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Dangers of lumbar spinal needle placement.

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LETTERS
Dangers of Lumbar Spinal
Needle Placement
Dewey A. Nelson, MD, FACP
Spinal punctures are usually performed at the L4-L5 or L5-
s1 interspace. The current trend toward performing “high”
spinal punctures probably entered neurology through teachings received by neurology residents on rotations through
neuroradiology. The L2-L3 interspace is often used during
myelography and is advocated in recent neuroradiology textbooks El, 21. In the text edited by Ramsey 121, the L2-L3
interspace is recommended, with the caveat that “fluoroscopic control” should always be used.
This departure from usual standards of spinal punctures
raises concerns, particularly in light of two recent case histories and radiographs which I reviewed from outside this
geographical area. Both of these young adults developed
conus medullaris syndromes during myelography. Needle
placement in both instances was at L2-L3. In addition, the
cephalic angulation of the spinal needles placed the needle
tips another half interspace higher or more. During followup, magnetic resonance imaging (MRI) in one patient revealed an enlarged conus medullaris, and a lesion was
identified and described as either a benign tumor or a cavitary lesion. On MRI it is difficult to identify the tapered
termination of the conus medullaris which is concealed by
spinal fluid that emits a high signal. During an attempt to
visualize the tip of the spinal cord by computed tomography
(CT), the conus appears higher than it really is owing to
volume averaging.
Work by Reimann and Anson 131 in 1944 and a careful
review by Dripps and Vandam (41 in 1951 remain cogent. It
was found, in dissections of more than 800 specimens, that
the usually accepted termination of the spinal cord (at L-1 to
upper half of L-2) is the apogee of a bell-shaped curve of
normal biological variants. The spinal cord terminates below
mid-L2 in 3 1% of normal individuals and may lie as low as L3 in 2%% 131. Similarly,Taveras and Morello [5] stated that
the termination of the conus medullaris may normally lie 4
cm higher or lower than at LI-L2.
Many physicians are now using the “European” or “Bellevue” spinal tap in which the patient is seated with elbows
upon thighs, with the spine acutely flexed. This draws the tip
of the conus cephalad and broadens the canal. This maneuver
creates high hydrostatic pressure (300-700 mm HzO) such
that the various ligaments and meninges are easily identified.
When resistance is lost, one can assume that the epidural
space has been entered. The “blade” of the bevel should be
turned parallel to the long axis of the spine to avoid cutting
the meninges. Then, by using the technique of “push and
test,” the needle is advanced no more than 2 mm at a time,
after which the stylet is withdrawn: the physician must wait
10 seconds between “tests” because the bevel of the needle
presents a minuscule pathway to the spinal fluid when the
arachnoid membrane is first perforated. With experience, it
is possible to place the needle’s bevel just inside the arachnoid. One must avoid crossing the entire canal for reasons of
patient safety. Often overlooked is the routine of replacing
the stylet, then giving the needle a half turn before finally
removing it. This ensures that no strand of arachnoid will be
threaded back through the dura to produce prolonged spinal
fluid leakage. The spinal needle is rarely displaced when the
patient is carefully tilted into the lateral decubitus position.
Interestmgly,when the L4-L5 interspaceis used, it gives one the
impression that the tent-shaped interspinous ligaments guide
the needle; by contrast, the space at L5-S1 seems to be loose
or unstable, allowing sideways drift of the spinal needle.
Section of Neurology
The Medical Center of Delaware
Wilmington, DE
References
1. Shapiro R. Myelography. Chicago: Year Book, 1984:60
2. Ramsey RG. Neuroradiology. Philadelphia: WB Saunders, 1987:
676
3. Reimann AF, Anson BJ. Vertebral level of termination of the
spinal cord with report of a case of sacral cord. Anat Rec 1944;
88:127-138
4. Dripps RD, Vandam LD. Hazards of lumbar puncture. JAMA
1951;147:1118-1121
5. Taveras JM, Morello F. Normal neuroradiology. Chicago: Year
Book, 1979:503
Cerebrospinal Fluid
Monoamine Metabolites
in Narcolepsy: Reanalysis
Kym F. Faull, PhD,* Christian Guilleminault, MD,”
Philip A. Berger, MD, and Jack D. Barchas, MDX
Reanalysis of an earlier publication (1) showed that the control group included 14 subjects who were recruited for a
different protocol than the rest of the control subjects. A
revised analysis of the “before probenecid” data, after elimi-
Concentration of Free Monoamine Metabolites (nglml)
in Human Lumbar Cerebrospinal Fluid
Before Probenecid Administration
Subject Groups
Metabolite
N”
Meanb
SE
Normal controlsb
DOPAC
HVA
MHPG
5-HIAA
DOPAC
HVA
MHPG
5-HIAA
23
26
26
26
0.45
37.9
8.7
22.7
0.40
37.4
9.7
30.1
0.08
3.4
0.7
2.2
0.03
2.3
0.7
2.3
Narcoleptics
5
6
6
6
“One-way analyses of variance of the before probenecid values for
each metabolite showed no significant differences ( p < 0.05) between subject groups or between the normal subjects and the combined groups of patients.
”Twenty-six male subjects (age: 20-59 years, mean 32.3; height:
143.5-190.5 cm, mean 169.3 cm; weight: 60.3-102.1 kg, mean
73.2 kg).
DOPAC = 3,4-dihydroxyphenylaceticacid; HVA = homovanillic
glycol; 5-HIAA
acid; MHPG = 3-methoxy-4-hydroxyphenylethylene
= 5-hydroxyindoleacetic acid.
310 Copyright 0 1989 by the American Neurological Association
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