**Core Concept**
The figure of 8 configuration on a chest x-ray is indicative of a specific type of cardiac abnormality involving the great vessels. This radiographic finding is associated with a congenital heart defect characterized by a malformation of the aortic arch and the ductus arteriosus.

**Why the Correct Answer is Right**
The figure of 8 configuration is typically seen in a condition known as **Coarctation of the Aorta**. In this condition, there is a narrowing of the aortic isthmus, which is the part of the aorta that passes through the thoracic cavity. This narrowing can lead to increased pressure in the aorta and a characteristic "figure of 8" or "3 sign" appearance on a chest x-ray due to the presence of the aortic knob and the left subclavian artery. The aortic knob represents the dilated portion of the aorta proximal to the narrowing, while the left subclavian artery represents the narrowed portion of the aorta. The ductus arteriosus, which is a normal fetal structure that connects the pulmonary artery to the aorta, often remains patent in individuals with coarctation of the aorta and can contribute to the figure of 8 configuration.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the figure of 8 configuration is not typically associated with aortic aneurysm, which would more likely present with a "3 sign" or a "double aortic knob" appearance.
* **Option B:** This option is incorrect because pulmonary arteriovenous malformation would not typically present with a figure of 8 configuration on a chest x-ray.
* **Option C:** This option is incorrect because tetralogy of Fallot would more likely present with a boot-shaped heart or a "3 sign" on a chest x-ray due to the presence of right ventricular hypertrophy and an overriding aorta.

**Clinical Pearl / High-Yield Fact**
The figure of 8 configuration on a chest x-ray is a classic sign of coarctation of the aorta, a condition that often presents with hypertension, decreased lower extremity pulses, and a characteristic "rib notching" on a chest x-ray due to the presence of collateral vessels.

**Correct Answer: C. Coarctation of the Aorta**