What is a "Spinal"?

QUESTION: I recently spent several days in a hospital for stomach problems.
My roommate was very anxious about a procedure his doctor called a "spinal"
and which he knew would be most painful. On the morning of my discharge, a
group of doctors and technicians entered the room, pulled the curtains around
my roommate's bed and, I suppose, performed the spinal. I never did see what
happened and am most curious to know what a spinal is and why it is performed.
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ANSWER: I can appreciate your curiosity, particularly when you had to leave
before the end of the story. To start with the medical name is "lumbar
puncture" (LP) and refers to a diagnostic test which is performed to obtain a
fluid (it's called cerebrospinal fluid or CSF) which bathes the brain and the
spinal cord. The spinal cord, a bundle of nerves running from the brain
through the spinal column to all parts of the body, is the main "cable" of
nerves that carries the current that permits our magnificent brain to control
so many of our body's functions. The spinal column, constructed of
alternating layers of bone (vertebrae) and cartilage (disks), commonly called
the back bone, has a hole running through its entire length, to contain and
protect this cord. However, the cord becomes thinner and thinner as it sends
out branches to the body, and in the area of our low back (lumbar region), it
no longer occupies the full space. Instead the CSF (fluid) fills the space
between two membranes which cover the spinal cord. This permits the physician
to insert a long, but thin, needle between two vertebrae into the space and
collect CSF for analysis. The procedure is performed under local anesthetic
to reduce discomfort as much as possible, but the idea of a needle in one's
back is certainly intimidating. It is an important procedure, however, and
can help in determining brain hemorrhage, infections in the central nervous
system, as well as changes which can occur in some maladies of the spinal cord
itself. The "spinal" or LP may also be used to administer medications,
anesthetics, and radiopaque materials used in performing special x-rays of
this vital structure.