**Core Concept**
Radio-opaque stones are gallstones that contain calcium and are visible on plain abdominal radiographs. They are often associated with gallbladder cancer and are a contraindication for medical management of gallstones. Medical management typically involves dissolution therapy with ursodiol, which is less effective for radio-opaque stones.

**Why the Correct Answer is Right**
Radio-opaque stones are less responsive to medical dissolution therapy due to their high calcium content. These stones are often larger and more likely to be associated with gallbladder cancer, making surgical intervention a safer and more effective option. Unlike radiolucent stones, which can be dissolved with ursodiol, radio-opaque stones require more aggressive treatment, such as laparoscopic cholecystectomy.

**Why Each Wrong Option is Incorrect**
**Option B:** Radiolucent stones, typically composed of cholesterol, are ideal candidates for medical management with ursodiol. They are more responsive to dissolution therapy and are a common indication for medical management of gallstones.
**Option C:** A normal functioning gallbladder is not a contraindication for medical management of gallstones. In fact, medical management is often preferred in patients with a functioning gallbladder, as it avoids the risks associated with surgical intervention.
**Option D:** Small stones can be managed medically, especially if they are radiolucent. In fact, medical management is often more effective for small stones, as they are more likely to dissolve with ursodiol.

**Clinical Pearl / High-Yield Fact**
When considering medical management of gallstones, it is essential to identify the type of stone and assess the patient's overall clinical status. Radiolucent stones are ideal candidates for dissolution therapy, while radio-opaque stones require more aggressive treatment. A high index of suspicion for gallbladder cancer should be maintained in patients with radio-opaque stones.

**Correct Answer:**
✓ Correct Answer: A. Radio-opaque stones.