Genitourinary Mass in a Four-Week-Old Infant

A 4-week-old female, former 34-week twin, presented to the pediatric emergency department with a new genitourinary mass noted 3 days before presentation (Fig). The infant was voiding and stooling well without a palpable abdominal mass or posterior midline abnormality. External genitalia were normal except for a mass extending 1cm beyond the introitus; the tissue had the appearance of vaginal mucosa and, although it was easily reducible, immediately returned to a prolapsed state.