## **Core Concept**
A double aortic arch is a rare congenital anomaly of the aortic arch. It results from an abnormal persistence of embryonic aortic arches. Normally, the fourth aortic arch develops into the aortic arch on the left side, while the right fourth arch contributes to the proximal part of the right subclavian artery.

## **Why the Correct Answer is Right**
The correct answer, **D. Right and left fourth aortic arches**, is right because a double aortic arch occurs when both the right and left fourth aortic arches persist, instead of the usual regression of the right fourth arch. This persistence leads to the formation of two aortic arches that encircle the trachea and esophagus.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because the first and second aortic arches typically regress early in embryonic development and do not contribute to the formation of the aortic arch anomalies like a double aortic arch.
- **Option B:** This option is incorrect because, although the fifth aortic arch is sometimes considered to contribute to the development of the aortic sac, its persistence does not lead to a double aortic arch.
- **Option C:** This option is incorrect because the sixth aortic arch gives rise to the pulmonary arteries and the ductus arteriosus (which usually closes to form the ligamentum arteriosum), not to the aortic arches.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that a double aortic arch can cause symptoms due to compression of the trachea and esophagus, such as difficulty breathing (dyspnea) and difficulty swallowing (dysphagia). Imaging studies like a barium swallow or CT angiography are diagnostic.

## **Correct Answer: D. Right and left fourth aortic arches**