Linear shadows that connect oblique fissures and costal pleurae on the superior segments of lower lobes: evaluating the imaging findings on thin-slice lung CT

Objective To retrospectively analyse the imaging findings of the linear shadows that connect the oblique fissures and the costal pleurae on the superior segments of the lower lobes on thin-slice lung CT. Materials and methods Thin-slice CT scans of 221 cases of normal lungs and 86 abnormal lungs were collected. The parameters of the imaging observations included the existence of the superior segmental linear shadow, its morphology, length, and starting position, bird-beak sign, and adjacent structures on the pleural end. Results The linear shadows were more common on the left lower lobe (43.44%) than on the right side (19.46%). The pleural origins of the linear shadows were mainly located above the carina (69.78%); the adjacent structure on the left lung was the descending aorta (70.83%), and for the right lung, it was next to the thoracic vertebrae (60.47%). In the presence of pulmonary lobectomy or atelectasis, the linear shadows could be extended, which could pull the oblique fissures and costal pleurae to form the bird-beak sign. Conclusion The linear shadows on the superior segments of the lower lobes are common structures fixing the oblique fissures. Recognition of the linear shadows can help radiologists distinguish normal structures from abnormal ones.