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

IV. Cellular Composition of Normal CSF
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TABLE 26-4 Total White Blood Cell Count of Normal CSF in Domestic Animals
Species Collection Site a N b Cells/ul c Reference
Dog C 50 0–2 Jamison and Lumsden, 1988
Dog C, L 31 0–4 Bailey and Higgins, 1985
Cat C 33 0–2 Rand et al ., 1990 b
Horse Pooled C & L 44 0–6 Mayhew, 1977
Horse C 14 0–5 Furr and Bender, 1994
Cow L 16 0.85–3.52 d Welles et al. , 1992
Llama L 17 0–3 Welles et al. , 1994
Sheep L NS 0–5 Fankhauser, 1962
Goat NS NS 0–4 Brewer, 1983
Pig NS NS 0–7 Fankhauser, 1962
Ferret C 42 0–8 Platt et al., 2004
Holsten calf, 8 weeks old C 10 0–10 St. Jean et al. , 1995
a
C cerebellomedullary cistern. L lumbar subarachnoid space.
b
N number of animals.
c
Range.
d
95% confi dence interval.
NS not stated.
on the CSF hydrostatic pressure; as the pressure rises,
the absorption rate increases ( Davson and Segal, 1996 ).
If intracranial pressure falls below a critical point, bulk
absorption decreases, a homeostatic response to stabilize
the intracranial pressure and the CSF volume. The primary
site of bulk absorption, at least in people, is the arachnoid
villi that project into the dural sinuses. Two other routes
are through lymphatic channels in the dura and through the
perineural sheaths of cranial nerves (particularly the olfactory
nerves) and spinal nerves. Perineural absorption may
be through arachnoid villi projecting into perineural veins,
lymphatics, or connective tissue ( Davson and Segal, 1996 ;
Milhorat, 1987 ). The importance of these various absorption
routes varies with the species ( Bell, 1995 ).
Absorption through the arachnoid villi occurs transcellularly
through micropinocytotic vesicles and giant
intracellular vesicles, but it may also occur through endothelium-lined,
intercellular clefts. The mechanisms appear
to vary among species ( Bell, 1995 ). Absorption is unidirectional
from the CSF into the venous blood—the villi act
like one-way valves. The basis for the valve-like mechanism
appears to be transport by the giant vesicles (see
Section II.A.2). Particles ranging in size from colloidal
gold (0.2 μ m) to erythrocytes (7.5 μ m) can be transported
across the villi. In disease conditions, accumulations of
larger size particles (e.g., protein molecules, erythrocytes,
leukocytes) within the villi may impair absorption leading
to hydrocephalus ( Fishman, 1992 ; Milhorat, 1987 ).
The choroid plexus also has an absorptive function, acting
on specific substances in the CSF rather than by bulk fluid
absorption. A variety of compounds are actively transported
from the CSF, in a fashion reminiscent of the proximal
renal tubule. Solutes may also be cleared from the
CSF by diffusion into adjacent brain cells or capillaries
( Fishman, 1992 ; Milhorat, 1987 ).
IV . CELLULAR COMPOSITION OF
NORMAL CSF
A . Total Erythrocyte and Nucleated Cell
Count
Cerebrospinal fluid normally does not contain erythrocytes
( Chrisman, 1992 ; Cook and DeNicola, 1988 ; Rand et al.,
1990b ; Wilson and Stevens, 1977 ). Erythrocytes in a CSF
sample are most commonly iatrogenic, because of trauma
associated with the needle placement. However, CSF erythrocytes
may also originate from pathological hemorrhage.
The normal nucleated cell count of CSF in domestic animals
is in Table 26-4 . The most widely accepted reference
ranges for the numbers of leukocytes in the CSF of dogs
and cats is 0 to 5 cells/ μ L ( de Lahunta, 1983 ; Oliver and
Lorenz, 1993 ) to 0 to 8 cells/ μ L (Duncan, 1994). However,
these ranges are too broad in our experience and other studies
confirm this ( Jamison and Lumsden, 1988 ). Jamison
examined 50 clinically and histopathologically normal
dogs and derived cerebellomedullary CSF reference limits
of 0 to 2 cells/ μ L ( Jamison and Lumsden, 1988 ). In fact,