roja said:
From extensive review of the literature the proverbial fear of herniation is one of those things of mythos. If you actually look at the literature, it is incredibly sketchy.
In general, most of the attendings here (when talking about meningitis, not SAH) if there is nl nuerologic/ms exam will do the LP without head CT.
For SAH, I scan first because if its there, I don't have to LP
Not true, ask any old time neurosurgeon. You just don't see it anymore because the CAT scans are readily available. Medical lit in the 70s and before was always sketchy, in fact it was badly written. Doesn't mean it didn't describe a real phenomenon
I've personally herniated a 21 y/o female with delerium, AMS, fever, a whited out lung and no focal neuro findings. Didn't have a scanner at Baltimore City in '78, would have taken 5 hours to send her to JHH. She had a symmetrical hydrocephalus. The pneumonia was an aspiration secondary to the CNS problem. We got her out of it with an emergency twist drill, but it's not a situation you want to be in.
I've also seen two small children herniate after tap (they had midbrain tumors). One didn't make it.
I think that the incidence of bacterial meningitis is going down, while the incidence of viral CNS infection and brain mass or abscess is the same or higher.
Probably USC diver's criteria are pretty safe, but why not get the study? Even if there is no risk of herniation, it often gives you a lot of information that you wouldn't get with just the tap (like a mass that hasn't raised the pressure much yet and won't affect the CSF findings.)
Here's how I do it:
1. Acute Meningitis Syndrome (fever and AMS). Give them antibiotics, get the CT, get the tap. If they have bacterial meninigitis its very unlikely their CNS results will be equivocal on the basis of some anitibiotics given shortly before.
NOte that this is a small group consisiting of 1/3 of allABM, Cerebral abscess and oSepsis elsewhere
2. Subacute meningitis syndrome (fever and HA, normal neuro) Send them for the CT, do the tap, antibiotics if necessary. Larger group consisitng of 2/3 of all ABM, most viral infections and simple non-cns infections.
3. Encephilitis syndrome (AMS, focal findings, +/- fever). CT or MRI, tap if safe and indicated. Consists of most encepahlitis, brain abscesses, SAH and many other CNS conditions
The CAT scanner is your friend.