Hyperchloremic metabolic acidosis as a clue to recto-urethral fistula in an infant with anal atresia.

An infant with high anal atresia and transverse colostomy, in whom initial radiologic evaluation of the urinary tract had been normal, developed hyperchloremic metabolic acidosis at 24 days of age. Gastroenteritis and renal tubular acidosis as possible causes for this metabolic disturbance were excluded, which prompted a repeat investigation of the possibility of a communication between the urinary tract and the rectum. A recto-urethral fistula was demonstrated by urethrography. Analysis of the fluid obtained from the left colon as compared to urine in the bladder and voided urine demonstrated that electrolyte exchange was taking place in the colon, resulting in hyperchloremic hypokalemic acidosis. Treatment with oral sodium bicarbonate and daily lavage of the left colon resulted in normalization of the acid-base status and catch-up growth of the baby. Hyperchloremic acidosis associated with anal atresia and recto-urinary communication appears to be uncommon. However, early diagnosis and treatment of the metabolic derangement are of importance as it may determine the infant's overall prognosis.