Rounded Atelectasis

Epidemiology

  • History: rounded atelectasis was first described in 1928 (in the setting of intentional pneumothorax associated with plombage therapy for tuberculosis)
  • Mean Age of Presentation: 65 +/- 13 y/o [MEDLINE]
  • Association with Tobacco Abuse: 83% of cases are active or former-smokers [MEDLINE]

Physiology

  • Rounded Atelectasis: circularly-folded atelectatic lung tissue, typically with adhesions to the visceral pleura
    • Rounded atelectasis is a visceral pleural lesion (in contrast to asbestos-related pleural plaques, which are of parietal pleural origin)
  • Theoretical Mechanisms of Rounded Atelectasis Formation
    • Folding/Pleural Effusion Theory: initial event is lung parenchymal compression -> invagination by localized accumulation of pleural fluid
    • Fibrosing/Pleural Injury Theory: initial event is local visceral pleural inflammation -> repair with fibrosis -> contraction of visceral pleura with formation of rounded atelectasis
    • Microbronchial Distortion Theory: stargnulation of small airways with gas resorption -> focal atelectasis

Etiology

Rounded Atelectasis Associated with Mineral Dust Exposure

  • Asbestos Exposure
    • Epidemiology: most common etiology (accounts for 29-86% of cases)
    • Exposures: see Asbestos
    • Clinical: asbestos-related rounded atelectasis usually occurs in the presence of other asbestos-related lung disease (asbestosis) or asbestos-related pleural disease (asbestos pleural plaques), but can occur without other asbestos-related lung or pleural manifestations
  • Silicosis (see Silicosis)
  • Mixed Mineral Dusts

Rounded Atelectasis Associated with Exudative Pleural Effusion

Rounded Atelectasis Associated with Pneumothorax (see Pneumothorax)

  • Intentional Pneumothorax (aka “Collapsotherapy”): plombage (therapeutic collapse of regions of the lung) was previously used to treat tuberculosis
  • Iatrogenic Pneumothorax: due to procedures with inadvertent entry of the pleural space
  • Lymphangioleiomyomatosis (LAM)-Associated Pneumothorax (see Lymphangioleiomyomatosis): case reports of rounded atelectasis occurring in association with pneumothorax and chylothorax
  • Spontaneous Pneumothorax

Rounded Atelectasis in the Absence of Significant Pleural Disease


Clinical Manifestations

Round/Spindle/Ovoid/Wedge-Shaped Lung Lesion

Diagnosis

  • CXR
    • Sensitivity: only 50%
  • Chest CT
    • Number: usually solitary (although occasionally multiple)
    • Density: soft-tissue density (may contain centrally-located air bronchogram or less dense center)
      • In silicosis-related cases, silcotic nodules may be present inside the rounded atelectasis lesion (as well in other parts of the lung)
    • Borders: hazy or irregular (blurred hilar margins)
    • Size: usually 3.5-7 cm in diameter
    • Location: present in the lower lobes in 66% of cases (seldom seen in RUL, almost never seen in LUL)
      • Non-Asbestos-Related Cases: commonly located in dependent regions (basal, posterior, paraspinal regions) of the lung, as well as middle lobe and lingula
      • Asbestos-Related Cases (preferentially located in areas with greatest degree of inahalational asbestoc deposition): commonly located in the lower lobes, lingulam and middle lobe
    • Appearance
      • Volume Loss of Affected Lobe: may have fissure or mainstem bronchial displacement (toward lesion, due to volume loss)
      • Whirled or “Comma” Appearance
      • “Cranial Tilting Sign”: originally described by Hanke, described as “the abrupt cephalad displacement of the linear opacities (pulmonary vessels) immediately after exiting the lesion”
      • “Comet Tail Sign” (seen in almost all cases): due to crowded incoming vessels pointing toward hilum
    • Subpleural/Pleural-Based: abutting a thickened and/or calcified pleural surface
      • Acute angle formed with visceral pleura, indicating that the lesion is parenchymal in origin (not pleural in origin)
    • Absence of Mediastinal Lymphadenopathy
  • Most Useful CT Criteria [MEDLINE]
    • Contiguity to Areas of Diffuse Pleural Thickening
    • Lentiform or Wedge-Shaped Outline
    • Volume Loss
    • “Comet-Tail Sign”
  • High-Resolution Chest CT: no advantage over normal chest CT in defining rounded atelectasis (although may be useful to define co-existing interstitial lung disease)
  • Thoracic U/S
    • Pleural-based hyper-echogenic area
    • Adjacent pleural thickening with extrapleural fat
    • Highly echogenic line extending from the pleura into the “mass”: represent scarred, invaginated visceral pleura
  • Thoracic MRI:
    • “Kidney-Like Pattern”: hypointense lines converging towards the center of the lesion
  • PET Scan: metabolically inactive
  • PFT’s: usually normal (in the absence of other associated parenchymal lung disease)

Clinical Features

  • Asymptomatic: most cases
  • Dyspnea (see Dyspnea): may be seen in cases with underlying asbestosis or other associated lung disease
  • Chest Pain (see Chest Pain)
  • Cough (see Cough)

Treatment

  • Natural History: rounded atelectasis lesions may regress spontaneously, remain stable in size, or grow slowly
  • Differentiation from Malignancy: necessary in cases of lung masses that demonstrate enlargement over time

References

  • Asbestos-related focal lung masses: manifestations on conventional and high-resolution CT scans. Radiology. 1988 Dec;169(3):603-7 [MEDLINE]
  • Rounded atelectasis formation following decrease of pleural effusion: a case report. Radiat Med 1996;14(6):331–3 [MEDLINE]
  • Round atelectasis. Rev Clin Esp 2001;201(6):303–7 Abstract [MEDLINE]
  • Prognosis of patients with rounded atelectasis undergoing long-term hemodialysis. Nephron 2001;88(1):87–92 [MEDLINE]
  • Pulmonary lymphangioleiomyomatosis and rounded atelectasis. JBR-BTR. 2004 May-Jun;87(3):152-3 [MEDLINE]
  • Rounded atelectasis of the lung. Respir Med. 2005 May;99(5):615-23 [MEDLINE]
  • Rounded atelectasis associated with pulmonary lymphangioleiomyomatosis. Intern Med. 2005 Jun;44(6):625-7 [MEDLINE]