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Neuroscience Research, Department of Laboratory Medicine and Pathobiology, Sunnybrook and Women's College Health Sciences Centre, University of Toronto, Toronto, Ontario, M4N 3M5
Arachnoid villi and granulations
are thought to represent the primary sites where cerebrospinal fluid
(CSF) is absorbed. However, these structures do not appear to exist in
the fetus but begin to develop around the time of birth and increase in
number with age. With the use of a constant pressure-perfusion system
in 2- to 6-day-old lambs, we observed that global CSF transport
(0.012 ± 0.003 ml · min
1 · cmH2O
1)
and CSF outflow resistance (96.5 ± 17.8 cmH2O · ml
1 · min) were very
similar to comparable measures in adult animals despite the relative
paucity of arachnoid villi at this stage of development. In the
neonate, the recovery patterns of a radioactive protein CSF tracer in
various lymph nodes and tissues indicated that CSF transport occurred
through multiple lymphatic pathways. An especially important route was
transport through the cribriform plate into extracranial lymphatics
located in the nasal submucosa. To investigate the importance of the
cribriform route in cranial CSF clearance, the cranial CSF compartment
was isolated surgically from its spinal counterpart. When the
cribriform plate was sealed extracranially under these conditions, CSF
transport was impaired significantly. These data demonstrate an
essential function for lymphatics in neonatal CSF transport and imply
that arachnoid projections may play a limited role earlier in development.
arachnoid villi; arachnoid granulations; intracranial pressure; cerebrospinal fluid outflow resistance; cerebrospinal fluid conductance; cribriform plate; hydrocephalus
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