25.5 CSF Production Flashcards
a) Outline the production and circulation of cerebrospinal fluid (CSF) and how intracranial pressure
affects production and absorption. (5 marks)
> > Choroid plexuses (tufts of capillaries)
secrete sodium into the
lateral and 4th ventricles
creating osmotic pressure that draws water
with it thus creating CSF.
> > Production rate of 500 ml/day,
but constant reabsorption means volume
present is only approximately 150 ml.
> > Circulation of CSF occurs throughout
the ventricles and down the spinal canal.
It enters the subarachnoid space via the
foramina of Luschka and Magendie.
> > Absorption is via arachnoid granulations, outpouchings of the arachnoid
through the dura that exist in close proximity
to venous sinuses.
CSF pressure is higher than venous pressure, favouring reabsorption of the
CSF into the venous system.
> > Small increases in ICP can be ‘buffered’ by movement of CSF out of the
ventricles and down to the spinal cord.
> > Production is opposed if intracranial pressure rises, causing CSF hydrostatic pressure to oppose the osmotic pressure generated by sodium secretion.
> > Reabsorption is dependent on pressure gradient from CSF to venous system so the r
ate of reabsorption is increased if
intracranial pressure rises.
b) How does the biochemistry of CSF differ from plasma? (4 marks)
> > Osmolarity of CSF and serum is equal.
> > CSF sodium levels are higher than plasma
due to active secretion.
Chloride is also higher as it
accompanies sodium to maintain
electrical neutrality.
> > All other ions found in plasma
are also found in the CSF
but at a lower level.
> > CSF glucose is approximately two-thirds
of the level of plasma or more.
> > CSF protein content is very low
in disease-free state.
c) List the indications for lumbar puncture. (6 marks)
Diagnosis
> > Central nervous system (CNS) infections
such as meningitis or
encephalitis due to viral,
bacterial, fungal or mycobacterial causes.
> > Subarachnoid haemorrhage.
> > CNS diseases such as Guillain–Barré,
multiple sclerosis.
> > Carcinomatous meningitis.
> > Intrathecal administration of contrast
media for myelography or cisternography.
Therapy
» Intrathecal administration of
chemotherapy or antibiotics.
> > Therapeutic relief of idiopathic intracranial hypertension or for spinal drain insertion.
Anaesthesia
» Spinal anaesthesia.
d) Which factors predispose to the development of a post-dural puncture headache after lumbar
puncture? (5 marks)
> > Multiple punctures.
> > Larger-gauge needle.
> > Use of traumatic,
cutting needle rather than pencil-point.
> > Age:
increased incidence in young adults (20–40 years), lower incidence in older adults, lower perceived rate in children but probably due to failure to report.
> > Gender: more common in women.
> > Increased incidence in pregnancy.
> > Lower body mass index.
