Transsphenoidal Surgery: DI Rx

Diabetes insipidus (DI) is a known complication of transsphenoidal surgery. Untreated, patients may develop hypernatremia and hyperosmolality, with the potential for the development of dehydration, lethargy, and seizures. The primary symptoms of DI are polyuria and polydipsia. These symptoms should be especially concerning for DI in the setting of transsphenoidal surgery.

To confirm the diagnosis, urine studies and blood work can be obtained. A urine specific gravity <1.005, urine osmolality <300 mOsm/kg, serum osmolality >300 mOsm/kg, and an elevated serum sodium are all consistent with the diagnosis of DI. High urine output is the hallmark of DI, but there is no agreed upon urine output threshold characteristic of DI. Some of the various thresholds used in the literature include >2 mL/kg/hr, >30 mL/kg/day, and >250-500 mL/hr.

Post-operatively, DI can follow several courses. Transient DI has onset typically within the first 2 postoperative days and gradually resolves over several days. Permanent DI manifests in those patients who suffered damage to the hypothalamus or proximal infundibulum and does not resolve. A triple-phase response is a rare manifestation of post-operative DI in which the first phase is similar to transient DI, the second phase is clinically similar to the syndrome of inappropriate antidiuretic hormone secretion, with the third and final phase being the development of permanent DI.

To treat DI, fluid intake in encouraged in the awake patient with an intact thirst mechanism. If the patient is able to maintain their fluid balance with water intake, then no further intervention is required. In those patients unable to take an adequate volume of water by mouth, in those patients with hypernatremia or hyperosmolality, other causes of fluid loss should be ruled out. Once ruled out, DI can be treated with desmopressin (DDAVP), a synthetic analog to arginine vasopressin, the absence of which results in central DI. If patients are treated with DDAVP, care should be taken to avoid “iatrogenic SIADH” with attendant morbidity and mortality.

Risk factors for the development of post-operative DI appear to include tumor size (more common with smaller tumors), presence of a craniopharyngioma, and the presence of a Rathke’s cleft cyst. Close monitoring in the postoperative setting is critical to identify and manage DI in a timely fashion.