Rounded Atelectasis

Rounded atelectasis is a form of peripheral lung collapse in which a portion of lung tissue folds inward upon itself, creating a rounded or oval mass-like opacity on imaging. The condition develops when an area of visceral pleural thickening or fibrosis causes the adjacent lung parenchyma to buckle and collapse, with the affected tissue becoming entrapped by the thickened pleura.¹

In the majority of cases, rounded atelectasis is a consequence of asbestos-related pleural disease. The condition is considered benign and does not itself undergo malignant transformation. However, it serves as an important radiological marker of prior asbestos exposure and, more critically, can closely mimic the appearance of a peripheral lung cancer on imaging — creating a diagnostic challenge that may require biopsy to resolve.²

The hallmark radiological feature of rounded atelectasis is the "comet tail sign" — a pattern of curving bronchovascular structures sweeping into the collapsed lung mass, best visualized on computed tomography. When this characteristic sign is present along with adjacent pleural thickening, volume loss in the affected lobe, and an obtuse angle between the mass and the pleural surface, the diagnosis can be made with confidence on imaging alone, potentially avoiding unnecessary invasive procedures.³

Despite its benign nature, rounded atelectasis has medical and legal significance. Its presence confirms meaningful asbestos exposure and places the individual in a population at elevated risk for mesothelioma and asbestos-related lung cancer. As part of the spectrum of asbestos-related pleural disease, it may support legal claims for asbestos-related compensation.⁴

Rounded atelectasis is frequently asymptomatic and discovered incidentally on chest imaging. When symptoms do occur, they are typically mild:¹

• Mild dyspnea — if the area of atelectasis is large or combined with other pleural disease
• Dull chest pain — localized to the affected area
• Chronic cough — non-productive, from associated pleural irritation

More commonly, symptoms are attributable to the underlying pleural disease (diffuse pleural thickening or plaques) rather than the atelectasis itself. Many patients are entirely asymptomatic.

Rounded atelectasis develops as a mechanical consequence of pleural disease:²

• Asbestos-related pleural disease — the most common cause; visceral pleural thickening causes adjacent lung to fold and collapse
• Prior pleural effusion — resolved effusions can leave residual pleural thickening that traps lung tissue
• Pleural infection (empyema) — post-infectious pleural fibrosis
• Post-thoracic surgery — scarring and adhesions
• Therapeutic pneumothorax — historical tuberculosis treatment that caused pleural scarring

• Asbestos exposure history — the dominant risk factor; most cases occur in exposed individuals
• Existing pleural disease — diffuse pleural thickening or plaques
• Prior pleural effusion — benign asbestos pleural effusion often precedes rounded atelectasis
• Posterior/lower lobe location — anatomic predilection due to gravity-dependent fluid accumulation

Diagnostic Criteria

The diagnosis of rounded atelectasis is primarily radiological. Classic CT features include:³

• Comet tail sign — curving bronchovascular structures sweeping into the periphery of the mass (pathognomonic)
• Rounded or oval mass — 2-7 cm, typically in the posterior lower lobes
• Adjacent pleural thickening — the mass contacts a thickened pleural surface
• Obtuse angle with pleura — the mass forms a wide angle where it meets the pleural surface
• Volume loss — local volume reduction in the affected lobe
• Air bronchograms — may be present within the collapsed lung

When all classic features are present, the diagnosis is reliable and biopsy is unnecessary. If any atypical features exist — growth on serial imaging, absence of the comet tail sign, or PET avidity — biopsy is warranted to exclude malignancy.

• Observation — standard approach when imaging features are characteristic; serial CT at 3, 6, and 12 months, then annually
• CT-guided biopsy — when imaging is not diagnostic or when the mass shows interval growth
• PET-CT — may help differentiate from malignancy, though rounded atelectasis can show mild FDG uptake
• Surgical resection — rarely indicated; reserved for cases where malignancy cannot be excluded after biopsy or when symptoms are significant

The underlying pleural disease is managed according to its own treatment protocols. Smoking cessation is encouraged to reduce the additional risk of lung cancer.⁴

Rounded atelectasis itself has an excellent prognosis. It is a stable, benign condition that does not progress to malignancy. The primary concern is the associated asbestos exposure, which independently elevates the risk for mesothelioma and lung cancer. Patients require long-term surveillance not for the atelectasis itself but for the detection of any new asbestos-related malignancy.¹

Prevention of rounded atelectasis requires preventing the underlying pleural disease through elimination of asbestos exposure. Workers with known exposure should undergo regular surveillance imaging to identify pleural changes early.²