ct then LP

[GiJoe]

ok forgive me if this is a stupid question...maybe im having a brain cramp.

whenever we do LP's on adults (for meningitis or SAH), we always get a ct first to r/o any abnormailties that may cause increased ICP. but what about fever/lethargy in the neonate/small infant where we are doing a septic wu? i never get a ct on them. Why not?

dont get me wrong, i dont wanna expose all these kiddos with tons of radiation, I just want an answer.

not too long ago I had a 6 month old kid come in looking lethargic, low grade temp, not takin po too well...somthing wasn't right and we wanted to do a septic wu. we ended up scanning his head for for some reason first and he ended up havin a brain tumor with with mass effect. if we didnt get the ct first and did the tapped, chances are, we'd be f'ed.

questions? comments?

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[EMCC]

To be perfectly honest, there are very few indications for a CT prior to an LP. We do it for CYA reasons more often than not. If a patient is alert, then a CT is not indicated--unless you are worried about ICH/SAH/SDH/EDH. In that case, a positive scan means you don't need an LP.

Put another way, the sensitivity for a CT scan is >90% for ICH within 12 hours of onset of cephalgia. Greater than 12 hours, however, and you should follow up with an LP if your suspicion is high.

In the pediatric population, things are slightly different. Children have more brain mass to skull volume than adults do (partly because of less alcohol consumption). If you are worried about meningitis, get the LP and don't wait for a CT scan. Sounds like something in the history or physical set alarms bells off in your attending's head. Nice pickkup on his/her part. Perhaps he looked at the anterior fontanelle (should not be bulging in meningitis). Perhaps the attending was somehow able to look at the fundi (good luck with that). Oh, and your kid was >2 months old, so yes, a CT is indicated prior to an LP (outside of the "normal" septic workup window)...

So, to sum up, if you are worried about ICH, get the LP--even with a negative CT (basically, if you do not LP patients, you will miss 1-2 ICH in 1000 patients with headache). This assumes, of course, that your suspiciion is high.

 

[Chronic Student]

Just a thought, but an LP is contraindicated in the presence of a mass lesion (i.e., you can precipitate a herniation). Could that be the reason for the CT prior to the LP?

 

[EMCC]

Not necessarily. For example, you can get mass effect from a meningioma, but an LP will not cause herniation. Usually, if you find a mass lesion on the CT, then a second source for the AMS is unlikely.

Basically, a mass is not a contraindication to an LP, but if it is a new lesion, perhaps that it the cause of the change in the patient...

 

[Flopotomist]

There are a few studies using ultrasound measurements of the optic sheath to assess ICP - it seems to be very fast, cheap, relatively simple to perform and accurate - is this actually be done anywhere INSTEAD of CT before adult LPs?

(Caveat - just a medical student here, so there may be some glaring error of logic in the above)

http://www.ncbi.nlm.nih.gov/pubmed/...ez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSum

 

[kungfufishing]

The concept of increased ICP vs. mass lesion is important. ICP is elevated in bacterial meningitis, but nothing is moving your brain around. The H&P determines if you think the patient has something shifting his brain over. Unless there is something in the story or a focal neuro deficit the CT is unnecessary.

Having said that, I think stuff like this requires us to rely on a gestalt sense that is only developed with experience. I suspect I am many unnecessary CT scans away from my gut comfortably adhering to what my brain tells it is true.

 

[BKN]

Basically, a mass is not a contraindication to an LP,

Well, not exactly IMneverHO. Try this one:
http://www.eboncall.org/CATS/1751.html

Having herniated somebody without AMS, fever and no focal nor eye ground findings in the pre-CT era, I'm pretty cautious. We got her out of it, but it was a near thing.

 

[kungfufishing]

Another thing that is scary is that there are reports of LP herniation in bacterial meningitis - I actually researched this very question a couple years ago.

