The biopsy of an enlarged lymph node is a common diagnostic procedure. As part of a prime line of defense, lymph nodes react against a wide variety of pathogens affecting the human body. Additionally, they may participate in various autoimmune diseases or are involved by circulating tumor metastases. Finally, lymph nodes in various locations may be the site of localized or systemic lymphomas. Because of this wide range of pathologic possibilities and their relative easy accessibility, lymph nodes very often are biopsied whether by needle aspiration or by surgical removal. Not infrequently, the biopsied lymphoid tissues pose challenging diagnostic problems. To solve them requires the careful observation and recognition of histologic alterations combined with the selective use of the many technologies available in the modern laboratory.
In the present issue of Pathology Case Review, in keeping with the format of this publication, we examine a number of pathologic conditions starting from real cases of lymph node biopsies submitted for pathologic diagnosis. For this issue, I was fortunate to enroll several of the leading experts in the vast fields of hematopathology to assist us in navigating through a maze of difficult differential diagnoses. Professor Konrad Müller-Hermelink, director of the prestigious Institute of Pathology of the University of Würzburg and follower of the famous Kiel school of lymphoid pathology, is internationally recognized for his work on the genetics and classification of thymomas and lymphomas. In the present context he gives us well-defined guidelines for one of the most common and difficult differential diagnosis in the pathology of lymphoid tissues, the distinction between follicular hyperplasia and follicular lymphoma. The second article, because it explores diffuse interfollicular hyperplasias of lymph nodes, is to some extent a counterpart of the first. These quite common histologic patterns induced by a variety of viruses, drugs, and other unidentified factors are particularly difficult to interpret. The author, Dr. Susan Abbondanzo, is chair of the department of Hematopathology at the Armed Forces Institute of Pathology, which evidently provides a most abundant source of material that she has previously used well in multiple published studies. Following that is an explanation of necrotizing lesions of lymph nodes by Drs. Kikuchi and Ohshima of the Fukuoka University in Japan, starting from a case of histiocytic-necrotizing lymphadenitis, or Kikuchi disease, which was originally described in 1972 by our present author. Next is an article by H. L. Ioachim on lymphoid hyperplasias and lymphomas of salivary glands. Because salivary glands, more than any other organ, are associated intimately with lymph nodes, the pathologies of the 2 tissues are often combined, raising questions about their pathogenesis, diagnosis, and treatment. Benign lymphoid hyperplasias may accompany viral infections, particularly HIV or autoimmune diseases, whereas lymphomas, more often of the marginal zone cell type or metastatic carcinomas, may occur in these locations. Their correct differential diagnosis is of essential importance for the determination of treatment. There has been recent progress in understanding the biology of small lymphocytic lymphoma/chronic lymphocytic leukemia by recognizing the prognostic implications of the mutational status of immunoglobulin variable heavy chain genes as reflected in the expression of CD38 and ZAP-70 proteins. Identifying in this way indolent versus aggressive forms of small lymphocytic lymphoma/chronic lymphocytic leukemia opens the door to more specific treatments. This interesting subject is discussed by Dr. Jeffrey Medeiros, head of the Hematopathology department of the M.D. Anderson Cancer Center, and his associates. An unusually prolific author, Dr. Medeiros in his writings approaches with equal expertise the morphologic, molecular, and genetic aspects of his topics. The last and certainly not the least is the article of Drs. Al-Quran and Braylan on the use of flow cytometry in the characterization of lymphoid neoplasia. Although routinely used in the diagnosis of leukemias, flow cytometry in general has not been used as equally in the processing of solid tumors. Yet, flow cytometry has proven to be an invaluable diagnostic tool in the hematopathology laboratory and in my own as well as others’ experience, indispensable in the identification of clonal proliferations and of the distinctive immunophenotypes of small cell lymphomas. I could think of no one better qualified than Raul Braylan, from the University of Florida in Gainesville, well-recognized master of the method, to present the use of flow cytometry and the interpretation of its results in the analysis of various types of lymphoma.
In my (albeit heavily biased) opinion, the articles of the present issue of Pathology Case Review have in common important topics in hematopathology that are expertly treated and succinctly written. Just as important, they comprise updated, comprehensive reference lists and clear, contributory illustrations. I can only hope that the readers will agree.