3 signs to actually detect rupture (J Ultraso Med 2005;24:1077)
Other Imaging Studies:
Cross Table Lateral X-Ray (Actually not bad, we should probably be ordering it if no UTS available, obviously has no sensitivity (67%), but ok specificity)
CT (Do not need contrast to see AAA, but should use it to see rupture)
Aortography (Gold standard, we order it all the time, huh)
Anatomy:
Enters abdomen through the aortic hiatus at T12 (below Xiphoid process)
Just anterior to the spine
Bifurcates at L4 level (1-2 cm below the umbilicus)
3 cm is the upper limit of normal width, usually tapers to 1.5 cm at bifurcation
Easily visualized branches:
Insert Anatomy diagram from handout
Technique:
Use 2 to 3.5 MHz transducer, curved or linear
Patient should be supine
Get 1 Sag view from celiac axis to bifurcation, obtained in the midline just under Xiphoid
4 Transverse Views
· High at Celiac Axis
· Middle at Renal Vessels
· Low, just above bifurcation
· Bifurcation
Aorta/IVC are seen in transverse as sun (aorta) and moon (IVC) rising over hill (spine)
The IVC should collapse with deep breath
Better to use pulse/color power Doppler if there is any doubt
If bowel gas makes imaging impossible, consider placing pt in LLR and scan using the liver as the acoustic window in coronal
Aneurysms
>3 cm is abnormal, measured outer wall to outer wall (Best done in transverse, measuring in the AP plane)
90% of aneurysms are infrarenal
The larger the diameter, the greater the chance of rupture
Clinical picture of rupture in the presence of AAA on EMBU=confirmed rupture
Check FAST exam for intraperitoneal blood to improve accuracy
Pitfalls
· Assuming visualized hydronephrosis is the result of a stone. AAA can compress the ureters giving hydro as well as hematuria.
Measuring off direct AP angle when in Sagittal (Safer to measure in transverse)
Lateral View of the Aorta
All patients were scanned in the supine position. Images of the aorta from ciliac axis to the bifurcation were obtained from the following 2 approaches: (1) traditional midline transverse approach (saving a video clip of scanning down the aorta and still images of the proximal, mid, and distal aorta) and (2) lateral midaxillary longitudinal view from the RUQ tracking the aorta distally to the bifurcation. Study sonographers graded the adequacy of aortic visualization in the midline view as entire aorta visualized, limited but adequate visualization (> 2/3 of aorta meaning measurements of proximal, mid, and distal but not full visualization between), inadequate visualization (< 2/3 meaning only 1 or 2 of the 3 measurements could be obtained), or no view. The lateral RUQ view was graded as entire aorta visualized, limited visualization (> 2/3 of the aorta if a longitudinal segment of > 10 cm was measured), inadequate visualization (< 2/3 of the aorta visualized), or no view. Time to acquisition of images was recorded. Images were saved as Digital Imaging and Communications in Medicine format video clips to the ultrasound machine’s hard drive and later burned to DVD. Images were reviewed by a blinded ultrasound-trained emergency medicine physician. Abdominal CTs were reviewed and measured by research assistants to determine the length of the abdominal aorta and for the presence of AAA, defined as diameter greater than 3 cm.
http://pmid.us/24374356
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