Final diagnosis: Atelectasis with pleural fibroelastosis consistent with rounded atelectasis

Discussion: Rounded atelectasis (RA) is a pleural-based lesion that is the result of pleura and subpleural scarring and atelectasis of adjacent lung tissue.¹ Rounded atelectasis is a clinical diagnosis that is also known by many other names including: folded lung, shrinking pleuritis with atelectasis, atelectatic pseudotumor, and pleuroma.² When a mass is formed, it has been referred to as Blesovsky syndrome (due to his description in 1966).³ RA is usually a solitary lesion and rarely presents as multiple/bilateral lesions.¹ Patients with RA are predominantly men (>90%) and are often smokers, with a mean age of 60 years (range, 20 to 83 years). RA is asymptomatic and found incidentally on imaging for other reasons. When symptoms do occur, they most often include cough, dyspnea, and fever with fatigue or weight loss. Rarely, hemoptysis and chest pain.² There is often a history of asbestos exposure. While RA is known to occur in association with asbestos, which is thought to have no role in development of mesothelioma and can occur with pleural fibrosis due to any cause.^4,5 Trauma, post coronary artery bypass surgery, post-thoracotomy or rib fracture with hemorrhagic pleural effusion may cause RA too. Other causes/ associations include lymphangioleiomyomatosis, cardiac failure, end-stage renal failure, textile fiber, glass fibers, silicone, stone dust and Pergolide (Parkinson drug).^3,5

Radiographically, RA appears as a rounded pleural nodule or a mass-like opacity with pulmonary vessels and bronchi converging on and swirling around. This phenomenon gives the appearance of a comet tail and a reported specificity of 92%.^2,3,5 The nodule typically 2.5-5 cm in diameter that abuts an area of pleura thickening or pleural effusion.³ RA may occur anywhere in the lungs but the most common location is the posterior surface of the lower lobe.² Chest CT with contrast usually confirms the diagnosis and precludes further treatment. However, the comet tail sign is not always present. Confounding the issue further, FDG-PET can be falsely positive.³ Therefore, these lesions can simulate carcinoma or mesothelioma clinically. Both RA and these malignancies share significant clinical overlap (older men, smokers, and asbestos exposure).² Typical cases can be diagnosed by radiology and can be followed without need of surgery. Biopsy is generally pursued for ambiguous cases.⁵

Grossly, a pleural-based nodule/mass can be identified adjacent to a firm, yellow, polygonal visceral pleural plaque. Beneath the plaque the pleura is often folded into the lung. The folds may be perpendicular to the surface but often radiate in many different directions. Occasionally, a lesion may disappear upon sectioning. The adjacent lung is typically firm.1,3

Histologically, RA consists of nonspecific pleural fibrosis with changes of chronic atelectasis in the underlying lung.⁵ The pleural fibrosis is superficial to the elastic and interstitial layer of the pleura. It is hyalinized with no nuclei vessels or elastic fibers.^2,3 The folded pleura has a normal complement of lymphatics, blood vessels, and elastic fibers. The pleura transports fat into atelectatic parenchyma and twists the components into a curl. Large conducting airways and blood vessel lumina are located abnormally close together in the artificial lobules of atelectatic lung.³ Chronic changes include alveolar macrophage accumulation with or without parenchymal fibrosis. In cases with asbestos exposure asbestos fibers may be found.⁵ Lymphoid follicles, chronic inflammation, and active pleuritis may be identified.¹The appearance of the underlying parenchyma is variable; it often appears collapsed but otherwise unremarkable.² The clinical differential is broad, but the histologic findings are characteristic.⁵

References

1. Travis WD, Colby TV, Koss MN, Rosado-de-Christenson ML, Muller NL, Jr. TEK. Occupational Lung Diseases and Pneumoconioses. In: King DW, ed. Non-Neoplastic Disorders of the Lower Respiratory Tract. Washington, DC: American Registry of Pathology and the Armed Forces Institue of Pathology:827-829.

2. Yi E, Aubry MC. Pulmonary Pseudoneoplasms. Archives of pathology & laboratory medicine. 2010;134(3):417-426.

3. Hasleton P, Galateau-Salle F, King J, et al. Diseases of the pleura. In: Hasleton P, Flieder DB, eds. Spencer's Pathology of the Lung. Vol 2. 6th ed. New York: Cambridge University Press; 2013:1448-1451.

4. Corrin B. Pleura and Chest Wall. In: Corrin B, ed. Pathology of the Lung. 1st ed. London: Churchill Livingstone; 2000:614.

5. Wright JL. Inflammatory and Fibrosing Pleural Processes. In: Zander DS, Farver CF, eds. Pulmonary Pathology. 1st ed. Philadelphia, Pennsylvania: Churchhill Livingstone; 2008:742-744.