Hyponatremia after transsphenoidal surgery for pituitary tumors.

We studied the incidence of postoperative hyponatremia in 91 consecutive patients (44 males and 47 females; age, 45 yr; range, 12-76) operated on transsphenoidally for pituitary tumors. A postoperative serum sodium concentration less than 135 mmol/L (the lowest, 109 mmol/L) was observed in 32 (35%) patients. Hyponatremia occurred most commonly in patients operated on for Cushing's disease (11 of 18 patients; 61%). Hyponatremia was symptomatic in 18 (56%) of the patients. Neither the size nor the operability of the tumor or transient postoperative polyuria predicted the development of hyponatremia. Hyponatremia was first observed on the sixth or seventh postoperative day. The patients were treated with water restriction and by increasing the hydrocortisone replacement dose in the case of ACTH deficiency, and recovery took place, on the average, within 5 days. High urinary osmolality and plasma arginine vasopressin concentration during hyponatremia in a subgroup of study patients with these measurements indicated that inappropriate vasopressin secretion was involved in the pathogenesis of hyponatremia. In conclusion, postoperative hyponatremia after transsphenoidal surgery is common and may put the patients at increased risk of severe hyponatremic symptoms. Therefore, all patients should be screened for serum electrolytes for 1 week after transsphenoidal surgery.