 

[Homunculus]

luckily in infants they have a built in "pop-off" valve-- their open fontanel. classically we can see this with neonates in the NICU with IVH and full fontanels. if an infant's fontanel is soft chances are their ICP is ok. i don't think tapping your 6mo with the tumor would have caused herniation if the fontanel was normal. if it were bulging, i'd likely get a scan first. i was involved with the diagnosis of an 11mo with a brain tumor-- her presentation was potential seizure + full fontanel. thinking back, can you recall the "for some reason" that the CT was ordered on your 6mo old?

i have no data supporting any of this, just my training and experience. i've never scanned an infant prior to a tap ruling out sepsis. older kids with obvious mental weirdness i have scanned, but like kungfu pointed out, that gut vs brain discord rears its ugly head a lot.

good discussion

--your friendly neighborhood zantac munching caveman

 

[docB]

I think that the gurus of EM have been leaning away from the mandatory CT prior to LP mantra. Despite the case reports I have heard that the herniation from LP possibility is so low that it doesn't merit the delay in diagnosis, cultures and gram stain of an early LP.

That said I still do it. I don't disagree with any of the above but I find that #1 I can get the CT done in the time it takes me to get the patient into a suitable place (out of the chair in the hallway) and #2 that I seem to be looking for SAH way more than meningitis these days. When you're working up SAH instead of meningitis then the CT is always indicated before the LP.

 

[roja]

Another thing that is scary is that there are reports of LP herniation in bacterial meningitis - I actually researched this very question a couple years ago.

Do you have your references? I would to have them

 

[southerndoc]

Do you have your references? I would to have them

What's funny is that my institution published a study several years ago about criteria for when to order a head CT prior to LP. We still order them a lot -- a lot more than needed. On the pedi side, it's a rare thing to order a head CT prior to LP.

 

[TysonCook]

A couple of notes:

1) We've published (Tayal) on ICP and optic nerve sheath diameter in NON TRAUMATIC suspected elevated ICP (I'll find the reference tonight). It has been shown several times to be very accurate IN ADULTS (and very easy), a pediatric study I'm not too sure of.

2) We had a large M+M conference on LP w/ICP and risks of herniation. I'll track down the studies (something like 4-5 studies), but at the end it all summed up to very minimal to NO risk for herniation in relation to LP (one paper was very good at discussing amt of CSF vs space and relation of time vs herniation and basically no relation.

(this was after our ED had a AMS, did a scan which looked tight, was d/w the radiologist who said "its normal, not tight", did the LP with herniation ~10min later)

I'll definitely find the lecture and citations for what looks like to be a good discussion here

 

[roja]

A couple of notes:

1) We've published (Tayal) on ICP and optic nerve sheath diameter in NON TRAUMATIC suspected elevated ICP (I'll find the reference tonight). It has been shown several times to be very accurate IN ADULTS (and very easy), a pediatric study I'm not too sure of.

2) We had a large M+M conference on LP w/ICP and risks of herniation. I'll track down the studies (something like 4-5 studies), but at the end it all summed up to very minimal to NO risk for herniation in relation to LP (one paper was very good at discussing amt of CSF vs space and relation of time vs herniation and basically no relation.

(this was after our ED had a AMS, did a scan which looked tight, was d/w the radiologist who said "its normal, not tight", did the LP with herniation ~10min later)

I'll definitely find the lecture and citations for what looks like to be a good discussion here

That would be great. If I remember (and its been about 2-3 years) the data is really poor. It boils down to a few case studies. And the experience of those in practice long enough to have actually seen a herniation case. It makes one wonder if these are patients who would have herniated regardless. There was just the bad timing of doing the LP before the herniation happened.

 

[Rendar5]

That would be great. If I remember (and its been about 2-3 years) the data is really poor. It boils down to a few case studies. And the experience of those in practice long enough to have actually seen a herniation case. It makes one wonder if these are patients who would have herniated regardless. There was just the bad timing of doing the LP before the herniation happened.

Wouldn't be the first time bad timing and theoretical mechanisms lead to false cause-effect associations.

