대한흉부영상의학회 Korean Society of Thoracic Radiology

Discussion

Diagnosis With Brief Discussion

Diagnosis

Trilobar atelectasis (RML, RLL, and LUL)

Radiologic Findings

Chest PA radiograph shows elevated left hilum and left main bronchus, which suggest complete LUL atelectasis. You can see the triangular-shaped opacity in right paracardiac area with obliteration of right heart border and right diaphragm, which means RML & RLL collapse. Lateral radiograph shows anterosuperiorly displaced left major fissure with LUL atelectasis, inferiorly displaced right minor fissure with RML atelectasis, and inferiorly displaced upper half of right major fissure with RLL atelectasis. The bronchoscopic examination revealed tuberculous bronchostenosis of these bronchi.
Obliterated bronchi of LUL, RML, and RLL are well visualized on 3D-reformated airway image (arrows).

Brief Review

In combined lobar atelectasis, the volumes of two lobes of a lung decrease simultaneously. Because the right lung has three lobes, three combinations of combined atelectasis are possible within the right hemithorax. The most frequent combination is that of RML and RLL atelectasis caused by obstruction of the bronchus intermedius. Less commonly seen are combined atelectasis of the RUL and RML, and combined RUL and RLL atelectasis. Because the bronchus intermedius is the common pathway to the RML and RLL, a single localized lesion involving the bronchus intermedius gives rise to combined atelectasis of these lobes. The bronchial obstruction can be caused by a tumor, a foreign body, a mucous plug, or an inflammatory stricture.
In combined RML and RLL atelectasis, the atelectatic RLL obscures the right hemidiaphragm, while the atelectatic RML obscures the right cardiac border on PA radiographs. Both the major and minor fissures are depressed by the hyperexpanding RUL, and the depression is most marked laterally. Interestingly, the two depressed fissures cross each other, the major fissure being more vertical in orientation to climb higher to meet the hilum, whereas the minor fissure extends laterally to reach the lateral costophrenic angle. On lateral view, the overinflated RUL fills the almost whole hemithorax, and the atelectatic RML and RLL manifest as a low-lying opacity which traverses from the front to the back of the thorax. Other signs of combined atelectasis of the RML and RLL include a small and depressed right hilum, decreased vascularity of a hyperexpanded RUL, mediastinal shift to the right, and elevation of the right hemidiaphragm. On CT scans, the atelectatic RML and RLL occupy the lower hemithorax and abut the right cardiac border medially and the right hemidiaphragm inferiorly.
Complete combined RML and RLL atelectasis can be difficult to detect on PA and lateral radiographs. The diagnosis should be suspected in the patients with a small right hilum and an apparently oligemic right lung, which represents the hyperexpanded RUL.

References

1. Lee KS, Kim TS. Atelectasis. In: Taveras JM, Ferrucci JT, eds. Radiology, diagnosis-imaging-intervention. Vol. 1, Chap. 56. Philadelphia: Lippincott-Raven Publishers, 1998: 1-32

Keywords

Lung, Airway, atelectasis, Trilobar atelectasis (RML, RLL, and LUL)