James J. Fenton, MD, FCCP and Glenn N. Levine, MD, FACC, FAHA

1. Describe a systematic approach to interpreting a chest radiograph (chest x-ray [CXR]) (Fig. 4-1).

    Common recommendations are to:

2. Identify the major cardiovascular structures that form the silhouette of the mediastinum (Fig. 4-2)

3. How is heart size measured on a chest radiograph?

    Identification of cardiomegaly on a CXR is subjective, but if the heart size is equal to or greater than twice the size of the hemithorax, then it is enlarged. Remember that a film taken during expiration, in a supine position, or by a portable anteroposterior (AP) technique will make the heart appear larger.

4. What factors can affect heart size on the chest radiograph?

5. What additional items should be reviewed when examining a chest radiograph from the intensive care unit (ICU)?

    On portable coronary care unit (CCU) and ICU radiographs, particular attention should be paid to:

A careful inspection should be made for pneumothorax (Fig. 4-3), subcutaneous emphysema, and other factors that may be related to instrumentation and mechanical ventilation.

6. How can one determine which cardiac chambers are enlarged?

7. What are some of the common causes of chest pain that can be identified on a chest radiograph?

All patients with chest pain should undergo a CXR even if the cause of the chest pain is suspected myocardial ischemia.

8. What are the causes of a widened mediastinum?

    There are multiple potential causes of a widened mediastinum (Fig. 4-4). Some of the most concerning causes of mediastinal widening include aortic dissection and/or rupture and mediastinal bleeding from chest trauma or misplaced central venous catheters. One of the most common causes of mediastinal widening is thoracic lipomatosis in an obese patient. Tumors should also be considered as a cause of a widened mediastinum—especially germ cell tumors, lymphoma, and thymomas. The mediastinum may also appear wider on a portable AP film compared with a standard posteroanterior/lateral chest radiograph.

9. What are the common radiographic signs of congestive heart failure?

10. What is vascular redistribution? When does it occur in congestive heart failure?

    Vascular redistribution occurs when the upper-lobe pulmonary arteries and veins become larger than the vessels in the lower lobes. The sign is most accurate if the upper lobe vessels are increased in diameter greater than 3 mm in the first intercostal interspace. It usually occurs at a pulmonary capillary occlusion pressure of 12 to 19 mm Hg. As the pulmonary capillary occlusion pressure rises above 19 mm Hg, interstitial edema develops with bronchial cuffing, Kerley B lines, and thickening of the lung fissures. Vascular redistribution to the upper lobes is probably most consistently seen in patients with chronic pulmonary venous hypertension (e.g., mitral valve disease or left ventricular dysfunction) because of the body’s attempt to maintain more normal blood flow and oxygenation in this area. Some authors think that vascular redistribution is a cardinal feature of congestive heart failure, but it may be a particularly unhelpful sign in the ICU patient with acute congestive failure. In these patients, all the pulmonary arteries look enlarged, making it difficult to assess upper and lower vessel size. In addition, the film is often taken supine, which can enlarge the upper lobe pulmonary vessels because of stasis of blood flow and not true redistribution.

11. How does LV dysfunction and RV dysfunction lead to pleural effusions?

12. How helpful is the chest radiograph at identifying and characterizing a pericardial effusion?

    The CXR is not sensitive for the detection of a pericardial effusion, and it may not be helpful in determining the extent of an effusion. Smaller pericardial effusions are difficult to detect on a CXR but can still cause tamponade physiology if fluid accumulation is rapid. A large “water bottle” cardiac silhouette (Fig. 4-5), however, may suggest a large pericardial effusion. Distinguishing pericardial fluid from chamber enlargement is often difficult.

13. What are the characteristic radiographic findings of significant pulmonary hypertension?

    Enlargement of the central pulmonary arteries with rapid tapering of the vessels is a characteristic finding in patients with pulmonary hypertension (Fig. 4-6). If the right descending pulmonary artery is greater than 17 mm in transverse diameter, it is considered enlarged. Other findings of pulmonary hypertension include cardiac enlargement (particularly the right ventricle) and calcification of the pulmonary arteries. Pulmonary arterial calcification follows atheroma formation in the artery and represents a rare but specific radiographic finding of severe pulmonary hypertension.

14. What is the Westermark sign and a Hampton hump?

    The Westermark sign is seen in patients with pulmonary embolism and represents an area of oligemia beyond the occluded pulmonary vessel. If pulmonary infarction results, a wedge-shaped infiltrate (a “Hampton hump”) may be visible (Fig. 4-7).

15. What is rib notching?

    Rib notching is erosion of the inferior aspects of the ribs (Fig. 4-8). It can be seen in some patients with coarctation of the aorta and results from a compensatory enlargement of the intercostal arteries as a means of increasing distal circulation. It is most commonly seen between the fourth and eighth ribs. It is important to recognize this life-saving finding because aortic coarctation is treatable with percutaneous or open surgical intervention.

16. What does the finding in Figure 4-9 suggest?

    The important finding in this figure is pericardial calcification. This can occur in diseases that affect the pericardium, such as tuberculosis. In a patient with signs and symptoms of heart failure, this finding would be highly suggestive of the diagnosis of constrictive pericarditis.

17. What is subcutaneous emphysema?

    Subcutaneous emphysema is the accumulation of air in the subcutaneous tissue, often tracking along tissue plains. Subcutaneous emphysema in the chest can be caused by numerous conditions, including pneumothorax, ruptured bronchus, ruptured esophagus, blunt trauma, stabbing or gunshot wound, or invasive procedure (e.g., endoscopy, bronchoscopy, central line placement, or intubation). The finding of subcutaneous emphysema almost always is associated with a serious medical condition or complication. The example of subcutaneous emphysema in Figure 4-10 emphasizes the importance of examining the entire chest x-ray.

Bibliography, Suggested Readings, and Websites