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Introduction to Chest Radiology For medical students Basic principles of x-ray film X-rays reach the film and darken it, therefore the more xrays that reach an area of the film the darker the area will be, such as the lung. If an object is very dense, less x-rays reach the film and the object will appear white, such as the bones. There are five radiographic densities. In order of increasing brightness they are; air, fat, fluid, bone and metal. The closer an object is to the film, the sharper the borders. Objects further from the film will be magnified and the borders will not be as sharp. When two structures of the same density are next to each other the border between them is lost. Basic views The standard chest examination consists of a posterioranterior (PA) and lateral chest x-ray. These two films are taken in the upright position. In ill patients who cannot assume the upright position an AP (anteriorposterior) film by a transportable device can be taken in their room, hence the name “portable” film. Posterioranterior (PA) view The PA view is taken with the patient six feet from the x-ray tube. To prevent enlargement and blurring of the heart and great vessels in the anterior chest, these are placed closest to the film. The patient places their chest against the film and the x-ray beams are shot from the patients back, therefore called the posterioranterior or PA view. Hands should be placed on the hips so the scapula will be out of the lung fields. Lateral view The lateral view is taken with the patients in profile. Since the heart lies more in the left chest, this side is placed toward the film to avoid any enlargement or blurring. The patient arms are raised to move the scapula out of the lung fields. Anteroposterior (AP) view The AP view is taken with the patient supine and 40 inches from the x-ray tube. Because the heart and great vessels are further from the film they appear enlarged and the borders are not as sharp. Comparison of PA and AP view Compare the PA and AP views PA AP Decubital view Decubital films are taken with the patient lying on their side. This view is helpful to assess the volume of pleural effusion and whether it is mobile or loculated. If an effusion is suspected on the right, have the patient lie with the right side down (right lateral decubitus view) so the fluid would accumulate against the right chest wall. This view can also be used to assess for ptx in a patient who cannot sit upright. Place the patient with the suspected side of the ptx up so the air can be seen under the chest wall. Here is an example of a mobile, right pleural effusion Is the film technique adequate? Things to assess when looking at a film: Inspiration Penetration Rotation Motion Inspiration The lungs should span 9 posterior ribs to ensure that inspiration is adequate and a good image was obtained. This image is an example of good inspiration. If there is poor inspiration the patient can appear to have an abnormal CXR. Penetration Overpenetration: the film appears too dark and the vessels in the lungs cannot be seen Underpenetration: the film appears too white and the spine cannot be visualized behind the heart Rotation Rotation: make sure the distance between each clavicle is equal distance from the thoracic spinous processes. If there is rotation the mediastinal contents can appear distorted. Notice the rotation of the clavicles. How to read a CXR Always verify pt data, compare old films and ensure technique is adequate. Note the following findings: Trachea: midline or deviated, caliber, mass Lungs: abnormal opacity or lucency Pulmonary vessels: artery or vein enlargement Hila: masses or lymphadenopathy Cardiothoracic ratio: cardiomegaly, heart borders Mediastinal contour: width or mass? Pleura: effusion, thickening, calcification Bones: lesions or fractures Soft tissues: breast shadows, mastectomy, hematoma or subq air ICU Films: identify tubes / lines first; look for ptx How to read a CXR It is best to develop a systemic method and follow it. This will ensure that all areas are inspected, and that nothing is overlooked. Below is a recommended pattern for scanning the lung fields. Anatomy of the mediastinum