Ultrasound evaluation of urachal abscess in a young infant.

The urachus is a tubular structure extending from the dome of the bladder to the umbilicus. Normally, this allantoic and cloacal remnant obliterates into a fibrous band by late fetal development. Urachal abnormalities include a patent urachus, urachal cyst, umbilical urachal sinus, and a vesicourachal diverticulum. These abnormalities are most often asymptomatic and only come to clinical attention when associated with infection. A 2-month-old male infant presented to our tertiary pediatric hospital with several days of intermittent fevers and a focal region of swelling and erythema over the umbilicus. On physical examination, a tender mass was palpated in the umbilical region. Ultrasound revealed a long tubular structure coursing from the dome of the bladder anteriorly and superiorly to the subumbilical region. This tubular structure was fluid filled with internal echoes suggestive of infection with abscess formation. The urachal abscess was drained surgically, at which time a patent urachus was also excised. This case demonstrates the importance of having a thorough understanding of urachal anomalies when evaluating infants presenting with umbilical pathology.