Rounded atelectasis is a benign form of lung collapse in which a section of lung tissue folds inward against thickened or scarred pleura, creating a mass-like appearance on imaging that can closely resemble a lung tumor. It occurs most often in people with a history of asbestos exposure or chronic pleural effusion, and it is discovered incidentally on chest imaging far more often than it is suspected from symptoms.1PubMed Central. Round Atelectasis: A Peculiar Pseudotumor Seen on Echocardiogram The condition matters primarily because recognizing it on a CT scan can spare a patient from an unnecessary and sometimes invasive cancer workup.
How Rounded Atelectasis Forms
In a healthy lung, the visceral pleura (the membrane covering the lung surface) slides smoothly against the parietal pleura lining the chest wall. When disease, injury, or chronic fluid causes the pleura to thicken, scar, or develop adhesions, it can tether a portion of the underlying lung. Over time that tethered section folds inward and collapses, trapping air passages and blood vessels inside the fold. The result is a rounded or oval mass of atelectatic (collapsed) lung tissue intermingled with pleura, bronchi, and blood vessels.2The Annals of Thoracic Surgery. Rounded Atelectasis: Clinical Experience and Diagnostic Criteria Because the mass sits right against the pleural surface and pulls surrounding structures into it, the radiologic picture is distinctive once you know what to look for.
The key driver is pleural disease, not lung disease. Anything that inflames or thickens the pleura can set the stage. The pleural scarring acts like a drawstring, cinching a pocket of lung tissue inward and holding it in place. That pocket then loses volume as trapped air is absorbed, forming the characteristic rounded shape rather than the wedge-shaped collapse typical of other forms of atelectasis.3Chest Imaging. Subsegmental and Rounded Atelectasis
Asbestos as the Leading Cause
Asbestos exposure is far and away the most common association. In a series of 74 patients with rounded atelectasis, 64 had a documented history of asbestos exposure.4PubMed. Rounded atelectasis. Clinical experience with 74 patients Among those patients, the condition sometimes followed a recognized episode of benign asbestos pleurisy, sometimes developed gradually alongside slowly worsening pleural fibrosis, and in many cases appeared suddenly on imaging that had previously shown only pleural plaques or had been entirely normal. This range of presentations reflects the fact that asbestos-related pleural disease evolves unpredictably over years and decades.
Seven early cases of rounded atelectasis were described in patients with asbestos-induced pleural disease, and the authors noted that the radiographic features were characteristic enough in the setting of chronic pleural thickening from asbestos to make the diagnosis confidently and avoid further invasive workup.5PubMed. Rounded atelectasis and its association with asbestos-induced pleural disease Understanding that rounded atelectasis can be an isolated finding from asbestos exposure also helps clinicians set up appropriate long-term surveillance, because patients with asbestos-related pleural changes remain at elevated risk for more serious conditions like mesothelioma.6PubMed. Rounded atelectasis in an asbestos exposed worker
Causes Beyond Asbestos
While asbestos dominates the literature, rounded atelectasis can develop after any process that leaves behind pleural thickening or scarring. Chronic pleural effusions from heart failure, kidney disease, infection, or surgery are well-documented triggers.7PubMed Central. Rounded atelectasis of the lung: A pictorial review Post-surgical cases are particularly worth noting. Two patients developed rounded atelectasis after coronary artery bypass grafting, with lesions that initially raised suspicion for a primary lung tumor before further workup confirmed benign collapsed lung.8PubMed. Two cases of rounded atelectasis presenting after coronary artery surgery
Other reported associations include tuberculosis, radiation therapy to the chest, prior thoracic surgery unrelated to the heart, and even some autoimmune conditions that involve the pleura. The unifying thread is always the same: something damages or inflames the pleura, the pleura heals with scarring or thickening, and the adjacent lung gets pulled inward. If your doctor mentions rounded atelectasis and you have no history of asbestos exposure, the question is usually what else has affected your pleura.
