Radiology Respiratory Radiology 576becd0 Flat waist sign is seen in A Right upper lobe collapse B Right middle lobe collapse C Left upper lobe collapse D Left lower lobe collapse High-Yield Explanation FLAT WAIST SIGN Flattening of the contours of the aoic knob and adjacent main pulmonary aery. Seen in left lower lobe collapse Caused by leftward displacement and rotation of the hea