Isolated hyponatremia after transsphenoidal pituitary surgery.

A retrospective analysis was performed to study the fluid and sodium status of patients undergoing transsphenoidal surgery (TS) for Cushing's disease. We evaluated the time of onset, duration, and relative incidence of isolated hyponatremia and identified possible factors associated with it. Of 58 patients that underwent TS over 1 yr, 52 without postoperative diabetes insipidus or volume depletion were studied. Isolated hyponatremia after TS for Cushing's disease occurred in 21%, and symptomatic hyponatremia (plasma sodium, < or = 125 mmol/L) with new onset headache, nausea, and emesis occurred in 7.0% of all operated. These later patients escaped monitoring and intervention for 24 h. The development of hyponatremia began early in the postoperative period and progressed slowly over 7 days. Maximum antidiuresis occurred on postoperative day 7. Vasopressin levels measured in two patients while hypoosmolar suggested that unregulated vasopressin release contributed to the hyponatremia. Cortisol levels, glucocorticoid replacement, and pituitary adenoma size were similar in normonatremic and hyponatremic patients. Patients combining a history of an estrogenic milieu and documented posterior pituitary trauma at surgery experienced lower nadir plasma sodium. All hyponatremic patients were fluid restricted, and none developed progressive neurological symptoms, morbidity, or mortality. We speculate that the mild degree and slow rate of development of hyponatremia and/or active monitoring and intervention contributed to the good outcome.