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Cystic lung disease: Systematic, stepwise diagnosis

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ABSTRACTOnce cystic lung disease is confirmed on computed tomography, one can arrive at the likely diagnosis in most cases by taking a systematic, stepwise approach based on the clinical and radiographic features. Here, we describe the features of cystic lung disease that point to lymphangioleiomyomatosis, Birt-Hogg-Dubé syndrome, pulmonary angerhans cell histiocytosis, interstitial pneumonia, congenital cystic lung disease, pulmonary infection, and systemic disease.

KEY POINTS

  • Pulmonary cysts should be differentiated from cyst-mimics.
  • Adults with cystic lung disease can be grouped by the clinical presentation: ie, insidious dyspnea or spontaneous pneumothorax; incidentally found cysts or recurrent pneumonia; signs and symptoms of primary pulmonary infection; or signs and symptoms that are primarily nonpulmonary.
  • Characterization of pulmonary cysts and their distribution plays a key role in diagnosis. Radiographically, cystic lung disease can be subclassified into two major categories according to the distribution of cysts: discrete (focal or multifocal) and diffuse (unilobular or panlobular).


 

References

Air-filled pulmonary lesions commonly detected on chest computed tomography. Cystic lung lesions should be distinguished from other air-filled lesions to facilitate diagnosis. Primary care physicians play an integral role in the recognition of cystic lung disease.

The differential diagnosis of cystic lung disease is broad and includes isolated pulmonary, systemic, infectious, and congenital etiologies.

Here, we aim to provide a systematic, stepwise approach to help differentiate among the various cystic lung diseases and devise an algorithm for diagnosis. In doing so, we will discuss the clinical and radiographic features of many of these diseases:

  • Lymphangioleiomyomatosis
  • Birt-Hogg-Dubé syndrome
  • Pulmonary Langerhans cell histiocytosis
  • Interstitial pneumonia (desquamative interstitial pneumonia, lymphocytic interstitial pneumonia)
  • Congenital cystic lung disease (congenital pulmonary airway malformation, pulmonary sequestration, bronchogenic cyst) Pulmonary infection
  • Systemic disease (amyloidosis, light chain deposition disease, neurofibromatosis type 1).

STEP 1: RULE OUT CYST-MIMICS

A pulmonary cyst is a round, circumscribed space surrounded by an epithelial or fibrous wall of variable thickness.1 On chest radiography and computed tomography, a cyst appears as a round parenchymal lucency or low-attenuating area with a well-defined interface with normal lung.1 Cysts vary in wall thickness but usually have a thin wall (< 2 mm) and occur without associated pulmonary emphysema.1 They typically contain air but occasionally contain fluid or solid material.

A pulmonary cyst can be categorized as a bulla, bleb, or pneumatocele.

Pulmonary cysts can be categorized as bullae, blebs, or pneumatoceles

Bullae are larger than 1 cm in diameter, sharply demarcated by a thin wall, and usually accompanied by emphysematous changes in the adjacent lung.1

Blebs are no larger than 1 cm in diameter, are located within the visceral pleura or the subpleural space, and appear on computed tomography as thin-walled air spaces that are contiguous with the pleura.1 The distinction between a bleb and a bulla is of little clinical importance, and is often unnecessary.

Pneumatoceles are cysts that are frequently caused by acute pneumonia, trauma, or aspiration of hydrocarbon fluid, and are usually transient.1

Figure 1. Pulmonary cysts and cyst-mimics on computed tomography.

Mimics of pulmonary cysts include pulmonary cavities, emphysema, loculated pneumothoraces, honeycomb lung, and bronchiectasis (Figure 1).2

Pulmonary cavities differ from cysts in that their walls are typically thicker (usually > 4 mm).3

Emphysema differs from cystic lung disease as it typically leads to focal areas or regions of decreased lung attenuation that do not have defined walls.1

Honeycombing refers to a cluster or row of cysts, 1 to 3 mm in wall thickness and typically 3 to 10 mm in diameter, that are associated with end-stage lung fibrosis.1 They are typically subpleural in distribution and are accompanied by fibrotic features such as reticulation and traction bronchiectasis.1

Bronchiectasis is dilation and distortion of bronchi and bronchioles and can be mistaken for cysts when viewed en face.1

Loculated pneumothoraces can also mimic pulmonary cysts, but they typically fail to adhere to a defined anatomic unit and are subpleural in distribution.

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