**Question:** A 52 year old lady with a vesicovaginal fistula after abdominal hysterectomy is not responding to conservative management. Most useful and important next investigation is:

A. Abdominal MRI
B. Pelvic ultrasound
C. Urodynamic study (UDS)
D. Transvaginal ultrasound

**Core Concept:**

A vesicovaginal fistula (VVF) is a type of urological complication that occurs following surgery, particularly after abdominal hysterectomy. Conservative management typically involves bed rest, bladder catheterization, and antibiotics. In cases where conservative management fails, a detailed evaluation is necessary to guide further management.

**Why the Correct Answer is Right:**

Choice C, urodynamic study (UDS), is the most appropriate investigation in this context. UDS evaluates the function of the lower urinary tract, including bladder capacity, emptying, and compliance. Given the history of VVF, UDS can help assess the severity of the fistula and determine if it is obstructive or non-obstructive. UDS may reveal impaired bladder function, which could confirm the diagnosis and guide management options such as reconstructive surgery.

**Why Each Wrong Option is Incorrect:**

A) Abdominal MRI: While MRI can provide detailed anatomy, it is not specific to the lower urinary tract and does not assess the function of the bladder. MRI is less sensitive than UDS in detecting VVF.

B) Pelvic ultrasound: Ultrasound is a valuable tool in assessing bladder size, shape, and anatomy. However, it does not evaluate bladder function like UDS and is not as accurate in detecting VVF.

D) Transvaginal ultrasound: Transvaginal ultrasound could assess the size and position of the fistula, but it does not evaluate bladder function or guide management options. UDS is a more comprehensive investigation for assessing the lower urinary tract and guiding management.

**Clinical Pearl:**

Understanding the correct investigation for VVF management is crucial, as UDS can help diagnose the condition and guide management options. Inaccurate investigations may lead to misdiagnosis and suboptimal treatment.