Toddler with a fever

US of acute pyelonephritis / acute lobar nephronia
Sagittal US of the right kidney (above) shows an ill-defined hypoechoic mass in the right upper pole that is obscuring the normal outline of the echogenic fat in the renal hilum. The mass was hypoperfused on color and power doppler US. AP image from a voiding cystourethrogram (below) shows bilateral vesicoureteral reflux, grade II on the left and grade III on the right

The diagnosis was acute pyelonephritis in a patient with vesicoureteral reflux.