Robert L. Lebowitz, M.D. Children' s Hospital, Harvard Medical School Boston, Massachusetts

This 7-year-old girl had several months of intermittent left-sided pain. She finally had ultrasonography, which showed left UPJ obstruction (Figure 1). At surgery the obstruction was found to be due to a crossing renal vessel.

When a child has obstruction at the UP junction that was not detected prenatally, but presents with pain at an older age, approximately 50% are due to intrinsic stenosis and 50% to extrinsic obstruction from a crossing vessel. This latter cause of UP obstruction is usually intermittent, and imaging may show a normal kidney when the patient is not having pain and hydronephrosis only when the patient is having pain.

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