ICP and Hydrocephalus

Question 1

What are the components of the ICP?

Answer 1

Brain = 1300-1750ml (80-85%), consists of tissue, intracellular fluid and extracellular fluid 
Blood = 100-150ml (5-8%)
CSF = 100-150ml (8-12%)

Question 2

What is the ICP?

Answer 2

Pressure exerted by the cranium onto brain tissue, CSF and intracranial circulating blood volume

Question 3

Does the ICP stay constant?

Answer 3

Nope, constantly fluctuating = about 7-15mmHg at rest, can be negative in vertical position

Question 4

What are the immediate mechanisms for compensating for an expanding mass in the cranium?

Answer 4

Decrease in CSF volume by moving it out of foramen magnum

Decrease in blood volume by squeezing sinuses

Question 5

What is the delayed mechanism for compensating for an expanding mass in the cranium?

Answer 5

Decrease in extracellular fluid

Question 6

What is the flow of CSF?

Answer 6

Choroid plexus - ventricular system - subarachnoid space - venous system

Question 7

How is the cerebral perfusion pressure calculated?

Answer 7

CPP = MAP - ICP

Question 8

How is the cerebral blood flow calculated?

Answer 8

Cerebral perfusion pressure/cerebral vascular resistance

Remains constant over wide range of BP

Question 9

How is the cerebral blood flow autoregulated by pressure and metabolic factors?

Answer 9

Pressure = arterioles dilate/constrict in response to changes in blood pressure or ICP
Metabolic = arterioles dilate in response to chemicals

Question 10

What effect does increased CO2 have on cerebral blood flow?

Answer 10

Increased blood pressure and cause vasodilation = increases cerebral blood flow

Question 11

What is the mechanism of autoregulation of the cerebral blood flow?

Answer 11

Unknown = direct reaction of smooth muscle to stretch, action of metabolic by-products or action of perivascular nerves

Question 12

What are the four main reasons for increased ICP?

Answer 12

Mass effect, brain swelling, increase in central venous pressure or problems with CSF flow

Question 13

What are some causes of a mass effect in the brain?

Answer 13

Tumour, infarct, contusions, haematoma, abscess = distort surrounding brain

Question 14

What are some causes of brain swelling?

Answer 14

ischaemia, acute liver failure, encephalopathy, IIH, hypercarbia = decrease cerebral perfusion pressure but cause minimal tissue shift

Question 15

What are some causes of increased central venous pressure?

Answer 15

Venous sinus thrombosis, heart failure or obstruction of jugular veins

Question 16

What are the different ways CSF flow can be disrupted?

Answer 16

Obstruction = masses, Chiari syndrome
Increased production = choroid plexus papilloma
Decreased absorption = SAH, meningitis, malignant meningeal disease

Question 17

What are the normal range of values for ICP?

Answer 17

Adults = 7-15mmHg
Older children = 10-15mmHg
Young children = 3-7mmHg
Newborns = 1.5-6mmHg (often <0)

Question 18

What are the early signs of raised ICP?

Answer 18

Decreased level of consciousness and headache
Pupillary dysfunction +/- papilloedema
Changes in vision and nausea/vomiting

Question 19

What are the late signs of raised ICP?

Answer 19

Coma, hemiplegia, fixed dilated pupils, bradycardia, hyperthermia and increased urinary output

Question 20

What are the aims of interventions for raised ICP?

Answer 20

Maintain cerebral perfusion pressure and prevent ischaemia or brain compression

Question 21

What are some non-medical interventions for raised ICP?

Answer 21

Maintain head in midline to facilitate blood flow and elevate head of bed to 30-45%
Maintain fluid balance, normal electrolytes and normocarbia

Question 22

What is the medical management of raised ICP?

Answer 22

Use diuretics = mannitol, hypertonic saline, furosemide
May give anti-epileptics for seizure or barbiturate for coma
Surgery = decompression, remove mass lesions, CSF diversion

Question 23

What are the different classifications of hydrocephalus?

Answer 23

Communicating vs non-communicating

Congenital vs acquired

Question 24

What are some features of normal pressure hydrocephalus?

Answer 24

Idiopathic disease of elderly
Hakin’s triad = abnormal gait, urinary incontinence, dementia
May be due to decreasing brain elastance

Question 25

What are the differentials of normal pressure hydrocephalus?

Answer 25

Other forms of dementia, cervical myelopathy, all urinary problems, Parkinson’s disease, depression

Question 26

What investigations are done for normal pressure hydrocephalus?

Answer 26

Lumbar puncture, lumbar drain test and lumbar infusion studies

Question 27

How is normal pressure hydrocephalus treated?

Answer 27

VP shunt, medium-low or low pressure valve

Question 28

What is the epidemiology of idiopathic intracranial hypertension?

Answer 28

Women of child bearing age = Western world, overweight

Aetiology = CSF imbalance, oestrogen, transverse/sigmoid sinus stenosis

Question 29

What are the symptoms of idiopathic intracranial hypertension?

Answer 29

Headache, double vision, blurring, tinnitus, radicular pain and papilloedema
No ventricular dilation
25% develop severe or permanent visual loss

Question 30

What are the differentials of idiopathic intracranial hypertension?

Answer 30

Any other type of headache
Any other reason for raised ICP
Cervical radiculopathy

Question 31

What investigations cane be done for idiopathic intracranial hypertension?

Answer 31

Lumbar puncture, CT or MRI of head, CTV, fundoscopy

Question 32

What is the treatment of idiopathic intracranial hypertension?

Answer 32

Weight loss, diuretics or ONSF
Carboanhydrase inhibitors (acetazolamide, topiramate)
CSF diversion = LP or VP shunt
Interventional radiology = intracranial venous sinus plasty or stenting