What is a chest X-ray?
A chest X-ray (CXR) or chest radiograph is an image obtained by passing ionizing X-rays (electromagnetic radiation) through the chest (thorax). This is helpful in screening and diagnosing various diseases of the organs in the thoracic cavity including the airways and alveoli (lungs), pleura, heart and blood vessels, bones, diaphragm, and certain gastrointestinal conditions. Although the chest X-ray is the most widely performed diagnostic imaging study, it does have several limitations. However, several other imaging studies are available as a follow up to the chest X-ray thereby providing better visualization of underlying disease.
Chest X-Ray Views
The x-ray of chest is may be taken from different angles based on the direction of passing the ionizing X-rays. It is referred to as ‘views’.
- Posterior-anterior (PA) view refers to X-ray images taken by allowing x-rays to pass from the back side of the body to the front side of chest and fall on the x-ray film placed in front of chest. This the most common view for diagnosing diseases of lung and chest.
- Anterior-posterior (AP) view refers to X-ray images taken by allowing the ionizing rays to pass from front to the back of the chest where the x-ray film is placed. This is the least commonly used view as the interpretation of the information in these films is difficult. Hence this view is preferred only in bed ridden patients, in conditions to see posterior parts of lungs and for abnormalities of vertebrae and scapula.
- Lateral view refers to films obtained by pass X-rays from one side of the patient towards the other side where film is placed.
Structures which can be examined in chest X-rays are airways, cardiac shadow, ribs and thoracic vertebra, position of trachea, costophrenic angle (angle between diaphragm and rib cage), cardiophrenic angle, diaphragm, lung parenchyma, breast shadow and other soft tissue shadows.
Chest X-Ray Opacities
- Localised opacities are seen in pneumonia (inflammation of lung parenchyma), lung inflammation due to radiation exposure (radiation pneumonitis), infarction of lung, and certain lung malignancies.
- Single well-defined opacities are seen in lung cancer, tuberculosis, localized bacterial and fungal infections, cyst arising from the bronchus, blood vessel malformation and in autoimmune diseases (rheumatoid arthritis and Wegener’s granulomatosis).
- Multiple diffuse patchy opacities are seen in lung fibrosis, Pneumocystitis carnii pneumonia, allergic pneumonitis, and in occupational lung diseases (pneumoconiosis).
- Diffuse alveolar patchy opacities are seen in lung edema in heart failure, alveolar haemorrhage, acute respiratory distress syndrome and sarcoidosis.
- Diffuse nodular opacities are seen in metastatic cancer of the lung, haematogenous (blood) spread of bacteria, virus and fungus to lung, and in occupational lung diseases.
Lung Diseases on X-Rays
- Tuberculosis classically present with upper lobe cavities and infiltrates. Sometimes it may present as solitary nodule or diffuse alveolar opacities. Tubercular pneumonia present with localized opacities in the lung. Tuberculosis may also present with pleural effusion.
- Pneumonia (inflammation of lung parenchyma) presents with localized opacities in the lung. Presence of pneumatoceles indicates that the cause of pneumonia as staphylococcal infection. Patchy opacity with cavitary lesion in apex of lung is usually due to tubercular infection.
- Bronchial asthma can cause hyperinflation in patients with severe bronchial asthma, whereas in mild and moderate bronchial asthma it appears normal.
- Acute and sub-acute allergic pneumonitis can present with poorly defined, diffuse and patchy infiltration of lung. Chronic allergic pneumonitis and progressive allergic pneumonitis present with honey comb appearance.
- Lung fibrosis is usually secondary to pulmonary tuberculosis, hence more common near the apex of the lungs. Lung fibrosis characteristically pulls the trachea towards the side of fibrosis.
- Pleural effusion (collection of fluid in pleural sac) presents with uniform homogenous opacity which is obliquely inclined with more opacities towards the outer end of the lung margin. Trachea and heart might be displaced towards the opposite side of pleural effusion. Costophrenic and cardiophrenic angles are typically obliterated in pleural effusion.
- Chronic obstructive pulmonary disease (COPD): Increased translucency, diminished lung marking, flattening of the diaphragm, hyperinflation of lung and presence of bullae suggest emphysema. Other findings suggestive of COPD on X-ray include pneumonic opacities and heart failure features.
- Pneumothorax (collection of air in pleural sac): There will be uniform opacity on one side of lung and trachea and heart will be pushed towards the opposite side of pneumothorax.