 

[roja]

http://en.wikipedia.org/wiki/Image:FSM_Pirates.png

 

[kungfufishing]

I PM'd roja about this, but to follow up my comment earlier, pretty much all I have come across regarding hernaition post LP were case reports, and I had the ssame question of whether they were headed for herniation anyway. The other side of the coin shows some with mass lesions who arent effected by the tap. Seems like most of the time you arent going to harm them with the LP, and the other subset of patients are sort of like predicting the weather. You can find case reports of bad outcomes from lots of procedures.

 

[Rendar5]

http://en.wikipedia.org/wiki/Image:FSM_Pirates.png

Brilliant!

 

[roja]

I PM'd roja about this, but to follow up my comment earlier, pretty much all I have come across regarding hernaition post LP were case reports, and I had the ssame question of whether they were headed for herniation anyway. The other side of the coin shows some with mass lesions who arent effected by the tap. Seems like most of the time you arent going to harm them with the LP, and the other subset of patients are sort of like predicting the weather. You can find case reports of bad outcomes from lots of procedures.

And here I was hoping for some fancy academic articles.

 

[kungfufishing]

depends on what you consider "fancy" and "academic"

 

[DrQuinn]

To make it a bit scarier, we had this case in the ED (this is basically how you hear about bad cases):

"Dr. X had this guy, came in with BS backpain, as they were going to DC him, he developed a headache and a fever of 101, kinda acted a little squirrely. She told Dr. Intern to do an LP, and when Dr. Intern did the LP the patient herniated!"

No CT was done, and he sure did herniate. Ended up having a brain abscess.

Yikes!

Q

 

[EMCC]

To make it a bit scarier, we had this case in the ED (this is basically how you hear about bad cases):

"Dr. X had this guy, came in with BS backpain, as they were going to DC him, he developed a headache and a fever of 101, kinda acted a little squirrely. She told Dr. Intern to do an LP, and when Dr. Intern did the LP the patient herniated!"

No CT was done, and he sure did herniate. Ended up having a brain abscess.

Yikes!

Q

When did that happen (what year)? Just curious, because when I order a CT and LP tray, it seems the CT is done and read long before I am ready to do the LP...

Also, I am really curious to see the stats on how often a patient herniates due to an LP. I would imagine it is something like 1 in 100000000000000 (how many zeros is that, I lost count)...

 

[nymbarra]

1. Just wondering how the probability of herniation in LP when there are no signs of ICP plays into the concept of "standard of care." How have juries/the public viewed these unfortunate cases in the past? Any notable successes in helping the public to better understand that for each test or procedure (in this case LP) there are benefits as well as risks?

Googled this briefly and found this recent--for lack of a better term--case study:

http://www.philly.com/philly/hp/news_update/20080112_Penn_sued_in_students_death.html?text=xlg&c=y

http://cbs3.com/topstories/Anne.Ryan.Lawsuit.2.627754.html


2. The study (Noble et al) that Flopotomist cited shows that compared to intracranial pressure monitors: "ONSD > 5 mm performed well to detect ICP > 20 cm H(2)O with a sensitivity of 88% (95% CI = 47% to 99%) and specificity of 93% (95% CI = 78% to 99%)."

The Blaivas/Carolinas study shows U/S had sensitivity of "100% (95% confidence interval [CI] 68% to 100%) and specificity was 63% (95% CI 50% to 76%)", but it compares U/S to CT, so the gold std in this case is not the same as in the Noble study.

Overall, it seems like U/S is excellent (well if don't look at the CIs!) but not sure how that compares to CT or fundoscopic when there is a common gold standard like invasive pressure monitoring...

Excellent discussion, hope this keeps going...

 

[DrQuinn]

When did that happen (what year)? Just curious, because when I order a CT and LP tray, it seems the CT is done and read long before I am ready to do the LP...

Also, I am really curious to see the stats on how often a patient herniates due to an LP. I would imagine it is something like 1 in 100000000000000 (how many zeros is that, I lost count)...

This happened last month.

Q