Question

A $44$-year-old woman, G $3$ P $3$, comes to the office due to a $1$-week history of continuous, involuntary watery vaginal discharge. Four weeks ago, she underwent a complicated total abdominal hysterectomy for severe endometriosis and large uterine leiomyomas. Her postoperative course was notable for right-sided back pain and a fever of $38.3^\circ\text{C}$ ($101.0^\circ\text{F}$) on postoperative day $14$. She was evaluated at an urgent care clinic where urinalysis was inconclusive, and she was advised to follow up. Her pain and fever spontaneously resolved a week later, which precisely coincided with the onset of the constant vaginal leakage. The patient notes that despite the continuous leakage, she still feels the urge to urinate and voids normally in the toilet every $3$ to $4$ hours. Vital signs today are within normal limits. On pelvic examination, the vaginal cuff appears well-healed with no erythema, but there is pooling of clear fluid in the vaginal vault. A tampon is placed in the vagina, and a dilute methylene blue solution is instilled directly into the bladder via a urethral catheter. Thirty minutes later, the patient is asked to walk around the clinic. The tampon is then removed and shows no blue staining. Which of the following is the most appropriate next step in evaluation?