see also: [[Abdominal Aortic Aneurysm]] > - 95% of AAAs are infrarenal and terminate proximal to the bifurcation > - abdo/back/flank pain + hypotension, POCUS is 99% sensitive and 98% specific for rupture ## Indications - abdo pain - undifferentiated shock or hypotension - syncope - abdominal mass - flank or back pain in pts age > 50 ## anatomy - Aorta passes through the diaphragm at level of T12 vertebrae. - It lies slightly to left of midline traveling caudally for approximately 13cm until it bifurcates into the 2 common iliac arteries at level of the L4 vertebrae. - The renal arteries arise either side of the aorta within 2 cm of the origin of the SMA. these vessels are often difficult to identify. - 90% of AAAs are **distal** to the renal arteries. When the renal arteries cannot be identified in the setting of an AAA, **the distance from the origin of the SMA to the proximal part of the aneurysm can be measured.** - ==If the distance is >2cm, the aneurysm can confidently be diagnosed as being infrarenal.== ![[Pasted image 20241118182433.png]] ![[Pasted image 20241118182515.png]] ## Exam overview > **ACEM protocol**: > - minimum 3 transverse images and 1 longitudinal > - one measurement in transverse and one longitudinal measurement, ideally taken at the same level as the proximal as possible > - if aneurysm is present: > - take multiple images and clips to demonstrate its position and size > - measure aneurysm's largest diameter from **anterior to posterior**, outer wall to outer wall, both in transverse and longitudinal > - also measure its length in longitudinal > - note that A/P is more accurate than side-to-side due to *edge artefact* - save 4 images in transverse plane, but ideally image entire aorta 1. proximal aorta - at the level of porto-splenic confluence 2. mid aorta - at level between proximal and distal aorta 3. distal aorta - just proximal to the bifurcation 4. bifurcation of common iliac **1. start transverse epigastrium** - use as low a depth as possible; the abdominal aorta becomes more superficial as you scan caudally, so use the shallowest depth setting **2. identify coeliac trunk** ![[CFD46CA5-1B6B-40CC-A6B6-C40EB0882EDE.png]] **3. identify SMA** ![[Pasted image 20241118183333.png]] **4. attempt to identify renal arteries** ![[34A3E859-F512-45FD-A42D-7B9D6A6D4FFF.png]] **5. identify bifurcation to common illiac arteries** ## Pitfalls **Transverse vs longitudinal measurement** - transverse aorta measurement can over-estimate diameter if beam is oblique to the aorta and causes an oval - longitudinal measurements are prone to under-estimation if your beam foreshortens the aorta ![[Pasted image 20241118184521.png]] ## pathologies - AAA - aortic dissection - aortic graft - bilat iliac artery aneurysms