Page 366 - Color Atlas Of Pathophysiology (S Silbernagl Et Al, Thieme 2000)

Cerebrospinal Fluid, Blood–Brain Barrier
Cerebrospinal fluid (CSF) flow (→ A). CSF is great diagnostic significance in certain brain
formed mainly in the choroid plexus of the lat- diseases:
eral ventricles. It flows via the interventricular CSF is normally as clear as water and does
foramina (→ A1) into the third ventricle and not contain any erythrocytes and only very
from there into the fourth ventricle via the few leukocytes (< 4 per µL, largely lympho-
Systems aqueduct (→ A2). It then circulates via the fo- CSF), and after hemorrhage (e.g., a brain tu-
cytes). However, in infections (e.g., meningitis)
leukocytes may pass into the CSF (→ cloudy
ramina of Luschka and Magendi (→ A3) into
the subarachnoid space and the arachnoid villi
mor) erythrocytes may be found in CSF (⇒
of the sinuses of the dura mater (Pacchionian
Neuromuscular and Sensory (→ A4). indicate the presence of blood pigments or
bodies) and from there into the venous sinuses
reddish discoloration). A yellowish CSF may
bilirubin-binding plasma proteins.
CSF flow may be slowed or interrupted at
The protein concentration in CSF is in-
each of the named structures. This results in
CSF backward congestion (hydrocephalus)
creased if there is no CSF absorption in the
with raised pressure. Depending on the site of
arachnoid villi or in infection (especially for-
mation by immune competent cells).
the obstruction, one distinguishes a communi-
cating hydrocephalus, in which CSF flow be-
The glucose concentration in CSF is de-
non-communicating hydrocephalus, where the
tuberculosis, fungal infections of the brain as
well as defective glucose transport in rare
connections between the ventricles are ob-
10 tween the ventricles is uninterrupted, from a creased by tumors, acute bacterial infections,
structed.
cases.
Obstruction of the CSF channels, especially Blood–brain barrier (→ C). The endothelial
the aqueduct, can be the result of malforma- cells of the blood capillaries in the brain (ex-
tions, scars (as after an infection or bleeding), cept for the posterior pituitary, area postrema,
or tumors. The absorption of CSF in the arach- choroid plexus, and circumventricular organs)
noid villi is impaired if drainage in the sinuses under the influence of astrocytes form dense
is obstructed (e.g., in thrombosis) or the sys- tight junctions that prevent the passage of
temic venous pressure is raised (e.g., in heart substances dissolved in blood (electrolytes,
failure). Drainage can also be reduced after proteins) or of cells. In this way the extracellu-
subarachnoid hemorrhage or meningitis as lar milieu of the brain is separated from the
well as by a high protein concentration in CSF blood, thus preventing nerve cells being ex-
(tumors or infection), because the arachnoid posed to electrolyte changes, transmitters,
villi can be obstructed by proteins. Lastly, ab- hormones, growth factors, and immune reac-
sorption may be reduced for no obvious exter- tions. Under abnormal circumstances the tight
nal reasons. An increase of the CSF space junctions can be opened. This happens, for ex-
caused by primary cerebral atrophy is termed ample, in brain tumors that contain no func-
hydrocephalus e vacuo. tional astrocytes. The blood–brain barrier may
In congenital hydrocephalus the cranial also be breached in hyperosmolarity (brought
bones may be separated because their sutures about by infusion of hypertonic mannitol solu-
have not yet fused, resulting in an enlarged cra- tions) or in bacterial meningitis.
nium (“water on the brain”, the literal meaning The blood–brain barrier is not yet closed in
of the term hydrocephalus) (→ A5). Once the newborns. As a result, in hyperbilirubinemia of
bony sutures have fused, an excess of CSF the newborn bilirubin can reach the brain and
causes an increased CSF pressure (→ p. 358). damage nuclei (“Kerne”) in the brain stem
Composition of CSF (→ B). The normal com- (hence kernicterus). Damage to the basal
position of CSF is approximately the same as ganglia may, for example, cause hyperkinesias
that of serum. However, it has lower protein (→ p.134).
and protein-bound Ca 2+ concentrations. The
+
356 K concentration is also lower (about 1 mmol/
l). Changes in the composition of CSF are of
Silbernagl/Lang, Color Atlas of Pathophysiology © 2000 Thieme
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