A number of urologic and non-urologic disease processes produce flank pain as the initial symptom. Pain originating from the urinary tract is frequently felt in the costovertebral angle just lateral to the sacrospinalis muscle and beneath the twelfth rib posteriorly. It may radiate anteriorly to the epigastric area. The pain is usually caused by distention of the renal capsule; the severity of the pain is determined by the acuteness of the distention. The patient with a slowly developing obstructive process (e.g., staghorn calculus,) may present with minimal flank pain; the pain associated with acute ureteral obstruction due to a small stone may be quite severe.

The right kidney may be palpable in children and thin adults. The left kidney is difficult to palpate, as it lies higher within the retroperitoneum than the right kidney. Examination is best performed bimanually, with one hand behind the patient in the costovertebral angle and the other anteriorly just below the costal margin. With inspiration, the kidney may be felt as it moves downward. In neonates, examination is performed by palpating the flank between the thumb anteriorly and the remaining fingers posteriorly in the costovertebral angle. Both kidneys can be outlined reliably in this fashion.

The normal central echo pattern within the mid-portion or hilum of the kidney is hyperechoic due to the fat and vascular structures. In the hydronephrotic kidney, the collecting system becomes distended with urine (fluid), which can easily be detected by ultrasound. Ultrasound imaging is very useful in detecting the presence of distention of the intrarenal collecting system to help establish a diagnosis of hydronephrosis.

The causes can be divided into congenital or acquired. Congenital ureteropelvic junction obstruction is an entity that is often now found prenatally. In as much as prenatal ultrasonography is routinely) performed it will present as one of the differential diagnoses of prenatal or postnatal hydronephrosis or abdominal mass. Acquired ureteropelvic obstruction may be the result of ureteral manipulation, urinary calculi, or retroperitoneal disease

It is believed that there is a disorganization of the renal pelvis-upper ureteral junction during the recanalization process in utero. This disorganization of the smooth muscle leads to a lack of motility or perhaps collagen deposition, and thus there is a lack of peristalsis, with narrowing at this site.

Pyeloplasty is usually performed in the neonate. There are several types of pyeloplasty procedures, the most common being the dismembered pyeloplasty.

It may be that vesicoureteral reflux may cause a secondary ureteropelvic junction obstruction. 'This is most commonly found in children.

Diuretic renal nuclide scanning is usually performed either to make the diagnosis of ureteropelvic junction obstruction or to confirm the diagnosis.

Boys more than girls by a 5:2 ratio

It is more common on the left than the right, again with a 5:2 ratio. Bilateral obstruction occurs in 15% of cases.

This diagnosis usually is made by intravenous pyelography, renal ultrasonography, or diuretic renal scanning.

1. A crossing renal vessel at the ureteropelvic junction
2. Previous passage of a urinary calculus
3. Manipulation of the urinary system either with a ureteroscope or nephroscope.
4. A retroperineal process impinging on the ureter externally (e.g., inflammation or enlarged lymph nodes)
5. Neurologic malignancies such as gynecologic cancers or colonic cancers can causing obstruction either through enlarged lymph nodes or actual compression of that area by the tumor burden
6. Abdominal and aortic aneurysm leakage may produce an inflammatory response in the retroperitoneal area near the upper ureteropelvic junction, causing ureteropelvic junction obstruction as well etroperineal area near the upper ureteropelvic junction, causing uretopelvic junction obstruction as well
7. Infection, either hematogenous or ascending

Most commonly, a dismembered pyeloplasty is performed in the adult. Other types of pyeloplasties also may be performed. Minimally invasive techniques such as endopyelotomy, a procedure performed via a percutaneous opening through the skin to the kidney, allowing access to the ureteropelvic junction area from below, or through the ureter in a retrograde fashion (a retrograde ureteral endopyelotomy) can be performed as well.