MSFinals-1622

A 14-year-old girl has had apparently normal appearance of secondary sexual characteristics, except that she has not menstruated. A pelvic examination reveals a mobile mass in her left labium major and a shallow, blind-ending vagina without a cervix, but otherwise normal female external genitalia. Ultrasound reveals no cervix, uterus or ovaries. Karyotype analysis reveals 46,XY.
What is the most likely diagnosis?