.
In some patients an extra joint is seen in the anterior part of the first rib at the point where the bone meets the calcified cartilageneous part . This may simulate a lung mass.
Inspiration & Expiration Films On a film taken in full inspiration, the right hemidiaphragm should project over the 6th anterior interspace or 10th rib posteriorly. This patient’s chest x-ray is normal in full inspiration. In relative expiration, the cardiac silhouette appears enlarged and the pulmonary vasculature appears crowded and indistinct. This appearance is easily mistaken for pulmonary edema.
Pectusexcavatum Pectus excavatum is a congenital deformity of the ribs and the sternum producing a concave appearance of the anterior chest wall. In patients with a pectusexcavatum the right heart border can be ill-defined, but this is normal. It produces a silhouette signand thus simulating a consolidation or atelectasis of the right middle lobe. The lateral view is helpful in such cases.
Lateral view On a normal lateral view the contours of the heart are visible and the IVC is seen entering the right atrium. The retrosternal space should be radiolucent, since it only contains air. Any radiopacity in this area is suspective of a process in the anterior mediastinum or upper lobes of the lung. As you go from superior to inferior over the vertebral bodies they should get darker, because usually there will be less soft tissue and more radiolucent lung tissue. If this is not the case, look carefully for pathology in the lower lobes.
The contours of the left and right diaphragm should be visible. The right diaphragm should be visible all the way to the anterior chest wall. Actually we see the interface between the air in the lungs and the soft tissue structures in the abdomen. The left diaphragm can only be seen to a point where it borders the heart. Here the interface is lost, since the heart has the same density as the structures below the diaphragm.
The left main pulmonary artery passes over the left main bronchus and is higher than the right pulmonary artery which passes in front of the right main bronchus.
Once you know how the normal hilar structures look like on a lateral view, it is easier to detect abnormalities. In this case on the PA-view there is hilar enlargement. On the PA-view it is not clear whether this is due to dilated vessels or enlarged lymph nodes. On the lateral view there are round structures in areas where you don't expect any vessels.
On the PA-view the superior mediastinum is widened. The lateral view is helpful in this case because it demonstrates a density in the retrosternal space. Now the differential diagnosis is limited to a mass in the anterior mediastinum (4 T's).
Systematic Approach From inside to outside or • Cardia • Mediastinum/ Hili • Lung Field • Domes of diaphragm. • Costo-pherenic angles • Thoracic cage From outside to inside • Thoracic cage • Costo-pherenic angles • Domes of diaphragm. • Lung Field • Mediastinum/ Hili • Cardia Abdomen Abnormality Pattern Differential Diagnosis
Old films It is extremely important to always compare with old films, as we will demonstrate in this case. Old Film Once you compare it to the old film, things become more obvious and you will be much more confident in your diagnosis: The size of the heart is slightly increased compared to the old film. The pulmonary vessels are slightly increased in diameter indicating increased pulmonary pressure. There are subtle interstitial markings as a result of interstitial edema. There is pleural fluid bilaterally. Notice that the inferior border of the lower lobes has changed in position.
Silhouette Sign • When two objects of same density overlaps, edge between them disappears. RUL – loss of upper right mediastinal border • RML – loss of right heart border • RLL – loss of right hemidiaphram • LUL – loss of upper left mediastinal border • LINGULA – loss of left heart border • LLL – loss of left hemidiaphram Examples include: – Atelectasis – Pneumonia – Neoplasm
The PA-film shows a silhouette sign of the left heart border. Even without looking at the lateral film, we know, that the pathology must be located anteriorly in the left lung.
On a normal lateral chest film the silhouette of the left diaphragm 2- can be seen from posterior up to where it is bordered by the heart, which has the same density. One should be able to follow the contour of the right diaphragm -1- from posterior all the way to anterior, because it is only bordered by the lung. Here we cannot follow the contour of the right diaphragm all the way to posterior, which indicates that there is something of water-density in the right lower lobe.
