Intermittent hydronephrosis as a cause of a false-negative pressure-flow study.

A case is reported of a negative pressure-flow study in a patient with intermittent hydronephrosis. This is the first known report of a properly performed pressure-flow study failing to diagnose obstruction due to the intermittent nature of the obstruction itself. This case also supports the concept that the ureteropelvic junction (UPJ) can be intrinsically normal in patients with intermittent hydronephrosis secondary to a crossing renal vessel. It also reaffirms the need to study these patients while they are symptomatic.