Abdominal Aorta Ultrasound Cheat Sheet Clinical Application

Abdominal Aorta Ultrasound Cheat Sheet


Clinical Application

Basics

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  90% mortality rate of rupture
  
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  Suspect AAA in any pt >60 yo with abdominal or back pain
  
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  Screen all > 60 yo males with hx of HTN or smoking at least once
  
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  Small AAAs (<4.5 cm) rupture less frequently than larger AAAs
  

Sensitivity & Specificity

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  High sensitivity for presence of AAA
  
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  Poor sensitivity for acute rupture
  
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  Rupture usually into retroperitoneal space & US isn’t great at detecting retroperitoneal bleeds
  

Anatomy

Normal Anatomy

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  Aorta bifurcates at umbilicus (T5)
  
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  1st branch: celiac trunk
  
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  Hepatic and splenic artery come off CT
  
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  2nd branch: super mesenteric artery
  
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  SMA is about 1 cm caudal to CT & runs parallel to aorta
  

Anatomy of AAA

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  Two types of AAA: fusiform and saccular
  
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  Fusiform: dilation of entire circumference
  
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  Saccular: asymmetric out pouching
  
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  Fusiform more common
  
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  Majority of AAA are infrarenal
  
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  Aneurisms can extend into iliacs
  

Technique

Basics

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  Curvilinear probe (best) or phased array
  
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  Start just caudal to xyphoid process
  
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  End caudal to bifurcation (umbilicus)
  
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  Transverse view: probe marker to pt’s rt
  
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  Longitudinal view: probe marker to pt's head
  
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  Adjust gain until vessel lumen is black (makes identifying an intra-luminal thrombus easier)
  
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  Always scan in both planes (trans & longitude)
  

Images

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  Identify vertebral body to get oriented
  
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  Vertebral body: horseshoe shaped with hyperechoic anterior & posterior shadowing
  
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  Aorta is anterior & slightly left of vertebral body
  
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  IVC is anterior & right of vertebral body
  
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  Identify the CT, SMA, and bifurcation
  

Measurements

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  Measure in transverse view
  
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  Measure from outer wall to outer wall
  
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  Normal aorta: < 3 cm
  

Pathology

Dissections

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  A dissection looks like a flap in the vessel area
  
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  Flaps are the intima floating out into the vessel
  
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  Watch out for these. They can be subtle!
  

Aneurisms

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  Aneurisms look like a widening of the aorta
  
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  Scan the whole length of the abdominal aorta, so you don’t miss one!
  
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  Saccular aneurisms are easier to miss than fusiform, so look for them
  

General

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  Measure from outer walls, otherwise a mural thrombus or plaque may cause you to underestimate diameter
  
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  Transverse views at a slight angle can exaggerate the diameter
  
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  Ectatic aortas are not straight and can take an irregular track through abdomen
  
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  Just because there isn't intraperitoneal fluid doesn't mean there isn't an acute rupture (aortas are retroperitoneal)
  
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  Aorta and IVC can be confused in longitudinal view: aorta is rounder, less compressible, & has brighter thicker walls
  
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  If clinical suspicion for AAA is high & ultrasound is equivocal, get a CT with contrast
  

Tips and Tricks

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  Bowel gas & body habitus can make imaging difficult
  

Bowel Gas

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  Apply steady pressure to move gas
  
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  Jiggle the probe to move bowel aside
  
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  Fan to view through windows in loops of bowel
  

Obesity

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  Have pt lie completely flat
  
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  Flex pt's hips & knees to relax ab muscles
  
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  Lower probe frequency to improve sound wave penetration
  

SonoMojo Ultrasound Cheat Sheets

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