Benign lymphoid hyperplasia (pseudolymphoma) of soft tissue.

Benign lymphoid hyperplasia (pseudolymphoma) has been reported in the skin, lungs, orbit, and gastrointestinal tract, but only rarely in soft tissues. These lesions mimic lymphoma both clinically and histologically. We describe a case of a pseudolymphoma of the deep soft tissues of the lower extremity. The lesion was composed of nonencapsulated lymphoid tissue with involvement of adjacent fat and connective tissues and multiple variably sized well-polarized germinal centers. Immunohistochemical staining, flow cytometry, chromogenic in situ hybridization for κ/λ light-chain restriction, and polymerase chain reaction for T- and B-cell gene rearrangements all revealed a polyclonal population of T and B cells, consistent with a benign reactive process. So far as we know, pseudolymphoma of the deep soft tissues has been described only once previously in the medical literature.