**Core Concept**
Onion skin thickening of an arteriolar wall is a characteristic histopathological feature seen in conditions characterized by vascular inflammation and damage, particularly in the context of systemic vasculitis.

**Why the Correct Answer is Right**
This thickening is due to concentric layers of fibrinoid necrosis and inflammatory cell infiltration, leading to the appearance of an onion skin-like pattern. It is a hallmark of conditions such as polyarteritis nodosa (PAN), where damaged arterioles exhibit this distinctive appearance. The involvement of the arteriolar wall is a key feature of systemic vasculitis, which can lead to various complications, including ischemia and organ dysfunction.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not relevant to the question, as onion skin thickening is not typically associated with conditions like this.
**Option B:** This option is incorrect because onion skin thickening is not primarily a feature of hypertension, although it can be seen in some cases of severe hypertension.

**Clinical Pearl / High-Yield Fact**
Onion skin thickening is a classic histopathological feature of systemic vasculitis, particularly in conditions like polyarteritis nodosa. It is essential to recognize this pattern in biopsy specimens to guide further management and treatment.

**Correct Answer: C.**