Diabetes insipidus after cranial surgery is due to damage to the hypothalamus or pituitary gland. Which statement best explains why this occurs?

• A. Excess release of antidiuretic hormone
• B. Inadequate release of antidiuretic hormone
• C. Increased aldosterone production
• D. Decreased renin production

Answer: (B)

Central diabetes insipidus after cranial surgery happens because ADH release from the hypothalamus/posterior pituitary is reduced. ADH normally signals the kidneys to reclaim water in the collecting ducts by increasing aquaporin-2 channels; when ADH is deficient, these channels are not stimulated, so the kidneys excrete large volumes of dilute urine. This lack of ADH leads to polyuria and risks of dehydration and hypernatremia. The problem isn’t excess ADH (which would cause water retention) and it isn’t driven by aldosterone or renin changes, which affect electrolyte balance in different ways.