a syndrome that occurs after head injury or neurosurgical procedures
initiating event is loss of sodium and chloride in the urine, which results in a decrease in intravascular volume leading to water retention and hyponatraemia because of a baroreceptor-mediated stimulus to arginine vasopressin (AVP) secretion.
CSW resembles SIADH: both are hyponatremic disorders seen after head injury with relatively high urine sodium excretion rates and urine osmolality, along with plasma arginine vasopressin (AVP) levels that are inappropriately high in relation to serum osmolality
in patients with CSW the increase in AVP is secondary to volume depletion
this contrasts with SIADH where a high AVP level is the primary aetiologic event - who are euvolaemic or have a modest increase in plasma volume from water retention
high urine sodium is not the cause of the hyponatraemia in SIADH - it consequence of the modest volume expansion and need to maintain sodium balance in the face of continuing sodium intake
relative distribution of CSW and SIADH among neurosurgery patients with hyponatraemia is unknown
aetiology of CSW has not been definitively established
differentiation of CSW from SIADH - requires establishment that a period of urinary sodium loss and volume depletion preceded development of hyponatraemia
Reference:
(1) hyponatraemia Treatment Guidelines 2007: Expert Panel Recommendations.American Journal of Medicine 2007; 120 (11);S1:S1-S21.
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