## **Core Concept**
Onion peeling of renal vessels refers to a characteristic histopathological finding seen in certain vascular conditions affecting the kidneys. This phenomenon is associated with the concentric laminations of collagen around the arterioles and small arteries, resembling the layers of an onion. It is a hallmark feature of a specific type of vasculopathy.

## **Why the Correct Answer is Right**
The correct answer, **C. Fibromuscular dysplasia**, is associated with onion peeling due to the characteristic histological changes seen in this condition. Fibromuscular dysplasia (FMD) is a non-atherosclerotic, non-inflammatory vascular disease that primarily affects medium- and large-sized arteries, most commonly the renal and internal carotid arteries. The histological features of FMD include medial fibroplasia, which is characterized by the presence of concentric laminations of collagen around the arterioles and small arteries, giving an "onion-skin" appearance.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because it does not correspond to a known condition associated with onion peeling of renal vessels.
- **Option B:** This option is incorrect as it does not accurately represent a condition characterized by onion peeling.
- **Option D:** This option is incorrect because it does not relate to the specific vascular condition known for onion peeling.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that fibromuscular dysplasia (FMD) often presents with renovascular hypertension and is more commonly found in young to middle-aged women. The condition can lead to renal artery stenosis, which may cause hypertension and potentially lead to ischemic nephropathy. Recognizing the association of FMD with onion peeling of renal vessels is crucial for diagnosing and managing patients with this condition.

## **Correct Answer:** . Fibromuscular dysplasia