Raised intracranial pressure

Question 1

List the risk factors for raised intracranial pressure.

Answer 1

• Mass lesions e.g. haematoma, tumour, abscess
• Focal or diffuse oedema or swelling e.g. infarction, trauma, tumour, encephalitis, meningitis, diffuse head injury, SAH, Reye’s syndrome, hypertensive encephalopathy.
• Disturbance of CSF circulation e.g. hydrocephalus (obstructive and comminicating), benign intracranial hypertension, choroid plexus papilloma
• Increased cerebral blood volume e.g. vasodilation (hypercapnia), venous outflow obsruction, venous sinus thrombosis

Question 2

What criteria is used to diagnose IIH?

Answer 2

Modified Dandy criteria (for IIH):

• Signs and symptoms of raised ICP
• CSF opening pressure of ≥25 cm H2O
• No localising neurological signs
• Patient awake and alert
• No deformity, displacement or obstruction of ventricles and normal imaging (except for raised ICP signs)
• No cause for the raised ICP

Question 3

What is the normal ICP?

Answer 3

0-135mm CSF (7-15mmHg in the supine position)
Small increases in CSF volume may be accommodated by CSF expulsion to the lumbar theca.

Question 4

What are some signs of raised intracranial pressure on imaging?

Answer 4

• Empty sella
• Venous stenoses
• Globe flattening

Question 5

What factors affect cerebral vascular resistance?

Answer 5

Chemoregulation e.g. reduction of ICP with hyperventilation by reduing blood flow
Autoregulation - maintains cerebral blood flow by vasoconstriction and vasodilation

Question 6

How much CSF is produced per day? Where is it absorbed?

Answer 6

500ml - mainly by choroid plexus of the later, third and fourth ventricles
Absorbed in the arachnoid granulations to enter the venous system.

Question 7

What are the clinical features of raised ICP?

Answer 7

• Headache - worse on coughing, nocturnal
• Vomiting - projectile as ICP rises
• Visual disturbance e.g. blurring, obscurations (transient blindness), papilloedema, retinal haemorrhages (if rise was rapid)
• Pupillary irregularities
• Fundoscopy showing blurring of disc margins, loss of venous pulsations
• 3rd or 6th nerve palsies
• Cushing’s triad = widening pulse pressure, braducardia, irregular breathing
• Seizure
• Cushing’s peptic ulceration
• Slowly increasing head size in infants

Question 8

What does a gradual dilatation of a pupil after injury suggest?

Answer 8

Gradual dilatation and decreasing responsiveness to light = expansion of a clot over the ipsilateral hemisphere

Question 9

How can you monitor the ICP?

Answer 9

Ventricular catheter or surface pressure recording device
Usuallly started when pressure exceeds 30mmHg

Question 10

What are some treatment options for reducing intracranial pressure?

Answer 10

Investigate and treat the underlying cause
Head elevation to 30 degrees
Hyperosmolar therapy e.g. IV mannitol is an osmotic duiretic, ?hypertonic saline.
Sedation and paralysis
Controlled hyperventilation - aim is to reduce pCO2 → vasoconstriction of the cerebral arteries → reduced ICP. This causes a rapid but temporary lowering of ICP. Caution with reducing flow to ischaemic parts of brain
Hypothermia - cooling to 35 degrees
Steroids - good for tumour related raised ICP
CSF removal - drain from intraventricular monitor, repeat LPs or ventriculoperitoneal shunt
Surgery -e.g. burr hole for external drain, decompressive craniectomy

Question 11

What is the cerebral perfusion pressure calculation?

Answer 11

CPP = mean arterial pressure - ICP

Question 12

What investigations would you do in raised ICP?

Answer 12

MRI/CT head - find underlying cause
Invasive ICP monitoring- lateral ventricular catheter is inserted, small amounts of CSF may also be drained
>20mmHg - usually requires further treatment