A 51-year-old man Sonu with a history of passing stones in urine, presents to the emergency room with excruciating flank pain and blood in the urine. Imaging of kidneys and ureters revealed stag-horn calculi occupying the right renal pelvis. This patient is likely to have which of the following underlying disorders?

**Core Concept**
Stag-horn calculi are a type of kidney stone that forms in the renal pelvis and calyces, often associated with chronic infection and inflammation. This condition is typically seen in patients with urinary tract infections and underlying genitourinary anomalies.

**Why the Correct Answer is Right**
The development of stag-horn calculi is closely linked to the presence of an underlying urinary tract anomaly, such as a ureterocele, ectopic ureter, or other congenital abnormalities. In this case, Sonu's history of passing stones and recurrent urinary tract infections suggests a possible underlying condition that predisposes him to stone formation. The correct answer is likely related to an anatomical or functional abnormality of the genitourinary system.

**Why Each Wrong Option is Incorrect**

* **Option A:** Hyperparathyroidism is a condition characterized by elevated levels of parathyroid hormone, leading to increased calcium levels in the blood, which can contribute to kidney stone formation. However, it is not directly associated with stag-horn calculi or the specific clinical presentation described.
* **Option B:** Analgesic nephropathy is a condition caused by long-term use of analgesics, leading to chronic kidney damage and stone formation. While it can cause kidney stones, it is not typically associated with stag-horn calculi or the specific clinical presentation described.
* **Option C:** Sickle cell disease is a genetic disorder that can cause hematuria and kidney damage, but it is not directly associated with stag-horn calculi or the specific clinical presentation described.

**Clinical Pearl / High-Yield Fact**
Stag-horn calculi are often associated with chronic infection and inflammation, which can be a clue to the underlying diagnosis. A high index of suspicion for underlying genitourinary anomalies is essential in patients presenting with this type of kidney stone.

**Correct Answer:** C.

✓ Correct Answer: B. Chronic Proteus infection