With a hiatal hernia, part of the upper stomach protrudes through the diaphragm into the chest. Some hiatal hernias are quite small. The larger ones usually lead to symptoms.
I'm not sure why you think your pain is from a hiatal hernia. Without knowing more about your pain, it is hard for me to judge whether the search for a hiatal hernia is warranted. I'd want to know the precise location of your pain, whether it is related to eating, if the pain has a burning or pressing quality, whether it spreads to other parts of your body and so on.
Typical symptoms of a hiatal hernia are:
- A burning sensation in the chest caused by acid reflux
- Discomfort under the breastbone when lying down after a large meal
- Food regurgitation (if the hernia is very large)
- Trouble swallowing (if the hernia twists upon itself within the chest)
The easiest and best way to diagnose a hiatal hernia is the good, old-fashioned upper GI series. (GI stands for gastrointestinal.) With this test, you swallow a liquid (called barium), which fills the esophagus and stomach. This makes it easy for the radiologist to see whether the upper part of the stomach sits within the chest cavity.
Fluoroscopy (an X-ray video) lets the radiologist check if stomach contents are backing up into the esophagus. This is called reflux.
Some doctors use endoscopy to identify hiatal hernias, but this is not nearly as simple a procedure as the GI series. Endoscopy uses a flexible tube with a small TV camera and a light on one end and an eyepiece on the other.
And you are correct about an ultrasound. It is not a good way to search for a hiatal hernia.
Please talk to your doctor about your pain. Your doctor will suggest the right test to get at the root of it.