UPJ obstruction is the most common obstructive lesion in childhood. Prior to the use of prenatal ultrasound, most patients with UPJ obstruction presented with pain, hematuria, urosepsis, failure to thrive, or a palpable mass. Approximately 60% of cases occur on the left side, and the male-to-female ratio is 2:1. In 10% of cases, UPJ obstruction is bilateral. In kidneys with UPJ obstruction, renal function may be significantly impaired as a result of pressure atrophy.[1,2,3]
Congenital UPJ obstruction most often results from intrinsic disease. A common defect in congenital UPJ obstruction is an aperistaltic segment of the ureter. In these cases, histopathologic studies have revealed that the spiral musculature normally present has been replaced by abnormal longitudinal muscle bundles or fibrous tissue. This results in failure to develop a normal peristaltic wave for the propagation of urine from the renal pelvis to the ureter. Further investigations into the etiology of UPJ obstruction have shown decreased interstitial cells of Cajal at the UPJ in children.
In addition, the cytokine produced in the urothelium is also theorized to exacerbate UPJ obstruction. A less common intrinsic cause of congenital UPJ obstruction is true ureteral stricture. True congenital ureteral strictures are most often found at the UPJ, although they may be situated at sites anywhere along the ureter. Abnormalities of the ureteral musculature have been implicated because of the deposition of too much collagen at the site of the stricture. Intrinsic obstruction at the UPJ may also result from kinks or valves produced by infoldings of the ureteral mucosa and musculature. In these cases, the obstruction may be, essentially, at the level of the proximal ureter. Grossly, this can manifest as external bands or adhesions that appear to cause the obstruction. In most cases, however, these bands or adhesions are likely to be a secondary phenomenon associated with intrinsic obstruction; therefore, operative pyeloplasty would generally be the most effective procedure.[1,2,3,4]
The presence of these kinks, valves, bands, or adhesions may also produce angulation of the ureter at the lower margin of the renal pelvis in such a manner that, as the pelvis dilates anteriorly and inferiorly, the ureteral insertion is carried further proximally. In these cases, the most dependent portion of the pelvis is inadequately drained, and the apparent "high insertion" of the ureteral ostium is actually a secondary phenomenon. In at least some cases, however, the high insertion itself is likely the primary obstructing lesion because this phenomenon is frequently found in cases of renal ectopia or fusion anomalies. As such, a high insertion can have implications in the ensuing surgical management.
An accessory artery and/or vein to the lower pole of the kidney also may cause extrinsic obstruction. Although these lower-pole arteries have often been referred to as aberrant, this variant is found in 20% of people. In some patients, these lower-pole vessels cross the ureter posteriorly and truly have an aberrant course. Although some have speculated that the crossing vessel plays a role in the pathogenesis of UPJ obstruction, the associated vessel is unlikely to cause the primary obstruction on its own. In fact, the true etiology is an intrinsic lesion at the UPJ or proximal ureter that causes dilatation and ballooning of the renal pelvis over the polar or aberrant vessel.[3,4,5]
UPJ obstruction may also result from acquired lesions. In children, vesicoureteral reflux can lead to upper tract dilatation, with subsequent elongation, tortuosity, and kinking of the ureter. Other acquired causes of obstruction at the UPJ include benign tumors (such as fibroepithelial polyps), urothelial malignancy, stone disease, and postinflammatory or postoperative scarring or ischemia.[4,5]
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Cite this: Arun Phophalia, Madhu Phophalia. Fever, Pain, and Failure to Thrive in a 9-Year-Old Boy - Medscape - Dec 16, 2015.