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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.
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.
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.
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.
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.
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.
Ureterovesical junction (UVJ) obstruction: Obstruction at the junction where the ureter enters the bladder causes a hydroureter and usually hydronephrosis without an enlarged bladder.
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.
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.
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.
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.
References
Farrugia M.K.
Hitchcock R.
Radford A.
British Association of Paediatric Urologists consensus statement on the management of the primary obstructive megaureter.
Pediatric vesicoureteral reflux guidelines panel summary report: clinical practice guidelines for screening siblings of children with vesicoureteral reflux and neonates/infants with prenatal hydronephrosis.
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