Cystic Interstitial Lung Diseases: Recognizing the Common and Uncommon Entities
Introduction
A variety of pulmonary and systemic diseases may manifest with lung cysts on high-resolution computed tomography (HRCT). Knowledge of the specific cyst characteristics and associated HRCT findings may be useful in differentiating among these various disorders. An accurate diagnosis of cystic lung disease may be achieved in 74%-84% of cases using HRCT.1, 2 Incorporating the clinical context often further improves the diagnostic accuracy.
The Fleischner Society defines a cyst as a “round parenchymal lucency or low-attenuating area with a well-defined interface with normal lung.”3 It is important to differentiate between true lung cysts and their mimics. Common mimics that should be considered include emphysema, honeycombing, bronchiectasis, pneumatoceles, and cavities (Fig 1 and Table 1). Cystic lung diseases that are discussed include pulmonary Langerhans cell histiocytosis (PLCH), lymphangioleiomyomatosis (LAM), Birt-Hogg-Dubé syndrome (BHD), lymphocytic interstitial pneumonia (LIP), and light chain deposition disease (LCDD).
Section snippets
Emphysema
Emphysema is extremely common and must be excluded before diagnosing a cystic lung disease. Emphysema may be difficult to recognize on chest radiography, unless it is severe. Radiographic signs of lung hyperinflation suggest the diagnosis and include a flattened diaphragm, tubular or small heart, decreased lung vascular markings, or a barrel-shaped chest on the lateral radiograph (Fig 2). On computed tomography (CT) scan, emphysema presents as multiple, small, low-attenuation lucencies that are
Pulmonary Langerhans Cell Histiocytosis
PLCH is an idiopathic disorder that affects smokers; it is estimated that 80% of the affected patients are either current or former smokers.4 It has been referred to with various names in the past, including pulmonary histiocytosis X and eosinophilic granulomatosis. PLCH generally presents at an age younger than 40 years, with men affected more frequently than women. Clinical presentation usually consists of progressive cough and dyspnea5; up to 15% of individuals can have a pneumothorax on
Conclusion
Many disease processes can give the appearance of pulmonary cysts on HRCT. It is important to remember that cyst mimics are much more common than true cystic lung diseases and need to be ruled out first (Table 1). After excluding cyst mimics, one should consider the possibility of cystic lung disease. Differentiating between the cystic lung diseases can be achieved by taking into account the clinical context as well as the cyst characteristics and associated HRCT findings (Table 2).
Upper lung
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