UPJ obstruction is another common congenital abnormality which under some circumstances can lead to significant renal scarring and chronic kidney diseases. About 50% of ultrasounds during pregnancy which detect antenatal hydronephrosis turn out to have UPJ obstruction.
UPJ obstruction is defined as any blockage of urine flow from the renal pelvis to the proximal ureter. The subsequent back pressure within the pelvis can lead to dilatation of the renal collecting system and, if left untreated, can lead to permanent renal damage.
Children with UPJ obstruction typically present with pain, hematuria, recurrent UTIs, failure to thrive, and palpable mass--however, with the increased use of ultrasound, it is not uncommon now to make the diagnosis with routine ultrasound.
UPJ obstruction is a relatively non-specific diagnosis: an anatomical obstruction here can occur due to several reasons: scarring of ureteral valves due to recurrent UTIs, ureteral hypoplasia or abnormal insertion of the ureter into the renal pelvis which might occur as a result of congenital problems of kidney development, and fibrosis following surgery for stone disease are all possible etiologies for UPJ obstruction.