Neurophysiology - CSF

Question 1

What are the functions of the CSF

Answer 1

1. Buoyancy and cushioning (1400g –> 50 g effective weight)
2. Maintenance constant ionic environment
3. Buffering changes in ICP
4. Control Respiration (no protein PCO2)
5. ‘Glymphatic’ (astrocytes) system –> waste removal

Question 2

Where is CSF produced

Answer 2

1, 2, 3 and 4th ventricles by the choroid plexus

Question 3

How is CSF produced and how much is produced per minute, hour, day

Answer 3

Combination of filtration and secretion

0.3 ml/minute
20 ml/hour
500 ml/day

Question 4

What propels the CSF through the ventricles and spinal cord. Describe the path of flow of CSF from 1 and 2nd ventricels

Answer 4

Ependymal cells make up the inner lining of the ventricles and spical cord. These are ciliated cells. ciliary action propels CSF through the ventricles.

Lateral ventricles
Foramina of Monro
Third Ventricle (between R and L thalamic nuclei)
Aqueduct of Sylvius
Fourth ventricle (within the pons)
- lateral foramina of Luschka
- midline foramen of Magendie
Enters subarachnoid space to flow around the cerebral hemispheres and the spinal cord

Question 5

Compare the contents of CSF with plasma

Answer 5

More chloride CSF 120 and Plasma 110 (therefore pH CSF 7.32 vs plasma 7.4)

Much less protein CSF 0.2 g/L to plasma 70 g /L

Much fewer WBC CSF 0 - 5 to plasma 4000 - 11000

Other parameters are simlar

Glucose in CSF is slightly lower 4 vs 6 plasma

Sodium and bicarbonate are the same 140 and 24 respectively in both fluids

Question 6

What is the total volume of CSF and where is it distributed at any 1 time

Answer 6

Total = 100 - 150 mL

Half in ventricular system
Half in subarachnoid space

Question 7

Where is CSF absorbed. What proportions of CSF is absorbed in the various regions

Answer 7

Arachnoid granulations are villi the project from the arachnoid space, through the dura mater and into the dural venous sinuses.

90% CSF reabsorbed from arachnoid villi in the sagittal and sigmoid dural sinuses

10% CSF reabsorbed by the spinal arachnoid villi

Question 8

How does CSF absorption occur

Answer 8

Hydrostatic pressure difference between CSF (15 cmH2O and venous blood (8 cmH2O).

Oncotic pressure difference between plasma (25 mmHg) and CSF oncotic pressure 0 mmHg

Increased CSF pressure (TBI) –> increased CSF absorption

Question 9

Define hydrocephalus

Answer 9

Abnormal resistance to circulation of CSF or imparied absorption of CSF.

The rate of CSF production exceeds the rate at which CSF can circulate past the obstruction

OR

The rate of CSF production exceeds the rate of CSF absorption.

Enlargement of the ventricles and compression of adjacent brain parenchyma.

Question 10

Classify the causes of hydrocephalus

Answer 10

No obstruction (rare)
- Choroid plexus papilloma --> increased production

Obstructed foramina of Monro (tumour)

Aqueduct of Sylvius (tumour/stenosis)

Luschka / Magendie
- SAH / chronic meningitis / Arnold Chiari

Arachnoid granulations
- SAH –> blood clots that obstruct absorption CSF

Question 11

What is the management of hydrocephalus

Answer 11

1. Surgical removal of obstruction (if possible)

2. Diversion of CSF flow

Question 12

What types of surgical diversion of CSF flow can be done to reduce hydrocephalus

Answer 12

1. External ventricular drain (EVD)
   - temporary
   - Allows for sampling and drug administration
   - Risk infection
2. Ventricular shunt
   - permanent
   - CSF diverted to peritoneal cavity or right atrium
3. Endoscopic 3rd ventriculostomy
   - hole at base of 3rd ventricle allowing CSF into the basal cisterns (subarachnoid space)