**Core Concept**
The "Figure of 8" sign in a chest X-ray is indicative of a specific pathophysiological phenomenon involving the great vessels of the thorax. It is a radiological clue associated with a particular type of cardiac tamponade.

**Why the Correct Answer is Right**
The Figure of 8 sign is produced by the compression of the superior and inferior vena cava by a large pericardial effusion, causing the contrast material to form an inverted 8-shape on the chest X-ray. This occurs when there is a significant accumulation of fluid in the pericardial sac, which leads to an increase in intrapericardial pressure. As a result, the vena cavae are compressed, impeding venous return to the heart. This compression can also affect the right atrium and right ventricle, leading to cardiac tamponade.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not describe the pathophysiological mechanism associated with the Figure of 8 sign.
**Option B:** This option is incorrect because it refers to a different radiological sign, not the Figure of 8 sign.
**Option C:** This option is incorrect because it describes a different type of cardiac tamponade, not the one associated with the Figure of 8 sign.

**Clinical Pearl / High-Yield Fact**
The Figure of 8 sign is a classic radiological sign of cardiac tamponade, and its presence should prompt immediate investigation for pericardial effusion. It is essential to recognize this sign to avoid missing a potentially life-threatening condition.

**Correct Answer:** C. Cardiac tamponade.