Different functional characteristics of residual nephrons in infantile vs adult diffuse cortical necrosis

In this report we study the functional characteristics of residual nephrons in a 37 year-old woman, 7 months after diffuse bilateral cortical necrosis (CN) of unknown etiology, and in two infants, aged 13 and 15 months, who suffered CN in early infancy after surgical shock and acute dehydration, respectively. In the three cases CN was proven histologically by renal biopsy but undamaged nephrons were only present in the juxtamedullary area in the adult patient whereas in the two infants they were located in the outer part of the cortex. At the time of the study all patients presented a similar degree of renal insufficiency (creatinine clearance: 17-23 ml/min/1.37 m2). The adult patient showed a partly conserved ability to concentrate the urine, a marked free water formation in relation to the degree of distal sodium delivery and an unimpaired capacity to acidify the urine after an acid load. Both infants, by the contrary, were unable to concentrate the urine, had lower free water formation at similar rates of distal sodium delivery and presented a clear incapacity to acidify the urine. These results confirm previous finding indicating the sparing of juxtamedullary nephrons after CN in the adult subject but favor the existence of a surviving population of superficial nephron when CN occurs in early infancy. These differences are probably in relation with associated damage of deep cortex and medulla infancy due to the specific characteristics of blood flow distribution present at that age.