**Core Concept**
The patient's symptoms suggest a ureteral obstruction, which is likely caused by a stone. The composition of the stone is crucial in determining its likelihood of causing such an obstruction.

**Why the Correct Answer is Right**
Uric acid stones are more likely to cause ureteral obstruction due to their irregular shape and size. Uric acid stones tend to form in acidic urine and are more common in patients with leukemia or other conditions that lead to high levels of uric acid. The irregular shape of uric acid stones can cause them to become lodged in the ureter, leading to dilation of the renal pelvis and the upper third of the ureter. This is in contrast to other types of stones, such as calcium oxalate stones, which are more likely to pass through the urinary tract without causing obstruction.

**Why Each Wrong Option is Incorrect**
**Option A:** Cystine stones are more likely to cause recurrent kidney stones, but they are less likely to cause ureteral obstruction due to their smooth, rounded shape.
**Option B:** Calcium oxalate stones are a common type of kidney stone, but they are less likely to cause ureteral obstruction due to their smooth, rounded shape and the fact that they are more likely to pass through the urinary tract without causing problems.
**Option D:** Struvite stones are often associated with urinary tract infections and are more likely to cause kidney stones in women, but they are less likely to cause ureteral obstruction due to their smooth, rounded shape.

**Clinical Pearl / High-Yield Fact**
Uric acid stones are more likely to cause ureteral obstruction due to their irregular shape and size, and are often seen in patients with leukemia or other conditions that lead to high levels of uric acid.

**Correct Answer:**. Uric acid