Question:medium
The aortic knob silhouette on a chest X-ray (PA view) is obliterated by consolidation of which portion of the lung?
The aortic knob silhouette on a chest X-ray (PA view) is obliterated by consolidation of which portion of the lung?
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Which lung segment is draped directly against the aortic arch high on the left mediastinum?
Updated On: Jun 24, 2026
- Apicoposterior segment of left upper lobe
- Superior lingular segment of left upper lobe
- Apical segment of left lower lobe
- Inferior lingular segment of left upper lobe
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The Correct Option is A
Solution and Explanation
Reading a chest film border by border is the fastest way to localise consolidation. Each mediastinal margin that stays crisp tells you the abutting lung is clear, and each margin that disappears points to the segment in contact with it.
The aortic knob projects high on the left mediastinum where the arch turns. The only lung tissue draped against the arch at this height is the apicoposterior segment of the left upper lobe. When this segment fills with fluid or exudate, the air interface against the arch is lost and the knob blurs out.
The lingula (superior and inferior lingular segments) sits lower and faces the left ventricular border, so disease there erases the heart border rather than the arch. The apical segment of the left lower lobe lies posteriorly and inferiorly and never touches the aortic arch. Therefore loss of the aortic knob points specifically to the apicoposterior segment of the left upper lobe.
\[\boxed{\text{Apicoposterior segment of left upper lobe}}\]
The aortic knob projects high on the left mediastinum where the arch turns. The only lung tissue draped against the arch at this height is the apicoposterior segment of the left upper lobe. When this segment fills with fluid or exudate, the air interface against the arch is lost and the knob blurs out.
The lingula (superior and inferior lingular segments) sits lower and faces the left ventricular border, so disease there erases the heart border rather than the arch. The apical segment of the left lower lobe lies posteriorly and inferiorly and never touches the aortic arch. Therefore loss of the aortic knob points specifically to the apicoposterior segment of the left upper lobe.
\[\boxed{\text{Apicoposterior segment of left upper lobe}}\]
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