## Core Concept
Ureterosigmoidostomy is a surgical procedure that involves implanting the ureters into the sigmoid colon. This procedure is typically performed in cases of bladder exstrophy or when the bladder is not functional. The main goal is to allow urine to drain from the kidneys into the bowel, thereby bypassing the bladder.

## Why the Correct Answer is Right
The correct answer, **D. Metabolic acidosis**, is a well-known complication of ureterosigmoidostomy. When urine is diverted into the sigmoid colon, the intestinal mucosa absorbs urinary constituents, including ammonia, chloride, and other ions. This can lead to a decrease in bicarbonate levels and an increase in chloride levels, resulting in hyperchloremic metabolic acidosis.

## Why Each Wrong Option is Incorrect
- **Option A:** While certain electrolyte imbalances can occur, **hypokalemia** is not the most directly associated complication with ureterosigmoidostomy compared to metabolic acidosis.
- **Option B:** **Hematuria** can occur due to surgical complications but is not a long-term complication specifically associated with the metabolic or functional changes due to ureterosigmoidostomy.
- **Option C:** **Urinary tract infection** is a risk with many urinary diversion surgeries, but it's not as uniquely characteristic of the complications arising from the specific pathophysiological changes of ureterosigmoidostomy as metabolic acidosis.

## Clinical Pearl / High-Yield Fact
A key clinical pearl is that patients undergoing ureterosigmoidostomy require long-term monitoring of their renal function and electrolytes to manage the risk of **metabolic acidosis**. This may involve bicarbonate supplements or other treatments to manage electrolyte imbalances.

## Correct Answer Line
**Correct Answer: D. Metabolic acidosis**