Radio opaque stone is
**Core Concept**
Radio-opaque stones are formed when the normal composition of urinary stones is altered, typically due to an increase in the concentration of calcium salts, magnesium salts, or uric acid. These stones appear radiopaque on plain abdominal radiographs due to their high density.
**Why the Correct Answer is Right**
The formation of radio-opaque stones involves the precipitation of calcium salts, such as calcium oxalate or calcium phosphate, from the urine. This occurs when the concentration of calcium in the urine exceeds the solubility limit, leading to the formation of crystalline structures that can aggregate to form stones. The presence of magnesium salts, such as magnesium ammonium phosphate, can also contribute to the formation of radio-opaque stones.
**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because radio-opaque stones are not typically formed from cystine, which is an amino acid that can form stones, but they are usually radiolucent.
**Option B:** Incorrect because xanthine stones are rare and usually radiolucent, not radio-opaque.
**Option C:** Incorrect because uric acid stones are radiolucent, not radio-opaque.
**Clinical Pearl / High-Yield Fact**
Radio-opaque stones are often associated with hypercalcemia, which can be caused by conditions such as hyperparathyroidism or vitamin D toxicity.
**Correct Answer: D. Radio-opaque stones are typically formed from calcium salts, such as calcium oxalate or calcium phosphate, which appear radiopaque on plain abdominal radiographs.**