Specific signs Silhouette sign Air bronchogram Kerly B lines Golden S sign Silhouette sign When two structures that are the same density are next to each other the border between them is lost. This is the silhouette sign. This is often seen when a water density process such as pneumonia is next to a water density structure such as the heart or diaphragm. The location of this abnormality can help to determine the location anatomically. Silhouette sign and locations The following are examples of silhouette signs and the associated anatomic abnormalities, such as collapse or pneumonia. Right heart= RML Left heart border= lingula Right hemidiaphragm=RLL Left hemidiaphragm= LLL Aortic knob/Descending aorta=LUL Silhouette sign On this film the right heart border is lost, or silhouetted out. This indicates pathology of the Right middle lobe. Air Bronchogram Normally the thin walls of the bronchi are not visible because they are filled with air and surrounded by air. If the alveoli are surrounded by fluid then the air in the bronchi can be seen. This is called an air bronchogram. This is a non-specific finding and can indicate pus, blood or fluid. Kerly B sign Kerly B lines are small horizontal lines that are seen in the periphery of the lung and always extend to the pleura. They are seen when there is increased fluid density in the interlobular septa. This often results from pulmonary edema seen in CHF. Golden S sign This sign is often seen in RUL collapse and resembles a reverse S sign. It is also called “the reverse S sign of Golden”. RUL collapse causes the minor fissure to assume this reverse S shape, with a lateral concavity and medical convexity. Note the convexity (arrowhead) from the mass and the concavity (arrow) of the minor fissure. Most common Abnormalities on CXR Atelectasis Pulmonary edema Pneumonia Bacterial, viral and atypical PCP, Tb, other opportunistic infections Pneumothorax Pulmonary embolism Emphysema Pulmonary embolism Pleural effusion Interstitial pulmonary fibrosis Emphysema Lung nodules/mass Enlarged cardiac silhouette Pericardial effusion Atelectasis Atelectasis or “collapse” refers to volume loss. The affected area appears white because of the loss of air. When a portion of lung collapses it pulls its adjacent fissure with it. This is an example of RUL atelectasis with superior displacement of the minor fissure. Atelectasis is due to: Obstruction-air cannot fill the alveoli. Compression-air pushed out of lung. Traction-scarring contracts the lung and distorts the alveoli. Pulmonary Edema There are 2 types of Pulmonary Edema, cardiogenic and noncardiogenic. Cardiogenic pulmonary edema is due to pump failure and increased hydrostatic pressure. Noncardiac pulmonary edema is due to altered permeability or decreased oncotic pressure. Etiologies include NOTCARDIAC Near drowning Oxygen therapy Transfusion, trauma CNS disorder ARDS, Altitude sickness Renal disease-most common cause Drugs Inhaled toxins Allergic Contusion, Contrast (IV) Cardiogenic Pulmonary Edema On CXR this can appear as cephalization of the pulmonary vessels, Kerly B lines, peribronchial cuffing, or “bat wing” pattern and cardiomegaly. Here is an example of “bat wing” pattern in a patient with pulmonary edema. Pneumonia Pneumonia can present as a focal opacity or diffuse interstitial disease. Bacterial or pyogenic pneumonia often causes silhouette or air bronchogram signs. It may involve part or all of a lobe and is often caused by bacterial infection. Diffuse pneumonia is often bilateral and appears as multiple white lines. It is mainly caused by viruses and atypical bacteria. Tuberculosis is another type of pneumonia and can either be a primary, secondary or miliary TB. Pneumonia can also be due to opportunistic organisms such as Pneumocystis. Bacterial pneumonia Bacterial pneumonia is a focal area of opacity. This is an example of RUL pneumonia. Viral and atypical pneumonia Diffuse interstitial pneumonia is usually viral or atypical in etiology. It is often bilateral and appears as multiple white lines. Tuberculosis Primary TB infection usually results in air space disease of the lower lobes with hilar lymph node enlargement. Secondary TB occurs weeks to years later and tends to