History: rounded atelectasis was first described in 1928 (in the setting of intentional pneumothorax associated with plombage therapy for tuberculosis)
Association with Tobacco Abuse: 83% of cases are active or former-smokers [MEDLINE]
Physiology
Rounded Atelectasis: circularly-folded atelectatic lung tissue, typically with adhesions to the visceral pleura
Rounded atelectasis is a visceral pleural lesion (in contrast to asbestos-related pleural plaques, which are of parietal pleural origin)
Theoretical Mechanisms of Rounded Atelectasis Formation
Folding/Pleural Effusion Theory: initial event is lung parenchymal compression -> invagination by localized accumulation of pleural fluid
Fibrosing/Pleural Injury Theory: initial event is local visceral pleural inflammation -> repair with fibrosis -> contraction of visceral pleura with formation of rounded atelectasis
Microbronchial Distortion Theory: stargnulation of small airways with gas resorption -> focal atelectasis
Etiology
Rounded Atelectasis Associated with Mineral Dust Exposure
Asbestos Exposure
Epidemiology: most common etiology (accounts for 29-86% of cases)
Clinical: asbestos-related rounded atelectasis usually occurs in the presence of other asbestos-related lung disease (asbestosis) or asbestos-related pleural disease (asbestos pleural plaques), but can occur without other asbestos-related lung or pleural manifestations
Lymphangioleiomyomatosis (LAM) (see Lymphangioleiomyomatosis): case reports of rounded atelectasis occurring in association with pneumothorax and chylothorax
Parapneumonic Effusion/Empyema (see Pleural Effusion-Parapneumonic) (second most common etiology, accounting for 14-64% of cases): usually occurs during the resolution phase of the pleural effusion, rather than during the active development phase
Rounded Atelectasis Associated with Pneumothorax (see Pneumothorax)
Intentional Pneumothorax (aka “Collapsotherapy”): plombage (therapeutic collapse of regions of the lung) was previously used to treat tuberculosis
Iatrogenic Pneumothorax: due to procedures with inadvertent entry of the pleural space
Lymphangioleiomyomatosis (LAM)-Associated Pneumothorax (see Lymphangioleiomyomatosis): case reports of rounded atelectasis occurring in association with pneumothorax and chylothorax
Spontaneous Pneumothorax
Rounded Atelectasis in the Absence of Significant Pleural Disease
Childhood Malignancy
Chronic Kidney Disease (CKD) (see Chronic Kidney Disease): typically in the setting of end-stage/chronic renal disease with clinically absent pleurisy
Number: usually solitary (although occasionally multiple)
Density: soft-tissue density (may contain centrally-located air bronchogram or less dense center)
In silicosis-related cases, silcotic nodules may be present inside the rounded atelectasis lesion (as well in other parts of the lung)
Borders: hazy or irregular (blurred hilar margins)
Size: usually 3.5-7 cm in diameter
Location: present in the lower lobes in 66% of cases (seldom seen in RUL, almost never seen in LUL)
Non-Asbestos-Related Cases: commonly located in dependent regions (basal, posterior, paraspinal regions) of the lung, as well as middle lobe and lingula
Asbestos-Related Cases (preferentially located in areas with greatest degree of inahalational asbestoc deposition): commonly located in the lower lobes, lingulam and middle lobe
Appearance
Volume Loss of Affected Lobe: may have fissure or mainstem bronchial displacement (toward lesion, due to volume loss)
Whirled or “Comma” Appearance
“Cranial Tilting Sign”: originally described by Hanke, described as “the abrupt cephalad displacement of the linear opacities (pulmonary vessels) immediately after exiting the lesion”
“Comet Tail Sign” (seen in almost all cases): due to crowded incoming vessels pointing toward hilum
Subpleural/Pleural-Based: abutting a thickened and/or calcified pleural surface
Acute angle formed with visceral pleura, indicating that the lesion is parenchymal in origin (not pleural in origin)
High-Resolution Chest CT: no advantage over normal chest CT in defining rounded atelectasis (although may be useful to define co-existing interstitial lung disease)
Thoracic U/S
Pleural-based hyper-echogenic area
Adjacent pleural thickening with extrapleural fat
Highly echogenic line extending from the pleura into the “mass”: represent scarred, invaginated visceral pleura
Thoracic MRI:
“Kidney-Like Pattern”: hypointense lines converging towards the center of the lesion
PET Scan: metabolically inactive
PFT’s: usually normal (in the absence of other associated parenchymal lung disease)
Clinical Features
Asymptomatic: most cases
Dyspnea (see Dyspnea): may be seen in cases with underlying asbestosis or other associated lung disease
