Clinical Biochemistry of Domestic Animals (Sixth Edition) - UMK ...

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Chapter | 26 Cerebrospinal Fluid
people with brain injury, but its utility in veterinary medicine
is unproven ( Shimada et al., 2005 ). The usefulness of these
substances in veterinary medicine has yet to be established.
G . Concentration Gradient along the
Neuraxis
In cats (Hochwald et al., 1969 ), dogs (Bailey and Higgins,
1985 ; Vaughn et al., 1988b ), horses (Andrews et al., 1 990a ;
Vaughn and Smyth, 1989 ), rhesus macaques ( Smith and
Lackner, 1993 ), and people ( Davson and Segal, 1996 ;
Fishman, 1992 ), the total protein concentration increases
along the neuraxis from rostral to caudal. For example, in
people the total protein concentration of ventricular, cerebellomedullary
cistern, and lumbar subarachnoid fluid is about 26,
32, and 42 mg/dl, respectively ( Weisner and Bernhardt, 1978 ).
Total protein, albumin, and globulin content of cerebellomedullary
cistern and lumbar subarachnoid CSF for dogs,
cats, and horses is given in Tables 26.5, 26.6, and 26.7 , respectively.
The concentration of the albumin and globulin fractions
also increases from ventricular to lumbar fluid. The increased
protein content may be the result of a greater permeability of
the spinal blood-CSF barrier than of the ventricular barrier to
albumin ( Fishman, 1992 ), additions of protein from adjacent
nervous tissue (e.g., IgG from lymphocytes located in or near
the CSF pathway ( Weisner and Bernhardt, 1978 ), progressive
equilibration of CSF with plasma through the capillary walls
( Weisner and Bernhardt, 1978 ), and low flow rates of lumbar
CSF ( Davson and Segal, 1996 ).
A study of healthy dogs also identified a small but significant
gradient for the CSF WBCs; lumbar fluid contained
significantly fewer cells than cerebellomedullary fluid
( Bailey and Higgins, 1985 ). Another study did not find a
difference in WBC counts between fluids from the two sites
(Vaughn et al., 1988b ). However, 4 of the 10 dogs in this
study had CSF total WBC counts 3/ μ l, and none of the
dogs was necropsied to verify its health. Therefore, some of
these dogs may have had subclinical neurological disease,
disguising a small cellular gradient. The small number of
WBCs in normal fluid may make a cellular gradient more
of a theoretical issue than a practical issue, however. If a
cellular gradient exists, it may be due to fewer cells entering
the lumbar CSF than the cerebellomedullary CSF, a greater
rate of cell lysis in the lumbar CSF, a greater migration rate
of WBCs from lumbar CSF back into the blood, or loss of
WBCs that entered the CSF rostrally and lysed as CSF circulated
to the caudal subarachnoid space.
A gradient has also been reported for CSF neurotransmitter
metabolites in the dog ( Vaughn et al., 1988b ) and the
horse ( Vaughn and Smyth, 1989 ). In each species, the neurotransmitter
metabolite content of cerebellomedullary CSF
was greater than that of lumbar subarachnoid CSF. This gradient
probably reflects the major source of the neurotransmitter
(brain) and transport of the metabolite from the CSF
into the blood along the spinal axis ( Vaughn et al., 1988a ).
VI . CSF COLLECTION AND ANALYTICAL
TECHNIQUES
A . Collection
1 . General Techniques
Specific details about the collection of CSF from the various
species are covered in many excellent articles and textbooks
( Boogerd and Peters, 1986 ; Brewer, 1983 , 1987, de
Lahunta, 1983 ; Fowler, 1989 ; Holbrook and White, 1992 ;
Kornegay, 1981 ; Mayhew, 1989 ) and will not be covered
here except for the authors ’ preferred technique for collection
from the cerebellomedullary cistern of dogs and cats
(discussed later). Considerations that apply regardless of species
are sterility, use of a specialized spinal needle, and collection
from animals with increased intracranial pressure. To
prevent iatrogenic central nervous system infection, sterility
during the collection procedure is essential. A generous area
around the puncture site should be clipped and surgically prepared.
Preparation of too small an area can lead to contamination
if any difficulty in palpating landmarks or entering the
subarachnoid site is encountered. Additionally, the use of a
fenestrated drape is highly recommended. Spinal puncture is
contraindicated in an area of severe pyoderma/furunculosis
or cellulitis. A needle with a stylet (spinal needle) should be
used to prevent implantation of a plug of epidermis in the subarachnoid
space that not only could lead to infection but also
could seed an epidermoid tumor. Replacement of the stylet
upon withdrawal is controversial, either preventing or causing
entrapment and severance or dislocation of nerve root filaments
( Fishman, 1992 ). Collection of CSF from animals with
increased intracranial pressure may result in brain herniation.
Appropriate anesthetic agents, hyperventilation, and mannitol
(to treat intracranial hypertension) may decrease the probability
of herniation. Use of the smallest gauge needle possible
may also help prevent herniation by decreasing CSF leakage
through the puncture hole in the meninges. Only the minimal
amount of CSF necessary to perform the desired tests should
be withdrawn. Brain herniation can occur following lumbar
taps as well as cerebellomedullary cistern taps.
2 . Collection Site
Cerebellomedullary puncture should be done under general
anesthesia. In most instances, lumbar puncture can be done
with sedation and local anesthesia. Therefore, if general anesthesia
is contraindicated, a lumbar puncture should be done.
The choice of collection site is influenced by the species
and breed of animal, the location of the neurological
lesion, and anesthetic considerations. The size of some animals
may make lumbar subarachnoid puncture difficult, if
not impossible. However, cerebellomedullary puncture usually
can be accomplished even in large or obese animals.
Because of differences in anatomy, the type or breed influences
the exact site for lumbar puncture in the dog; L4-5 is