Acute aortic syndrome

Acute aortic syndrome describes the presentation of patients with one of a number of life-threatening aortic pathologies that give rise to similar clinical presentations.

Exactly which entities are included under the umbrella term acute aortic syndrome varies somewhat from publication to publication. Three conditions are generally included, sharing epidemiological and clinical presentation as well as having overlapping and sometimes co-existing imaging features ^1-5. 

1. aortic dissection
2. aortic intramural haematoma
3. penetrating atherosclerotic ulcer

Although some authors also include unstable aortic aneurysmal rupture (leak) and traumatic aortic injury (e.g. thoracic aortic injury and abdominal aortic injury) ¹, this article will limit itself to the aforementioned three core conditions.  

Epidemiology

Generally, patients are elderly, more frequently male and with a long history of hypertension ^2,5. Additionally, connective tissue disorders (e.g Marfan syndrome, Ehlers-Danlos syndrome), as well as bicuspid aortic valve and annuloaortic ectasia, are risk factors, particularly for aortic dissection ^2,5.  

Clinical presentation

Patients will presents similarly, with acute "aortic pain" characterised by severe chest pain that has a tearing and sometimes migratory character ². The location of the pain correlates with the location of pathology. Pain located anteriorly in the chest or in the neck and jaw typically denotes ascending aortic involvement. In contrast, pain in the back and abdomen suggests descending aortic pathology ². 

Radiographic features

Imaging of patients presenting with suspected acute aortic syndrome in most centres typically involves a CT of the chest as it is readily available, has been show to have very high sensitivity and specificity and able to image not only the aorta but also the remainder of the neck, chest and abdomen. MRI and transoesophageal echocardiography are also helpful in some situations, however, access is usually more restricted ⁶. 

CT

Although exact imaging parameters will depend on individual and institutional preferences, typically patients are imaged with bi-phasic or tri-phasic CT ^6,7.

1. non-contrast:
   • technical considerations: 
     • in low-risk patients or if dual-energy CT with virtual non-contrast imaging is available then the non-contrast phase may be omitted
   • to assess:
     • hyperdense intramural hematoma
     • displaced intimal calcification within the lumen of the aorta
2. arterial phase: 
   • technical considerations: 
     • preferably right arm injection to avoid streak artefact from undiluted contrast in the brachiocephalic vein
     • consider cardiac gating, but typically results in higher radiation 
   • to assess:
     • morphology of dissection/ulcer
     • side-branch patency
3. venous phase
   • to assess:
     • distal organ enhancement/perfusion

Imaging features of individual conditions are discussed separately:

1. aortic dissection
2. aortic intramural haematoma
3. penetrating atherosclerotic ulcer