Infectious mononucleosis. Appendiceal lymphoid tissue involvement parallels characteristic lymph node changes.

Appendectomy with mesenteric lymph node biopsy was performed in an 18-year-old man because of acute abdominal pain that was subsequently attributed to infectious mononucleosis. The appendix demonstrated intense hyperplasia of the lymphoid tissue with marked expansion of the interfollicular lamina propria by a mixed diffuse proliferation of immunoblasts including Reed-Sternberg-like forms, together with large and small lymphoid cells. Germinal centers were reactive but inconspicuous. This pattern was distinguishable from malignant lymphoma and, like the characteristic lymph node changes, may be strongly predictive of infectious mononucleosis. Involvement of gut-associated lymphoid tissue may contribute importantly to abdominal symptomatology in this infection.