Richter syndrome with follicular colonization of chronic lymphocytic leukemia/small lymphocytic lymphoma cells mimicking follicular lymphoma.

Follicular colonization is occasionally observed in marginal zone lymphoma. In rare cases, it has also been associated with mantle cell lymphoma. Chronic lymphocytic leukemia typically involves nodal or extranodal tissues as diffuse proliferation by complete effacement of the normal architecture. The involvement of chronic lymphocytic leukemia may be less frequently limited to the interfollicular areas. Here, we report a case of Richter syndrome of the small intestine that was initially diagnosed as follicular lymphoma of the gastrointestinal tract because of a partial follicular growth pattern in addition to a mainly diffuse proliferation pattern. The follicular pattern mimicking follicular lymphoma was shown to be composed of reactive follicles with follicular colonization of the original chronic lymphocytic leukemia cells. As the prognoses of Richter syndrome and follicular lymphoma of gastrointestinal tract are quite different, clinicians must carefully diagnose these conditions to avoid a misdiagnosis.