AVP and Hyponatremia: It has been reported that SIADH is difficult to distinguish from cerebral salt wasting syndrome, another cause of hyponatremia characterized by renal loss of sodium and decreases in extracellular fluid volume during intracranial disorders [6]; nonetheless, the abnormal ADH secretion and lack of clinical symptoms of dehydration in our patient were consistent with the characteristics of SIADH [7], although precise evaluation of the volemic state has been considered difficult [8].