Figure 1. Flow chart showing the diagnostic approach to hyponatremia.

Figure 2. Effects of hyponatremia on the brain. Minutes after the development of hyponatremia, the decreased osmolality causes swelling of the brain. Rapid adaption occurs within hours as a result of the cellular loss of electrolytes. Slow adaption occurs over several days through the loss of organic osmolytes from brain cells to normalize brain volume. Aggressive correction of hyponatremia may lead to irreversible brain damage (osmotic demyelination); however, proper correction of hyponatremia reestablishes normal osmolality without the risk of brain damage. From Adrogue HJ, Madias NE: Hyponatremia. N Engl J Med 342:1581–1589, 2000; reprinted with permission.

Figure 3. Algorithm for the evaluation and treatment of patients who have undergone neurosurgery and have hyponatremia and natriuresis. CVP = central venous pressure. From Docci D, Cremonini AM, Nasi MT, et al: Hyponatremia with natiuresis in neurosurgical patients. Nephro Dial Transplant 15:1707–1708, 2000; by permission of Oxford University Press.

Figure 4. A sagittal diagram of the anatomy of the pituitary gland, hypothalamus, and pituitary stalk. The anterior gland, or adenohypophysis, is composed of the pars distalis (PD), the rudimentary pars intermedia, and the pars tuberalis (PT). The posterior gland, or neurohypophysis (located in the hypothalamus), is composed of the median eminence (ME), the infundibular stem (IS), and the neural lobe (NL). The large neurons located in the supraoptic nucleus (SON) and the paraventricular nucleus (PVN) project to the neural lobe, where they store and release oxytocin and vasopressin into the systemic circulation under the appropriate stimulus. ARC. N. = arcuate nucleus; MB = mammillary bodies; OC = optic chiasm. Figure 35-3 from Couldwell WT, Simard MF, Weiss MH, et al: Pituitary and Adrenal, in Schwartz SI (ed): Principles of Surgery, ed 7, vol 2, New York: McGraw-Hill, pp 1613–1659; reprinted with permission.