[Re: Brain Sag (was: Cerebro-spinal fluid in semen?)]

Tony Zador zador-anthony at CS.YALE.EDU
Tue Oct 20 20:54:00 EST 1992

>>I have had the unfortunate experiance of needing to have some of my spinal
>>fluid removed for testing. They use a somewhat large needle for this (not
>>painful though) and in many cases, including mine, the hole left by the 
>>puncture continues to leak for a while. This leakage is often great enough
>>that the brain does "sag" under its now unsupported weight (at least accordi

>This all sounds strange if plausible. I wonder if there are some
>clinicians on the net who would like to comment? Are the volumes of CSF
>removed not a very small proportion of the total? Are these symptoms
>common? Is there a magic threshold for producing such symptoms?
>Paul Knox

Last week I had the unfortunate experience of tapping a guy for 50
(yes, fifty) ml of csf; the usual amount is about 5 ml.  This is way
more than anyone on our service had ever heard of before (it wasnt my
idea, it was the attending's: we were "just following orders" as they

Before we did it, we checked how much csf there is. It turns out there
are about 250 ml. So in a normal lp, you take off about 2% of the
total; in our case, we took 20%!

Re mechanism of lp headache: according to Harrison's Textbook of
Internal Medicine, 

"Its cause is persistent leakage of csf into the lumbar tissues
through the needle site. The csf pressure is low...  It is probable
that in the upright position a low intraspinal and negative
intracranial pressure exerts traction on dural attachments and dural
sinuses by caudal displacement of the brain...As soon as the leakage
of csf stops and csf pressure is gradually restored (usually from a
few days up to a week or so), the headace disappears"

Tony Zador
zador at cs.yale.edu

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