Postoperative polyuria with a very dilute urine and high serum sodium after pituitary surgery is most consistent with which condition?

Postoperative polyuria with a very dilute urine and high serum sodium after pituitary surgery is most consistent with which condition?

• A. Osmotic diuresis from mannitol
• B. Hyperglycemia
• C. Nephrogenic diabetes insipidus
• D. Central diabetes insipidus

Answer: (D)

Central diabetes insipidus caused by loss of antidiuretic hormone after pituitary surgery best explains this picture. When ADH is deficient, the kidneys cannot reabsorb water in the collecting ducts, so large volumes of very dilute urine are produced. The result is polyuria with a low urine osmolality and rising serum sodium from free-water loss. This scenario fits post‑op pituitary injury best. In contrast, osmotic diuresis from mannitol or hyperglycemia would typically affect urine composition differently (they tend to keep urine osmolality higher due to solute load), and nephrogenic diabetes insipidus would present with a similar dilute urine but has ADH present and would not be the immediate post-op cause. Desmopressin is the treatment to replace the missing ADH.

Central diabetes insipidus caused by loss of antidiuretic hormone after pituitary surgery best explains this picture. When ADH is deficient, the kidneys cannot reabsorb water in the collecting ducts, so large volumes of very dilute urine are produced. The result is polyuria with a low urine osmolality and rising serum sodium from free-water loss. This scenario fits post‑op pituitary injury best. In contrast, osmotic diuresis from mannitol or hyperglycemia would typically affect urine composition differently (they tend to keep urine osmolality higher due to solute load), and nephrogenic diabetes insipidus would present with a similar dilute urine but has ADH present and would not be the immediate post-op cause. Desmopressin is the treatment to replace the missing ADH.