URETEROPELVIC JUNCTION OBSTRUCTION
Obstruction of the ureteropelvic junction (UPJ), located where the renal pelvis meets the proximal ureter, typically reflects congenital abnormalities of either the ureter or surrounding structures. These are often detected during routine ultrasound examination of a growing fetus. The incidence of congenital UPJ obstruction is approximately 1:1000, with a slight male and left-sided predominance. In 10% to 40% of cases, the obstruction is bilateral.
PATHOGENESIS
There are multiple possible causes of congenital UPJ
obstruction, which include:
·
A congenital lack of
spiral muscle around the affected segment of the renal pelvis
·
Developmental failure
to recanalize the ureteral lumen
· Ureteral kinking that results
from persistence of ureteral folds, which normally disappear during development
· Insertion of the
ureter superior to the most dependent portion of the renal pelvis, thereby
limiting drainage
· Direct compression by
accessory vessels crossing from the renal artery or aorta to the lower pole of
the kidney (i.e., extrinsic obstruction)
Acquired UPJ obstruction, in contrast, may occur
during childhood or adulthood, typically in the setting of stones, chronic
inflammation with stricture formation, polyps, malignancy, or surgical insult.
PRESENTATION AND DIAGNOSIS
In fetuses and neonates, the diagnosis is usually first
suspected when unilateral or bilateral intraparenchymal hydronephrosis
accompanies normal ureteral width. In some circumstances, it may be difficult to
distinguish the dilated calices seen in hydronephrosis from the large
intraparenchymal cysts seen in multicystic dysplastic kidney (MCDK).
Radiographic continuity between the dilated regions suggests hydronephrosis,
while dilated regions that are distinctly separate favors MCDK. Nuclear
scanning may help further differentiate the two conditions because radiotracer
will concentrate in the hydronephrotic kidney, which retains some function, but
not in the MCDK, which lacks function. In cases of bilateral hydronephrosis,
high grade unilateral hydronephrosis, or congenital abnormalities such as
horseshoe kidney, voiding cystourethrogram may be indicated to assess for
vesicoureteral reflux (see Plate 2-21) and other causes of congenital hydronephrosis.
In older children and adults, undiagnosed congenital
or acquired UPJ obstructions may cause intermittent, severe flank pain following
increased fluid or diuretic intake. In addition, patients may experience
hematuria after mild trauma, the theory being that distention of the renal
pelvis causes mucosal vessels to become more friable. The diagnosis of UPJ
obstruction in this population is often first suggested on contrast enhanced CT or ultrasound. In adults and children
older than 3 months of age, diuretic renography using 99mTc-MAG3 nuclear tracer
should be performed once negative urine cultures have been obtained because it
permits precise measurement of renal drainage. If a crossing vessel is
suspected, duplex ultrasonography, CT angiography, or magnetic resonance angiography may help guide further
management.
TREATMENT
Surgical intervention for UPJ obstruction is indicated
for increased hydronephrosis on ultrasound (initially performed every 1 to 3
months), symptoms, stones, infection, deterioration of renal function, or
hypertension. Techniques for intervention are primarily minimally invasive, and
common ones are described in detail in Plate 10-16. A subset of neonates with
suspected UPJ obstruction have spontaneous resolution, and efforts to prospectively identify these patients are ongoing.
