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Two patients with opacification of the lower portion of one lung. Despite the similar radiographic appearance of the PA views, the cause of the opacification is quite different. This is reflected by the differences in their lateral views.

  • Patient 14A. A 32-year-old woman was hospitalized for an asthma exacerbation. She also had a history of alcoholism and was intoxicated at the time of her presentation to the ED (Figure 1).
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  • Patient 14B. A 32-year-old man complained of left-sided pleuritic chest pain (Figure 2).
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  • What is the explanation of the radiographic findings in these patients?

Patient 14A: What Is the Differential Diagnosis of Opacification of the Lower Portion of a Hemithorax?

The first possibility is consolidation due to pneumonia. Although this is consistent with the patient’s clinical presentation, several radiographic findings argue against this diagnosis. First, it is unusual for pneumonia to cause such homogeneous opacification of the lung. With pneumonia there usually are aerated alveoli and bronchi interspersed within the infiltrate (air-alveolograms and air bronchograms) that gives pneumonia a mottled appearance (inhomogeneous opacification).

Second, pneumonia usually has ill-defined margins. An infiltrate can have a well-defined margin when it is adjacent to an interlobar fissure. In this patient’s PA view, the upper margin of the opacity is sharp (Figure 3A). This sharp horizontal margin seems as though it would represent the minor fissure (horizontal fissure) as would occur with consolidation of the right middle lobe. However, on the lateral view, the corresponding horizontal line lies posterior to the hilum, not anterior as would be expected if it were the minor fissure (Figure 3B).

A second possible diagnosis is a pleural effusion. A pleural effusion does cause homogeneous opacification, as is seen in this patient. In addition, on an upright chest radiograph, a pleural effusion characteristically has a sharp superior margin. However, the effusion’s upper margin usually curves upward at the lateral chest wall, forming a meniscus. In this patient, there is no meniscus. In addition, a right lateral decubitus chest radiograph (right-side down) was obtained, which did not show layering as would be expected with a pleural effusion (Figure 4).

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