Female infant with pelvic mass

US of hematocolpos
Transverse (above) and sagittal (below) US of the pelvis shows a large cystic structure filled with complex fluid posterior to the bladder which is visible on the right side of the sagittal image. The uterus was identified and was unremarkable and therefore the cystic structure was felt to represent a distended vagina.

The diagnosis was hydrocolpos.