Page 368 - Color Atlas Of Pathophysiology (S Silbernagl Et Al, Thieme 2000)

Cerebrospinal Fluid Pressure, Cerebral Edema
After the the cranial bone sutures have fused, Water can also accumulate in the interstitial
the brain is confined within a rigid casing. Its space when the blood–brain barrier is intact
volume cannot expand and any intracranial but the osmolarity of the interstitial space is
compartments can get larger only at the ex- higher than that of blood, for example, if there
pense of other compartments (→ A1). is a rapid fall in the concentration of blood sug-
Systems brain is open to the CSF space of the spinal ar (during treatment of diabetes mellitus), of
The cerebrospinal fluid (CSF) space of the
+
urea (dialysis), or of Na (interstitial cerebral
edema; → B3). In those conditions the in-
cord via the foramen magnum. The intravascu-
crease of interstitial space may be accompa-
lar space is momentarily increased with each
Neuromuscular and Sensory the pulse a small volume of CSF escapes sure (→ p. 356). An acute disorder of CSF drain-
nied by cell swelling.
systolic pulse wave, and synchronously with
CSF congestion also increases cerebral pres-
through the foramen magnum into the spinal
CSF space, i.e., the intravascular space is in-
age causes a rise in pressure that, via narrow-
ing of the vessel lumen, impairs cerebral per-
creased at the expense of the CSF space
(→ A2).
fusion (→ A4). Chronic drainage abnormality,
by bringing about the death of neurons, i.e., a
Similarly, an increase in interstitial or intra-
cellular volume at first occurs at the expense
decrease in intracellular space, will ultimately
and the CSF space has collapsed, CSF pressure
Tumors and bleeding (→ A3) take up intra-
cranial volume at the expense of other com-
quickly rises and there is a marked decrease
10 of the CSF space. Once this reserve is used up result in a decrease in cerebral mass (→ B5).
partments, especially the CSF space.
in cerebral perfusion (→ A3).
Several forms of cerebral edema are distin- Symptoms of increased CSF pressure. Due
guished (→ B): to the increased cerebral pressure, lymph
Cytotoxic edemas enlarge the intracellular from the back of the eye can no longer flow to-
space as a result of cell swelling (→ B1). ward the intracranial space via the lymphatic
Among causes are energy deficiency (e.g., due canal at the center of the optic nerve. Lymph
+
to hypoxia or ischemia). Impairment of Na / thus collects at the exit of the optic nerve and
+
+
K -ATPase raises the intracellular Na concen- causes bulging of the papilla (papilledema;
+
tration and decreases intracellular K concen- → C1). Other consequences of increased CSF
tration. Subsequent depolarization leads to pressure are headache, nausea, vomiting, dizzi-
–
Cl entry and cell swelling (→ p.10). ness, impaired consciousness (e.g., due to de-
Reduction of extracellular osmolarity can creased perfusion), bradycardia and arterial
also cause cell swelling, for example, in hypo- hypertension (through pressure on the brain
tonic hyperhydration (→ p.122). stem), squinting (compression of the abducens
Treatment of prolonged hypernatriemia de- nerve), and dilated pupils which are unrespon-
mands caution. The glial cells and neurons sive to light (compression of the oculomotor
compensate for the extracellular hyperosmo- nerve) (→ C2). The pressure gradients bear an
larity by intracellular accumulation of osmo- increasing risk of herniation of parts of the
lytes (e.g., inositol), a process that takes days. brain through the cerebellar tentorium
If the hypernatremia is corrected too quickly, (→ C3a) or the foramen magnum (→ C3b).
the osmolytes are not removed quickly enough The herniated parts compress the brain stem
and the cells swell. causing immediate death. If the increase in
Cerebral edemas of vascular origin occur CSF pressure is unilateral, the cingulate gyrus
when there is increased permeability of the may herniate under the falx cerebri (→ C3),
cerebral capillaries. The resulting capillary fil- causing compression of the anterior cerebral
tration of proteins with osmotically obliged vessels with corresponding deficits in cerebral
water (→ B2) thus increases the interstitial function (→ p. 360).
space. Among causes of increased permeability
358 are tumors, infections, abscesses, infarcts,
bleeding, or poisoning (lead).
Silbernagl/Lang, Color Atlas of Pathophysiology © 2000 Thieme
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