Cavity (Pathologic Definition): gas-filled space within a zone of pulmonary consolidation or within a mass or nodule, produced by the expulsion of a necrotic part of the lesion via the bronchial tree
Cavity (Radiographic Definition): lucency within a zone of pulmonary consolidation, a mass, or a nodule
Hence, a Lucent Area within the Lung that May or May Not Contain a Fluid Level and that is Surrounded by a Wall, Usually of Variable Thickness
Definitions Based on Wall Thickness
Cyst: ≤4 mm wall thickness at thickest point
Cavity: >4 mm wall thickness at thickest point (or with surrounding mass or infiltrate)
Physiology
Mechanisms of Cavity Formation
Suppurative Lung Necrosis
Example: pyogenic lung asbcess
Caseous Lung Necrosis
Example: tuberculosis
Ischemic Lung Necrosis
Example: pulmonary infarction
Cystic Dilation of Lung Structures
Example: Pneumocystis jirovecii pneumonia and ball valve obstruction
Displacement of Lung Tissue by Cystic Structure
Example: Echinococcosis
Treatment-Related Necrosis
Example: malignancy
Internal Cyst Formation
Example: malignancy
Internal Desquamation of Tumor Cells with Subsequent Liquefaction
Example: malignancy
Probability of Malignancy
Wall Thickness: wall thickness is positively correlated with the probability of malignancy (although there is considerable overlap, so it is not a good discriminatory tool)
Wall Thickness <4 mm: 92% of lesions are benign
Wall Thickness >15 mm: 95% of lesions are malignant
Presence of Air-Fluid Level: presence of air-fluid level is not associated with the probability of malignancy
Etiology of Cystic Lesion
Congenital Cystic Lung Lesions
Bronchogenic Cyst (see Bronchogenic Cyst): approximately 33% are located within the lung parenchyma (usually within the lower lobes), although most are within the mediastinum
May contain air, fluid (with homogeneous appearance), or both
May become secondarily infected or impinge on other structures
Congenital Adenomatoid Malformation (see Congenital Adenomatoid Malformation): presents as cystic or solid lung mass, restricted to one part of the lung
Infection
Echinococcosis (see Echinococcosis): cystic lesions are more commonly multiple (than single), with wall thickness ranging in size from 2 mm-1 cm
Malignancy
Metastases to Lungs: rarely present with cystic lung lesions
Definition: cystic airspace within the lung which characteristically increases in size over days-weeks (probably due to ball-valve air trapping mechanism), but eventually resolves
Pneumocystis Jirovecii (see Pneumocystis Jirovecii): cystic lesions are usually seen in HIV-associated cases, are more common in upper lobes, and range in size from 1-5 cm
Bullae (see Chronic Obstructive Pulmonary Disease): defined as sharply demarcated air-containing space at least 1 cm in diameter, with smooth wall that is <1 mm thick
High-Resolution Chest CT (HRCT) (see High-Resolution Chest Computed Tomography): bullae usually result from coalescense of emphysematous airspaces or from ball-valve airway obstruction
Langerhans Cell Histiocytosis (see Langerhans Cell Histiocytosis): serial HCRT suggests progression from nodules -> cavitating nodules -> cystic lesions
High-Resolution Chest CT (HRCT) (see High-Resolution Chest Computed Tomography): upper zone cysts/honeycombing -> most cysts are <1 cm in diameter (however, large cysts may occur as disease progresses) with barely perceptible to few millimeter wall thickness
High-Resolution Chest CT (HRCT) (see High-Resolution Chest Computed Tomography): diffuse, thin-walled cysts (2-40 mm in diameter with walls 0.1-2 mm in thickness) -> usually, >10 cysts are present
High-Resolution Chest CT (HRCT) (see High-Resolution Chest Computed Tomography): ground-glass infiltrates and centrobular nodules, but may also have thin-walled cysts (in 66% of cases)
High-Resolution Chest CT (HRCT) (see High-Resolution Chest Computed Tomography): cysts (3-25 mm) are seen in 13% of patients with subacute HP, usually in association with ground-glass infiltrates
Cysts Resemble Those of Lymphoid Interstitial Pneumonia (see Lymphocytic Interstitial Pneumonia): like the cysts of lymphoid interstitial pneumonia, they are presumably caused by partial bronchiolar obstruction by the peribronchiolar lymphocytic infiltrates
High-Resolution Chest CT (HRCT) (see High-Resolution Chest Computed Tomography): diffuse thin-walled cysts -> usually <1 cm in diameter (may be as large as 3 cm in some cases), usually round/ovoid (may be polygonal in advanced disease), and more numerous/larger in females
Cavitation is Common in Post-Primary TB Predominantly Involving the Upper Lobes
Tuberculosis is the Most Common Infection to Result in Cavitation: due to the extent of caseous necrosis
Presence of Comorbid Conditions (Such as Diabetes Mellitus, HIV Infection, and Anti-TNFα Therapy) Increase the Incidence of Smear Positivity, Cavitation, Treatment Failure, and Non-Tuberculosis-Related Death (Epidemiol Infect, 2015) [MEDLINE]
Diagnosis: cavity walls may be smooth or irregular
Clinical: tendency to form cavities enhances propagation of tuberculosis, since cavities contain large numbers of organisms which can be aerosolized and transmitted to other hosts
Malignancy
Primary Lung Neoplasm
Lung Cancer (see Lung Cancer): cavitation occurs in 10-15% of lung cancers
Epidemiology
Cavitation Occurs on 7-11% of Lung Cancers (by CXR) and 22% of Cases (by CT scan)
Cavitation is More Common in Squamous Cell Histology
Presence of Cavitation Portends a Worse Prognosis
Metastases to Lung
General Comments: only 4% of mets to lung are cavitary by CXR
Serial HCRT suggests progression from nodules -> cavitating nodules -> cystic lesions
HRCT: upper zone cysts/honeycombing -> most cysts are <1 cm in diameter (however, large cysts may occur as disease progresses) with barely perceptible to few mm wall thickness
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