Acute Aortic Syndromes (AAS) are a set of acute,
non-traumatic,
emergent aortic pathologies that,
due to their clinical characteristics,
risk factors and similar prognosis,
were included in this common category.
Because they are clinically indistinguishable,
imaging plays an essential role in differentiating each of these syndromes and in establishing an accurate and rapid diagnosis.
AAS include aortic dissection,
intra-mural hematoma (IMH) and penetrating atherosclerotic ulcer (PAU).
Although they originate in different pathophysiological processes,
they can evolve from one entity to another.
The typical clinical presentation is one of an abrupt,
high-intensity onset chest pain that may be sharp,
oppressive or pulsatile.
This pain is often located in the chest,
but may also arise in the back (mostly in the inter-scapular region) or migrate to the abdomen.
The main risk factor is hypertension and the prognosis is reserved with a high risk of death.
Although they are not classically included in AAS,
aortic aneurysm (AA) rupture and aortitis may also present with a very similar clinical and prognosis,
and should therefore be included in the differential diagnosis of these patients.
The aorta is the largest artery in the human body,
divided into 4 segments: the ascending thoracic aorta,
the aortic crossa,
the descending thoracic aorta and the abdominal aorta (Fig. 1 and Fig. 2).
The ascending thoracic aorta extends from the aortic root to the emergence of the brachiocephalic arterial trunk (not including it); the crossa of the aorta extends from the emergence of the brachiocephalic arterial trunk to the insertion of the arterial ligament,
immediately distal to the emergence of the left subclavian artery; the descending thoracic aorta extends from the insertion of the arterial ligament to the aortic hiatus of the diaphragm; and the abdominal aorta extends from the aortic hiatus of the diaphragm to the bifurcation in the left and right common iliac arteries.
The aorta has 3 layers: the most internal,
or intima,
consisting of a single layer of endothelial cells; the media,
or muscular,
consisting of smooth muscle cells; and the external,
or adventitia,
constituted by connective tissue and containing the vasa vasorum.
These three layers are separated from each other by two thin layers of connective tissue: the inner and outer elastic laminas.
Currently,
the multidetector CT allows a high-quality CT angiography and has therefore become the method of choice for aortic evaluation.
The high speed of the scan,
the greater volume coverage and the possibility of making high quality reconstructions allow greater sensitivity and specificity for the study of acute and chronic aortic pathologies,
which are about 98% and 93%,
respectively.
When a AAS is suspected,
CT should include the entire aorta to assess the extent of the disease and the possible presence of ischemic disease in the territories of its branches.
Non-contrast images should be obtained initially,
to detect possible intra-mural hematoma or acute hemorrhage.
Subsequently,
the exam should be performed with intravenous contrast administration,
generally a bolus of 125-150 ml at a rate of 3 ml/second.
Optimal images will be obtained at 20-30 seconds for the thoracic aorta and 30-40 seconds for the abdominal aorta.