Duodenum ulcer The lesion most commonly affecting the duodenum is ulceration and it is now known that both antral infection with Helicobacter pylori and the presence of gastric acid are virtual prerequisites for itDuodenum Ulcer The lesion most commonly affecting the duodenum is ulceration, and it is now known that both antral infection with Helicobacter pylori and the presence of gastric acid are virtual prerequisites for it