Chapter 476

### Ureteropelvic Junction Obstruction

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.

#### Pathophysiology

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.

#### Diagnosis

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 post trauma.

#### Treatment

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%, and is appropriate in the great majority of mild and moderate hydronephrosis cases. Indications to ...

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