occur in the upper lobes. Miliary TB can occur during both primary or secondary and looks like very small pellets involving both lungs. Primary TB Primary TB is represented by consolidation, adenopathy and pleural effusion. A Ghon focus is an area of focal consolidation that occurs in the mid and lower lungs. A Ghon complex is the addition of calcified hilar lymphadenopathy. Secondary TB Secondary TB is often represented by fibrosis, cavitation and calcification primarily in the upper lobes. Note that the TB has caused a pneumothorax on the right. Opportunistic pneumonias Pneumocystis Pneumonia (PCP) is the most common opportunistic pneumonia in immunocompromised patients. Often presents with diffuse, symmetric finely granular/reticular interstitial infiltrates with a central location. It can also present with a normal CXR. Pneumothorax Pneumothorax is air inside the thoracic cavity. It can be idiopathic or due to asthma, COPD, infections, neoplasm or iatrogenic. On CXR you will see air without lung markings and a pleural line. If it is large there can be a shift in the mediastinum – tension ptx. This is an example of tension ptx with mediastinal shift. Pulmonary Embolism The CXR is usually normal in patients with pulmonary embolism. The main purpose of the CXR is to rule out other causes of dyspnea or hypoxia. There are two signs that can be seen with a pulmonary embolism Westermark’s sign Hampton’s Hump Westermark’s sign Westermark’s sign is a focal, hyperlucent, wedge-shaped area. This sign is due to lack of blood filling the vessels distal to the embolism. Hampton’s Hump Hampton’s hump is a white, wedge-shaped area of infarction. Pleural effusion On an upright film a pleural effusion will cause blunting of the costophrenic angles. The posterior costophrenic angle is the deepest, and fluid can collect here undetectable behind the dome of the diaphram. On the PA view approximately 200 cc of fluid must be present to be detected. The lateral view is superior to the PA view when assessing for an effusion. Approximately 75 cc of fluid are needed to detect an effusion. On the supine view the effusion layers out and will appear as a graded haze that is denser at the base. When in doubt a lateral decubitus will visualize an effusion. As little as 5-10cc can be seen on this view. Pleural effusions Here is an example of bilateral pleural effusions. Note the blunting of the costophrenic angles. Interstitial pulmonary fibrosis (IPF) On CXR IPF appears as a reticular or linear opacification with volume loss. Interstitial pulmonary fibrosis has many etiologies including: Idiopathic >50% of causes Collagen vascular disease Cytotoxic agents Pneumoconiosis Radiation Sarcoidosis Emphysema Emphysema is loss of elastic recoil of the lung with destruction of alveolar septa. This is primarily due to smoking, but is also seen in alpha-1 antitrypsin deficiency. CXR finding are hyperinflation, flattened diaphragms, increased retrosternal space, bullae and enlargement of pulmonary vasculature. Emphysema Example of hyperinflation and flattened diaphragms Example of increased retrosternal air space Solitary pulmonary nodule A nodule is a lesion that is less than 3 cm. After detection compare lesion to prior films. If the nodule does not change for 2 years it is usually benign. If the nodule is completely calcified or has central calcification it is usually benign. If the nodule has irregular calcifications it must be worked up further. Benign nodules usually have a smooth edge opposed to the spiculated borders of malignant lesions. Any lesion greater than 3 cm is considered a mass. Enlarged cardiac silhouette The simplest method of measuring the heart is the cardiothoracic ratio. This is the transverse diameter of the heart divided by the transverse diameter of the chest. If the ratio is >50% the heart is abnormally enlarged. This is only true for PA views since the AP projection will magnify the heart. Enlarged cardiac silhouette can be due to cardiomegaly or pericardial effusion. Pericardial effusion Pericardial effusion causes a globular enlargement of the heart shadow. A “fat pad” sign is a soft tissue strip >2mm between the epicardial fat and the anterior mediastinum. Approximately 400-500 