Chapter 11 Intensive Care Unit

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CHAPTER 11 • Intensive Care Unit Imaging

when applied with appropriate clinical correlation, widespread application of these criteria to evaluate the etiology of pulmonary edema has shown them to be less reliable than stated in the original investiga- tions. Because most of the radiographic deteriora- tion seen in ARDS occurs within the first 5 days of illness, a worsening CXR appearance after this time suggests superimposition of pneumonia, fluid over- load, CHF, or ventilator-induced lung injury (VILI). Although pulmonary edema is usually bilateral and symmetric, it may collect asymmetrically when medi- astinal tumor, bronchial cyst, or massive thromboem- bolism diverts flow preferentially to one lung. The recently transplanted lung is also prone to developing unilateral pulmonary edema. Asymmetry may also be observed following unilateral aspiration, reexpansion pulmonary edema, or in the presence of extensive bul- lous disease. Gravity may redistribute edema fluid and atelectasis to newly dependent lung regions over rela- tively brief periods after patient repositioning. Mediastinal Widening Mediastinal widening on a well-centered film (par- ticularly following chest trauma or an invasive pro- cedure) should raise suspicion of aortic disruption. (A rotated or lordotic film may be misleading.) A contrast-enhanced chest CT provides the definitive diagnosis. Obtaining a high-quality upright PA CXR, though desirable, is frequently not possible because of injuries or hypotension. Radiographic clues to aor- tic disruption include a widened superior mediasti- num (the most sensitive sign), a blurred aortic knob, rightward deviation of a nasogastric tube or aortic shadow, and tracheal deviation to the right and anteri- orly. Inferior displacement of the left main bronchus, left-sided pleural effusion (with or without apical capping), and displacement of intimal calcifications

of the aorta provide other signs suggestive of aortic disruption (see Chapter 35). Mediastinal widening with vascular injury is frequently associated with traumatic fractures of the sternum, first two ribs, or clavicle. Widening of the cardiac shadow should prompt careful review of the aortic contour because blood may dissect from the aorta into the pericar- dium. If aortic disruption is suspected, angiography by catheter (the diagnostic “gold standard” for many years) is seldom needed. Contrast-enhanced CT scanning, MRI, and echocardiography almost invari- ably provide definitive evidence. Pericardial Effusion Pericardial effusion is recognized radiographically by enlargement of the cardiac shadow. The classic “water bottle configuration” of the cardiac silhouette, although highly characteristic, is unusual. An epicardial fat pad visible on the lateral CXR should raise suspicion of a pericardial effusion, as should splaying of the tracheal bifurcation. Echocardiography is the procedure of choice for the detection and evaluation of pericardial effusions, and it simultaneously affords the opportu- nity to assess heart chamber size, contractile function, and vena caval diameter. When a transthoracic echo- cardiogram cannot obtain images of adequate qual- ity because of patient weight or chest hyperinflation, transesophageal echocardiogram is usually diagnostic.

Air–Fluid Levels (Lung Abscess vs. Empyema)

Several radiographic features help to distinguish whether an air–fluid level lies within the pleural space or within the lung parenchyma (Fig. 11-8). On an AP film, pleural fluid collections generate wide, moderately dense air–fluid levels, whereas

FIGURE 11-8.  Intraparenchymal versus intrapleural fluid collections. Fluid collections within the pleural space usually have a greater horizontal than vertical dimension, do not cross fissure lines, and may have sloping attachments to the pleural surface on one or more views. Furthermore, pleural collections typically have different dimensions on AP and lateral views. By contrast, intrapa- renchymal collections tend to be more spherical, with equal dimensions on AP and lateral views.