RAISED INTRACRANIAL PRESSURE
Physiology of ICP:The skull is a fixed structure not allowing expansion.
Intracranial volume consists of three compartments: brain, blood, CSF. If the volume of one of these compartments increases, the volume of another must decrease to maintain normal ICP (50-180mm water).
If the CSF pressure is further increased the brain may begin to herniate, then cerebral perfusion pressure will drop and ischemia result.
Causes of raised ICP
A. Space-occupying mass, for example, brain tumor, abscess, hematoma.
B. Brain oedema
C. Hydrocephalus
D. Venous thrombosis: impairs CSF reabsorption
E. Idiopathic intracranial hypertension
Clinical features of raised ICP
a. Headache
b. Morning vomiting
c. Papilloedema
d. Impairment of conscious level
e. Hypertension and bradycardia
f. Transient visual obscurations
g. False localizing signs
h. Herniation
Herniation
The rise in intracranial pressure from a mass lesion is not usually uniform within the cerebral substance and alterations in pressure relationships within the skull may lead to displacement of parts of the brain between its various compartments (herniation).
Cerebellar herniation (coning) may result in brain-stem haemorrhage and/or acute obstruction of the CSF pathways. As coning progresses, the patient may adopt a decerebrate posture and, unless rapidly treated, death almost invariably ensues.
Herniation may be acutely accelerated if the pressure dynamics are suddenly disturbed by lumbar puncture.
False localising signs
Pupillary dilatation
6th cranial nerve lesion (unilateral or bilateral)
Hemiparesis
Bilateral extensor plantar responses
Treatment of Elevated Intracranial Pressure
Elevate head of the bed; midline head position
Osmotherapy—mannitol or hypertonic saline.
Glucocorticoids—dexamethasone 4 mg q6h for vasogenic edema from tumor, abscess (avoid glucocorticoids in head trauma, ischemic and hemorrhagic stroke).
Hyperventilation
High-dose barbiturate therapy ("pentobarb coma")
Hypothermia
Hemicraniectomy
IDIOPATHIC INTRACRANIAL HYPERTENSION
This condition usually occurs in obese young women.The aetiology is uncertain but there may be a diffuse defect of CSF reabsorption by the arachnoid villi.
The condition can be precipitated by drugs, including tetracycline, and rarely vitamin A, retinoids, Addison's disease and withdrawal of corticosteroid therapy.
Clinical features
Characteristically, there is a headache (raised ICP headache), sometimes with transient diplopia and visual obscurations, but few other symptoms.
There are usually no signs other than papilloedema, but 6th nerve palsy may be present.
Investigations
1-Brain CT is normal
2-Lumbar puncture is safe and will allow confirmation of the raised CSF (CSF manometry) and CSF aspirate.
3-MRV (magnetic resonance venography) to exclude cerebral vein thrombosis
4-Thyroid function test to exclude hypothyroidism.
Management
Any precipitating condition should be sought and treated.
weight-reducing diet
The carbonic anhydrase inhibitor, acetazolamide, may help to lower intracranial pressure.
Repeated lumbar puncture and CSF aspirate can be considered, but is often unacceptable to the patient.
Patients failing to respond, in whom chronic papilloedema threatens vision, may require optic nerve sheath fenestration or a lumbo-peritoneal shunt.