HYPONATREMIA AFTER TRANSSPHENOIDAL SURGERY FOR PITUITARY-TUMORS

We studied the incidence of postoperative hyponatremia in 91 consecuti ve patients (44 males and 47 females; age, 45 yr; range, 12-76) operat ed on transsphenoidally for pituitary tumors. A postoperative serum so dium concentration less than 135 mmol/L (the lowest, 109 mmol/L) was o bserved in 32 (35%) patients. Hyponatremia occurred most commonly in p atients operated on for Cushing's disease (11 of 18 patients; 61%). Hy ponatremia was symptomatic in 18 (56%) of the patients. Neither the si ze nor the operability of the tumor or transient postoperative polyuri a predicted the development of hyponatremia. Hyponatremia was first ob served on the sixth or seventh postoperative day. The patients were tr eated with water restriction and by increasing the hydrocortisone repl acement dose in the case of ACTH deficiency, and recovery took place, on the average, within 5 days. High urinary osmolality and plasma argi nine vasopressin concentration during hyponatremia in a subgroup of st udy patients with these measurements indicated that inappropriate vaso pressin 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 hyponat remic symptoms. Therefore, all patients should be screened for serum e lectrolytes for 1 week after transsphenoidal surgery.