Hydrocephalus

Question 1

How to define hydrocephalus?

Answer 1

Enlargement of CSF compartment at the expense of brain tissue

Question 2

In hydrocephalus, the degree of dilatation of the CSF pathways and the amount of damage to the brain depend upon what?

Question 3

• The cause of hydrocephalus
• The severity
• Age of the patient at the time hydrocephalus develops

Question 4

How much of the ventricular lumen does the choroid plexus fill during the 3rd month of gestation?

Answer 4

75% - The size of the choroid plexus relative to the lateral ventricle gradually diminishes as the brain and ventricular system grow

Question 5

Choroid plexus has several functions in embryonic life, such as:

Answer 5

• Secrete proteins that modulate growth of progenitor cells in the ventricular zone of germinal matrix
  *

Question 6

Hydrocephalus in the embryo can have what affect?

Answer 6

Cause progenitor cells in ventricular walls to be less sensitive to proliferative effects of growth factors.

Therefore, fetal hydrocephalus can adversely affect brain development.

Question 7

What is the daily secretion of CSF in an adult?

Answer 7

500cc (.3-.4cc/min)

Question 8

What portion of CSF comes from Choroid Plexus?

Answer 8

60-90%

Question 9

What portion of CSF comes from parenchyma of the brain and spinal cord?

Answer 9

10-40%

Question 10

Is CSF in continuity with extracellular fluid in the brain and spinal cord?

Answer 10

Yes - exchnages occur constantly across the pial membrain, virchow-robin perivascular spaces, and ependyma

Question 11

What is bulk flow?

Answer 11

• Idea that CSF is created in lateral ventricles - flows into 3rd thru Monro, then 4th thru Aqueduct, then into Cisterna Magna (thru magendi) and Basilar Cisterns (thru Lushka).
• 80 then enters cisternal system - suprasellar/lamina terminalis, ambient/superior cerebellar - then flowing over convexities)
• Remaining 20% enters the spinal subarachnoid space - most (85%) will recirculate into cerebral subarachnoid space; 15% will be resorbed in spine.

Question 12

CSF circulation can be thought of as resulting from 2 processes, what are they?

Answer 12

• Bulk Flow (secretion-absorbtion process) - slow and passive (can be compared to lymphatics)
• Pulsatile process (fast) 60-80 pulsations/min (with cardiac cycle) related to molecules pulsating back and forth caused by pressure waves related to enlargement of arteries during systole. Force must be dampened by expansion of venous plexus, flexible dura, and flow into the spinal canal. When this is interrupted (ie increased venous pressure, spinal tumors, etc) the CSF will pulsate against parenchyma at full strength, causing compression of cerebral tissue and brain injury.

Question 13

What are some methods of CSF absorbtion?

Answer 13

• Major pathway - thru arachnoid granulations
• Minor pathways: as much as half of CSF may drain via other routes, such as:
  
  • intracerebral veins
  • lymphatics (through cribriform plate to lymphatic vessels in nasal submucosa; perineural spaces/orbital lymphatics)

Question 14

CSF asorbtion in neonates/infants is more likely due to minor pathways (thru cerebral cortical veins/lymphatics) - why do we think this?

Answer 14

Because endoscopic third ventriculostomy is less effective in neonates and young infants than in older children and adults.