**Core Concept**
The question tests the understanding of the anatomical relationship between the ureters and surrounding structures, specifically the **obturator nerve**. This nerve is responsible for innervating the medial thigh and perineum.

**Why the Correct Answer is Right**
Pain radiating to the medial side of the thigh and perineum suggests irritation of the **obturator nerve**, which can occur when a renal stone lodges in the **distal ureter**, specifically near the pelvic brim where the ureter crosses over the **obturator internus muscle** and near the **obturator nerve**.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because it doesn't specifically relate to the pathway of the ureter near the obturator nerve.
**Option B:** Incorrect as the stone's location doesn't typically cause referred pain to the medial thigh.
**Option C:** Incorrect because the location doesn't usually involve the obturator nerve.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that the **obturator nerve** can be irritated by a stone in the distal ureter, causing pain to radiate to the medial thigh and perineum, a classic presentation in males.

**Correct Answer:** D. Distal ureter