## Core Concept
The aortic opening in the diaphragm, also known as the aortic hiatus, is one of the three major openings in the diaphragm that allows for the passage of structures between the thoracic and abdominal cavities. It is located at the level of T12 vertebra.

## Why the Correct Answer is Right
The aortic hiatus typically allows for the passage of the **aorta**, **azygos vein**, and **thoracic duct**. These structures pass through the aortic opening in the diaphragm. The aorta, specifically the descending aorta, passes through this opening, along with the azygos vein, which is a tributary of the superior vena cava, and the thoracic duct, which is the main lymphatic duct of the body.

## Why Each Wrong Option is Incorrect
- **Option A:** The **aorta** indeed passes through the aortic hiatus, making this option incorrect as an "EXCEPT" choice.
- **Option B:** The **thoracic duct** also passes through the aortic hiatus, which is crucial for lymphatic drainage.
- **Option D:** The **azygos vein** passes through the aortic hiatus as well.

## Why Option C is Correct
- **Option C:** The **esophagus** does not pass through the aortic hiatus; instead, it passes through the **esophageal hiatus**, which is another opening in the diaphragm.

## Clinical Pearl / High-Yield Fact
A key point to remember is that there are three major openings in the diaphragm: the caval opening (for the inferior vena cava), the esophageal hiatus (for the esophagus and vagus nerves), and the aortic hiatus (for the aorta, azygos vein, and thoracic duct). Understanding these is crucial for anatomy and for clinical procedures.

## Correct Answer: C. esophagus