I was reading today (3/25/14) “Myths in Emergency Medicine: Part 2” in ACEP Now.

I wanted to ask you about myth number four: CT before LP. You state: “Consider the number-one treatment for idiopathic intracranial hypertension (pseudotumor cerebri). Not only is it safe to LP these patients without risk of herniation, it’s recommended.”

I would like to point out the error in this argument. The etiology of idiopathic intracranial HTN is different than getting a CT for other etiologies. In this condition, LP is safe because the pressures are equal since it is communicating hydrocephalus, thus pressure in ventricles and the subarachnoid space is equal to that of the lumbar cistern, thus LP is safe.

For other causes, I would argue LP before CT is not safe. In the study you cite, 52 of 56 patients had uneventful LP in spite of abnormal CT—well, what if one of the four was a family member? I don’t care for stats always because when that small percent is me, I would be demanding a CT before the LP. Also, what happened to those four patients? I did not find the study so was not able to see.

Thank you, and great article!

–Max Rollins, MD
Atlanta, Georgia

Dr. Klauer Responds

You bring up a very reasonable point worth careful consideration. If a provider feels more comfortable obtaining a CT prior to LP, they should probably order one.

However, it is important to note that increased ICP is not truly associated with herniation following LP; brain shift is the phenomena we should be concerned about.

In the Hasbun study you noted, the 56 patients had abnormal findings on CT and the four did not have bad outcomes associated with LP, but the clinician decided not to perform the LP due to noted mass effect (three severe and one mild).

In addition, the authors note that all four had one or more clinical characteristics predicting this finding.

In closing, despite this age-old teaching, there is little evidence supporting the presumption that CT must be performed routinely prior to LP.

Thank you for your letter.

–Kevin Klauer, DO, EJD, FACEP
Canton, Ohio