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Findings: The left kidney demonstrates multiple large communicating cysts. The renal parenchyma is markedly thinned.

Diagnosis:: Hydronephrosis secondary to ureteropelvic junction obstruction.

Discussion: Obstruction of the urinary tract causing hydronephrosis most commonly occurs in the ureteropelvic junction. The cause of UPJ obstruction may be from an intrinsic abnormality such as abnormal musculature or fibrosis thought caused by extrinsic mechanical compression by either an aberrant vessel, a fibrous band, or inflammatory kinks. The majority of UPJ obstructions are on the left side, with an incidence of contralateral UPJ obstruction of approximately 20%.

Obtaining a VCUG is also necessary to exclude VUR as the cause for hydronephrosis. Grade IV or V VUR can simulate UPJ.

Young children with UPJ obstruction often have gross hematuria because the dilated renal pelvis is more prone to trauma. Ultrasound evaluation of the retrovesical region is mandatory to exclude a primary megaureter or ectopic ureterocele

References:
1. Blickman JG. Pediatric Radiology: The Requisites. 1994. Mosby.

2. Teele RL and Share JC. Ultrasonography of Infants and Children. 1991. WB Saunders.

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