Before you waltz off to the ER because of that thunderclap headache induced by another segment on arachnoid hemorrhages, make sure you're over 40 and you came by ambulance, otherwise you'll have to fight to not get discharged. Mizuho and Stuart discuss the new Canadian guidelines.
Aaron M. - March 5, 2014 4:25 PM
Great episode this month, EM:RAP crew. I'm hoping to get some clarification on a comment Dr. Spangler made in her discussion with Dr. Swadron. She mentioned that she frequently sees patients in the community being sent home without an LP if a CT angiography is negative. I agree that there may be patients in whom a subarachnoid hemorrhage could be missed by both a non-contrast CT scan as well as a CT angio of the head, but these cases must be exceedingly rare. CT angiography is reported to be 97% sensitive for cerebral aneurysm, and CT head without contrast is at least that sensitive for acute hemorrhage, especially in patients presenting within six hours, and when the study is read by an experienced radiologist. CT angiography is less likely to miss larger aneurysms (>5mm), and these are the ones more likely to bleed. The bleed rate is less than 1% per year for aneurysms smaller than this.
If a patient refuses an LP after a process of informed refusal, I think we're obligated to offer them the next best alternative, which is, most of time, a CT angio. If a patient has a negative head CT and a negative CT angio, I think most of the time they can safely go home if they're unwilling to undergo an LP, given the high sensitivities of these two CTs. Is it possible that you could still miss a tiny subarachnoid bleed from a tiny aneurysm? Sure. But, I think the bigger risk of the CT angio approach to diagnosis is more likely to be overdiagnosis of non-bleeding aneurysms than underdiagnosis of bleeding ones.
I agree that LP is the most sensitive approach, but CT angio is not a terrible alternative to LP if the LP is either declined by the patient or cannot be safely performed for a variety of reasons.
Again, thank you so much for the service you provide to our specialty, and I hope you keep it going for years to come.
Aaron Matlock, MD
Madigan Army Medical Center
Tacoma, WA
aaron.g.matlock.mil@mail.mil
Mizuho M. - March 13, 2014 11:00 AM
Hi Dr.Matlock,
Thank you for your comments. Listen, I'm with you…I work in the community as well, and when its busy and slammed, the idea of obtaining a CT angio as an alternative if the patient refuses LP always sounds tempting! I think much of your concern comes down to your pretest probability. If it is low, then I suspect if your patient is really refusing an LP than it is worth gambling the potential miss rate. However if your pretest probability for SAH is high, well then I'm not sure I'm willing to miss that 1%.
However the bigger concern with using CTA in lieu of LP is all of the incidental aneurysms you are bound to pick up, that aren't leaking at all. Then what?
Dr.Swadron did an excellent segment on this a few yrs ago, and he interviewed one of our most seasoned neurosurgeons at USC. I encourage you to listen to this short segment (even just the clip on this very question from 5:50-8:00minutes) to get this neurosurgeons perspective.
https://www.emrap.org/episode/2010/december/saha
He points out that often these CTA's are SO sensitive in picking up small aneurysms that with imaging alone, we still aren't getting to the ultimate diagnosis of a bleeding aneurysm or not? And ultimately raises a good question: are we doing more harm to the patient with unnecessary workup chasing these incidental aneurysms with added radiation, expense and unnecessary workup etc? Whereas had the Gold STD LP been negative without a CTA we could have simply ruled out SAH & sent the patient home?
All in all, yes, I agree with you, its a decent alternative when the pt is refusing, but given the definitive diagnosis still requires LP, this train of thought of using CTA as an acceptable alternative for EVERY patient can potentially open up pandoras box of "incidentalomas" and start the slippery slope of unnecessary workup for us and the neurosurgeon that we ultimately will have to involve and hand the patient off to.
Its an interesting discussion and I'm certainly not criticizing my colleagues who do CTA when appropriate, but in the end, one needs to ask ourselves, what is best for the patient. :)
Thanks Aaron. ~Mizuho