In relation to diffuse cerebral oedema; discuss the pathophysiology, and the clinical and CT manifestations.
(30%- 30%- 40% marks)
Cerebral oedema is often classified based on 3 different mechanisms by which oedema results:
Cytotoxic oedema: failure of ionic pumps to maintain cellular homeostasis, accumulation of water and swelling of cells. Blood brain barrier (BBB) is intact. Metabolic derangements and ischaemia most common causes. E.g. CVA, post cardiac arrest, encephalopathy e.g. due to hepatic impairment.
Vasogenic oedema: breakdown of endothelial junctions of the BBB allowing intravascular proteins and fluid into extracellular space. Due to trauma, tumours, inflammation (e.g. infection), late stage of ischaemic insults, high altitude sickness. Mechanism relates to hydrostatic pressure in arterial HT, tumour released endothelial destructive factors (e.g. vascular endothelial growth factor - secretion reduced by Dexamethasone).
Osmotic oedema: Dilution of plasma leading to shift of water down the osmolarity gradient to the brain.
E.g. Excess H2O intake, SIADH, dialysis, rapid decrease in blood glucose when treated for a hyperosmolar hyperglycaemic state.
Cytotoxic and vasogenic oedema often coexist e.g. in setting of infarction or trauma.
May be similar to and superimposed on manifestations of the underlying cause
Related mostly to elevated ICP or mass effect
Agitation, delirium early
Hypertension, bradycardia (Cushing’s response)
Pupillary dilatation and decreased light reflex Papilledema
(Lateralising signs may be present with unilateral uncal/cerebellar herniation)
Loss of sulci
Loss of grey-white differentiation
Basal cistern/lateral ventricle effacement
Herniation of cerebellar tonsils into foramen magnum.
There are several agreed-upon mechanisms which can generate cerebral oedema:
For the majority of the clinical features listed below, the main source was the UpToDate article on high altitude cerebral oedema, as that seemed like a cause of diffuse oedema which was sufficiently insidious in onset to produce symptoms instead of immediate coma.
With raised ICP:
Hydrocephalus-associated "interstitial" oedema
Oedema in general
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