Round atelectasis is a form of atelectasis that occurs due to infolding of lung parenchyma adjacent to thickened visceral pleura, presenting as a round or oval-shaped lesion. It is most commonly associated with asbestos exposure but can also be seen after pleural effusion, pleurisy, pneumothorax treatment, and cardiac surgery. The comet tail sign on CT — bronchovascular structures curving from the pleural surface toward the mass — is a pathognomonic finding. It may mimic lung cancer but does not require surgery when correctly diagnosed.
Age Range
40-70
Peak Age
55
Gender
Male predominant
Prevalence
Uncommon
Round atelectasis occurs through infolding (invagination) of lung parenchyma beneath thickened or fibrotic visceral pleura. The mechanism works as follows: pleural disease (asbestos plaques, pleural effusion, pleurisy) creates thickening and fibrosis of the visceral pleura → fibrotic pleura contracts and pulls underlying parenchyma inward → lung parenchyma folds and creates a round mass appearance. Bronchi and vessels in the folding parenchyma are pulled together, forming the characteristic 'comet tail' pattern. The acute-angle pleural attachment seen on CT proves the mass originates from the pleural surface. Volume loss is present and confirmed by adjacent fissure retraction. The strong association between asbestos exposure and round atelectasis stems from asbestos fibers' propensity to cause pleural irritation and fibrosis.
Bronchovascular structures curving and converging from the pleural surface toward the round mass. Reflects infolding (invagination) of lung parenchyma due to pleural fibrosis. Pathognomonic finding for round atelectasis that prevents unnecessary biopsy/surgery when correctly diagnosed. Best evaluated on MPR and MIP reconstructions.
Comet tail sign: bronchovascular structures curving and converging toward the mass, the pathognomonic CT finding of round atelectasis. Bronchi and pulmonary vessels show an oblique, curvilinear course from the pleural surface toward the mass — creating a morphology resembling a comet's tail.
Report Sentence
Bronchovascular structures curving toward the hilum of a pleural-based round mass in the posterior lower lobe are identified (comet tail sign), consistent with the diagnosis of round atelectasis.
Adjacent pleural thickening: a finding that almost always accompanies round atelectasis. Appears as calcified or non-calcified pleural plaques in asbestos exposure, and diffuse pleural thickening in other causes. Pleural thickening continues toward the mass and forms acute-angle attachment.
Report Sentence
Prominent pleural thickening adjacent to the round mass is identified, supporting the diagnosis of round atelectasis.
Round atelectasis shows homogeneous and significant enhancement on contrast-enhanced CT. The degree of enhancement is generally close to or equal to normal lung parenchyma. This finding indicates that the atelectatic parenchyma has lost aeration but is viable (perfused) lung tissue.
Report Sentence
Homogeneous enhancement is observed in the round mass on contrast-enhanced series, supporting perfused atelectatic parenchyma and arguing against neoplasia.
Volume loss findings in adjacent lobe or segment: fissure retraction, bronchial displacement, ipsilateral hemidiaphragm elevation. Volume loss proves the atelectatic nature of round atelectasis and is an important finding in distinguishing from neoplastic mass.
Report Sentence
Fissure retraction and volume loss findings are observed adjacent to the round mass, supporting the atelectatic nature.
On MRI, round atelectasis shows low-intermediate signal on T1 and intermediate signal on T2. May show similar signal characteristics to solid tumors, but the comet tail sign is also recognizable on MRI. Does not show significant diffusion restriction on DWI — this feature may help distinguish from malignant mass.
Report Sentence
Low-intermediate signal on T1 and intermediate signal on T2 are observed in the round mass on MRI with no significant diffusion restriction; these findings support atelectatic parenchyma.
Round atelectasis may show mild to moderate FDG uptake on PET-CT (SUVmax typically 2-4). This uptake results from chronic inflammation and atelectatic tissue metabolism and may cause false-positive suspicion for malignancy. High FDG uptake (SUVmax >5) strongly supports malignancy.
Report Sentence
Mild FDG uptake is observed in the round mass on PET-CT (SUVmax: ...); this level of uptake may be consistent with round atelectasis, however clinical and morphological correlation is recommended.
Criteria
Asbestos exposure history + pleural plaques (calcified or non-calcified) + typical posterior lower lobe location.
Distinct Features
Most common form (70-80%). Bilateral pleural plaques are characteristic. Usually appears after 20+ year latent period. Calcified plaques strongly support diagnosis. May grow slowly or remain stable — malignant transformation risk is not increased.
Criteria
Round atelectasis developing after pleural effusion drainage or during resolution. Asbestos history is not required.
Distinct Features
As pleural effusion resolves, the lung cannot fully expand due to fibrin adhesions on visceral pleura and folding occurs. Effusion cause may be various (transudate, exudate, hemothorax). Usually develops within weeks after effusion drainage.
Criteria
Round atelectasis developing after thoracic surgery (cardiac surgery, lung resection).
Distinct Features
Surgical manipulation causes pleural adhesion and fibrosis. Most commonly seen in left lower lobe after CABG (related to pleural opening for left internal mammary artery graft). Appears weeks to months after surgery.
Distinguishing Feature
Adenocarcinoma typically has spiculated margins, irregular contours, and does not show comet tail sign. Adjacent pleural thickening is usually absent or present as asymmetric/nodular thickening (pleural invasion). Mass effect rather than volume loss is present. High FDG uptake on PET-CT (SUVmax >5) supports malignancy.
Distinguishing Feature
Pulmonary metastasis typically appears as multiple, bilateral, randomly distributed nodules. A single pleural-based metastasis may resemble round atelectasis, but comet tail sign, volume loss, and adjacent pleural plaques are absent. Known primary malignancy history is critical clinical information.
Distinguishing Feature
Solitary fibrous tumor appears as a pleural-based, well-defined, intensely enhancing mass — may resemble round atelectasis. However, solitary fibrous tumor lacks comet tail sign and volume loss, shows very intense heterogeneous enhancement (hypervascular), may be pedunculated and mobile (position-dependent location change). No association with asbestos plaques.
Urgency
routineManagement
conservativeBiopsy
Not NeededFollow-up
12-monthRound atelectasis is a benign condition and does not require surgery or biopsy when typical CT findings (comet tail sign + pleural thickening + volume loss + posterior lower lobe) are present. Follow-up CT at 6-12 months is recommended for initial confirmation of stable size. Follow-up may be discontinued if stability is demonstrated over 2 years. In patients with asbestos exposure, since concurrent mesothelioma or lung cancer risk is increased, further evaluation (PET-CT, biopsy) should be considered if round atelectasis changes in size, new symptoms develop, or atypical findings emerge.
Round atelectasis is a benign condition and requires no treatment. Typical CT findings (comet tail sign + pleural thickening) are diagnostic. In atypical cases, PET-CT or biopsy is used to exclude malignancy.