
hydrocephalus: changes in formation and absorption
of cerebrospinal fluid within the
cerebral ventricles
formation, flow and absorption of
cerebrospinal fluid were measured in normal
and progressively hydrocephalic dogs by
steady-state studies during ventricular per-
fusion.  the formation of cerebrospinal fluid
was found to be constant, independent of
hydrostatic pressure, and unaffected by the
development of hydrocephalus.  the normal
dog produced 0.016 ml. cerebrospinal fluid
/min. in the lateral ventricles, 0.011 ml. cere-
brospinal fluid/min. in the 4th ventricle and
0.20 ml. cerebrospinal fluid/min. in the sub-
arachnoid space.  the intraventricular forma-
tion of fluid was calculated to be 0.24 ml.
cerebrospinal fluid/min./gm. of choroid
plexus, and 0.3x10-3 ml. cerebrospinal fluid
/min./cm.2 of ependymal surface.
absorption of cerebrospinal fluid was
found to take place within the ventricles as
well as in the subarachnoid spaces.  the re-
sistance to absorption of cerebrospinal fluid
in the normal ventricle was much higher than
in the hydrocephalic ventricle.  the decrease
in resistance occurred as the ventricular
volume increased and the ependyma became
flattened so that in chronic hydrocephalus
the resistance was not significantly different
than in the normal dog.  the theory of re-
stricted diffusion was applied to the data to
calculate the diffusive permeabilities of crea-
tinine and urea, and from this the mean pore
radius within the ventricle.
using formation of cerebrospinal fluid
and data on absorption, the hydrocephalic
animals could not be distinguished from the
normal with sufficient accuracy to suggest
using this as a clinical test.  the reason for
this is that intraventricular pressure has
always been considered as if it were constant
when, in fact, it is changing constantly.  the
problem of ventricular enlargement concerns
the ability of the craniospinal contents to
adjust to and absorb the small but very rapid
changes in intracranial contents that occur
with each beat of the pulse.
