Protocoling CT A/P imaging question

[thegenius]

Hello fellow physicians, I'm an EM trained doc and I have a question for my esteemed Radiologists.

The ultimate high level question is whether we in ER should be generally ordering
- CT Angiography Abdomen/Pelvis w/ IV contrast
vs
- CT Abdomen/Pelvis w/ IV contrast


Let me preface this by saying I was thinking about this the other day when I, perhaps luckily, picked up on a Type B dissection which would have theoretically been missed had I not protocoled the imaging in the arterial phase.

From my perspective, the true life-threatening abdominal / pelvic emergencies are mostly vascular:
(GROUP A)
- aortic dissection
- aortic aneurysm
- aortic rupture -> internal bleeding
- trauma imaging (e.g. bleeding from some artery)
- organ ischemia (e.g. necrotic bowel, ovarian torsion)
- perforated viscous

all of the above are vascular in origin except the last (Ruptured ectopic pregnancy is also vascular in origin but should never be picked up by CT!)

Other emergencies where the patient needs to be admitted but won't die within hours would be
(GROUP B)
- many of the "itis"....e.g. appendicitis, cholecystitis, pancreatitis, diverticulitis, colitis, hepatitis
- bowel obstruction
- renal colic / nephrolithiasis
- some cancers
- random other stuff



My understanding is angiography can pick up everything in GROUP A and most/everything of GROUP B, but venous phase CT will miss most in GROUP A but appropriate for GROUP B.

If my assumption above is correct, shouldn't we be protocoling CT A/P for the undifferentiated, critically ill abdominal pain with angiography?

Maybe another way to look at it is (I used to be a programmer):

if (our pretest probability is high of a diagnosis in GROUP A), then do angiography CT;
else if (our pretest probability is high of a diagnosis in GROUP B), then do conventional CT;
else if (we don't know what is going on and pt is critically ill), then do angiography CT;
else if (we don't know what is going on but the patient is stable and not sick), think it over some more and get it right;
else throw new Exception("go back to residency");

What do you think?

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[Dave1980]

I think you are somewhat misinformed. Almost everything you listed in group A will be picked up on a normal CT with contrast. A dissection will 100% be picked up on a normal CT as the normal CT has contrast in the aorta.

A CTA is usually not indicated although it should be ordered if you are looking for arterial bleeding in a hematoma or lacerated organ and some other specific indications.

 

[Aurum]

Agree with Dave1980 above. Furthermore, the likelihood of missing (or poorly characterizing) one of your "Group B" pathologies on a CTA abdomen is higher than the probability of missing a "Group A" pathology on routine portal venous CT.

 

[thegenius]

Oh thank you for clarifying...so it sounds I should almost never be doing CT Angiography A/P. All the dangerous vascular (arterial or venous) pathology can be seen on a regular CT A/P with good fidelity.

Thanks I appreciate it.

 

[Dave1980]

Oh thank you for clarifying...so it sounds I should almost never be doing CT Angiography A/P. All the dangerous vascular (arterial or venous) pathology can be seen on a regular CT A/P with good fidelity.

Thanks I appreciate it.

Correct! A good CTA is basically a non con CT with the arteries super bright. It is not good except for very specific questions

 

[Cognovi]

What a portal venous phase CT would miss or mischaracterize that a CTA would be good at are problems with medium sized arteries (celiac/mesenteric, renal, etc) - active bleeding, dissection, severe atherosclerotic stenoses.

My place has started compromising for trauma cases by doing a split bolus - one part in the arterial phase, one part in portal venous phase. The arterial phase does make the spleen psychedelic looking which can be confusing for infarct/laceration on occasion but everything else looks okay.

My place's CTA also includes a precontrast and a 2 min delayed phase. The precontrast is good for looking for aortic intramural hematoma, which can be subtle when contrast is on board. The delayed phase is good to distinguish arterially enhancing foci as extravasating or not because bleeding should spread out on the delay. The delayed phase is not exactly portal venous phase but provides at least some parenchymal contrast enhancement. Because of this, I wouldn't say that CTA 'is not good' for the soft tissue, but this protocol is like triple the radiation dose, which you don't want to be doing routinely.