Department of neuroradiology
University Tübingen Germany
Cardiac-related pulsations of the
cerebrospinal fluid (CSF) can be investigated
using ECG-gated FLASH magnetic resonance imaging
(MRI). However, because 256 exitationts are
required to obtain an image with a 256 x 256
matrix other components of the CSF flow are
lost. By measurements on animals and humans it
was established in the last century that CSF
pressure also changes with respiration.
However, the resulting changes in CSF flow have
not been studied by X-ray contrast
cinecisternography or cineventriculography nor
by cine-MRI. We have studied respiration-related
CSF dynamics by employing a new real-time MRI
technique. [...]
Discussion : As early as 1886,
Knollproved that pressure fluctuations in the
cisterna magna of the rabbit changed not only
with the heart beat, but also with respiration.
Expiration was accompanied by an increase in
CSF pressure, while a drop in pressure
occurred with inspiration. After Quinke
introduced spinal puncture into clinical
practice at the end of the 19th century, Becher
was able to confirm in humans the animal
experiments showing the dependence of
intracranial pressure fluctuations on heart beat
and respiration. Since the pressure fluctuations
were measured with an open water manometer, the
results were relatively coarse; however, they
were later confirmed by many other
researchers.
Through precise measurements with membrane
manometers, Ewig and Lullies showed a CSF
pressure drop in the lumbar dural sac throughout
inspiration, with a pressure increase during
expiration, in thoracic respiration. During
abdominal breathing an inspiratory increase and
an expiratory decrease were observed.
Using ECG-gated FLASH-2D measurements it was
possible to confirm that the cardiac-related
oscillating CSF motion in the cervical spinal
canal is superimposed on a bulk flow moving in
separate channels, directed mainly downwards in
the anterior subarachnoid space and upwards
laterally. In addition, through modification of
the FLASH-2D technique and with the help of RACE
(real time acquisition and evaluation) it can be
shown that the opposed components of CSF flow
are not only anatomically separate, but
alternate with time: caudad CSF flow in the
anterior cervical subarachnoid space dominates
during inspiration, whereas expiration is
accompanied by an increase in cephalad flow.
Caudad flow acceleration occurs; immediately on
beginning inspiration, but ceases with abdominal
compression.
In the aqueduct the cardiac-related CSF
pulsation is affected in a similar way by
respiration. The systolic pulsatile flow
component downwards from the third to the fourth
ventricle is increased during inspiration, but
after a delay of 2-3 cardiac cycles (Fig. 10),
whereas during the late phase of expiration
backflow from the fourth to the third is
accelerated. These observations can be
interpreted as follows.
During thoracic inspiration, the spinal
epidural veins are emptied, because of the
inspiratory partial vacuum in the thoracic
cavity; this leads to rapid caudad acceleration
of CSF flow in the spinal canal. The increased
inspiratory venous inflow to the heart does not
reach the brain until passing through the lungs.
This results in acceleration of the CSF
pulsation in the aqueduct 2-3 cardiac cycles
later. However, during predominantly abdominal
breathing or a Valsalva manoeuvre outflow from
the large veins caudal to the diaphragm is
obstructed. This results in a volume-pressure
increase in the epidural venous plexus of the
thoracolumbar spinal canal, which can thus be
discounted as a compliance system for
craniospinal CSF pulsation.
Not all components of the "third
circulation" in the spinal and intracranial
subarachnoid space can be assessed, even with
RACE. However, it shows that even minute changes
in CSF flow following complex, physiological
stimuli can be detected and explained.
In a patient examined late in the evening
RACE showed reproducible changes in spinal
CSF flow while yawning rapid flow in the
anterior cervical subarachnoid space at the
beginning of the yawn, ceasing after a
few seconds. Using the saturation technique in
this patient, who had asymmetrical internal
jugular veins with small on the right and large
on the left, blood flow in the vein was seen to
increase significantly for several seconds.
Yawning begins with a deep thoracic
inspiration, followed by an increase in
intra-abdominal pressure after closure of the
glottis, with simultaneous reflex opening of the
mouth. The result of the initial deep thoracic
inspiration is rapid caudad CSF flow in the
spinal canal due to emptying of the epidural
veins, ending after closure of the glottis and
the increase in pressure in the abdomen. The
inspiratory increase in blood volume blood
reaches the intracranial system two or three
heart beats later, after its passage through the
lungs. Compliance of the craniospinal CSF system
is stopped meanwhile, because of the rise in
abdominal pressure. Therefore, only the
expressible intracranial venous blood confers
compliance, resulting in laster blood flow in
the internal jugular vein. The slow course of
the yawning reflex could be
teleologically interpreted as ensuring the
necessary delay between the emptying of the
spinal veins and the arrival of the increased
inspiratory blood volume in the cranial cavity
two to three heart beats later. Its
accompaniment by pleasurable sensations can be
seen as an additional indication to the body
that it must not cut short this physiologically
necessary interval.
