Ultrasound Evaluation of Renal Anomalies

Allison Faucett, MD Maternal‐Fetal Medicine University of Colorado School of Medicine • Review the systematic evaluation of the fetal kidneys Learning • Describe the normal embryology of kidney Objectives development • Review the different categories of cystic renal disease Renal Sonographic Transverse Plane: Assess number, location, renal pelvis size, echogenicity Assessment Coronal Plane: Assess size, location, morphology, renal arteries Embryology & Renal Variants Embryonic Development Urogenital Ridge

• Arises from the intermediate mesoderm • Embryo develops three sets of tubular nephric structures • Pronephros (cranial) • Mesonephros (mid) • Metanephros (caudal) Renogenesis

• Mesonephric duct forms the ureteric bud which becomes the collecting ducts, calyces, and ureters • Metanephric blastema forms the renal parenchyma • Process of reciprocal induction and differentiation via growth factors • Problems with induction and differentiation lead to renal variants Unilateral • Disruption of ureteral bud growth Renal Agenesis • No kidney formation or renal hypoplasia Duplication

• Ureteric bud divides prematurely before entering the blastema • Double kidney • Duplicated ureter and renal pelvis Duplicated Collecting System

• Upper pole drained by ectopic ureter with ureterocele in bladder • Lower pole drained by normotopic ureter prone to reflux Kidneys form in the sacral region near the fetal bladder. Growth of the embryo causes kidneys to ascend to their final position in the lumbar region. Renal Ascent Transient renal arteries form during ascent and involute until a single main renal artery remains. Disorders of Renal Ascent

• Pelvic Kidney • Adjacent to iliac wing or bladder • Variable blood supply • May be smaller in size with abnormal morphology • Horseshoe Kidney • Developing kidneys fuse anterior to aorta • Trapped in abdomen by inferior mesenteric artery Horseshoe Kidney

• A: Axial/Transverse • Inferior poles fused by isthmus • Malrotation of lower poles • Renal pelvis ventral to parenchyma • B: Coronal • Low‐lying position • Aorta is midline between pelvises Cystic Renal Disease Multicystic Dysplastic Kidney

• Enlarged kidney with multiple cysts • No functional renal parenchyma • Atretic ureter • Most often unilateral, L>R • Malformation of the contralateral kidney in 40% of cases Sonographic Features

• Cystic paraspinal flank mass • Cysts of various sizes • Cysts are noncommunicating • Large cysts can distort kidney shape Autosomal Recessive Polycystic Kidney Disease

• Single gene disorder • Autosomal recessive inheritance with 25% recurrence risk • Bilateral, symmetric, cystic renal disease • Hepatic fibrosis also present • Poor prognosis if associated oligohydramnios and pulmonary hypoplasia • In survivors, mean age at diagnosis of chronic renal failure is 4 years Sonographic Features

• Kidney size >2 SD above mean for GA • Hyperechoic as compared to liver parenchyma • Diffuse • Confined to renal pyramids • Cysts may be visible but do not predominate • Oligohydramnios • Pulmonary hypoplasia Conditions Associated with Renal Cysts

• Chromosome abnormalities • Trisomy 13 and 18 • Triploidy • Turner syndrome/Monosomy X (also associated with horseshoe kidney) • Single gene disorders • Tuberosclerosis • Meckel‐Gruber syndrome • Other Syndromes • Beckwith‐Wiedmann syndrome • Noonan syndrome • Duke University Medical School. Embryology Learning Resources: Urogenital Development. embryology.oit.duke.edu • Callen: Ultrasonography in Obstetrics and References Gynecology, 5th ed, 2008. • Woodward PJ, et al. Diagnostic Imaging Obstetrics, 3rd ed, 2016. • Bianchi DW, et al. Fetology, 2nd ed, 2010.