Measure the main pulmonary artery against the ascending aorta, look at the right heart, then search for the cause — chronic thromboembolism, lung disease, a shunt or left heart disease — because the cause is the report.
Orient first
- Pulmonary hypertension is diagnosed by right heart catheterisation; CT suggests it and, more usefully, suggests its group.
- A main pulmonary artery diameter above about 29–30 mm, or wider than the adjacent ascending aorta, raises the possibility — verify the threshold used locally.
- Chronic thromboembolic disease is the treatable cause not to miss: eccentric mural thrombus, webs and bands, mosaic perfusion.
Acquire the study
- CT pulmonary angiography with thin slices; lung windows for parenchymal disease; ECG gating is optional.
The manoeuvre
- Axial slice at the bifurcation: main pulmonary artery diameter in mm and its ratio to the ascending aorta.
- Right heart: RV/LV diameter ratio on axial images, septal flattening, contrast reflux into the IVC and hepatic veins.
- Arterial phase: eccentric thrombus, webs, abrupt narrowing and pouching (chronic thromboembolism); bronchial artery hypertrophy.
- Lung window: mosaic attenuation, emphysema, fibrosis, centrilobular ground-glass nodules (veno-occlusive disease).
- Shunts and the left heart: atrial or ventricular septal defect, anomalous venous return, left atrial enlargement.
What confirms it
- An enlarged pulmonary trunk with right heart strain and a named likely group.
What licenses you to exclude it
- A normal-calibre pulmonary artery does not exclude pulmonary hypertension; echocardiography and catheterisation decide.
The classic misread
- Missing chronic thromboembolic disease because the eye is trained on acute emboli — look for webs and eccentric thrombus.