FETAL ALCOHOL SYNDROME(FAS); HEARING LOSS; MEM-
ORY AND MEMORY IMPAIRMENT; SPEECH DISORDERS.
lumbar puncture A diagnostic procedure, collo-
quially called spinal tap, in which the doctor
inserts a needle between the lumbar vertebrae in
the lower back to withdraw CEREBROSPINAL FLUID
from the spinal canal for laboratory examination.
The point of entry into the spinal canal is below
the end of the SPINAL CORD, so there is no risk of
the needle entering the spinal cord.
Reasons for Doing This Test
Cerebrospinal fluid may contain BACTERIA, BLOOD,
or alterations of its composition that may suggest
or confirm numerous conditions affecting the
BRAINand spinal cord such as INFECTION, INFLAMMA-
TION, cancer, certain brain tumors, BRAIN HEMOR-
RHAGE, and MULTIPLE SCLEROSIS. Lumbar puncture
may also return negative results that rule out such
conditions. The doctor may use therapeutic lum-
bar puncture to administer medications, such as
baclofen as treatment for severe spasticity due to
cerebral palsy or other neurologic disorders, or
CHEMOTHERAPYdrugs for certain cancers affecting
the brain or spinal cord.
Preparation, Procedure, and RecoveryThere is no advance preparation for lumbar punc-
ture. Immediately before the procedure the doctor
cleanses the area where the needle will enter the
spinal canal. The person may lie on his or her side
with knees drawn to chest, or sit with the head on
a pillow that is resting on a table. These postures
bend the spine in such a way as to open the spaces
between the vertebrae. The doctor administers a
local anesthetic to numb the SKINat the insertion
site. The doctor measures the pressure of the cere-
brospinal fluid immediately upon the needle’s
entry, then allows small samples of fluid, usually
about three milliliters total, to drip through the
needle into collection containers. The laboratory
will run different tests on each sample.
Some people experience discomfort or tingling
sensations when the doctor inserts the needle into
the spinal canal; occasionally the needle contacts a
spinal NERVErootlet. When finished collecting fluid
samples, the doctor withdraws the needle and
puts a pressure bandage over the site. Some doc-
tors recommend lying flat in bed for three to four
hours after the lumbar puncture to reduce the risk
for postlumbar puncture HEADACHE, though lying
flat does not always prevent this common compli-
cation. The brain’s ventricles continuously replen-
ish cerebrospinal fluid, completely replacing the
full volume circulating in the brain and spinal
cord three to four times a day.
The entire procedure takes about 20 minutes.
Some results may be available from the laboratory
within a few hours, while other results may take
several days to several weeks, depending on what
tests the doctor requested.Risks and Complications
The primary risk of lumbar puncture is introducing
bacteria into the cerebrospinal fluid that causes
infection, which occurs rarely. Some people experi-
ence bleeding after the procedure. Headache is the
most common complication, affecting about one
fourth of people who have lumbar puncture. The
headache may be mild to severe and typically lasts
24 to 48 hours. Unfortunately PAIN-relief medica-
tions (ANALGESIC MEDICATIONS) do not usually help
the headache. Tiredness and backache are also
common for a day or two after the procedure.
See also BRAIN TUMOR; NEUROLOGIC EXAMINATION.lumbar puncture 259