AVP and inappropriate ADH syndrome: Some experts believe that in hydrocephalus patients, increased pressure on the hypothalamus leads to the release of antidiuretic hormone (ADH), which in turn causes hyponatremia. The true etiology of hyponatremia is critical to diagnose, as it will determine the treatment. So while both SIADH and CSW may result in hyponatremia, the former is treated with fluid restriction, while the latter requires fluid repletion; treating SIADH as CSW, and vice versa, will exacerbate the hyponatremia.