What is the upper limit of pulmonary artery size?

From the Guidelines

The upper limit of normal pulmonary artery size is generally considered to be 29 mm in diameter when measured at the level of the pulmonary artery bifurcation on CT imaging. This measurement is based on the most recent and highest quality study available, which reported that an MPA diameter of 29 mm on CT is 87% sensitive and 89% specific, with a positive predictive value (PPV) of 97% for PH 1.

Key Considerations

• The ratio of the MPA to the adjacent ascending aorta is an extremely sensitive CT finding for PH, with PH nearly always present when the MPA is larger than the adjacent ascending aorta (PPV of 96%) 1.
• Additional findings of PH on CT include true right and left descending PA diameters of 16 mm and 21 mm, respectively, a ratio of segmental PA to accompanying bronchus >1:1, enlargement of the right ventricle, RV lumen/LV lumen 1, straightening of the interventricular septum, RV free wall thickness 6 mm, pericardial thickening or effusion, and enlargement of the bronchial arteries to a diameter of >1.5 mm 1.
• Evaluation with RHC remains necessary to confirm PH detected on CT before initiating therapy 1.

Clinical Implications

• Pulmonary artery dilation often correlates with increased pulmonary arterial pressure, though the relationship is not perfectly linear.
• If pulmonary artery enlargement is detected, further evaluation with echocardiography or right heart catheterization may be warranted to assess pulmonary arterial pressure and right heart function directly.
• It's essential to consider that measurements can vary slightly based on imaging technique, patient size, age, and gender when evaluating pulmonary artery size.

From the Research

Upper Limit Pulmonary Artery Size

The upper limit of the pulmonary artery diameter can be an important indicator of pulmonary arterial hypertension.

• The study 2 measured the main pulmonary artery diameter in 100 normal subjects and found it to be 2.72 cm (SD = 0.3) using unenhanced contiguous 10 mm CT slices.
• The same study found that a pulmonary artery diameter of 3.32 cm (main pulmonary artery diameter + 2 SD) had a 58% sensitivity and 95% specificity for the presence of pulmonary arterial hypertension.
• Another study 3 determined the age- and sex-specific distribution and normal reference values for main pulmonary artery diameter (mPA) and ratio of mPA to ascending aorta diameter (ratio PA) by CT in an asymptomatic community-based population, and established 29 mm in men and 27 mm in women as sex-specific normative reference values for mPA.

Comparison of Studies

• The study 2 used a different method to determine the upper limit of normal main pulmonary artery diameter, and found it to be 3.32 cm.
• The study 3 found that the mean mPA diameter in the overall cohort was 25.1±2.8 mm, and the 90th percentile cutoff value for mPA diameter was 28.9 mm in men and 26.9 mm in women.
• It is worth noting that the studies 4, 5, and 6 do not provide information on the upper limit of pulmonary artery diameter, but rather focus on the treatment of pulmonary arterial hypertension using phosphodiesterase-5 inhibitors such as sildenafil and tadalafil.