<prompt> A child presented with intermittent episodes of left sided flank pain. Ultrasonography reveals large hydronephrosis with dilated renal pelvis and coical thinning with a normal ureter. Kidney differential function was observed to be 19 which of the following is the best management -NephrectomyPyeloplastyExternal drainageEndopylostomy  <response>: Ans. is b i.e., Pyeloplasty Pelvi-ureteral junction PUJureteropelvic UPJ o UPJ obstruction is the most common obstructive lesion in childhood and is the most common cause of hydronephrosis found on prenatal and early postnatal ultrasonography. o It is most commonly caused by intrinsic stenosis of a segment of ureter which is usually localized to the region of pelviureteric junction. Other causes include ureteric folds extrinsic obstruction by crossing lower pole vessels. Presentation o Hydronephrois revealed by maternal USG Dilated renal pelvis but normal ureter. o Palpable renal mass in new borns or infants. o Abdominal flank or back pain typically exacerbated by drinking large volumes of liquid. o UTIHaematuria after minimal trauma. Epidemiology Left side more commonly involved than right Bilateral 10. Male more commonly involved than females M : F 2 : 1. Initial Diagnosis by Ultrasonography o Hydronephrosis with dilated renal pelvis. Ureter i f visualized is of normal caliber not dilated. Renal Differential function Nuclear Renography is used to determine Renal Differential function o A differential function of 40 is considered significant and often an indication for surgical management. Management Management depends on the differential renal function and AP diameter of PUJ : - 1Differential renal function 40 especially when AP diameter of PUJ 30 mm -- Conservative treatment. 2Differential renal function 40 especially when AP diameter of PUJ 30 MM Surgical treatment is indicated. Pyeloplasty is the surgical procedure of choice. Other surgical procedures used are external drainage nephrostomy, endopyelotomy and nephrectomy. o Differential function of 10 is often considered as an arbitary cut off for nephrectomy. 