Raised Intracranial Pressure Flashcards
What is contained in the intracranial space?
Brain
Dura mater
Blood
CSF
Is there more arterial blood or venous blood in the intracranial space?
Venous blood
What is intracranial pressure?
Refers to pressure within the intracranial space
What is normal intracranial pressure?
5-15 mmHg
How is intracranial pressure measured?
Lumbar puncture with a manometer, this is a tube which CSF runs up in, measure its height
How is intracranial pressure regulated?
Regulation of blood flow to the brain by
- autoregulation
- chemoregulation
What is autoregulation in terms of regulating intracranial pressure?
Vasoconstriction and vasodilation
What is chemoregulation in terms of regulating intracranial pressure?
Vasodilation in response to low cerebral pH, high pCO2
How is increasing intracranial pressure regulated?
Vasoconstriction to reduce venous blood volume
Reduced volume of CSF
Eventually cannot do this any further
How does brain injury cause raised intracranial pressure?
Reduced arterial blood supply to brain cells
Reduced delivery of oxygen to brain cells
Reduced aerobic metabolism
Reduced ATP
Reduced function of Na+ K+ ATPase
Increased concentration of sodium ions in the brain cells
Water moves into the brain cells by osmosis
Oedema of brain cells
Further compression of arteries supplying the brain
What are the signs and symptoms of raised intracranial pressure?
Headache
Vomiting
Visual disturbances, CN6 palsy
Depression of conscious level
In infants, may present as slowly increasing head size
What are the characteristics of the headache with raised intracranial pressure?
Generalised ache
May wake the patient up from sleep
Worst when wake up in the morning
Aggravated by bending, stooping
Aggravated by coughing, sneezing
Severity gradually progresses
Why do the aggravating factors of a headache with raised intracranial pressure make it worse?
Increased venous blood volume in the intracranial space, further raising the intracranial pressure
Why is there vomiting with raised intracranial pressure?
Ischaemia and hypoxia of vomiting centre in the brain
How does the vomiting change with the duration of the raised intracranial pressure?
Starts off as nausea, progresses to vomiting, then to projectile vomiting
What are the visual disturbances with raised intracranial pressure?
Blurring
Obscurations
Papilloedema
Retinal haemorrhages
What causes the visual disturbances with raised intracranial pressure?
Compression of the CN2 optic nerve
Because it is an extension of the brain so it surrounded by dura and CSF
What does the optic disc look like on fundoscopy with raised intracranial pressure?
Enlarged
Blurred outline
What does the retina look like on fundoscopy with raised intracranial pressure?
Cannot see blood vessels on retina
Retinal haemorrhages tend to occur with raised intracranial pressure that happened…
Rapidly
Why does a CN6 abducens nerve palsy occur with raised intracranial pressure?
CN6 abducens nerve runs closely to the pons and the skull, easily compressed by raised intracranial pressure
What are the signs and symptoms of a CN6 abducens nerve palsy?
Patient’s eye is adducted due to unopposed pull of the medial rectus muscle
Patient cannot abduct their eye due to loss of innervation to lateral rectus muscle
Why is there a depression in consciousness level with raised intracranial pressure?
Due to effects of ischaemia on raised intracranial pressure
What are the complications of raised intracranial pressure?
Herniation syndromes
Cushing’s reflex
What are the different types of herniation syndromes? Which is the most common?
Subfalcine herniation - most common
Uncal herniation
Tonsillar herniation
What is a subfalcine herniation?
Refers to the herniation of the brain under the falx cerebri
What are the signs and symptoms of a subfalcine herniation?
Asymptomatic
Contralateral leg weakness if anterior cerebral artery is compressed
What does a subfalcine herniation look like on a CT head scan?
Midline shift
What is an uncal herniation?
Uncus of temporal lobe herniates through the opening of the tentorium cerebelli
Uncus compresses the midbrain
What are the signs or symptoms of uncal herniation?
Dilated pupil
Contralateral weakness
Decreased level of consciousness
Why does uncal herniation cause a dilated pupil?
Compression of CN3 oculomotor nerve
Loss of parasympathetic innervation to the constrictor pupillae muscle on same side
Why does uncal herniation cause contralateral weakness?
Compression of cerebral peduncles
Which contain sensory and motor fibres running between the cerebral hemispheres and the pons
Why does uncal herniation cause decreases level of consciousness?
