CT Imaging for Acute Aortic Syndrome

Cleveland Clinic Journal of Medicine 2008; 75(1):7-24

ABSTRACTAcute aortic syndrome can be due to

– acute aortic dissection– intramural hematoma– penetrating atherosclerotic ulcer– unstable thoracic aneurysm

These life-threatening conditions are clinically indistinguishable, often presenting with acute chest pain.

Contrast-enhanced, cardiac-gated MDCT is a highly accurate imaging method for determining the cause of acute aortic syndrome.

KEY POINTSAcute aortic syndrome typically presents

with chest pain in patients with a history of hypertension. In young patients with aortic dissection, one should consider Marfan syndrome and other connective tissue abnormalities.

Cardiac gating is essential to avoid cardiac motion artifacts when evaluating the aortic root with contrast enhanced multidetector CT.

Urgent surgical repair is often necessary, especially for acute aortic dissection and intramural hematoma in the ascending aorta and aortic arch, unstable or ruptured thoracic aneurysm, and symptomatic penetrating atherosclerotic ulcers.

Risk FactorsAcquired and congenital

disorders of the aortic wall• Bicuspid aortic valve• Coarctation• Connective tissue disorders• Ehlers-Danlos syndrome• Familial annuloaortic

ectasia• Familial aortic dissection• Marfan syndrome

Vascular inflammation• Behçet disease• Giant cell arteritis• Syphilitic aortitis• Takayasu arteritis

Multifactorial complex acquired conditions

• Atherosclerosis• Diabetes• Dyslipidemia• Hypertension• Renal disease

Iatrogenic factors• Endovascular instrument• Valvular or aortic surgery

Modifiable risk factors• Cocaine or other illicit

drug use• Smoking

Patient presents with acute chest pain and history of hypertension

Perform history and physical examination and appropriate cardiac workup, including ECG, laboratory tests, and CXR, to r/o acute coronary syndrome, pulmonary embolism, andother common causes of acute chest pain

Obtain intravenous access (18-gauge catheter in forearm or large-bore central line)

Order contrast-enhanced cardiac-gated MDCT of the chest; include abdomen and pelvis if visceral organ or thrombotic symptoms are present

Penetratingatheroscleroticulcer

Unstable thoracic aneurysm

Type A acute aortic dissection or intramural hematoma

Type B acute aortic dissection or intramural hematoma

Surgical consult Aggressive medicalmanagement*

*Surgical consult is recommended if imaging features of visceral vessel ischemia, acute vessel thrombosis, or progression of aneurysmal dilatation are seen or if Marfan syndrome is suspected or known

Imaging Studies for Acute Aortic SyndromeIMAGING STUDY ADVANTAGES DISADVANTAGES

Cardiac-gated MDCT

• Highly specific and sensitive• Can diagnose major causes of

acute aortic syndrome• Rapid scan and interpretation

time

• Large doses of ionizing radiation

CXR

• Very rapid result • Very helpful to exclude

nonaortic causes for acute aortic syndrome

• Low-to-moderate specificity for acute aortic syndrome

• Low sensitivity for aortic pathology

TEE

• Highly specific and sensitive for ascending aortic dissection and aneurysmal disease

• Requires skilled personnel to perform and interpret

• Often unavailable in the emergency department

Angiography

• Highly specific and sensitive for aortic dissection and aneurysmal disease

• Invasive• Requires contrast• Cannot diagnose intramural

hematoma

MRI

• Highly specific and sensitive• Can diagnose major causes of

acute aortic syndrome• Can be accurate without using

contrast

• Difficult to arrange in an emergency

• Prolonged scanning time and limited ability to manage unstable patients during scan

Left, contrast-enhanced, nongated CT study with 3-mm slices of the aortic root from a patient with acute aortic syndrome demonstrates cardiac motion artifact mimicking an acute aortic dissection (arrows, left panel).

Right, contrast-enhanced, cardiacgated CT with 0.75-mm slices of the aortic root reveals no dissection, although the aortic root is dilated.

Type A Dissection

Coronal reformatted image (left) and oblique reformatted image (right) from contrast-enhanced, cardiac-gated CT in a patient with acute aorticsyndrome show a type A aortic dissection involving the aortic root, extending around the aortic valve, and aneurysmal dilatation of the aortic root.

Type A Dissection

Oblique reformatted images from contrast-enhanced, cardiac-gated CTbefore (left) and after (right) surgical aortic root repair with aortic valve replacement in a patient who initially presented with acute aortic syndrome and had a type A acute aortic dissection with aneurysmal dilatation of the aortic root.

Type B Dissection

A coronal reformatted image (left) and an axial image (right) CT show a type B aortic dissection extending from the aortic arch into the abdomen. Hemorrhage from recent rupture is seen in the left and right hemithorax and in the mediastinum (arrow).

Aortic Intramural Hematoma

Coronal reformatted image (left) and axial image (middle) CT in a patient with an acute type A intramural hematoma and a penetrating ulcer. Note the eccentric increased attenuation in the lateral aspect of the aortic arch representing the hematoma (arrow, middle panel) and the contrast-filled outpouching laterally representing the penetrating ulcer.

Follow-up imaging several months later (right) shows that the intramural hematoma resolved although the penetrating ulcer persisted (arrow, right panel).

Aortic Intramural HematomaAcute intramural hematoma is easily

recognized in CT without contrast enhancement by the higher Hounsfield-unit value of the blood products in the wall in comparison with the flowing blood in the lumen, eccentric aortic wall-thickening and displacement of intimal calcifications.

Rupture of the AortaCT in a patient with acute aortic syndrome and hypotension demonstrates aneurysmal dilatation of the descending thoracic aorta with a contained aortic rupture anterolaterally (arrow). A layering left hemithorax is also visible (star).The patient underwent urgent endovascularstent repair.

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Unstable Thoracic AneurysmAn aortic aneurysm is defined as a

permanent dilation at least 150% of normal size, or larger than 5 cm if in the thoracic aorta or larger than 3 cm if in the abdominal aorta.

Dilations are more likely to rupture if they grow at least 1 cm per year or measure 6.0 cm or more (if in the ascending aorta) or 7.2 cm (if in the descending thoracic aorta).

Patients are typically treated when a dilation in the ascending aorta reaches 5.5 cm or when one in the descending aorta reaches 6.0 cm; patients with Marfan syndrome should undergo invasive treatment for aneurysms with smaller diameters.

Unstable Thoracic AneurysmCT signs of imminent rupture include a

high-attenuating crescent in the wall of the aorta, discontinuous calcification in a circumferentially calcified aorta, an aorta that conforms to the neighboring vertebral body (“draped” aorta), and an eccentric nipple shape to the aorta.

CT signs of rupture include hemothorax (usually in the left hemithorax) and stranding of the periaortic fat.

Penetrating Atherosclerotic Ulcer

CT in a patient with acute aortic syndrome demonstrate a focal contrast-filled outpouching of the distal thoracic aorta consistent with a penetrating atherosclerotic ulcer (arrows)

Penetrating Atherosclerotic UlcerSurgery to stabilize disease is

recommended for a penetrating ulcer that causes acute aortic syndrome, or in patients with hemodynamic instability, aortic rupture, distal embolization, or a rapidly enlarging aorta.