Question:
Which is the most reliable objective sign for identifying pulmonary plethora on a chest X-ray?
Which is the most reliable objective sign for identifying pulmonary plethora on a chest X-ray?
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The vertically running interlobar vessel beside the right heart border is the one you can measure cleanly.
Updated On: Jun 24, 2026
- Diameter of the main pulmonary artery >16 mm
- Diameter of the left pulmonary artery >16 mm
- Diameter of the descending right pulmonary artery >16 mm
- Diameter of the descending left pulmonary artery >16 mm
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The Correct Option is C
Solution and Explanation
Step 1: Pulmonary plethora means increased pulmonary blood flow, typically from a left-to-right shunt, producing enlarged, prominent pulmonary vessels on the chest radiograph.
Step 2: The most reproducible and measurable (objective) vessel on a plain frontal chest film is the descending (interlobar) branch of the right pulmonary artery, because it runs vertically alongside the right heart border against aerated lung and its margins are sharply seen.
Step 3: The accepted upper limit of normal for the diameter of the descending right pulmonary artery is about 16 mm; a value greater than 16 mm indicates enlargement and is taken as a reliable objective sign of increased pulmonary flow or pulmonary arterial enlargement.
Step 4: The main and left pulmonary arteries are partly obscured by the mediastinum and overlying structures, so they cannot be measured as cleanly and are less reliable for this purpose; the descending left pulmonary artery is also less consistently profiled than the right.
Conclusion: The correct answer is diameter of the descending right pulmonary artery greater than 16 mm.
Step 2: The most reproducible and measurable (objective) vessel on a plain frontal chest film is the descending (interlobar) branch of the right pulmonary artery, because it runs vertically alongside the right heart border against aerated lung and its margins are sharply seen.
Step 3: The accepted upper limit of normal for the diameter of the descending right pulmonary artery is about 16 mm; a value greater than 16 mm indicates enlargement and is taken as a reliable objective sign of increased pulmonary flow or pulmonary arterial enlargement.
Step 4: The main and left pulmonary arteries are partly obscured by the mediastinum and overlying structures, so they cannot be measured as cleanly and are less reliable for this purpose; the descending left pulmonary artery is also less consistently profiled than the right.
Conclusion: The correct answer is diameter of the descending right pulmonary artery greater than 16 mm.
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