- Hydropneumothorax presents with uniform opacities with the meniscus exactly transverse to the line of patient. Trachea and heart will be pushed towards the opposite side of hydropneumothorax.
- Empyema which is characterized by collection of pus in the pleural cavity shows the fluid level similar to the hydropneumothorax.
- Lung abscess is characterized by collection of pus in the lungs which is characterized by presence of cavity filled with fluid and air in the X-ray.
- Bronchiectasis (destructive dilatation of larger airways): This may appear normal on X-ray, but certain types of bronchiectasis may show cystic dilatations with or without air fluid levels. Dilated airways may appear to run parallel giving tram track appearance when viewed longitudinally, or may show ring shadows when seen in cross section.
- Pulmonary embolism : This may present with focal reduced blood flow (oligemia), wedge shaped opacities, and sometimes there might be enlargement of right pulmonary artery.
- Atelectasis is collapse or closure of alveoli affecting a part or whole of lung. Alveoli are typically deflated and exert negative pressure which pulls the trachea and heart towards the side of atelactasis.
- Lung cancer may present as solitary pulmonary nodule mainly near the apex of lung, and serial x-ray show characteristic doubling time of 6 to 18 months in malignant cancers, and doubling time of more than 24 months in case of benign cancers. Sometimes cancers may also present as cavitary lesion in the lung.
- Pneumoconiosis (occupational lung diseases) are due to chronic exposure to minerals, metals and organic material which characteristically present with allergic pneumonitis. Silica and coal dust exposure is characterized by small round opacities, and asbestosis exposure is characterized by linear opacities.
Heart Diseases on X-Rays
- Heart failure may be associated with enlargement of heart, prominence of vascular marking in lungs, and variation in shape of heart. Acute heart failure presents with features of pulmonary and interstitial edema.
- Coarctation of aorta is constriction of aorta distal to left subclavian artery and this presents with dilatation of left subclavian artery and ascending aorta. There might be notching of 3rd to 9th rib due to erosion of inferior rib by dilated collateral blood vessels.
- Dilated cardiomyopathy presents with increased heart size. Hypertrophic and restrictive cardiomyopathy may show very mild cardiac enlargement on X-ray.
- Pericardial effusion is a collection of fluid in the pericardial sac. X-ray may show marked enlargement of heart and heart appear in the shape of water bottle.
- Tetrology of fallot is a congenital heart disease characterized by pulmonary stenosis, right ventricular hypertrophy, ventricular septal defect and overriding of aorta. In chest X-ray heart appears boot-shaped and vascular marking in the lung may be diminished.
Valve Diseases on X-Rays
- Pulmonary stenosis is obstruction to the flow of blood from right ventricle to pulmonary artery due to narrowing of the pulmonary artery, and is associated with enlargement of the right ventricle.
- Mitral stenosis is a narrowing of the mitral valve opening hence it causes resistance to flow of blood from left atrium to left ventricle. X-ray shows straightening of left upper border of heart, pulmonary arteries will be very prominent, and the esophagus will be pushed back.
- Mitral regurgitation is back flow of blood from left ventricle back to left atrium due to incomplete closure of mitral valve. X-ray characteristically shows enlargement of left atrium, there will be increased prominence of pulmonary blood vessels. Calcification of mitral annulus may be visualized on X-ray.
- Aortic stenosis is narrowing of aortic opening hence left ventricle may not pump sufficient blood into aorta with each heart beat. Hypertrophy of left ventricle of heart may present with rounding off of apex of heart in chest X-ray.
- Aortic regurgitation is back flow of blood from aorta back to left ventricle. X-ray shows downward and outward displacement of apex of heart. Few cases might show aortic dilatation.
- Tricuspid stenosis is characterised by obstruction of blood flow from right atrium to right ventricle due narrowing of opening of tricuspid valve. This presents with enlargement of right atrium and increased prominence of vena cava.
Gastrointestinal Diseases on Chest X-Rays
- Hiatal hernias may be diagnosed with a chest X-ray. Large hernia may be made out in normal chest X-ray, and there might be features suggestive of aspiration in lower lobes of lung. Contrast chest X-ray of barium clearly show pouch near the lower end of esophagus.
- Perforation of the intestines or perforated gastric ulcer can show presence of gas under diaphragm on x-ray.
Motor Vehicle Accident Chest X-Rays
- Fracture of ribs and vertebral column may be made out in a chest X-ray.
- Other features due to traumatic injury like pneumothorax, hemorrhage in thoracic cavity and hydropneumothrorax may be diagnosed using a chest X-ray.