What It Looks Like on a CT Scan
CT imaging is the workhorse for diagnosing rounded atelectasis, and a confident diagnosis rests on a combination of features rather than any single sign. The classic appearance is a rounded or oval soft-tissue mass in the lung periphery, directly abutting an area of thickened pleura. In one study, CT showed rounded masses ranging from about 3.5 to 7 cm in diameter, all sitting against a thickened pleural surface at the lung’s edge.9PubMed. CT features of rounded atelectasis
The most distinctive feature is the “comet tail sign,” which refers to the curved sweep of blood vessels and bronchi arcing into the mass from the surrounding lung, resembling a comet’s tail streaming behind the rounded lesion. In one analysis, comet tail signs were present in about 92% of the nodules evaluated.10PubMed. CT features of rounded atelectasis in chronic inflammatory pleural effusions in cats and dogs Additional supporting features include the mass forming an acute angle with the adjacent pleura and signs of volume loss in the affected lobe.
Pleural thickening next to the mass and a pleural-based location have been called the most sensitive markers, present in essentially all cases. However, those features alone are not specific, since plenty of other conditions sit against the pleura too. It is the combination of the pleural-based location, the comet tail sign, and the clinical context (especially a history of asbestos exposure or known pleural disease) that clinches the diagnosis.11Respiratory Medicine. Update on rounded atelectasis
Why It Gets Mistaken for Lung Cancer
The fundamental problem with rounded atelectasis is that a round mass sitting in the lung looks, at first glance, like a tumor. Before the condition was well characterized, many patients ended up undergoing biopsies or even surgical resections for what turned out to be benign collapsed lung.12PubMed. Rounded atelectasis That is not a trivial concern: lung biopsies carry risks of pneumothorax and bleeding, and open surgical resection removes functioning lung tissue permanently. Recognizing the characteristic imaging features described above is the primary way to avoid these unnecessary procedures.
Adding to the confusion, PET scans, which are commonly used to evaluate suspicious lung masses, do not always help distinguish rounded atelectasis from malignancy. Rounded atelectasis typically shows low-to-moderate metabolic activity on a PET scan. But some cases show high uptake of the tracer, which is exactly the pattern that raises concern for cancer.13PubMed Central. Diagnostic Dilemma of Rounded Atelectasis in the Left Lower Lobe Showing High Uptake of 18F-Fluorodeoxyglucose: A Surgical Conundrum This means a “hot” PET scan does not automatically rule out rounded atelectasis, and a radiologist familiar with the CT features may still be able to make the correct diagnosis despite ambiguous PET results. When findings conflict or clinical suspicion remains high, biopsy becomes the fallback.
Symptoms and How It Is Usually Found
Most people with rounded atelectasis have no symptoms at all. The condition is typically discovered by accident when a chest X-ray or CT scan is done for something else entirely, such as a routine health screening, preoperative evaluation, or workup of an unrelated complaint.14Journal of Advanced Lung Health. Rounded Atelectasis When symptoms do occur, they tend to be vague: mild shortness of breath, a dry cough, or nonspecific chest discomfort. None of these symptoms point specifically to rounded atelectasis, which is why the imaging appearance does essentially all the diagnostic work.
In practice, the usual story goes something like this: a patient with known asbestos exposure or a history of pleural effusion gets a CT scan, the radiologist notices a rounded peripheral mass, and the question becomes “is this cancer?” The answer, more often than the initial alarm suggests, is no. But that answer requires someone familiar with the imaging pattern to recognize it.
How Rounded Atelectasis Behaves Over Time
One of the most reassuring aspects of rounded atelectasis is its stability. In a study that followed patients over an average of about 32 months (with some followed for over ten years), roughly 88% of lesions either stayed the same size or got smaller.15PubMed. Causative factors, imaging findings, and CT course of round atelectasis This stands in sharp contrast to lung cancer, which tends to grow steadily over time. A mass that remains unchanged on serial CT scans over a year or two provides strong additional evidence that it is benign collapsed lung rather than a tumor.
The remaining small percentage of cases that grew in size require closer attention, because growth in a lung mass always raises concern. In those situations, clinicians often recommend more frequent imaging or proceed to biopsy. The key point is that once the diagnosis of rounded atelectasis is established with confidence, watchful waiting with periodic CT scans is a safe and widely accepted strategy.
