**Core Concept**
Small vessel vasculitis refers to inflammation of the small blood vessels, including capillaries, venules, arterioles, and small arteries. This condition is characterized by damage to the blood vessel walls, leading to leakage of fluid and immune cells into the surrounding tissue.

**Why the Correct Answer is Right**
The correct answer is Polyarteritis nodosa (PAN). PAN is a type of small vessel vasculitis that affects the medium and small-sized arteries. It is characterized by the presence of granulomas and necrotizing inflammation in the affected vessels. The pathophysiology of PAN involves the deposition of immune complexes and the activation of complement, leading to the release of pro-inflammatory cytokines and the recruitment of immune cells to the site of inflammation.

**Why Each Wrong Option is Incorrect**
**Option A:** Giant Cell Arteritis (GCA) is a large vessel vasculitis that affects the aorta and its major branches. It is characterized by the presence of giant cells and granulomatous inflammation in the affected vessels.

**Option B:** Wegener's Granulomatosis (now known as Granulomatosis with Polyangiitis) is a type of small vessel vasculitis that affects the respiratory tract and kidneys. It is characterized by the presence of granulomas and necrotizing inflammation in the affected vessels.

**Option C:** Henoch-Schönlein Purpura (HSP) is a type of small vessel vasculitis that affects the skin, kidneys, and gastrointestinal tract. It is characterized by the deposition of IgA immune complexes in the affected vessels.

**Clinical Pearl / High-Yield Fact**
Small vessel vasculitis can present with a wide range of symptoms, including skin rash, joint pain, kidney disease, and gastrointestinal symptoms. It is essential to consider the presence of small vessel vasculitis in patients with unexplained symptoms or those with a history of autoimmune disorders.

**Correct Answer:** C. Henoch-Schönlein Purpura (HSP)