**Core Concept**
The question is testing the understanding of potential complications following hemorrhoidectomy, a surgical procedure used to treat hemorrhoids. Hemorrhoidectomy can be associated with various postoperative complications, including infections, bleeding, and urinary retention.

**Why the Correct Answer is Right**
Urinary retention is a common complication following hemorrhoidectomy. This occurs due to the proximity of the anal sphincter to the urinary sphincter, which can lead to temporary impairment of urinary function post-surgery. The anal sphincter is innervated by the pudendal nerve, and the urinary sphincter is innervated by the pelvic nerve. The surgical procedure can cause inflammation and swelling in the perianal area, leading to urinary retention.

**Why Each Wrong Option is Incorrect**
* **Option A:** Hematoma is a potential complication of hemorrhoidectomy, but it is not as common as urinary retention. Hematoma occurs due to bleeding from the surgical site, which can be managed conservatively or surgically.
* **Option B:** Infection is a possible complication of hemorrhoidectomy, but it is less common than urinary retention. Infection can occur due to poor wound care or an underlying infection.
* **Option C:** Urinary incontinence is not a direct complication of hemorrhoidectomy. While urinary retention is a common issue, urinary incontinence is not typically associated with this procedure.

**Clinical Pearl / High-Yield Fact**
Urinary retention following hemorrhoidectomy is often temporary and resolves on its own within a few days. However, it is essential to monitor patients post-operatively for signs of urinary retention, such as difficulty voiding or a distended bladder.

**Correct Answer: A. Urinary retention.**