We describe two cases of dysgenesis of the corpus callosum demonstrated by magnetic resonance. The first patient presented with chronic hyponatraemia. Investigation demonstrated re-setting of the osmoreceptor and thirst centres. The calculated threshold for arginine vasopressin (AVP) release was reduced at 252 mosmol/kg while severe thirst was perceived at a plasma osmolality of 260 mosmol/kg. Insulin-induced hypoglycaemia produced an exaggerated AVP response. The second patient presented with hypothermia. The calculated threshold of AVP release was 296 mosmol/kg with increased sensitivity of AVP response to hypertonic saline. The plasma AVP response to insulin-induced hypoglycaemia was absent. Both cases had normal anterior pituitary function and psychological assessment showed a similar prefrontal defect. Specific tests of callosal function were normal. These cases illustrate the importance of undertaking complete neuroradiological assessment of cases of unexplained hypothalamic disease regardless of the age of presentation to avoid overlooking this rare congenital association.
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