A. Introduction. It is often necessary to rely on your own interpretation of a chest radiograph pending a formal reading. This chapter provides a consistent, easy-to-use approach to such evaluation.
B. Preliminary Considerations
a. What kind of radiograph should I order?
i. A posterior-anterior (PA) view is always preferable to an anterior-posterior (AP) view because the latter exaggerates the size of the heart and other mediastinal structures. However, in emergencies, an AP view is often the only feasible option.
ii. A lateral view should be obtained to help confirm and localize abnormalities seen on the PA view.
b. Is it a good film? Assessing the quality of the radiograph can help avoid common misinterpretations.
i. Inspiration. Count the number of ribs; a good inspiration will reveal at least 10 posterior ribs. A poor inspiration may result in the false appearance of an interstitial process, leading to a misdiagnosis of pulmonary edema or atypical pneumonia.
ii. Rotation. Look at the position of the medial end of the clavicles: are they at the same level/symmetric with respect to the spine? Asymmetry is an indication of rotation. Rotation of the film may lead to erroneous estimates of cardiac, pulmonary artery, aortic, and mediastinal size.
iii. Penetration. You should be able to see the spine of individual vertebrae in a film that is appropriately exposed. Decreased penetration will make the lungs seem denser (i.e., white). Mild pulmonary edema or a small infiltrate might appear more significant, and even normal interstitial markings may appear abnormal if a film is overexposed.
c. Is there an old film available for comparison? There is no substitute for comparison with prior films. A new subtle area of consolidation may be found in a patient with suspected pneumonia, a nodule may be unchanged for 10 years and therefore presumed to be benign, or the mediastinum may be wider in a patient with suspected aortic dissection. In all cases, you need to make sure the view was the same (i.e., AP vs. PA). In addition, you must “mentally adjust” for variations in technique (i.e., inspiration, rotation, and penetration).
C. The Outside-in Approach. The structures visible on a chest radiograph can be evaluated in any order, but you should learn to be consistent every time you read a film. The outside-in approach is frequently used and ensures that commonly overlooked structures (e.g., bones) are not forgotten.
a. Bones and soft tissues. Look for lytic or blastic lesions that may signal a metastatic malignancy. Evidence of osteoporosis or compression fractures may also be found. Look for subcutaneous air to suggest pneumothorax or pneumomediastinum. Soft tissue masses may also be apparent.
b. Pleura. Follow the pleural border of each lung, looking for evidence of focal thickening suggesting scarring or mass, blunting of the costophrenic angle (suggesting pleural effusion), or calcifications suggesting old pleural inflammation from empyema or asbestos exposure.
c. Lungs. Look at both lung fields in an orderly fashion. Pay special attention to the diaphragms, the cardiac borders, and the apices. Although symmetric abnormalities may occur (e.g., pulmonary edema or bilateral pneumonia), asymmetric findings are particularly suspicious. Infiltrates are generally described as “alveolar” or “interstitial.” Alveolar infiltrates are fluffy, confluent, poorly demarcated opacities (think clouds). Air bronchograms (lucent airways surrounded by opaque consolidated lung) might be visible within infiltrates. An alveolar infiltrate may be blood, pus, water, or cells; thus, hemorrhage, pneumonia, cardiogenic pulmonary edema, and acute respiratory distress syndrome (ARDS) are all considerations. Interstitial infiltrates are linear, well-defined, reticular (lattice-like), occasionally nodular opacities. Interstitial infiltrates suggest atypical pneumonia, interstitial lung disease, and lymphatic congestion (seen in heart failure and malignancy).
1. If one of the hemidiaphragms is obscured, either an infiltrate is present in the lower lobe or there is a pleural effusion.
2. The retrocardiac area is a common place for abnormalities to be overlooked, so always look at lateral films if available. The left hemidiaphragm and descending aorta should be visible behind the heart. An obscured left hemidiaphragm suggests atelectasis or an infiltrate. The presence of air bronchograms favors consolidation.
3. Flattened diaphragms and hyperinflated lung fields are often found in chronic obstructive pulmonary disease (COPD).
4. An elevated hemidiaphragm suggests diaphragmatic paralysis, a subpulmonic pleural effusion, or a subdiaphragmatic process. If on the right side, consider liver-related pathologies (e.g., abscess, tumor).
5. Air under the diaphragm on an upright chest radiograph in a patient presenting with abdominal pain suggests visceral perforation and is usually a surgical emergency.
6. A depressed lateral hemidiaphragm with a poorly visible costophrenic angle and surrounding hyperlucency (“deep sulcus sign”) suggests pneumothorax.
ii. Cardiac borders
1. A lingular infiltrate (lower portion of the left upper lobe) is suggested if the left cardiac border is obscured.
2. A right middle lobe infiltrate is suggested if the right cardiac border is obscured.
1. Apical pneumothoraces are easy to miss; always look carefully at the apices in patients with chest pain or shortness of breath. Follow the interstitial markings to the chest wall to ensure absence of pneumothorax.
2. Congestive heart failure (CHF) can cause pulmonary venous congestion, which is characterized by prominence of the upper lobe vessels, known as cephalization (redistribution of blood flow toward the apices). Other common findings with CHF include cardiomegaly, pleural effusions, blurring of the sharp and well-demarcated blood vessels, prominent pulmonary arteries, Kerley B lines (horizontal lines extending from the pleura toward the heart), and alveolar infiltrates due to pulmonary edema.
i. Increased cardiac silhouette. The cardiac silhouette should be less than one-half of the thoracic diameter on a PA film; anything larger suggests cardiomegaly or pericardial effusion. This is known as the cardiothoracic ratio.
ii. Chamber enlargement
1. The left side of the cardiac silhouette represents the left ventricle, whereas the right side represents the right atrium. Prominence in either location may represent enlargement of the respective chamber.
2. Left atrial enlargement may be signified by:
a. The loss of the normal concavity of the left heart border
b. An elevated left mainstem bronchus
c. The “double-density” sign: two parallel lines on the right side of the heart representing the right atrium and the enlarged left atrial borders
iii. Pulmonary hypertension. The diameter of the pulmonary artery should generally not exceed that of a dime; prominent pulmonary arteries may signify pulmonary hypertension.
i. Aortic dissection. Mediastinal widening may signify aortic dissection, but the sensitivity and specificity of this finding are suboptimal. Always compare to prior films and consider cross-sectional imaging (e.g., computed tomography) if in doubt of this diagnosis.
ii. Lymphadenopathy. A widened paratracheal stripe (normally a narrow opaque stripe along the right side of the trachea) and fullness of the aortic-pulmonary window (a triangular space on the left side of the mediastinum below the aortic arch) occur with mediastinal adenopathy.
Suggested Further Readings
de Groot PM, Carter BW, Abbott GF, Wu CC. Pitfalls in chest radiographic interpretation: blind spots. Semin Roentgenol 2015;50:197–209.Find this resource:
Dixon AK. Evidence-based diagnostic radiology. Lancet 1997;350:509–12. (Classic Article.)Find this resource:
Goodman LR. Felson’s principles of chest roentgenology: a programmed text: Elsevier Health Sciences; 2014.Find this resource: