Question:hard
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?
Show Hint
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
Show Solution
The Correct Option is C
Solution and Explanation
Think about which pulmonary vessel a radiologist can actually measure with confidence on a standard PA chest film. The descending (interlobar portion of the) right pulmonary artery is ideal because it descends vertically next to the right atrial border, is surrounded by air-filled lung, and therefore has crisp, measurable edges.
Pulmonary plethora reflects an overcirculated lung, usually from a left-to-right shunt, and it shows up as dilated pulmonary arteries. Using the descending right pulmonary artery as the yardstick, a diameter above roughly 16 mm is the recognised objective threshold signalling abnormal enlargement and increased flow.
The other arteries fall short as objective markers: the main pulmonary artery and the left pulmonary artery lie partly within or behind the mediastinal shadow, so their borders are not reliably definable, and the descending left pulmonary artery is harder to profile than its right-sided counterpart.
Hence the single most reliable objective sign is a descending right pulmonary artery wider than 16 mm.
\[\boxed{\text{Descending right pulmonary artery } > 16\text{ mm}}\]
Pulmonary plethora reflects an overcirculated lung, usually from a left-to-right shunt, and it shows up as dilated pulmonary arteries. Using the descending right pulmonary artery as the yardstick, a diameter above roughly 16 mm is the recognised objective threshold signalling abnormal enlargement and increased flow.
The other arteries fall short as objective markers: the main pulmonary artery and the left pulmonary artery lie partly within or behind the mediastinal shadow, so their borders are not reliably definable, and the descending left pulmonary artery is harder to profile than its right-sided counterpart.
Hence the single most reliable objective sign is a descending right pulmonary artery wider than 16 mm.
\[\boxed{\text{Descending right pulmonary artery } > 16\text{ mm}}\]
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