CTICasesRight Middle Lobe Lateral Segment Atelectasis
Imaging findings
Incidental finding on chest radiograph shows a focal, triangular consolidation in the right mid-lung field. CT and lateral reconstructions confirm isolated atelectasis of the lateral segment of the right middle lobe. The consolidation contacts the minor fissure and projects posterior to the right pulmonary artery hilum. The medial segment of the middle lobe is normal, and the opacity resolved on follow-up.
Key takeaways
Isolated lateral segment atelectasis of the right middle lobe is an uncommon and benign finding typically caused by transient mucus plugging. Unlike complete middle lobe collapse (which projects anteriorly and silhouets the right heart border), lateral segment collapse projects posteriorly and contacts the minor fissure. Recognizing this specific segmental pattern prevents misinterpretation as a pulmonary nodule or mass.
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