cc of fluid must be present to detect changes on the CXR. Notice that in cardiomegaly the hila structures are pushed outward, opposed to a pericardial effusion where the hila is hidden behind the fluid/heart shadow. This is one way to determine the etiology of an enlarged heart shadow. Pericardial effusion Large, globular heart “Fat pad” sign Quiz #1 If there is silhouetting of the descending aorta, what lobe of the lung is involved? Right Middle Lobe Left Upper Lobe Lingula Left Lower Lobe Quiz If there is silhouetting of the descending aorta, what lobe of the lung is involved? Right Middle Lobe Left Upper Lobe Lingula Left Lower Lobe Quiz Recall the following examples of silhouette signs and the associated anatomic abnormalities. Right heart= RML pneumonia Left heart border= lingula Right hemidiaphragm=RLL Left hemidiaphragm= LLL Descending aorta=LUL Quiz #2 This sign is called the Luftsichel sign Golden S sign Kerly B sign Hilum overlay sign Quiz This sign is called the Luftsichel sign Golden S sign Kerly B sign Hilum overlay sign Quiz #3 When is the Golden S sign seen? RLL collapse RML collapse RUL collapse LLL collapse LUL collapse Quiz When is the Golden S sign seen? RLL collapse RML collapse RUL collapse LLL collapse LUL collapse Quiz Recall that this sign is often seen with RUL collapse and resembles a reverse S sign. It is also called “the reverse S sign of Golden”. Quiz #4 The most common cause of pulmonary fibrosis (IPF) is Cytotoxic Collagen vascular disease Radiation Idiopathic Pneumoconiosis Sarcoidosis Quiz The most common cause of interstitial pulmonary fibrosis (IPF) is Cytotoxic Collagen vascular disease Radiation Idiopathic Pneumoconiosis Sarcoidosis Quiz #5 This normal CXR is not technically adequate because there is Overpenetration Underpenetration Rotation Poor inspiration Quiz This normal CXR is not techinically adequate because there is Overpenetration Underpenetration Rotation Poor inspiration Quiz Recall that the film appears too white and the spine cannot be visualized behind the heart in underpenetration. Overpenetration: the film appears too dark and the vessels in the lungs cannot be seen Quiz #6 This is an example of Bacterial pneumonia Viral pneumonia Tuberculosis Pulmonary embolism Quiz This is an example of Bacterial pneumonia Viral pneumonia Tuberculosis Pulmonary embolism Quiz Bacterial pneumonia is a focal area of opacity. This case is an example of RUL pneumonia. Quiz #7 This is an example of Air bronchograms Hampton’s Hump Pneumothorax Westermark’s sign Quiz This is an example of Air bronchograms Hampton’s Hump Pneumothorax Westermark’s sign Quiz Westermark’s sign is a focal, hyperlucent, wedge-shaped area. This sign is due to lack of blood filling the vessels distal a pulmonary embolism. Quiz #8 Which of the following is most commonly seen on CXR of a patient with pulmonary embolism? Westermark’s sign Hampton’s hump None of the above Quiz Which of the following is most commonly seen on CXR of a patient with pulmonary embolism? Westermark’s sign Hampton’s hump None of the above The most common finding is a normal CXR. Quiz #9 What is this sign called? Atelectasis Kerly B Air bronchogram Hampton’s Hump Quiz What is this sign called? Atelectasis Kerly B Air bronchogram Hampton’s Hump Quiz Air bronchograms as seen when alveoli are surrounded by fluid. Normally the thin walls of the bronchi are not visible because they are filled with air and surrounded by air. This is a non-specific finding and can indicate pus, blood or fluid. Quiz #10 The CXR of this patient is indicative of Atelectasis Pulmonary edema Bilateral pneumonia Pneumothorax Quiz The CXR of this patient is indicative of Atelectasis Pulmonary edema Bilateral pneumonia Pneumothorax Quiz This is an example of a “bat wing” pattern in a patient with pulmonary edema due to congestive heart failure. On CXR this can appear as cephalization of the pulmonary vessels, Kerly B lines, peribronchial cuffing, or “bat wing” pattern and cardiomegaly. Resources Novelline, Robert. Squire’s Fundamentals of Radiology, 5th edition Brant, W., Helms, C. Fundamentals of Diagnostic Radiology. Ouelletts, H., Tetreault, P., Clinical Radiology made ridiculously simple. http://radiology.rsnajnls.org