Reactive immunoblastic proliferations.

The purpose of this report is to emphasize the criteria for recognizing the benign diseases such as viral lymphadenitis, necrotizing lymphadenitis, cat scratch disease, etc, in which a proliferation of immunoblasts is evident, and to discuss the criteria for distinguishing these diseases from neoplastic and atypical proliferations of immunoblasts. In this report, we use the term "immunoblasts" for transformed lymphoid cells of medium and large size. These cells may or may not have abundant quantities of cytoplasm, which may or may not be deeply staining. These immunoblasts may be of the B or the T cell type, and they may be mononuclear, binucleated, or multinucleated. The distinction between benign and malignant immunoblastic proliferations is not made on the basis of cytologic features, but by assessment of all histologic parameters including the architectural pattern, the cellular composition of the proliferation, the relationship of different cell types to one another, and the cytologic features of the immunoblasts.