A CT sign of chronic pulmonary arterial hypertension: The ratio of main pulmonary artery to aortic diameter

The aim of this study was to determine whether the ratio of the diameters o f the main pulmonary artery and of the ascending aorta (rPA), as assessed o n computed tomography (CT), is predictive of pulmonary arterial hypertensio n (PAH). We undertook a retrospective review of 50 patients with a wide ran ge of pulmonary and cardiovascular diseases, who had undergone bath chest C T and pulmonary arterial pressure measurements at right heart catheterizati on. Two independent observers made measurements of the diameter of the main pulmonary artery and of the ascending aorta on a single defined CT section . Body surface area (BSA, n = 48), pulmonary arteriolar resistance (n = 39) , total lung capacity (n = 40), and aortic pressures (n = 50) were also rec orded. rPA and pulmonary arterial diameter (dPA) were positively related to mean pulmonary artery pressure (R-s = 0.74, p < 0.0005 for both analyses). For patients younger than 50 years of age, mean pulmonary artery pressure correlated more strongly with rPA than dPA (R-s = 0.77, p < 0.00005, compar ed with R-s = 0.59, p < 0.005); and vice versa for patients older than 50 y ears of age (R-s = 0.63, p < 0.005, compared with R-s = 0.75, p < 0.00005). Using a mean pulmonary artery pressure greater than 20 mm HE as indicative of PAH and a value of rPA > I, the sensitivity, specificity, and positive and negative predictive values for determining PAH were 70% (26/37), 92% (1 2/13), 96% (26/27), and 52% (12/23), respectively. On multivariate analysis , rPA was positively related to mean pulmonary artery pressure (p < 0.0005) , and negatively related to age (p < 0.0005), but was not related to BSA. B y contrast, dPA showed some dependency on BSA (p < 0.0005), as well as on m ean pulmonary arterial pressure. In patients younger than 50 years of age, we have found a strong correlation between rPA and mean pulmonary artery pr essure in a heterogeneous study population, and this relationship is indepe ndent of BSA and sex. The presence of the sign "rPA > 1" is simple in pract ical CT reading to determine; if this is identified, there is a very high p robability of pulmonary arterial hypertension, and clinicians should be ale rted to this possibility.