Developmental Abnormalities of the Renal Tract

Developmental abnormalities of the Renal Tract Disorder of the number of kidneys    Renal agenesia (missing kidney) o This is a unilateral or bilateral condition in which the foetal kidneys fail to develop, leading to oligohydramnios – a deficiency in amniotic fluid, and thus resulting in a 40-fold increase in perinatal mortality. o Bilateral Renal Agenesis  Involves complete absence of both kidneys, and can occur with pulmonary hypoplasia and extremity and facial anomalies. Ultrasonography may demonstrate renal or hepatic cysts, however a definitive diagnosis will require a biopsy. The condition often initiates Potter’s syndrome, which is fatal within minutes to hours. o Unilateral Renal Agenesis  This is not uncommon, and is usually not of any major health consequence as long as the other kidney is healthy. It is accompanied by ureteral agenesis, with the absence of the ipsilateral trigone and ureteral orifice. There is compensatory hypertrophy of tubules in the remaining kidney as it maintains normal renal function. Duplication anomalies (too many kidneys) o The supernumerary collecting systems may be unilateral or bilateral, and may involve the renal pelvis and ureters (e.g. accessory renal pelvis, double or triple pelvis and ureter), calyx or ureteral orifice. o A duplex kidney, a single renal mass with >1 collecting systems, differs from a fused kidney, which involves the fusion of 2 renal parenchymal masses. o Some duplication anomalies have ureteral ectopy with or without a ureterocele. Management depends on the anatomy and function of each separately drained segment. Surgery may be needed to correct the obstruction or vesicoureteral reflux. Fusion anomalies (e.g. horseshoe kidney) o With fusion anomalies, the kidneys are joined but the ureters enter the bladder on each side. o These anomalies increase the risk of ureteropelvic junction obstruction, vesicoureteral reflux, congenital renal cystic dysplasia, and later in life injury from anterior abdominal trauma. o In horseshoe kidney, the renal parenchyma on each side of the vertebral column is joined at corresponding (usually lower) poles; an isthmus of renal parenchyma or fibrous tissue joins at the midline. Ureters course medially and anteriorly over this isthmus and generally drain well Rotational anomalies  Malrotation o In malrotation, the ureters cross the midline and enters the bladder on the side opposite to the kidneys. A fused pelvic kidney (pancake kidney) is much less common, where a single kidney is served by 2 collecting systems and ureters. If obstruction is present, reconstruction is needed. There can be occasional hydronephrosis – accumulation of urine in the kidneys. o Multicystic dysplastic kidney can also occur, where a non-functioning renal unit consists of non-communicating cysts with intervening solid tissue composed of fibrosis, primitive tubules and foci of cartilage. Usually, ureteral atresia is also present and hypertension may develop. Uncommonly, the kidney develops tumours or infection. Congenital ureteral abnormalities  Vesicorenal reflux o Backflow of urine into the kidneys, before and during urination due to a missing anti-reflux mechanism where the ureter empties into the bladder Normally, the uretero-vesical junction functions as a sphincter and urine can only flow out through the urethra. However, the urine can also flow back to the kidneys via the ureters as a result of a change of the vesico-ureteral junction Other general anomalies    Renal dysplasia o In renal dysplasia, histologically, renal vasculature, tubules, collecting ducts, or drainage apparatus develops abnormally. Diagnosis is by biopsy. If dysplasia is segmental, treatment is often unnecessary. But if dysplasia is extensive, renal dysfunction may necessitate nephrologic care, including renal replacement therapy Renal ectopia o Abnormal renal location usually results when a kidney fails to ascend from its origin in the true pelvis; a rare exception occurs with a superiorly ascended (thoracic) kidney. Renal hypoplasia o Renal hypoplasia usually occurs because inadequate ureteral bud branching causes an underdeveloped, small kidney with histologically normal nephrons