Multiple causes of human kidney malformations

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Abstract
The human kidney derives from two parts of the metanephros, its embryonic precursor. The first of these is the ureteric bud, which branches into the collecting ducts containing K+ secreting principal and H+ handling intercalated epithelia, and also forms the urothelium of the calyces, renal pelvis, ureter, and bladder trigone. The second is the renal mesenchyme, which differentiates into nephrons comprised of glomeruli, proximal tubules, and loops of Henle. The human metanephros appears at 5 weeks of gestation, the first glomeruli form by 9 weeks, and nephrogenesis is complete by 34 weeks.1 2 #### Key messages The term ‘renal malformation’ encompasses a mixed bag of developmental aberrations, all of which involve anatomical or major structural anomalies which are present at the time of birth.1 2 In the most extreme example, called renal agenesis, the kidney is absent. Renal dysplasia describes an organ comprised of undifferentiated and metaplastic cells: these organs may be tiny (renal aplasia) or can distend the abdomen (the multicystic dysplastic kidney). A hypoplastic kidney is small and has fewer nephrons than normal: these nephrons may be grossly enlarged in oligomeganephronia. This classification is ultimately based on histopathology, yet in clinical practice it is unusual to have the luxury of viewing renal biopsy material from these children. The diagnoses on discharge summaries are often best guesses based on a detailed review of the clinical …