Radiologic patterns of lobar atelectasis
- Paul Stark, MD
Paul Stark, MD
- Professor of Radiology
- University of California San Diego
Atelectasis describes the loss of lung volume due to the collapse of lung tissue. Radiologic findings characteristic of atelectasis are reviewed here. The appearance of atelectasis on a chest radiograph is emphasized, but its appearance on computed tomography (CT) is also described. The types and pathogenesis of atelectasis are discussed separately. (See "Atelectasis: Types and pathogenesis in adults".)
Radiologic signs of lobar atelectasis can be categorized as direct or indirect [1-5]. Direct signs include increased opacification of the airless lobe and displacement of fissures. Indirect signs include displacement of hilar and cardiomediastinal structures toward the side of collapse, narrowing of the ipsilateral intercostal spaces, elevation of the ipsilateral hemidiaphragm, compensatory hyperinflation and hyperlucency of the remaining aerated lung, and obscuration or desilhouetting of the structures adjacent to the collapsed lung (eg, diaphragm and heart borders). Additional radiologic features vary according to the site of atelectasis.
Right upper lobe — In right upper lobe atelectasis, the collapsed lobe tends to shift cephalad and medially, producing a triangular apical opacity on the frontal view of a chest radiograph (image 1). The opacity may be subtle when the right upper lobe is completely collapsed (especially if chronic), forming only a thin right apical cap. These findings are accompanied by elevation of the right hilum and the minor fissure, with the latter displaying a convex contour cranially . A juxtaphrenic peak (ie, a steeple-shaped shadow adjacent to the diaphragm) may also be present (image 2) . This finding is due to tenting of the ipsilateral diaphragmatic pleura at either the base of the inferior accessory fissure or, less likely, at the insertion site of the inferior pulmonary ligament.
These radiologic findings are different depending upon the orientation and shift of the upper lobe collapse. Medial collapse of the right upper lobe may mimic a right paratracheal mass on the frontal view of a chest radiograph. In contrast, lateral collapse, also called peripheral atelectasis, may generate a peripheral mass-like opacity that mimics a loculated pleural effusion (image 3) [7,8]. This is generally accompanied by superior and medial hyperexpansion of the right middle and right lower lobe.
When right upper lobe atelectasis is due to a central mass with or without an enlarged interlobar lymph node, the minor fissure may have a lateral upward convexity and a medial caudal convexity (similar to the inverted letter S) on the frontal view of a chest radiograph (image 1). This configuration of the minor fissure is called the inverted S-sign of Golden and is suggestive of a neoplastic etiology causing atelectasis of the right upper lobe.
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- LOBAR ATELECTASIS
- Right upper lobe
- Right middle lobe
- Right lower lobe
- Left upper lobe
- Left lower lobe
- MULTILOBAR ATELECTASIS
- Right middle and lower lobes
- Right upper and middle lobes
- Right upper and lower lobes
- ATELECTASIS OF AN ENTIRE LUNG
- SEGMENTAL ATELECTASIS
- Plate-like atelectasis
- Rounded atelectasis
- SUMMARY AND RECOMMENDATIONS