. Percentage of gall stones which are radio opaque –
**Core Concept**
Radio-opaque gallstones are those that contain enough calcium to be visible on plain radiographs. These stones typically form in the setting of chronic biliary tract disease and are more common in patients with a history of gallstones.
**Why the Correct Answer is Right**
The correct answer is D, 10%. Radio-opaque gallstones are composed of calcium salts, such as calcium carbonate or calcium phosphate, which make them visible on X-rays. These stones are relatively rare, accounting for only about 10% of all gallstones. They are more common in patients with a history of chronic biliary tract disease, such as gallstones, and are often associated with conditions like primary biliary cirrhosis.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is too high. While some sources may estimate that up to 20% of gallstones are radio-opaque, this figure is not universally accepted.
**Option B:** This option is incorrect because it is too low. While radio-opaque gallstones are relatively rare, estimating their prevalence at less than 5% is not supported by most studies.
**Clinical Pearl / High-Yield Fact**
Radio-opaque gallstones are often associated with conditions like primary biliary cirrhosis, and their presence can be an important clue in the diagnosis of these conditions. Remember that the presence of a radio-opaque gallstone on a plain radiograph is a strong indication of chronic biliary tract disease.
**Correct Answer: D. 10%**