Lymphoma of the terminal ileum
Mucosal nodularity in the small bowel has a limited differential.
If the nodules are small (1-3 mm) and discrete, nodular lymphoid hyperplasia should be considered.
If larger and more confluent, then lymphoma should be considered. Because of the predilection of both lymphoma and Crohn disease for the small bowel given the concentration of lymphoid tissue there, it is prudent to consider both diagnoses. The two have some overlapping features, but usually can be differentiated. Crohn disease usually has a different appearance, including ulceronodular changes and irregular fold thickening (as opposed to the smooth fold thickening of lymphoma). Also, although limited for differentiation between the two, Crohn disease tends to lead to strictures, whereas small bowel lymphoma may lead to a aneurysmally dilated small bowel.
In this case, the prior diagnosis of lymphoma and the activity on PET-CT leave the diagnosis in little doubt.