Obstruction of the flow of urine from the renal pelvis to the
proximal ureter due to ureteropelvic junction (UPJ) is the most
common cause of hydronephrosis in infancy and childhood.
Ureteropelvic junction (UPJ) obstruction is most often caused
by an intrinsic narrowing at the junction of the renal pelvis and
ureter. Extrinsic compression by an aberrant crossing vessel or
fibrous band is a less common etiology, usually being responsible
for obstruction in older children. The obstruction initially leads
to an increased intrapelvic pressure and accumulation of urine proximal
to the site of obstruction, resulting in pelvicalyceal dilation.
Long-standing severe obstruction will lead to progressive deterioration
in renal function or hamper normal renal development.
Most cases of ureteropelvic junction (UPJ) obstruction are detected
by prenatal ultrasonography. Management approaches are discussed
in Chapter 469. UPJ obstruction is suspected
when only the renal pelvis is dilated without accompanying dilatation
of the ureter. A voiding cystourethrogram (VCUG) may be required
to exclude vesicoureteral reflux, which can also produce significant
hydronephrosis. UPJ obstruction may be asymptomatic or presents
with age-dependent symptoms and signs. In infants, it may present
with a palpable abdominal mass that must be differentiated from
other causes of abdominal masses in the newborn. In older children,
it may cause pain, hematuria, hypertension, and urinary tract infections.
Initially, flank or abdominal pain may be attributed to gastrointestinal
disease because the pain follows ingestion of liquids, which causes
distention of the renal pelvis. It may also cause periodic severe
episodes of vomiting that present with a cyclic vomiting pattern.
When the renal pelvis is very dilated from UPJ, hematuria may occur
The management of prenatally suspected ureteropelvic junction
(UPJ) obstruction is conservative in most cases. A renal ultrasound obtained
too soon after delivery, within the first 3 days, may underestimate
the degree of dilatation because of the low newborn urine output during
the first days of life. In most cases, a renal ultrasound should
be obtained after the first week and within the first month. Up
to two thirds of prenatally suspected UPJ obstructions will have
preserved renal function. Some infants show improvement and even
resolution of the obstruction over the first 24 months of life.
The degree of obstruction and the differential function of the affected
kidney, as determined by diuretic renography, as well as the trend
observed by serial ultrasounds help confirm the diagnosis and direct
subsequent management.1 Early laparoscopic pyeloplasty, although
uncommon today, is indicated if the postnatal evaluation yields
evidence of functional impairment (relative function of involved
side < 30–40% of total function) and/or
massive dilation of renal pelvis (anteroposterior [AP] diameter
> 30 mm), signs of severe obstruction bilaterally or in a solitary
kidney.2 Conservative management is indicated if
the relative function of the affected kidney is greater than 40%,