Pyeloplasty

MEGAN S. SCHOBER

KEVIN M. FEBER

EVAN J. KASS

Improved antenatal ultrasonography techniques have clearly been a factor in identifying collecting system dilation in the neonatal period. Obstruction is not necessarily the cause of hydronephrosis in the neonate; however, ureteropelvic junction (UPJ) obstruction is the most common cause of significant renal pelvis dilation in this age group (1). An exact etiology of UPJ obstruction has yet to be determined, but multiple hypotheses exist as to the cause of the obstruction. Incomplete recanalization of the proximal ureter, functional or anatomic obstruction, and developmental arrest are a few theories as to why obstruction occurs at the UPJ. Although the etiology of the obstruction may be unknown, the classification of obstruction can be divided into three categories: intrinsic, extrinsic, and secondary. Intrinsic UPJ obstruction is usually characterized by a stenotic or adynamic segment of ureter. Less commonly, intrinsic obstruction can be caused by mucosal folds or “flaps” (2). It has been estimated that 60% to 80% of persistent hydronephrosis in infants is secondary to intrinsic obstruction. Extrinsic obstruction most often occurs from an aberrant crossing vessel typically traveling to the lower pole of the kidney. This is a more common presentation in older children and adults. Secondary obstruction is rarer than extrinsic or intrinsic obstruction. It occurs when the ureter is severely dilated and tortuous from vesicoureteral reflux causing a “kink” in the ureter that acts as an impediment to urine flow. Over time, this area can become the site of significant periureteral scarring requiring surgical correction.

DIAGNOSIS

Before routine prenatal ultrasonography, the most common presentation of an infant with UPJ obstruction was with a palpable abdominal mass. Prenatal ultrasound has significantly increased the number of infants diagnosed with asymptomatic hydronephrosis. Prior to maternal ultrasonography, children with UPJ obstruction presented later in childhood with flank pain, hematuria, recurrent urinary tract infections, abdominal mass, or urolithiasis. Extrinsic compression of the UPJ by crossing vessels is more commonly seen in older children and accounts for the second peak of UPJ obstruction diagnosis in later childhood and adolescents. These children are usually diagnosed after multiple episodes of periodic flank pain accompanied by nausea and vomiting. Neonates with a history of antenatal hydronephrosis should undergo postnatal renal ultrasound. If prenatal hydronephrosis was unilateral and mild to moderate, postnatal renal ultrasound should be performed at 1 to 2 weeks of life because transitory dehydration of the newborn usually lasts about 48 hours after birth and can underestimate the degree of hydronephrosis visualized. However, if the hydronephrosis detected prenatally was severe, bilateral, or associated with oligohydramnios, postnatal ultrasound should not be delayed. When the diagnosis of hydronephrosis has been confirmed postnatally, a voiding cystourethrogram (VCUG) is typically performed to exclude vesicoureteric reflux as the cause and also to determine if there are any other associated findings. Once the diagnosis of UPJ obstruction is suspected after completion of renal ultrasound and VCUG, a diuretic renal scan is the next study that should be performed. Mercaptoacetyl triglycine (MAG-3) with furosemide is the preferred test in this situation to determine relative renal function and if delayed drainage is present. There has been much debate regarding the use of calculated half-times in response to furosemide administration and half-time should not be the sole determining factor in the clinical decision-making process regarding UPJ obstruction (3).

INDICATIONS FOR SURGERY

Indications to proceed to pyeloplasty at our institution include the following: severe hydronephrosis (Society for Fetal Urology grade III or IV) detected postnatally accompanied by <40% differential renal function with no response to furosemide on renal scan, worsening hydronephrosis on serial ultrasound, symptomatic UPJ obstruction, loss of relative renal function on serial renal scans (>10%), or persistent delay in drainage on serial diuretic renography in a child with severe hydronephrosis.

ALTERNATIVE THERAPY

Multiple treatment options currently exist for the treatment of UPJ obstruction ranging from endopyelotomy to robotic pyeloplasty. At this time, endopyelotomy is not commonly performed in neonates and infants but has been used in preadolescent and adolescent children with some degree of success. It has also been demonstrated that endopyelotomy appears to be more successful as a secondary technique for failed pyeloplasty in children. However, more recent data suggest that redo pyeloplasty or ureterocalicostomy are more successful secondary treatments than endourologic procedures (4,5).

Pure laparoscopic or robotic-assisted laparoscopic pyeloplasty has gained significant popularity in the last decade, as the success rates, operative times, and hospital length of stay of these procedures are becoming comparable to open pyeloplasty (6,7). Robotic assistance has significantly decreased the learning curve for minimally invasive pyeloplasty by making intracorporeal knot tying a much simpler process. Although robotic pyeloplasty in small infants has been shown in the literature to be a successful operation, the open Anderson-Hynes pyeloplasty continues to be the gold standard for clinically significant UPJ obstruction in neonates and small infants with reported success rates consistently >90% to 95%. The most important factors in a successful pyeloplasty of any technique include formation of a funnel at the UPJ with dependent drainage and a tension-free anastomosis.

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