**Core Concept**
The patient in question is experiencing urinary incontinence following a hysterectomy, which is a surgical procedure involving the removal of the uterus. This situation may involve an injury to the bladder or the urethra, leading to urinary leakage.

**Why the Correct Answer is Right**
The most likely cause of urinary leakage in this scenario is **vesicovaginal fistula**. A vesicovaginal fistula is an abnormal connection between the bladder and the vagina, allowing urine to flow through the fistula and leak out of the vagina. This condition can occur due to surgical injury during the hysterectomy, such as a tear in the bladder or the vaginal wall. The fistula can be caused by a direct injury to the bladder or by a surgical procedure that compromises the integrity of the bladder or vaginal wall.

**Why Each Wrong Option is Incorrect**
* **Option A:** Urethral injury is less likely to cause urinary leakage in the form of a fistula, as the urethra is more likely to be repaired or closed during surgery.
* **Option B:** Ovarian vein thrombosis is a possible complication of surgery but is not directly related to urinary leakage.
* **Option C:** Hematoma formation can cause urinary retention but is not a direct cause of urinary leakage.

**Clinical Pearl / High-Yield Fact**
A vesicovaginal fistula can be diagnosed by performing a cystoscopy, which involves inserting a flexible tube with a camera into the bladder to visualize the fistula. This diagnosis can be confirmed by injecting dye into the bladder, which will leak out through the fistula and into the vagina.

**Correct Answer: C.**