**Core Concept**
Xanthogranulomatous pyelonephritis (XGP) is a rare, chronic inflammatory disease of the kidney, characterized by the presence of xanthoma cells and granulomatous inflammation. It is often associated with long-standing urinary tract obstruction and infection.

**Why the Correct Answer is Right**
XGP is typically seen in adults, especially women, and is rare in children. The condition is usually related to chronic urinary tract obstruction and infection, which can lead to the formation of xanthoma cells and granulomatous inflammation. The exact pathogenesis of XGP is not well understood, but it is believed to involve a combination of factors, including chronic bacterial infection, urinary stasis, and tissue damage.

**Why Each Wrong Option is Incorrect**
**Option A:**
This statement may be true, as XGP can be associated with long-standing urinary tract obstruction, which can occur due to various causes, including congenital anomalies or acquired conditions.

**Option B:**
This statement may be true, as XGP is characterized by the presence of xanthoma cells and granulomatous inflammation, which can lead to the destruction of renal tissue and the formation of a mass.

**Option C:**
This statement is false, as XGP is rare in children and typically presents in adults. The exact reason for the rarity of XGP in children is not well understood, but it may be related to the fact that children are less likely to have chronic urinary tract obstruction and infection.

**Clinical Pearl / High-Yield Fact**
A key clinical feature of XGP is the presence of a palpable mass in the flank, which can be mistaken for a renal tumor. However, XGP is usually associated with systemic symptoms such as fever, weight loss, and malaise, which are not typically seen in renal tumors.

**Correct Answer: C.**