Massive Hydronephrosis from Ureteropelvic Junction Obstruction Masquerading as a Paratubal Cyst in an 11-Year-Old Girl

Background: The differential diagnosis of a cystic pelvic mass in an adolescent girl is broad, and includes gastrointestinal, urologic, and gynecologic conditions. Case: A premenarchal 11-year-old girl presented with abdominal pain. On transabdominal ultrasonography, abutting the lateral side of the left ovary was a large mass with an appearance compatible with a large paratubal cyst measuring 16.7×11.9cm. On exploratory laparotomy, the patient's uterus, tubes and ovaries were normal and a massively dilated and displaced left kidney due to an ureteropelvic junction obstruction was ultimately diagnosed. Summary and Conclusion: A cystic pelvic mass in an adolescent girl may not always be of ovarian or müllerian origin. Urinary tract obstruction is often silent; an incidental finding of hydronephrosis on ultrasonography may be the first clue of the possibility of ureteropelvic junction obstruction as the underlying diagnosis. It is always best to know which organ system is involved prior to surgery, so that the correct surgical team is present and the correct surgical approach is utilized.