Cystic lung disease: Systematic, stepwise diagnosis
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).
STEP 4: PUT IT ALL TOGETHER
Diagnosis in insidious dyspnea or spontaneous pneumothorax
For patients who present with insidious dyspnea or spontaneous pneumothorax, the diagnosis of cystic lung disease can be made by characterizing the distribution, size, and shape of the cysts (Table 3).
Diffuse, panlobular distribution. Cystic lung diseases with this pattern include lymphangioleiomyomatosis, pulmonary Langerhans cell histiocytosis, and Birt-Hogg-Dubé syndrome. In this group, cysts that are uniform in size and regular in shape are invariably due to lymphangioleiomyomatosis. Those with variable size and irregular shapes can be due to pulmonary Langerhans cell histiocytosis or Birt-Hogg-Dubé syndrome. Patients with pulmonary Langerhans cell histiocytosis tend to be smokers and their cysts tend to be upper- lobe-predominant. Those with Birt-Hogg-Dubé syndrome will likely have renal cancer or skin lesions; their cysts tend to be basilar and subpleural in distribution.
Cysts that are focal or multifocal and unilobular are due to lymphocytic interstitial pneumonia or desquamative interstitial pneumonia. Patients with lymphocytic interstitial pneumonia tend to have underlying connective tissue disease; those with desquamative interstitial pneumonia are almost always smokers. The definitive diagnosis for lymphocytic interstitial pneumonia or desquamative interstitial pneumonia can require a tissue biopsy.
Diagnosis in patients with incidentally found cysts or recurrent pneumonia
In those who present with incidentally found cysts or recurrent pneumonia, suspicion for a congenital lung malformation should be raised. Patients with a type 1, 2, or 4 congenital pulmonary airway malformation typically have air-filled cysts in varying sizes; those with pulmonary sequestration have an anomalous arterial supply in addition to cysts that are usually located in the lower lobes. Bronchogenic cysts tend to be larger, with attenuation equal to or greater than that of water, and distinguishing them from congenital pulmonary airway malformation will likely require surgical examination.
Diagnosis in patients with signs and symptoms of pulmonary infections
Patients with signs and symptoms of pulmonary infections should be investigated according to clinical risk factors for P jirovecii pneumonia or echinococcal infections.
Diagnosis in patients with primarily nonpulmonary presentations
The distinction between amyloidosis and neurofibromatosis type 1 can be made by the history and the clinical examination. However, a definitive diagnosis of amyloidosis or light chain deposition disease requires tissue examination for the presence or absence of amyloid fibrils.
