From Lewis S Blevins Jr. MD: A 37-year-old woman presented with visual compromise and headache. MRI demonstrated a 2.0 cm cystic pituitary lesion thought to be representative of a Rathke’s cleft cyst. Pituitary functions were normal. She underwent a successful surgical procedure to resect this lesion.
Five days later she called the office complaining of weakness in her arms as well as a headache and other nonspecific symptoms resembling a flulike illness. She was strongly advised to report to the emergency department for evaluation including a serum sodium but decided not to follow advice. Twenty-four hours later she was seen by her primary physician for worsening symptoms.
Laboratory investigations revealed a normal serum cortisol, normal thyroid functions, and a serum sodium of 115 mEq per liter. The urine osmolarity was 250 mOsm per kilogram of water. On examination, she was mildly confused. There were no signs of either volume depletion or volume excess.
A diagnosis of postoperative Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH) due to unregulated vasopressin release from the posterior pituitary as a consequence of surgical manipulation was made. She was treated with 3% saline IV at 70 mL per hour for 4 hours until her symptoms improved and her serum sodium level measured 125 mEq per liter. Thereafter, she was treated with Tolvaptan 15 mg PO. Twenty-four hours later her serum sodium measured 137 mEq per liter. She felt well without any symptoms whatsoever of hyponatremia. The next day, her serum sodium measured 139 mEq per liter. She was discharged in good condition with her postoperative SIADH having resolved.
Postoperative SIADH is not uncommon after pituitary surgery. It usually presents within 5-7 days of the surgical procedure. It seems to be more common in patients who have had manipulation of the posterior pituitary to resect lesions such as a Rathke’s cleft cyst, craniopharyngioma, or posterior pituitary gland tumor.
This patient’s course is typical. She was treated with 3% saline to emergently resuscitate given that she had symptoms of cerebral edema. Thereafter, she was treated with Tolvaptan. Many similar patients require only 1-2 doses of Tolvaptan after surgery. The usual length of stay is 36-48 hours. If these patients are treated with fluid restriction alone the length of stay would probably be about 5-7 days.
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