**Core Concept**
Superior vena cava (SVC) syndrome is a clinical condition characterized by obstruction of the SVC, leading to impaired venous return from the upper body, resulting in congestion of the upper body veins and potentially life-threatening complications. This syndrome is often caused by external compression or obstruction of the SVC, most commonly by a mediastinal mass (such as a lymphoma or metastatic tumor).

**Why the Correct Answer is Right**
The correct answer is related to the pathophysiology of SVC syndrome, which involves the impaired venous return from the upper body. This is due to the obstruction of the SVC, which leads to increased pressure and congestion in the upper body veins, resulting in characteristic clinical features such as facial swelling, arm swelling, and shortness of breath. The key anatomical structure involved is the SVC, which is responsible for draining deoxygenated blood from the upper body to the right atrium.

**Why Each Wrong Option is Incorrect**
**Option A:** SVC syndrome can indeed cause facial swelling, as the obstruction of the SVC leads to increased pressure and congestion in the upper body veins, resulting in facial edema.
**Option B:** SVC syndrome can also cause shortness of breath, as the impaired venous return from the upper body can lead to decreased cardiac output and pulmonary congestion.
**Option C:** SVC syndrome typically presents with swelling of the upper body, including the face, neck, and arms, rather than the lower body.

**Clinical Pearl / High-Yield Fact**
One key feature of SVC syndrome is the presence of collateral venous circulation, which can be visualized on imaging studies as dilated veins in the chest or neck.

**Correct Answer:** C.