On CT pulmonary angiography (CTPA), what is the most common site of pulmonary embolism?
A. Right upper lobe pulmonary artery
B. Left lower lobe pulmonary artery
C. Right lower lobe pulmonary artery
D. Left upper lobe pulmonary artery
Explanation
Most Common Site of PE on CTPA
Key Point
The right lower lobe pulmonary artery is the most frequent site of pulmonary embolism, accounting for approximately 40–50% of emboli detected on CTPA.
Anatomical Basis
The right lower lobe artery is preferentially affected because:
1.
Larger caliber — The right lower lobe artery has a larger diameter than other segmental arteries, making it a lower-resistance pathway for emboli.
2.
Straighter course — The right lower lobe artery branches more directly from the right main pulmonary artery, allowing emboli to travel with less deflection.
3.
Gravity and flow dynamics — Emboli preferentially lodge in vessels with higher blood flow and less acute angles.
Distribution of PE Sites
Table
Site
Frequency
Reason
Right lower lobe
40–50%
Largest caliber, straight course
Right upper lobe
20–25%
Moderate flow
Left lower lobe
15–20%
Smaller than right lower
Left upper lobe
10–15%
Smallest caliber
High-YieldNEET PG
On CTPA, always scrutinize the right lower lobe pulmonary artery first when screening for PE — this is where the majority of emboli will be found.
Clinical Pearl
Isolated subsegmental PE in the right lower lobe is common but may be clinically insignificant in hemodynamically stable patients without cardiopulmonary disease.
CTPA Protocol Reminder
CTPAs are acquired during the pulmonary arterial phase (13–15 seconds after bolus arrival in the right atrium) to maximize contrast opacification of the pulmonary arteries and detect thrombi as filling defects.
Harrison 21e Ch 297
Practice similar questions
Sign up free to access AI-powered MCQ practice with detailed explanations and adaptive learning.
