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EXERCISE 4-15. INTERSTITIAL LUNG DISEASE
4-23. The most likely cause for this patient’s dyspnea and pleuritic chest pain (Figure 4-70 A–C) is
D. pulmonary fibrosis.
4-23. The chest x-ray (Figure 4-70 A,B) shows diffuse bilat-eral coarse interstitial opacities with slight basilar predominance. The hemidiaphragms are flattened on the lateral radiograph. The CT scan (Figure 4-70 C) demonstrates multiple small similar-sized cysts stacked along the lung periphery with some preserva-tion of normal lung centrally, particularly on the right. There is traction bronchiectasis present as well (D is the correct answer to Question 4-23).
The list of interstitial lung diseases is long, and the differenti-ation can be complex. However, pulmonary fibrosis can be readily identified. Fibrosis can be subtle, with visible linear markings in the lung periphery on CT, or as obvious as the cystic change seen in this patient. End-stage pulmonary fi-brosis is most readily recognized as stacks of air-filledlucencies in the lung periphery in a pattern called “honey-combing” (Figure 4-70 C). This is often seen as the end stage of multiple interstitial lung diseases, most frequently in usual interstitial pneumonitis (UIP). These patients are almost cer-tainly symptomatic, many requiring supplemental oxygen.
Lucencies in the lung can result from many causes. A lu-cency with a discernible wall is called a cavity. As described in previous exercises, infectious or neoplastic etiology can result in a cavity or air-filled lucency within the lung. However, these are rarely small and stacked as in this case. Empyema, or an infected pleural fluid collection, can also result in a cavity of air seen on chest radiograph. This cavity is generally larger and unilateral. Therefore, A, B, and E are incorrect.
In emphysema, the air-filled lucencies lack a discernable wall. (Figure 4-71 A). These lucencies are called bullae and, in centrilobular emphysema, have an upper lobe preponderance.
These lucencies are not cysts, because a true lung cyst is lined with epithelium. Emphysema is a common cause of dyspnea and is most often smoking-related. In these patients, the lung volumes are often larger than normal, and the lungs appear more radiolucent. The bullous lesions of centrilobular em-physema are more easily recognized on CT than on chest ra-diographs. Unlike other cystic lung diseases, a vessel can generally be seen coursing through the bulla rather than around the lucency. Another form of emphysema is parasep-tal emphysema, in which the bullae occur along the lung pe-riphery (Figure 4-71 B).
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