Cyst(S)
Jeffrey P. Kanne, MD
DIFFERENTIAL DIAGNOSIS
Common
Emphysema
Pneumatoceles
Less Common
Idiopathic Pulmonary Fibrosis
Pulmonary Langerhans Cell Histiocytosis
Lymphocytic Interstitial Pneumonia
Hypersensitivity Pneumonitis
Coccidioidomycosis
Rare but Important
Lymphangioleiomyomatosis
Cystic Adenomatoid Malformation
Laryngeal Papillomatosis
Birt-Hogg-Dubé Syndrome
Desquamative Interstitial Pneumonia
ESSENTIAL INFORMATION
Key Differential Diagnosis Issues
Definition of cysts
Round well-demarcated lung lesion with thin wall (< 2 mm)
Usually air-filled but may contain fluid
Large emphysematous bullae can mimic cysts
Compress adjacent lung
Distribution and morphology of cysts key to narrowing differential diagnosis
Helpful Clues for Common Diagnoses
Emphysema
Permanent enlargement of air spaces distal to terminal bronchiole
Not true cysts
No perceptible wall
Centrilobular emphysema
Associated with cigarette smoking
Upper lung zone predominant
Panlobular emphysema
Most frequently from alpha-1 antitrypsin deficiency
Intravenous methylphenidate abuse
Basal lung zone predominant
Paraseptal
Subpleural and peribronchovascular
May be paracicatricial as in sarcoidosis, silicosis, and coal worker’s pneumoconiosis
Spontaneous pneumothorax from rupture into pleural space
Pneumatoceles
Transient thin-walled cysts in association with pneumonia
Commonly develop later during course of pneumonia
Up to 30% in Pneumocystis pneumonia, almost exclusively in patients with AIDS
Other causes
Hydrocarbon ingestion
Trauma (pulmonary laceration)
Helpful Clues for Less Common Diagnoses
Idiopathic Pulmonary Fibrosis
Honeycomb cysts
Subpleural and basal predominant
Frequently occur in rows
Begins in subpleural lung and progresses centrally
Associated with reticulation, traction bronchiectasis, and architectural distortion
Pulmonary Langerhans Cell Histiocytosis
> 95% of adult patients cigarette smokers
Polyclonal proliferation of CD1a(+) histiocytes (Langerhans cells) in lungs
Disseminated, monoclonal form in children
Cysts of varying shapes and sizes
Upper lung zone predominant
Larger cysts frequently have bizarre shapes
Associated findings
Small nodules ± central lucency progressing to cysts over time
Ground-glass opacity
Spontaneous pneumothorax in < 10%
Lymphocytic Interstitial Pneumonia
Most commonly occurs in adults with Sjögren syndrome
Less commonly occurs in children with HIV and other immunodeficiency diseases
Cysts in about 80%
Usually < 20 in number, ranging from 2-30 mm in diameter
Basal predominance typical
Perilymphatic distribution of nodules (peribronchovascular, centrilobular, septal, and subpleural)
Associated patchy ground-glass opacity throughout lungs
Hypersensitivity Pneumonitis
Cysts few in number and occur in 10%
Other findings
Poorly defined centrilobular nodules
Lobular air-trapping characteristic
Patchy or diffuse ground-glass opacity
Higher incidence in nonsmokers
Agricultural and avian antigens most common
Coccidioidomycosis
Endemic fungal infection most common in arid regions of southwestern USA
Thin-walled cysts occasional in acute infection (5%) or later with evolution of pneumonia
Usually solitary (90%) and located in upper lobes
Helpful Clues for Rare Diagnoses
Lymphangioleiomyomatosis
Occurs exclusively in women of child-bearing age or patients with tuberous sclerosis
Diffuse lung cysts
2-20 mm with thin, smooth walls
May completely replace lung in advanced disease
Associated findings
Chylous pleural effusions
Renal angiomyolipomas
Lymphangiomas (mediastinal, retroperitoneal)
Pulmonary hyperinflation
Spontaneous and recurrent pneumothoraces may develop
Cystic Adenomatoid Malformation
Congenital hamartomatous malformation of the lungs with cysts resembling bronchioles
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