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Hydroureter

Published:September 07, 2021DOI:https://doi.org/10.1016/j.ajog.2021.06.044

      Introduction

      A hydroureter can be an isolated finding, but it is usually associated with other genitourinary tract anomalies. The finding of hydroureter can be useful in identifying associated anomalies and determining the location of obstructive lesions in the genitourinary tract.

      Definition

      Persistent visualization of the ureter on prenatal ultrasound is abnormal and warrants further evaluation. Megaureter is defined as a ureter of ≥7 mm in diameter in a fetus with a gestational age of >30 weeks.
      • Farrugia M.K.
      • Hitchcock R.
      • Radford A.
      British Association of Paediatric Urologists consensus statement on the management of the primary obstructive megaureter.

      Ultrasound Findings

      Hydroureter appears as a tortuous, tubular structure in the fetal pelvis communicating with the kidney, bladder, or both. (Figure). Observation of bowel peristalsis can help differentiate hydroureter from a dilated loop of bowel. Hydroureter is commonly found in conjunction with renal pelvis and calyceal dilation and, when observed, warrants a follow-up ultrasound examination and postnatal evaluation.
      • Nguyen H.T.
      • Benson C.B.
      • Bromley B.
      • et al.
      Multidisciplinary consensus on the classification of prenatal and postnatal urinary tract dilation (UTD classification system).
      Figure thumbnail gr1
      FigureKidney with severe hydronephrosis and hydroureter
      Kidney (between calipers) with severe hydronephrosis and hydroureter (arrow), seen as a tubular structure communicating with the kidney.
      Society for Maternal-Fetal Medicine. SMFM Fetal Anomalies Consult Series #4. Am J Obstet Gynecol 2021.

      Associated Anomalies

      Fetal hydronephrosis and hydroureter are often associated with other urinary tract or nonrenal congenital abnormalities, and hydroureteronephrosis is a feature of many genetic syndromes; these can include anomalies of any organ system. Hydroureter is commonly associated with vesicoureteral reflux or lower urinary tract obstruction, including a duplicated collecting system or bladder outlet obstruction. Fetuses with complete bladder outlet obstruction or significantly impaired fetal renal function will have associated oligohydramnios or anhydramnios.

      Differential Diagnosis

      Hydroureter can result from an anomaly intrinsic to the ureter in which abnormal development results in an aperistaltic segment and functional obstruction.
      • Nicotina P.A.
      • Romeo C.
      • Arena F.
      • Romeo G.
      Segmental up-regulation of transforming growth factor-beta in the pathogenesis of primary megaureter. An immunocytochemical study.
      More commonly, a hydroureter is due to either (1) vesicoureteral reflux (VUR) or (2) obstructive uropathy. VUR causes retrograde passage of urine from the bladder to the upper urinary tract, which can lead to pyelonephritis and end-stage renal disease after birth.
      • Skoog S.J.
      • Peters C.A.
      • Arant Jr., B.S.
      • et al.
      Pediatric vesicoureteral reflux guidelines panel summary report: clinical practice guidelines for screening siblings of children with vesicoureteral reflux and neonates/infants with prenatal hydronephrosis.
      VUR is a common cause of urinary tract dilation and can be accompanied by a hydroureter. Fluctuation in the size of the ureter and renal pelvis as the bladder contracts can be a marker for VUR.
      • Anderson N.G.
      • Allan R.B.
      • Abbott G.D.
      Fluctuating fetal or neonatal renal pelvis: marker of high-grade vesicoureteral reflux.
      Obstruction can occur at various points along the urinary tract, and the presence or absence of a hydroureter is useful in identifying the location and type of renal anomaly, as outlined below:
      • 1.
        Ureteropelvic junction obstruction: Obstruction at the junction between the kidney and ureter causes dilation of the renal pelvis and calyces but usually is not associated with a hydroureter, as urine is prevented from filling or dilating the ureter.
        • Bianchi D.W.
        • Crombelhome T.M.
        • D’Alton M.E.
        • Malone F.D.
        Fetology: diagnosis and management of the fetal patient.
      • 2.
        Ureterovesical junction (UVJ) obstruction: Obstruction at the junction where the ureter enters the bladder causes a hydroureter and usually hydronephrosis without an enlarged bladder.
        • Becker A.
        • Baum M.
        Obstructive uropathy.
        A common cause of obstruction at the UVJ is an ectopic ureter, which inserts in a location other than the normal position at the trigone of the bladder. Insertion into the bladder can be associated with ureterocele, a cystic dilation of the terminal ureter within the bladder.
        • Didier R.A.
        • Chow J.S.
        • Kwatra N.S.
        • Retik A.B.
        • Lebowitz R.L.
        The duplicated collecting system of the urinary tract: embryology, imaging appearances and clinical considerations.
        Approximately 90% of cases of ectopic ureter are associated with a duplicated collecting system.
        • Plaire J.C.
        • Pope 4th, J.C.
        • Kropp B.P.
        • et al.
        Management of ectopic ureters: experience with the upper tract approach.
      • 3.
        Bladder outlet obstruction: Bladder outlet obstruction should be suspected when bilateral hydroureter and hydronephrosis are seen in combination with a thick-walled, trabeculated bladder. The most common cause is posterior urethral valves in males and urethral atresia in females.
        • Farrugia M.K.
        Fetal bladder outlet obstruction: embryopathology, in utero intervention and outcome.

