Medical Mystery — The Answer

To the Editor: The medical mystery in the January 2 issue 1 involved a 55-year-old man with a history of recurrent flank pain that was due to renal stone disease. A metabolic evaluation led to the discovery of distal renal tubular acidosis, and an abdominal radiograph (Figure 1) showed numerous calcifications with a bizarre distribution on the left side. Retrograde pyelographic studies (Figure 2) showed that the patient also had a malformation of the urinary tract called “crossed renal ectopy,” with the right kidney in a transverse position in the left paramedian space at the level of the L4 vertebra.