Aphthous ulcers often appear as radiolucent ovals ("halos") with central punctate dots of barium These represent surface mucosal erosions (on the surface of hyperplastic lymphoid follicles) Aphthous ulcers are usually distinct from nearby smooth normal mucosa but they can be clustered and are sometimes found at the edge of more advanced disease

As Crohn disease progresses, individual aphthous ulcers may merge to form larger ulcerations