ICP

Question 1

def of high ICP

Answer 1

The volume inside the cranium is fixed, so any increase in the contents can lead to raised ICP.

this can be mass effect, oedema, or obstruction to fluid outflow. Normal ICP in adults is <15mmHg.

Question 2

aetiology fo high ICP

Answer 2

vascular- haemorrhage (extradural, subdural, subarachnoid, intracerebral, intravascular)

infection

• meningitis
• encephalitis
• brain abscess

trauma - head injury

tumours - primary/met

benign intracranial HTN

hydrocephalus

cerebral oedema

status epilepticus

Question 3

sx of high ICP

Answer 3

headache - worse on coughing, leaning forward, vomiting

altered GCS - drowsiness, listlessness, irritabilty, coma

history of trauma

low HR and high BP - (Cushing’s response), Cheyne-stokes respiration

pupil changes - constriction 1st, then dilation - dont mask signs by using tropicamide to dilate pupil to aid fundoscopy

reduced acuity

peripheral field vision loss

papilloedema is an unreliable sign, but venous pulsation at the disk may be absent - absent in 50% people but loss of it is a useful sign

Question 4

uncal herniation

Answer 4

caused by lateral supratentorial mass - pushes the ipsilateral inferomedial temporal lobe (uncus) through the temporal incisura and against the midbrain

the CN3 which travels in the space gets compressed = dilated ipsilateral pupil, then ophthalmoplegia (a fixed pupil localises a lesion poorly but is ipsilateralising)

may be followed quickly by contralateral hemiparesis (pressure on the cerebral peduncle) and coma from pressure on ascending reticular activating system in midbrain

Question 5

cerebellar tonsil herniation

Answer 5

caused by increased pressure in the posterior fossa -> cerebellar tonsils through the foramen magnum

ataxia, CN6 palsy and upgoing plantar reflexes occur 1st

then loss of consciousness, irregular breathing, apnoea

may proceed very rapidly given the small size of, and poor compliance in, the posterior fossa.

Question 6

subfalcian (cingulate) herniation

Answer 6

caused by frontal mass

cingulate gyrus (medial frontal lobe) forced under the rigid falx cerebri

may be silent unless the anterior cerebral artery is compressed and causes a stroke - eg contralateral leg weakness +- abulia (lack of decision making)

Question 7

Ix for high ICP

Answer 7

UE

FBC

LFT

glucose

serum osmolarity

clotting

blood culture

toxicology screen

CXR - any source of infection that could cause an abscess

CT head - mass lesions, midline shift, or effacement of the basilar cisterns

LP if safe - MEASURE THE OPENING PRESSURE