Imaging description

The aortic wall comprises three layers: intima, media, and adventitia. The wall is imperceptible and inferred on contrast-enhanced CT by a boundary separating two tissues of contrasting attenuations: arterial lumen and the periarterial soft tissue. Processes such as intramural hematoma (IMH) that thicken the media expand the wall and displace the intimal layer inwards toward the lumen.

Aortic calcifications are usually centered on the intima and are, therefore, peripherally located (Figure 59.1). A process in the media that displaces the intima renders the calcifications non-peripheral (Figures 59.2A and 59.3).

However, non-peripheral calcifications can also be dystrophic calcifications of the mural thrombus, also known as neointimal calcifications (Figures 59.2B, 59.4, and 59.5).

How can the distinction be made on unenhanced CT?

1. Neointimal calcifications are chunky and random, since any part of the thrombus can calcify (Figure 59.2B). Intimal calcifications are thin, linear, and circumferentially configured (Figure 59.2A).

2. Neointimal calcifications may co-exist with intimal calcifications, in which case there are calcifications peripheral to neointimal calcifications (Figure 59.4).

3. Mural thrombus is of a lower attenuation (< 30 HU) than acute intramural hematoma (50–80 HU) and blood pool (40–50 HU).

Importance

Distinguishing between neointimal calcifications and displaced intimal calcifications is important because the latter reflects acute aortic pathology such as IMH and dissection. Dystrophic calcifications of the mural thrombus reflect an indolent process. The pitfall can result in incorrect diagnosis of acute aortic syndrome.