Hidden Areas • There are some areas that need special attention, because pathology in these areas can easily be overlooked: • Apical zones • Hilarzones • Retrocardialzone • Zone below the dome of diaphragm • These areas are also known as the hidden areas.
An example of a large lesion in the right lower lobe, which is difficult to detect on the PA-film, unless when you give special attention to the hidden areas. Here a pneumonia which was hidden in the right lower lobe mainly below the level of the dome of the diaphragm. Notice the increase in density on the lateral film in the lower vertebral region
There is a subtle consolidation in the left lower lobe in the hidden area behind the heart. Again there is increased density over the lower vertrebral region.
Cardiac shadow Left Heart Size • Cardiac Transverse Diameter (CTD) = a+b < 15.5cm (males) < 15.0cm (females) • Cardio-Thoracic Ratio (CTR) =a+b÷c+d < 0.5
Cardiac configuration • Dilated left ventricle: -Ischaemic/dilated cardiomyopathy -Aortic reflux -Mitral reflux -VSD, PDA -Anaemia, hyperthyroid, Paget’s, AVF • Failing left ventricle: -AS, HTN, Coarctation • Cardiomegaly (CTR > 0.5) • Large third “mogul” • Double density right heart border • Displaced descending aorta • Dilated left atrium: -Mitral stenosis or myxoma -Mitral reflux, VSD, PDA, -ASD (late)
Right ventricle enlargement On these chest films the heart is extremely dilated. Notice that it is especially the right ventricle that is dilated. This is well seen on the lateral film. There is a small aortic knob , while the pulmonary trunk and the right lower pulmonary artery are dilated.
Left Atrium enlargement This is a patient with longstanding mitral valve disease and mitral valve replacement. Extreme dilatation of the left atrium has resulted in bulging of the contours
Pericardial effusion Whenever we encounter a large heart figure, we should always be aware of the possibility of pericardial effusion simulating a large heart.
The Mediastinum • Mediastinalposition • Ratio: - 1/3 to the Rt of midline - 2/3 to the Lt of midline The normal hilar shadow is for 99% composed of vessels - pulmonary arteries and to a lesser extent veins. Position of hilar point: -Right = 6th rib in mid-axillary line -Left = 0–2.5cm higher Hilar Region
The Mediastinum Left heart border • Aortic arch •Main (left) PA •Left atrial appendage •Left ventricle Right heart border •Brachiocephalic vein •SVC •Right atrium •IVC - blurred or obscured and 'indistinct' right heart border
Lungs Size •Transradiancy •Fissures •Focal or generalised pulmonary infiltration
Lungs • Lung abnormalities mostly present as areas of increased density, which can be divided into the following patterns: • Consolidation • Atelectasis • Nodule or mass - solitary or multiple • Interstitial
Pulmonary Consolidation Atelactatsis
Solitary Nodules Millary Nodules Lung nodules
Cavitory Lesion Bronchia tic changes Emphysematous Bullae L
Pleural Spaces • Effusions • Soft tissue masses • Calcification • Pneumothorax
When a suggested pneumothorax is not definitively observed on an inspiratory film, an expiratory film may be helpful. At end expiration, the constant volume of the pneumothorax gas is accentuated by the reduction of the hemithorax, and the pneumothorax is recognized more easily.
Pleuralopacities Tumor Mesotheiloma Metastasis Lipoma Fibrous Tumors Solitary Fluid collection Loculated Pleural Effusin Organized Empyema Multiple Pleural Plaques Asbestosis- related Fluid collection Loculated Pleural effusion
Bones • Fractures • Lyticor scleroticlesions When a rib fracture heals, the callus formation may create a mass-like appearance (blue arrow). Sometimes a CT is necessary to differentiate a healing fracture from a lung mass.
Abdomen The most obvious finding on this CXR is free air under the diaphragm. This finding indicates a bowel perforation, unless when the patient had recent abdominal surgery and there is still some air left in the abdomen, which can stay there for several days.
