Cystic lung disease is an umbrella term used to group the conditions coursing with multiple lung cysts.
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Clinical presentation
The clinical presentation is an important clue to the differential diagnosis of cystic lung diseases 12.
Diseases that present with insidious dyspnea or spontaneous pneumothorax:
Sjogren syndrome (confusingly attributed to lymphocytic interstitial pneumonia but more likely due to protein deposition) 15, 16
Congenital cystic lung diseases that present with recurrent pneumonia or are asymptomatic:
Diseases that present with signs/symptoms of infection:
Multi-systemic diseases that primarily present with extrapulmonary signs/symptoms:
neurofibromatosis type 1 - neurofibromatosis associated cystic lung disease 13
light chain deposition disease and clonal lymphoplasmacytic proliferative disorders 15, 16
lymphangioleiomyomatosis associated with tuberous sclerosis
Pathology
A lung cyst is a gas-filled structure with a thin perceptible wall, typically <2 mm in thickness but can be up to 4 mm. The diameter of a lung cyst is usually <1 cm. By conventional definition in the literature, a lung cyst can be distinguished from a cavity for which the wall thickness is greater than 4 mm. However, in practice, clear separation of the two entities can sometimes be difficult 1.
Etiology
Primary pulmonary disease where diffuse cysts are the predominant feature:
lymphangioleiomyomatosis 3 with or without tuberous sclerosis
Birt-Hogg-Dubé syndrome (rare) 4
Acquired cystic lung disease or cysts as a secondary feature of a primary disease:
honeycombing in usual interstitial pneumonia pattern 5
pulmonary laceration in trauma
Radiographic appearance
CT
The approach to cystic lung disease centers around the appearance on high resolution CT and history 10,12.
Once the lucencies are found to be true cysts (thin walled), the location should be determined. Subpleural or intrapleural cysts include:
bullae/blebs, including in paraseptal emphysema: upper lobe predominance
honeycombing due to pulmonary fibrosis: lower lobe predominance, stacked (multiple rows)
In contrast, intraparenchymal cysts are surrounded by lung parenchyma and can be further evaluated by their associated features:
Intraparenchymal cysts with associated ground glass opacities:
pneumocystis pneumonia: diffuse ground glass opacities with few cysts, septal thickening, in patients with immunodeficiency (e.g. HIV/AIDS)
desquamative interstitial pneumonia: lower lung predominant ground glass opacities with few cysts, in smokers
Sjögren syndrome or immunodeficiency (e.g. HIV/AIDS)
Intraparenchymal cysts with associated pulmonary nodules:
pulmonary Langerhans cell histiocytosis: upper lung predominant, bizarre shaped cysts with variable wall thickness, stellate nodules, in young smokers
light chain deposition disease: diffuse cysts, diffuse irregular nodules, lymphadenopathy, in patients with plasma cell dyscrasias
amyloidosis: peribronchovascular or subpleural cysts, often calcified nodules
Sjögren syndrome: centrilobular nodular or geographic ground glass opacity and nodules which may calcify
Most other causes of intraparenchymal cysts do not have associated findings and may be instead distinguished by their distribution:
Unifocal pulmonary cysts:
incidental pulmonary cyst
pneumatocele: usually transient, related to recent pneumonia or trauma
hydatid disease (echinococcosis)
Multifocal pulmonary cysts 11:
lymphangioleiomyomatosis: diffuse, uniformly round cysts, with spontaneous pneumothorax or chylothorax, in young women or patients with tuberous sclerosis
Birt-Hogg-Dubé syndrome: lower lobe predominant, disproportionately paramediastinal, elongated (floppy) cysts, with spontaneous pneumothorax and skin lesions or renal cancer
neurofibromatosis type 1: upper lobe predominant
Differential diagnosis
If the pulmonary lucencies in question are not true cysts (not thin walled airspaces), there are several considerations other than cystic lung disease:
cystic bronchiectasis: connected to tubular airways
centrilobular emphysema: without distinct walls
cavitating lung lesions: wall thickness >4 mm