Large volumes of dilute urine indicate diabetes insipidus (DI), which results in the absence of antidiuretic hormone (ADH). The posterior pituitary gland produces antidiuretic hormone, which acts on the distal convoluted tubule to reabsorb water, thus concentrating urine. The posterior pituitary can be harmed during brain surgery as it is a tiny organ, which leads to decreased or absent ADH, and subsequently DI. The thalamus, hypothalamus, and anterior pituitary gland are not involved in diabetes insipidus caused by the absence of ADH.