From the Guidelines
Pulmonary hypertension can be diagnosed on CT using criteria such as a main pulmonary artery diameter greater than 29 mm, a ratio of main pulmonary artery to ascending aorta diameter greater than 1, and other supportive findings like right ventricular enlargement and peripheral pulmonary artery enlargement. These criteria are based on the most recent and highest quality study available, which is the 2022 update of the ACR Appropriateness Criteria for suspected pulmonary hypertension 1. The study highlights that a main pulmonary artery diameter of 29 mm is 87% sensitive and 89% specific for pulmonary hypertension, with a positive predictive value of 97%. Additionally, the ratio of the main pulmonary artery to the adjacent ascending aorta is an extremely sensitive CT finding for pulmonary hypertension, with a positive predictive value of 96% 1.
Some key CT findings that suggest pulmonary hypertension include:
- Main pulmonary artery diameter greater than 29 mm
- Ratio of main pulmonary artery to ascending aorta diameter greater than 1
- Right ventricular enlargement with a right ventricle to left ventricle ratio exceeding 1:1
- Peripheral pulmonary artery enlargement (segmental artery-to-bronchus ratio greater than 1:1 in three or more lobes)
- Pruning of peripheral vessels
- Mosaic attenuation pattern of lung parenchyma
- Enlarged bronchial arteries
It's worth noting that while CT can provide valuable non-invasive evidence of pulmonary hypertension, right heart catheterization remains the gold standard for diagnosis and is necessary to confirm the diagnosis before initiating therapy 1. The 2017 ACR Appropriateness Criteria for suspected pulmonary hypertension also supports these findings, but the 2022 update provides more recent and relevant guidance 1.
From the Research
CT Criteria for Pulmonary Hypertension
- The size of the main pulmonary artery on CT angiography has a good predictive value regarding the severity of pulmonary hypertension (PHT) 2.
- A mean main pulmonary artery diameter of 3.55 +/- 0.66 cm and a pulmonary artery/ascending aorta ratio of 1.2 +/- 0.29 were found in patients with PHT 2.
- Main and right pulmonary artery diameters correlated with the pressure measurement by echocardiography (P=0.001) 2.
- A cutoff mean pulmonary artery diameter (MPAD) of >33.3 mm had 100% specificity and 100% positive predictive value for diagnosing PH, while a cutoff MPAD of <27.3 mm had 100% sensitivity with 100% negative predictive value 3.
- The measurement of MPAD by CT scanning can be used to screen for the presence of PH, with a proposed cutoff value of ≥3.15cm 4.
- However, the use of MPAD ≥3.15cm as a cutoff value is not specific for identifying patients with PAHTN, with a sensitivity of 82% and specificity of 62% 4.
- Incorporating right and left pulmonary artery measurements does not improve diagnostic accuracy, and assessment of comorbidities does not easily identify likely false positive cases 4.
- CT features such as peripheral calcification, peripheral dilatation, eccentric filling defects, and intra-arterial soft tissue in the pulmonary arteries, as well as findings in the lung parenchyma, heart, and mediastinum, can suggest a subtype or probable cause of PH 5.