A male presented to the emergency depament with renal calculi. Extracorporeal shock wave lithotripsy was suggested after a detailed examination. But the procedure failed. Which of the following type of stone is MOST resistant to lithotripsy?
**Core Concept**
Extracorporeal shock wave lithotripsy (ESWL) is a non-invasive treatment for kidney stones that uses shock waves to break down stones into smaller fragments that can then be easily passed out of the body. The effectiveness of ESWL depends on the composition and hardness of the stone.
**Why the Correct Answer is Right**
Stones composed of cystine are the most resistant to lithotripsy. Cystine stones are formed from the amino acid cystine and are relatively hard and dense, making them difficult to break down with shock waves. This is because cystine stones have a higher Mohs hardness, which is a measure of a mineral's scratch resistance. The higher Mohs hardness of cystine stones means they require more energy to break down, making them less responsive to ESWL.
**Why Each Wrong Option is Incorrect**
**Option A:** Uric acid stones are relatively soft and can be effectively treated with ESWL. They have a lower Mohs hardness compared to cystine stones, making them more susceptible to shock wave therapy.
**Option B:** Calcium oxalate stones are the most common type of kidney stone and can be effectively treated with ESWL. They have a moderate hardness and can be broken down with shock waves.
**Option C:** Struvite stones are composed of magnesium ammonium phosphate and are relatively soft. They can be effectively treated with ESWL and are often associated with urinary tract infections.
**Clinical Pearl / High-Yield Fact**
It's essential to identify the composition of kidney stones before deciding on a treatment plan, as the effectiveness of ESWL depends on the type of stone. A detailed examination, including imaging studies, can help determine the composition and hardness of the stone, allowing for more informed treatment decisions.
**Correct Answer:** C. Cystine stones are the most resistant to lithotripsy.