Okay, let's tackle this question. The patient is a 12-year-old with secondary hypertension, headaches, blurred vision, and retinal findings. The key here is the age—secondary hypertension is more common in younger patients. The renal arteriography shows segmental stenoses with multiple ridges.

First, I need to think about causes of secondary hypertension in children. Common ones include renal artery stenosis, which can be due to fibromuscular dysplasia or congenital abnormalities. Fibromuscular dysplasia (FMD) is a condition where there's abnormal development of the arterial wall layers, leading to stenosis. It's more common in women and often affects the renal arteries. The description of "segmental stenoses forming multiple ridges" sounds like the "string of beads" appearance typical of FMD.

Coarctation of the aorta usually presents with different findings, like upper extremity hypertension and lower extremity hypotension. Renal parenchymal disease would show signs of chronic kidney disease, not the arterial stenosis seen here. Neuroblastoma is a tumor that can cause hypertension but usually in younger children and might present with other symptoms like abdominal mass. Chronic glomerulonephritis would have different renal findings, not arterial stenosis.

The funduscopic findings suggest hypertensive retinopathy, which is consistent with chronic hypertension. The renal arteriography findings are crucial here. So the most likely diagnosis is fibromuscular dysplasia.

**Core Concept**
The question assesses the differential diagnosis of secondary hypertension in a pediatric patient, focusing on **fibromuscular dysplasia (FMD)** as a cause of renal artery stenosis. Key diagnostic clues include **segmental stenoses with ridges** on arteriography and **hypertensive retinopathy** (microaneurysms, cotton wool spots).

**Why the Correct Answer is Right**
Fibromuscular dysplasia is a non-atherosclerotic, non-inflammatory vascular disorder causing **segmental stenoses** in medium-sized arteries, notably the renal arteries. The **"string of beads"** appearance on imaging, due to alternating stenotic and dilated segments, is pathognomonic. In this case, the **young female** (FMD is 8–10x more common in women) with **hypertension, retinopathy**, and **renal artery stenosis** points to FMD as the most likely cause.

**Why Each Wrong Option is Incorrect**
**Option A:** Coarctation of the aorta typically presents with **upper extremity hypertension** and **lower extremity hypotension**, not isolated renal artery stenosis.
**Option B:** Renal parenchymal disease (e.g., chronic glomerulonephritis) causes **parenchymal scarring** and **reduced kidney size**, not arterial stenosis.
**Option C:** Neuroblastoma induces hypertension via **catecholamine excess**, often with **abdominal mass** and **paraspinal calcifications**, not vascular stenosis.

**Clinical Pearl / High-Yield Fact**
**"String of beads" on renal arteriography** is diagnostic of **fibromuscular dysplasia**

✓ Correct Answer: B. Fibromuscular dysplasia