Focal lymphoid hyperplasia of the terminal ileum presenting mantle zone hyperplasia with clear cytoplasm. A report of three cases.

We report three unusual cases of focal lymphoid hyperplasia of the ileocecal valve. The gross specimens showed thickening of the ileocecal valve. Low power magnification showed a dense lymphoid infiltrate in the mucosa and submucosa. This condition was characterized by reactive lymphoid follicles with large reactive germinal centers surrounded by a pale cuff of mantle zone lymphocytes presenting a marginal zone distribution pattern. These cells had intermediate- to- medium-sized round or slightly indented nuclei and a broad rim of clear cytoplasm. However, immunohistochemical study demonstrated that both the mantle zone lymphocytes and the pale cuff of the lymphoid cells were CD20+, sIgM+, sIgD+, CD5-, CD10-, CD23-, CD43-, Bcl-2+, Bcl-6-, CyclinD1-. The polytypic nature of these cells was demonstrated by immunohistochemistry and polymerase chain reaction. This unusual mantle cell hyperplasia with clear cytoplasm associated with focal lymphoid hyperplasia in middle-aged and elderly patients should be differentiated from the extranodal marginal zone B-cell lymphoma of mucosa associated lymphoid tissue type or mantle cell lymphoma showing a marginal zone distribution pattern. To avoid overdiagnosis and overtreatment, it is suggested that immunophenotypic and genotypic studies might be required, and careful attention should be paid to the morphologic examination.