Pathologic and Radiologic Correlation of Adult Cystic Lung Disease: A Comprehensive Review

Table 1

Cysts and cyst-like lesions based on the mechanism of cyst .

Mechanism of cyst formation	Principal pathophysiology	Associated diseases	Other features
Cystic dilatation of lung structures	Ball valve effect due to proximal obstruction by peribronchiolar infiltration	LAM [11]; Lymphoid Interstitial pneumonia [17, 19, 20]; PLCH [29]; RB-ILD [7, 16]; DIP [25]; P. jirovecii [26]; Primary neoplasms; Endobronchial neoplasms; Metastasis or micrometastases; Lymphoma [25]	Generally thin-walled (<4 mm)^3, uniform in size, and rounded in shape. May change size depending on phase of respiration due to communication with airways [5]; infiltration/nodules may be observed either radiologically or histopathologically proximal to cysts. May be diffuse (as in LAM, PLCH, and LIP) [6, 17] or focal (as in solitary neoplasms) [18, 56].
Cystic dilatation of lung structures	Traction bronchiolectasis or alveolar ectasia due to retraction from surrounding interstitial fibrosis	Honeycombing UIP/IPF [7]; Collagen vascular disorders,; asbestosis, hypersensitive pneumonitis, and drug induced fibrosis [56]; PLCH [29]; Viral bronchiolitis [5]; Follicular bronchiolitis [17]; Lymphoma [25]	Air spaces are clustered to resemble a honeycomb. Cysts are associated with other features indicating fibrosis including architectural distortion, interstitial thickening, and traction bronchiectasis. Granuloma induced fibrosis in PLCH results in irregular shaped cysts when compared to the more uniform shaped cysts as in LAM.
Cystic dilatation of lung structures	Cystic bronchiectatic air spaces formed due to fibrosing dilatation of the bronchi as a result of suppurative and/or necrotizing inflammation	Chronic infections,; immunodeficiency disorders, genetic syndromes, and cystic fibrosis [5, 31]	Air spaces can be confused for cysts when viewed “en face.” The bronchi have thick walls and do not taper when followed to the periphery. Cysts are more central than bullae and may contain fluid and change size with phase of respiration due to communication with airways [5].
Parenchymal necrosis	Suppurative necrosis	Abscesses (bacterial and amoebic) [45]; Fungal infections,; nontuberculous mycobacterial infections [52]; Postinfectious pneumatoceles [46]	Thick-walled (>4 mm) with irregular margins seen as low areas of attenuation within an area of pulmonary consolidation or nodule on CT^3. Air fluid levels present due to superimposed infection. May be thin-walled in resolved consolidations as seen in pneumatoceles [46].
Parenchymal necrosis	Caseous necrosis	Tuberculosis, cryptococcosis, coccidioidomycosis, and; histoplasmosis [51]	Thick-walled cavitations with irregular margins predominantly in upper lobes; NTM cavitations more thin-walled and commonly associated with bronchiectasis [40, 52, 80].
Parenchymal necrosis	Ischemic necrosis	Pulmonary infarcts; Vasculitides [54]; Amyloidosis [33]; Rheumatic disorders [53]; PLCH	Multiple or solitary thick-walled cavitations depending on the extent of involvement.
Parenchymal necrosis	Desquamation of tumor tissue with subsequent liquefaction	Malignancies; Squamous cell carcinoma [56], adenocarcinoma [18, 81]; Secondary pulmonary lymphoma, AIDS lymphoma [17]; Metastasis Mesenchymal sarcomas [58, 59], epithelial carcinomas [60, 82], and; airway papillomatosis [61]	Cavities are typically thick-walled and are usually found in an area of mass or nodule, multifocal or solitary. Very rarely thin-walled indicating formation by other mechanisms and can present as a diagnostic pitfall [83].
Alveolar rupture and/or confluence of air spaces	Alveolar dissolution from ischemia or alveolar rupture and further conflation resulting in large air spaces	Emphysematous bullae COPD, connective tissue syndromes (e.g., EDS [69])Later stages of MCLD including PLCH, amyloidosis; BHD syndrome [68]	Blebs and bullae have imperceptible walls (<1 mm). Tend to be peripheral and do not communicate with airways [5]. Bizarre large cysts are seen in later stages due to confluence of cystic air spaces [29].
Cystic expansion with lung displacement	Parasitic cysts	Parasitic cysts Echinococcosis [42]; Paragonimiasis [43]	See description in Sections 2 and 3.
Cystic expansion with lung displacement	Congenital cyst formations manifesting in adults	CPAM; Bronchogenic cyst [75]; Sequestration [73]	Cysts may present very similar to acquired cystic lesions.
Miscellaneous	Iatrogenic herniation of the bowel into; the thorax	Lucite plombage [5]; Traumatic diaphragmatic rupture [84]; Bochdalek hernia [85]	Apical distribution, in resistant tuberculosis.; Herniation of abdominal structures into the thorax, with a cystic appearance on CT.

Diseases whose cystic formation is predominated by the particular mechanism are written in italics. Different mechanisms involved in cyst formation including bronchiolectasis and cavitary necrosis of nodules in early stages with confluence of air spaces in end stages of disease.Various mechanisms proposed for cysts in amyloidosis including air trapping, ischemia by amyloid deposits on vascular walls, and bronchiolectasis.Majority of the solitary/multifocal neoplastic cavitations are due to squamous cell neoplasms and rarely due to adenocarcinomas.Rarely reported in adult lymphomas from check valve and traction fibrosis.
MCLD: multiple cystic lung disorder; IPF: idiopathic pulmonary fibrosis; LIP: lymphocytic interstitial pneumonia; LAM: lymphangioleiomyomatosis; PLCH: pulmonary Langerhans cell histiocytosis; HRCT: high-resolution CT scan; DIP: desquamative interstitial pneumonia; RB-ILD: respiratory bronchiolitis interstitial lung disorder; OP: organizing pneumonia.