**Core Concept**
The question is testing the understanding of a characteristic radiological feature in intravenous pyelography (IVP) that is associated with a specific kidney condition. The "spider leg" appearance is a descriptive term for a particular pattern of calcification or radiopacity seen on imaging studies.

**Why the Correct Answer is Right**
The correct answer is associated with Medullary Sponge Kidney (MSK), a benign congenital disorder characterized by cystic dilation of the collecting ducts and tubules in the medulla of the kidney. The "spider leg" appearance is due to the presence of calcifications within these cystic structures, which give a characteristic radiopacity on IVP. This is caused by the abnormal concentration of calcium salts within the cystic fluid.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the "spider leg" appearance is not typically associated with renal cell carcinoma, which usually presents with a solid mass or a cystic lesion with mural nodules.
* **Option B:** This option is incorrect because the "spider leg" appearance is not characteristic of simple cysts, which are usually round or oval and may have a thin wall.
* **Option C:** This option is incorrect because the "spider leg" appearance is not associated with polycystic kidney disease, which typically presents with multiple cysts of varying sizes throughout the kidney.

**Clinical Pearl / High-Yield Fact**
Medullary Sponge Kidney (MSK) is a benign condition that can be associated with an increased risk of nephrolithiasis and recurrent urinary tract infections.

**Correct Answer:** C.