Normal Pulmonary Artery Trunk Size on CT and MRI
The pulmonary artery trunk (main pulmonary artery) is the short, wide vessel arising from the right ventricle that bifurcates into the left and right pulmonary arteries. Accurate measurement of its diameter is essential because dilatation is a key imaging marker of pulmonary arterial hypertension (PAH) and other cardiopulmonary conditions. Routine reporting of this measurement on chest CT and MRI supports early detection and risk stratification.
Normal Reference Values
| Location | Measurement |
|---|---|
| Male (Average Value) | 27 ± 2.8 mm |
| Women (Average Value) | 25.9 ± 3 mm |
| Upper Limit | 28.6 mm |
Clinical Significance
A main pulmonary artery diameter exceeding 28.6 mm is considered above the normal upper limit and raises concern for pulmonary arterial hypertension. When the pulmonary artery diameter equals or exceeds the diameter of the adjacent ascending aorta, the positive predictive value for PAH increases substantially. Dilatation may also predispose to rare but life-threatening complications such as pulmonary artery dissection or compression of adjacent bronchi.
Measurement should always be interpreted in clinical context, as borderline enlargement can occur with high-output states, left-to-right shunts, or simply larger body habitus. Isolated mild dilatation without other supportive findings warrants correlation with echocardiography and clinical assessment before a diagnosis of PAH is established.
- Pulmonary arterial hypertension (idiopathic or associated)
- Chronic thromboembolic pulmonary hypertension (CTEPH)
- Congenital heart disease with left-to-right shunt (e.g., ASD, VSD)
- Connective tissue disease (e.g., scleroderma, SLE)
- High-output cardiac states (e.g., severe anemia, hyperthyroidism)
Reference: Karazincir S, Balci A, Seyfeli E et al. CT assessment of main pulmonary artery diameter. Diagn Interv Radiol. 2008;14(2):72-4.
Imaging Notes
On CT, the main pulmonary artery is measured at its widest point in the axial plane, perpendicular to its long axis, typically at the level of the bifurcation. Measurements should be made from inner wall to inner wall on mediastinal window settings. Electrocardiographic gating reduces cardiac pulsation artifact and improves reproducibility, though ungated chest CT is routinely used in clinical practice.
On MRI, steady-state free precession (SSFP) or black-blood sequences provide excellent vascular contrast without ionizing radiation. The measurement technique mirrors CT — axial or double-oblique planes perpendicular to the vessel axis at the level of bifurcation. MRI is particularly valuable for serial follow-up in younger patients and those with congenital heart disease, avoiding cumulative radiation exposure.