MALS is considered a diagnosis of exclusion — in part because there is no good test for it. The compression of the artery can be seen on CT and M.R.I., especially while the patient is exhaling. And an ultrasound can show the abnormality in blood flow from this compression. However, we know from autopsy studies that there are people with this anatomy who have no pain. So anatomy alone is not enough.

Other possible causes of pain must be ruled out to be certain that the pain is caused by MALS. And given the 70 percent success rate, some surgeons argue that even that is not enough.

Those who accept that nerve damage is an important component of the disorder sometimes use a different test to identify those who might benefit from surgery. They inject a numbing medicine directly into the celiac ganglion. If that completely relieves the pain, then these surgeons believe that the likelihood that the surgery will succeed is greater so long as the damaged nerves are removed during the surgery.

How the Diagnosis Was Made

This 43-year-old woman had an extensive work-up for the nausea and abdominal pain that frequently came on after eating. She was seen by several gastroenterologists.

Doctors at the Mayo Clinic in Rochester, Minn., finally gave her the diagnosis of gastroparesis, in which the passage of food through the gut is abnormally slow, causing nausea and obstruction. The cause of this slowed movement was not clear, but most of the time the cause of gastroparesis is never discovered. Sometimes the condition resolves on its own. Often, however, it does not.

There are no great treatments for gastroparesis. Patients with this disorder are told to eat frequent small meals and take medicines to stop nausea. If that doesn’t work, they can be put on a liquid diet or prescribed medications that make the intestines move faster. If none of that works, patients are fed through a tube that delivers nutrients directly to the small intestines.

Unsuccessful Treatments

The patient tried all of these treatments. Nothing really worked — not even the tube directly into her intestines. So, the woman ate small bits of food and drank supplements. She took a medicine to relieve the nausea. All that was helpful. But nothing seemed to help the pain that usually started an hour or two after she ate.