الفهرس 
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Abstract
Ureteropelvic junction (UPJ) obstruction is defined as an obstruction of the flow of urine from the renal pelvis to the proximal ureter. The condition is frequently encountered by both adult and pediatric urologists. Congenital abnormalities may be observed in both adults and children, but adults may also present with UPJ obstruction secondary to surgery or other disorders that can cause inflammation of the upper urinary tract.
UPJ obstruction is the most common cause of neonatal and antenatal hydronephrosis, occurring in one per 1500 live births. Prior to the use of prenatal ultrasonography, most patients with UPJ obstruction presented with pain, hematuria, urosepsis, failure to thrive, or a palpable mass. With the enhanced ability and availability of prenatal ultrasonography, urologic abnormalities are being diagnosed earlier and more frequently. Fifty percent of patients diagnosed with antenatal hydronephrosis are eventually diagnosed with UPJ obstruction upon further workup.
The critical decision to be made in dealing with suspected UPJ obstruction is whether the radiologic findings correlate with the physiologic picture. In other words, severely dilated hydronephrotic kidneys may, in fact, be found to be draining well when studied appropriately. Defining the exact anatomy and function of these kidneys is crucial when evaluating and treating these patients.
The treatment strategies for UPJ obstruction have shifted significantly in the last several years. The gamut of current surgical treatments for UPJ obstruction includes the following:
• Laparoscopic pyeloplasty
• Open pyeloplasty
• Endopyelotomy
• Endopyeloplasty
Initially, most children are treated conservatively and monitored closely. Intervention is indicated in the event of significantly impaired renal drainage or poor renal growth.
The structural parameters obtained by US examination were able to predict whether the level of renal function or the quality of drainage was abnormal. In patients with APD <30 mm, the probability of decreased renal function or poor renal drainage is appreciable. In the management strategy of patients with prenatally detected PPUJO, nuclear medicine examinations may be postponed in such patients if follow-up US examinations show no obvious changes in these structural parameters. On the contrary, precise estimation of DRF is recommended in patients with APD >30 mm, major calyceal dilatation and/or parenchymal thinning.