Make the Diagnosis: February 2023

L.R., a 15-year-old female, presented to an emergency department with an inability to void for 13 hours, as well as lower abdominal pain. She denied significant past medical history, except anxiety. She denied trauma, sexual activity, menses, and drug use. She had no dysuria, and a urinalysis was negative. A Foley catheter was placed after a bedside bladder scan showed >600mL. She was taught to perform straight catheterization as needed and was discharged with a diagnosis of urinary retention.

Another episode of urinary retention occurred 2 weeks later, while on an airplane, which she attributed to anxiety from flying. She again had similar symptoms a few weeks later. The symptoms resolved each time with catheterization. She then was referred to our pediatric urology practice.

On physical examination, her abdomen was soft and non-tender and the bladder was not palpable. She had normal appearing external female genitalia, her lower back was normal on exam, and she ambulated with a normal gait. A post-void bladder scan demonstrated >400 mL.

A renal bladder ultrasound and an MRI of her lumbosacral spine were ordered. MRI of the spine was unremarkable for spinal pathology. Ultrasound demonstrated a normal appearing bladder that was compressed by a posterior 14 x 7.5 cm fluid-filled structure.

What is the most likely diagnosis?