When Biopsy or Surgery Becomes Necessary
When the classic CT features are all present and the clinical history fits (particularly a clear history of asbestos exposure or chronic pleural disease), most pulmonologists and radiologists are comfortable making the diagnosis without tissue sampling. The imaging findings, when characteristic, are considered reliable enough to spare the patient invasive procedures.16PubMed Central. Rounded atelectasis of the lung: A pictorial review
Biopsy or surgical excision enters the picture when imaging is ambiguous. This happens when the mass lacks the comet tail sign, when the mass is growing on serial scans, when PET scanning shows unexpectedly high metabolic activity, or when the patient has no clear history of pleural disease to explain the finding. In those scenarios, the risk-benefit calculation shifts: the small risks of a biopsy become worth it to rule out cancer with certainty. Needle biopsy is usually tried first, but because the tissue in rounded atelectasis is collapsed and fibrotic, core biopsies can sometimes come back nonspecific, showing only pleural fibrosis without features of malignancy. That result is consistent with rounded atelectasis, but it does not definitively exclude a tumor lurking deeper in the mass. When doubt persists after biopsy, surgical excision with thoracoscopy may follow.
Occupational and Medicolegal Dimensions
Because asbestos exposure is the dominant risk factor, rounded atelectasis frequently comes up in occupational medicine and medicolegal contexts. Workers in shipbuilding, construction, insulation manufacturing, and automotive repair from decades past may have had heavy asbestos exposure and now present with pleural abnormalities. Rounded atelectasis in these patients is an indicator that asbestos has affected the pleura, and its presence should prompt careful long-term monitoring for more serious asbestos-related diseases.17PubMed. Rounded atelectasis in an asbestos exposed worker
From a compensation standpoint, rounded atelectasis itself does not carry the same weight as asbestosis or mesothelioma, but it is recognized as evidence of asbestos-related pleural disease. For workers going through occupational health evaluations or filing claims, having the condition properly documented and correctly distinguished from malignancy matters both medically and legally. A misdiagnosis of lung cancer followed by unnecessary surgery is a very different trajectory from a correctly identified benign condition managed with surveillance.
Rounded Atelectasis in Unusual Populations
Although the condition is overwhelmingly reported in adults, particularly middle-aged and older men with occupational asbestos exposure, it does occasionally appear in unexpected settings. Rare pediatric cases have been documented, including atypical rounded atelectasis in previously healthy children. In one report, a modified bronchoscopic technique involving segmental insufflation and surfactant instillation was used to treat a range of atelectasis types in children, including a case of rounded atelectasis.18Pediatric Pulmonology. Bronchoscopic treatment of pediatric atelectasis: A modified segmental insufflation‐surfactant instillation technique These cases are rare enough that they are typically reported individually in the literature, but they serve as a reminder that the condition is not exclusively a disease of asbestos-exposed workers.
The condition has also been identified incidentally during echocardiography. In one case, a mass seen adjacent to the heart on an echocardiogram initially raised concern for a pleural or cardiac tumor before CT imaging revealed the characteristic features of rounded atelectasis.19PubMed Central. Round Atelectasis: A Peculiar Pseudotumor Seen on Echocardiogram These incidental discoveries through non-chest-specific imaging underscore how easily the condition can trigger alarm when encountered outside the context in which radiologists expect to see it.
Naming and Terminology
You may see this condition referred to by several names. “Rounded atelectasis” and “round atelectasis” are the most common in the radiology and pulmonology literature and are used interchangeably. Older literature sometimes calls it “folded lung” or “Blesovsky syndrome,” after one of the surgeons who described it in the 1960s. The term “pulmonary pseudotumor” also appears, emphasizing the mass-like appearance that mimics a real tumor. All of these names describe the same entity. If you encounter any of them in a radiology report or clinical note, they point to the same benign condition of pleural-related lung collapse.
The variety of names reflects both the condition’s unusual appearance and the fact that different specialties encountered it independently over the years. Surgeons, radiologists, and pulmonologists all recognized it, sometimes using different labels. Modern usage has largely standardized around “rounded atelectasis,” but the other terms persist in older case reports and textbooks. If your imaging report uses an unfamiliar synonym, it is worth asking your physician to clarify, since the practical implications and follow-up plan are identical regardless of which name appears on paper.