Compression of reticular formation
What is a tonsillar herniation?
Cerebellar tonsils herniates through the foramen magnum
What are the signs and symptoms of a tonsillar herniation?
Decreased level of consciousness
Cardiovascular and respiratory dysfunction
Why does a tonsillar herniation cause decreased level of consciousness?
Compresses the reticular formation
Why does a tonsillar herniation cause cardiovascular and respiratory dysfunction?
Compresses the medulla which contains the cardiovascular and respiratory control centres
What is Cushing’s reflex?
Physiological nervous system response to continuous raised intracranial pressure
- high blood pressure
- bradycardia
- low respiratory rate
What causes high blood pressure and bradycardia in Cushing’s reflex?
Ischaemia of medulla results in activation of sympathetic nervous system
Which increases blood pressure and causes tachycardia
Baroreceptors react to this and stimulate bradycardia
What causes low respiratory rate in Cushing’s reflex?
Ischaemia of pons and medulla, which contain the respiratory centres, gives low respiratory rate
What are the causes of raised intracranial pressure?
Cerebral oedema
Increased cerebral blood volume
Increased CSF
Expanding mass
What are the causes of cerebral oedema?
Ischaemic stroke
Meningitis
Encephalitis
Diffuse head injury
What are the causes of increased cerebral blood volume?
Venous outflow obstruction
-venous sinus thrombosis
What are the causes of increased CSF?
Impaired absorption
- hydrocephalus
- benign intracranial hypertension
Excessive secretion
-choroid plexus papilloma
What are the causes of an expanding mass in the intracranial space?
Abscess
Tumour
Haemorrhage, haematoma
What is hydrocephalus?
Accumulation of CSF
What causes hydrocephalus?
Imbalance between production and absorption of CSF
More production or less absorption
What are the types of hydrocephalus?
Non-communicating
Communicating
What is non-communicating hydrocephalus?
CSF is obstructed within the ventricles
Or between the ventricles and the sub-arachnoid space
What are the causes of non-communicating hydrocephalus? Which is the most common cause?
Blockage of aqueduct
Can be congenital or acquired
Most common cause
Tumours compressing the ventricular system
What does non-communicating hydrocephalus look like on a CT scan?
Large third ventricle, small fourth ventricle
What is communicating hydrocephalus?
Communication between the ventricles and the subarachnoid space
What are the causes of communicating hydrocephalus? Which is the most common
Choroid plexus papilloma
Post-meningitis - most common
Sub-arachnoid haemorrhage
Trauma
Neoplastic infiltration of subarachnoid space
-all give blockage of arachnoid granulation
What does non-communicating hydrocephalus look like on a CT scan?
Whole ventricular system is enlarged
What are the most common ages with brain tumours?
Children
Late middle age
What are the most common types of brain tumours in children?
Astrocytomas
Medullablastomas
What parts of the brain are brain tumours in children most common in?
Midline
Posterior region
What are the most common types of brain tumours in middle-aged people?
Metastases from other types of tumours e.g. breast, lung, kidney cancer
What are the most common types of primary brain tumours in middle-aged people?
Gliomas
Meningiomas
What is idiopathic intracranial hypertension?
Raised intracranial pressure but no pathology
What group of patients most commonly have idiopathic intracranial hypertension?
Obese women after weight gain
How is idiopathic intracranial hypertension treated?
Weight loss
Carbonic anhydrase inhibitor diuretics
CSF drainage
How can CSF be drained to treat idiopathic intracranial hypertension?
Therapeutic lumbar puncture
Shunts
How is raised intracranial pressure due to cerebral oedema treated?
Treat the underlying cause
Give mannitol or hypertonic saline
Why is mannitol or hypertonic saline given to treat raised intracranial pressure due to cerebral oedema?
Makes the plasma hyper-osmotic to CSF
So water moves from the CSF to the plasma
Reducing the volume of CSF
How is raised intracranial pressure due to increased cerebral blood volume treated?
Anticoagulation for venous sinus thrombosis
Or stunting of venous sinuses
How is raised intracranial pressure due to increased CSF treated?
Shunts from the ventricles to the peritoneum
Tumour resection
Diuretics while waiting for other treatments e.g. carbonic anhydrase inhibitors
How is raised intracranial pressure due to an expanding mass treated?
Surgical resection
Draining abscess
Craniotomy, surgically removing part of skull to relieve pressure
