The normal proxima aorta, showing celiac trunk and SMA

Why scan the aorta?

Usually US is used to scan the aorta to identify or exclude an infrarenal AAA.  Is some cases is can be helpful in identifying the presence of a suprarenal AAA or a distal dissection. 

What is an AAA and why do we care?
AAA is diagnosed when the abdominal aorta is greater than 3cm in diameter or if any segment is greater than 1.5 times the diameter of an adjacent section.  A ruptured AAA is the 13^th leading cause of death in the US. 

Types of AAA:

Fusiform – most common, usually projects anteriorly and to left, thrombus is usually on anterior wall.

Saccular – less common, attached to main vessel lumen by mouth, thrombus partially or completely fill the aneurysm.  This is type is why it is important to scan entire length of abdominal aorta.

Clinical Features –

A ruptured aneurysm can cause sudden death as well as severe chest, abdominal, or back pain.   Sudden death is usually due to intraperitoneal rupture, which leads to massive, and rapid blood loss making it very difficult to resuscitate patient.  Pain is the most comment presenting sign although another common presentation is syncope with no warning signs followed by severe abdominal or back pain.  Pain is often described as “ripping” or “tearing”.  Atypical presentation is flank, groin, isolated abdominal quadrant, or hip pain.  Other symptoms may include bladder pain, tenesmus, N/V.  Must be included in the differential for patients with syncope, abdominal pain, chest pain, shock and patients with history consistent with renal colic.

Risk Factors for AAA:

Elderly – rare before 50, most patients greater than 60

Male gender

H/O of other aneurysms or peripheral arterial disease

Family history

Marfan Syndrome and other connective tissue disorders

Atherosclerotic risk factors (age as above, smoking, HTN, hyperlipidemia, and DM)

Pathogenesis-

Risk factors combine to increase the expansile force on aortic wall or to impair patient’s ability to withstand these forces.  Laplace Law (wall tension = pressure x radius) states that as the aorta dilates the force on the wall increases leading to further dilatation.  The larger the dilatation the more quickly it will expand (average rate of 0.25 to 0.5 cm/year), therefore anyone with documented dilation must be followed closely.  90% of AAAs are infrarenal.

Normal short axis of aorta with color flow doppler

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