Staghorn calculus is made of –
**Core Concept**
A staghorn calculus is a type of kidney stone that fills the renal pelvis and extends into the calyces, resembling the antlers of an elk or stag. This condition is characterized by the formation of large, branching stones that can cause obstructive uropathy and recurrent urinary tract infections.
**Why the Correct Answer is Right**
Staghorn calculi are typically composed of magnesium ammonium phosphate (struvite), which forms in alkaline urine. This type of stone is often associated with urinary tract infections caused by urease-producing bacteria, such as Proteus. The urease enzyme produced by these bacteria raises the urine pH, creating an environment conducive to struvite stone formation. The stones can grow rapidly and fill the renal pelvis and calyces, leading to obstruction and potential kidney damage.
**Why Each Wrong Option is Incorrect**
* **Option A:** Calcium oxalate stones are the most common type of kidney stone, but they do not typically form large, staghorn-like structures.
* **Option B:** Uric acid stones can form in acidic urine, which is the opposite environment of struvite stones.
* **Option C:** Cystine stones are rare and usually occur in patients with cystinuria, a genetic disorder that affects cystine transport in the kidneys.
**Clinical Pearl / High-Yield Fact**
Staghorn calculi are often associated with urinary tract infections and require prompt treatment to prevent kidney damage. Patients with recurrent urinary tract infections or obstructive uropathy should undergo imaging studies to rule out the presence of staghorn calculi.
**Correct Answer: D. Struvite**