What is rounded atelectasis?

What is Rounded Atelectasis?

Rounded atelectasis is a benign form of peripheral lung collapse that develops from infolding of thickened visceral pleura with collapse of the intervening lung parenchyma, most commonly associated with asbestos exposure, and presents radiographically as a mass that can be mistaken for lung cancer. 1

Alternative Names

Rounded atelectasis is also known by several other terms 1, 2:

• Folded lung
• Shrinking pleuritis
• Contracted pleurisy
• Pleuroma
• Blesovsky's syndrome

Pathophysiology

The lesion develops through a specific mechanism 1:

• Infolding of thickened visceral pleura occurs, with collapse of the intervening lung parenchyma
• The pleura shows one or several indentations, often with deep invaginations into the pulmonary parenchyma 3
• Histologic examination reveals folded and fibrotic visceral pleura with atelectasis and variable amounts of chronic inflammation in the adjacent lung parenchyma 1
• Dense fibrous thickening occurs outside the pleural folds 3

Etiology and Risk Factors

Asbestos exposure is the most common cause in contemporary practice 1:

• Clinical experience suggests it is more likely to occur today as a result of asbestos exposure than other causes 1
• Mean latency period of 30-38 years following asbestos exposure 1
• Can result from pleuritis of any cause, including empyema, tuberculosis, and pleural effusions 1, 3
• May develop following acute pleuritis with effusion 1
• Five of six cases in one series had past histories of pulmonary tuberculosis with therapeutic pneumothorax 3

Clinical Presentation

Most patients are asymptomatic, with the condition detected incidentally 4, 5:

• Usually found in older men 5
• When symptomatic, patients may present with cough, breathlessness, chest pain, or influenza-like symptoms 1
• Evidence of asbestos exposure may be present in the clinical history 1

Radiographic Features

Plain Chest Radiography

The condition presents as a mass on plain films 1:

• Appears as a rounded, pleural-based opacity 4
• Associated with adjacent pleural thickening 4
• Volume loss of the affected lobe is uniformly present 5
• A band connecting the mass to an area of thickened pleura is visible 1

CT and HRCT Findings

CT demonstrates characteristic features that are often diagnostic 1, 6:

• The pathognomonic "comet tail sign" results from crowding of vessels and bronchi as they enter the atelectatic region, more readily seen on HRCT than plain films 1, 4, 5
• Rounded mass measuring 3.5-7.0 cm in diameter, abutting a thickened pleural surface in the lung periphery 6
• The margin closest to the hilum is blurred by entering vessels in 92% of cases 6
• Curvilinear opacities of bronchi and vessels extend from the site toward the hilum 5
• May show constellation of pleural thickening, pleuro-parenchymal bands/"crow's feet" and folded lung 1

Distribution

Rounded atelectasis may be unilateral, bilateral, or multiple 1:

• Can be bilateral in some cases 1
• Multiple lesions can occur 1
• Most frequently occurs on the right side (69-76%) when associated with benign asbestos pleural effusion 1

Diagnostic Considerations

Key Distinguishing Features

Recognition of characteristic radiologic features can prevent unnecessary invasive procedures 4, 5:

• Slower evolution than lung cancer, so previous films will show a similar finding 1
• The constellation of CT findings (rounded mass, pleural thickening, comet tail sign, volume loss) is considered diagnostic by many authors 4
• Conventional CT is superior to chest films in identifying rounded atelectasis 1

Critical Pitfall

Rounded atelectasis is frequently removed surgically as a suspected peripheral lung cancer 1:

• It is important for diagnostic pathologists to recognize this entity 1
• When tissue is obtained, asbestos bodies and/or evidence of asbestosis should be carefully sought 1
• The condition usually remains stable over time, though slow growth or diminution in size has been described 4

Differential Diagnosis

The major differential diagnostic considerations include 1:

• Peripheral lung cancer - the most common misdiagnosis
• Malignant pleural mesothelioma - particularly when associated with asbestos exposure
• CT features suggesting malignancy include pleural thickening >1 cm, pleural nodularity, chest wall invasion, involvement of mediastinal pleura, and high-grade pleural irregularities 1
• PET-CT may have a limited role in cases of diagnostic uncertainty, with mesothelioma often exhibiting higher maximum standardized uptake values 1

Associated Findings

Concomitant signs of asbestos exposure are often present 1:

• Pleural plaques
• Diffuse pleural thickening
• Asbestosis
• Parenchymal bands