While standard CT pulmonary angiography (CTPA) is specifically timed to optimize right-sided heart opacification, pulmonary emboli are frequently detected as incidental findings or alternative causes of chest pain on standard Coronary CTAs — which are timed for left-sided enhancement.
1 Acute pulmonary embolism
CT findings. Emboli appear as central filling defects within the opacified pulmonary arteries, maintaining a sharp interface with the contrast material.
A saddle embolus is a massive clot that straddles the bifurcation of the main pulmonary artery.
2 Right heart strain
Massive acute emboli increase pulmonary pressures, resulting in right ventricular (RV) failure. CT signs of right-heart strain — which indicate a poorer prognosis — include:
The dilated RV becomes the dominant chamber on axial cuts.
The high RV pressure pushes the septum into the LV, distorting its normal D-shape.
Hemodynamic backup — contrast spills back through the tricuspid valve into the systemic venous side.
3 Pulmonary infarcts
Peripheral, wedge-shaped opacities — most commonly in the lower lobes — represent ischemic tissue necrosis from the obstructed segmental supply.
4 Chronic Thromboembolic Pulmonary Hypertension (CTEPH)
A small percentage of acute emboli fail to resolve, transforming into organized, fibrotic thromboemboli.
CT findings. Unlike the central defects of acute PE, chronic emboli form eccentric, wall-adherent filling defects that can appear as:
- Slits
- Webs
- Bands
These cause abrupt vessel narrowing rather than the smooth tapering of acute clot.
Secondary changes worth noting:
- The central main pulmonary artery will be massively dilated (> 2.9 cm) with pruning of the distal peripheral vessels.
- The lung parenchyma frequently demonstrates a mosaic attenuation pattern — where areas of hypoattenuation correlate with hypoperfusion.