Abstract : Cardiac-related motion of
the cerebrospinal fluid (CSF) was investigated
by analysis of the velocity-dependent phase of
CSF protons and flow-dependent signal
enhancement in magnitude images using ECG-gated
FLASH sequences. In the cerebral aqueduct, CSF
flow from the third to the fourth ventricle
begins 200 ms after the R-wave of the ECG and
simulates an arterial pulse wave pattern. It
lasts about 60% of the cardiac cycle and is
followed by backflow from the fourth to the
third ventricle, which is slower and shorter. In
the spinal canal, oscillating caudad motion
precedes flow from the third to the fourth
ventricle by about 50-100 ms and is superimposed
on a bulk flow, which moves simultaneously in
opposite directions in separate subarachnoid
channels; it is directed mainly caudally in the
anterior cervical subarachnoid space.
Schroth, G. and U. Klose (1992).
"Cerebrospinal fluid flow; Physiology of
cardiac-related pulsation." Neuroradiology
35(1): 1-9. Abstract :
Cerebrospinal fluid (CSF) flow in the
cerebral aqueduct and spinal canal was analysed
using real-time magnetic resonance imaging
measurement techniques. Respiration-induced
rhythmic modulation of the cardiac-related
oscillating CSF pulsation in the cerebral
aqueduct and spinal canal was found. Deep
inspiration was immediately followed by a marked
increase in downward CSF flow in the cervical
spinal canal, whereas a delay of about two heart
beats was seen before downward flow from the
third to the fourth ventricle increased. This
pattern was also detected during yawning and was
followed by a marked increase of blood flow in
the internal jugular vein.
Formation and circulation of cerebrospinal
fluid (CSF) have been studied in the isolated
brain ventricles of anesthetized cats by a new
approach and under direct observation. A plastic
cannula was introduced into the aqueduct of
Sylvius through the vermis cerebelli and the
outflow of CSFfrom the cannula was used asthe
CSF formation and circulation index. During the
60 min of observation at a physiological CSF
pressure not a single drop of CSF escaped out of
the end of the cannula. This indicatesthatCSF
netformation and circulation insidethe brain
ventricles, proposed by classical hypothesis
regarding CSF dynamics, should be at least
re-evaluated.
In conclusion, in spite of the fact
that in our model animals were under anaesthesia
and that the fourth ventricle was excluded from
the investigation, the classical hypothesis of
the CSF formation and circulation cannot be
upheld, because our results clearly show that
the net CSF formation does not take place inside
the other brain ventricles and that CSF does not
circulate as a slow river from the ventricles to
the subarachnoid space. It is very well known
(and commonly applied in routine clinical
practice) that the increase of blood osmolality
can decrease the CSF (intracranial) pressure,
simply by extraction of fluid from nervous
tissue. Our experimental results clearly
revealed that the increase in CSF osmolality
will subsequently lead to the increase of the
CSF volume inside the brain ventricles. This
drives to a conclusion that the osmolality
represents one of the major determinants of
fluid exchange in intracranial pressure. It
seems that the control of the CSF volume is
under the influence of hydrostatic and osmotic
forces between the CSF systern and the
surrounding tissue and that the CSF volume will
be changed, depending on the prevalence of those
forces, caused by (patho)physiological reasons
inside or outside the CSF system. Anyhow, the
results presented in this article call for a new
approach to the physiology and pathology of CSF
and we feel that time has come to re-evaluate
the classical hypothesis of the CSF
hydrodynamies to abandon this hypothesis as the
traditional framework of thinking.
Bergsneider, M. Evolving concepts of
cerebrospinal fluid physiology. Neurosurg
Clin N Am (2001) 12(4): 631-8.
This article reviews the basic known
functions of cerebrospinal fluid (CSF). The
traditional concepts of CSF production and
absorption are reviewed and recent challenges to
these concepts are discussed. MR imaging studies
have begun to elucidate the complex interaction
between pulsatile CSF movement, bulk CSF flow,
and intracranial compliance. An understanding of
a variety of disorders, including hydrocephalus
and Chiari malformations, continue to evolve as
knowledge of CSF physiology is increased.
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