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INTRODUCTION

The diffuse cystic lung diseases (DCLDs) are a diverse set of disorders that share a common radiologic phenotype of thin-walled parenchymal lucencies.1 Although often grouped together with other interstitial lung diseases (ILDs), the underlying pathobiology, differential diagnosis, mode of presentation, and natural history of disease progression in DCLDs are sufficiently distinct to warrant classification of DCLDs as a separate independent entity.2 The subsequent sections of this chapter will provide an overview of the classification and differential diagnosis of DCLDs; detail the clinical, radiologic, and histopathologic features of various DCLDs; and culminate with an integrated approach toward the appropriate diagnosis and management of patients presenting with DCLD.

DEFINITION OF PULMONARY CYST

A pulmonary cyst is defined radiologically as a thin-walled (<2 mm wall thickness) parenchymal lucency interfaced with normal pulmonary parenchyma.3 Table 61-1 lists the other parenchymal lesions that can mimic cysts and need to be carefully distinguished from cysts. Pathologically, cysts are defined as dilated spaces within the lung tissue that have an epithelial lining. Lung cysts may contain fluid or gas. Dilated spaces without an epithelial lining are referred to as pseudocysts and must be distinguished from true epithelial-lined lung cysts. Some lesions designated as cysts clinically and radiologically may not represent true cysts pathologically; the most common cyst mimics are bronchiectasis, honeycomb remodeling, pulmonary interstitial emphysema, centrilobular emphysema, α1-antitrypsin deficiency, and cavitary lesions.

TABLE 61-1Radiologic Definition of Pulmonary Cysts and Other Parenchymal Lucencies That Can Mimic Cysts

CLASSIFICATION OF DIFFUSE CYSTIC LUNG DISEASES

DCLDs can ...

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