      Genetic Evaluation

      Diagnostic testing with amniocentesis or chorionic villus sampling and chromosomal microarray analysis (CMA) should be offered when a hydroureter is detected, particularly with other associated anomalies. If ultrasound findings or screening test results are suggestive of a common aneuploidy, it is reasonable to initially perform karyotype analysis or fluorescence in situ hybridization, with reflex to CMA if these test results are normal. If there are additional anomalies, consanguinity, or a family history of a specific condition, gene panel testing or exome sequencing is sometimes useful because CMA does not detect single-gene (Mendelian) disorders. If exome sequencing is pursued, appropriate pretest and posttest genetic counseling by a provider experienced in the complexities of genomic sequencing is recommended. After appropriate counseling, cell-free DNA screening is an option for patients who decline diagnostic evaluation particularly if a common aneuploidy is suspected.

      Pregnancy and Delivery Management

      When a unilateral hydroureter is detected, careful examination of the contralateral collecting system and bladder should be undertaken. Associated urinary tract anomalies occur frequently and affect the prognosis for both normal amniotic fluid and pulmonary development during fetal life and renal function after birth. Fetuses with moderate or severe urinary tract dilation, and those with additional findings to suggest CAKUT, warrant surveillance with follow-up ultrasound examinations. These patients may also benefit from prenatal consultation with a pediatric urology or nephrology specialist to formulate a plan for postnatal evaluation. Timing of delivery should not be affected by the presence of hydronephrosis, as preterm delivery has not been demonstrated to improve outcomes. The presence of hydronephrosis should not alter the mode of delivery, which should be based on the usual obstetrical or medical indications.

      Prognosis

      The long-term outcome of hydroureter depends on the underlying etiology. The prognosis for primary megaureter is generally excellent and can be managed expectantly without surgical intervention in almost three-quarters of infants.
      • Di Renzo G.C.
      • Giardina I.
      Coronavirus disease 2019 in pregnancy: consider thromboembolic disorders and thromboprophylaxis.
      ,
      • Gimpel C.
      • Masioniene L.
      • Djakovic N.
      • et al.
      Complications and long-term outcome of primary obstructive megaureter in childhood.
      Infants with a hydroureter due to severe obstructive uropathy may present with renal failure requiring dialysis after birth.
      • Becker A.
      • Baum M.
      Obstructive uropathy.

      Summary

      A hydroureter is the visualization of the ureter on ultrasound, which is considered abnormal. It is commonly seen in association with hydronephrosis, and its presence can identify associated anomalies and determine the location of obstructive lesions in the genitourinary tract.

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