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Pitfalls or diagnostic errors in the interpretation of lymph node aspirates frequently have their origin in inadequate diagnostic material on the aspirate smears, inadequate triage of the aspirate during the initial on-site evaluation, lack of clinical data, cytologic, screening and interpretative errors or to pitfalls in the interpretation of ancillary methods used. [ABSTRACT FROM AUTHOR]

Infectious lymphadenitis can be caused by viral, bacterial, mycobacterial, fungal, and protozoal agents. Non-neoplastic noninfectious lymphadenitis can be associated with systemic processes such as collagen vascular diseases, Rosai–Dorfman disease, sarcoidosis, Castleman disease (CD), drugs, and foreign bodies. [ABSTRACT FROM AUTHOR]

Entities that clinically and/or cytologically mimic a lymphoproliferative disorder are described in this chapter. [ABSTRACT FROM AUTHOR]

Smears showing a monotonous (monomorphic) large cell pattern usually contain more than 50% large cells and frequently show more than 80% large cells. The remaining cells in such smears are usually small lymphocytes. Large lymphocytes measure more than 20 μm (or about 2.5–3 small lymphocyte diameters) in diameter in Romanovsky stained air-dried smears and appear slightly smaller in alcohol-fixed Papanicolaou or H&E-stained smears and cell block sections. The nuclei of large cells are by definition the same size or larger as the nuclei of histiocytes or endothelial cells. [ABSTRACT FROM AUTHOR]

The pleomorphic cell pattern is characterized by the presence of pleomorphic or anaplastic cells in a background of lymphoid cells. Pleomorphic cells present in lymph node aspirates measure 40–60 μm or more and show marked nuclear abnormalities, characterized by irregular nuclear shape, multinucleation and prominent nucleoli. [ABSTRACT FROM AUTHOR]

Small lymphocytes measure <12 μm in diameter, equivalent to the size of a histiocyte nucleus, a segmented neutrophil, or 1.5 to 2 times the size of an erythrocyte. The presence of a monotonous proliferation of small lymphoid cells in an enlarged round and rubbery lymph node is abnormal, and the cytologic findings should be correlated with the clinical scenario. Chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) and the resolving or quiescent phase of a reactive lymphoid hyperplasia are the main and most common entities considered in the differential diagnosis and must be distinguished from other neoplastic and non-neoplastic processes. The following is a list of entities showing the monotonous small-cell pattern. The cytologic description is based on Romanovsky-stained, air-dried smears. We use the WHO classification and nomenclature for lymphoid neoplasms unless otherwise is noted. [ABSTRACT FROM AUTHOR]

A small lymphocyte measures between 6 and 12 μm, and a large lymphocyte measures >20 μm. The intermediate-sized lymphocyte measurements are between those of small and large lymphocytes. [ABSTRACT FROM AUTHOR]

After exclusion of inadequate aspirates, lymph node FNAs can be broadly divided into those that are dominated by neutrophils, necrosis, and/or granulomas, smears showing cellular aggregates and smears with a dispersed single cell pattern. This broad classification can be made at the initial on-site assessment of the aspirate and will guide the differential diagnostic considerations, and the choice of ancillary studies as outlined in Algorithms 1, 2, and 3. The first algorithm is useful in the diagnosis of lymph node aspirates with a predominance of necrosis, neutrophils, or granulomas, where the most important ancillary tests are microbiologic cultures. The second algorithm is useful in the diagnosis of lymph node aspirates that show predominantly cellular aggregates, where the most important ancillary tests are immunohistochemical stains performed on cell block preparations. The third algorithm is useful in the diagnosis of the most commonly encountered lymph node aspirates, those where dispersed cells predominate; in these aspirates the most useful ancillary test is flow cytometry. [ABSTRACT FROM AUTHOR]

The following is a list of entities showing this pattern. The cytologic description is based on Romanovsky-stained, air-dried smears. We use the WHO classification and nomenclature for lymphoid neoplasms, unless otherwise is noted. [ABSTRACT FROM AUTHOR]

The questions that the pathologist tries to sequentially answer when evaluating fine needle aspiration biopsies of lymph nodes are Is the aspirate adequate? Is the nodule clinically considered to be a lymph node really a lymph node? Is the lymphadenopathy caused by a benign or malignant process? If it is a benign process, is it infectious? Can the infectious agent be identified? If it is malignant, is it a metastasis or lymphoma? If it is a metastasis what is the type (carcinoma, melanoma, sarcoma)? Where did it most likely originate? If it is lymphoma, is it non-Hodgkin or Hodgkin lymphoma? If it is non-Hodgkin lymphoma, is it of B or T cell type? What is the subtype? Is it possible to grade it? If it is Hodgkin lymphoma, is it possible to determine the subtype? [ABSTRACT FROM AUTHOR]

The goal of a lymph node FNA is essentially to distinguish benign from malignant lymphoid processes. Non-neoplastic disorders that can manifest in lymph nodes include those with specific diagnoses and nonspecific reactive hyperplasia (the most common diagnosis). The role of FNA is paramount in determining the etiology of non-neoplastic disorders so that appropriate management can be instituted. [ABSTRACT FROM AUTHOR]

The cytopathologic evaluation of a lymph node FNA requires knowledge of the patient΄s clinical history, physical examination, and available laboratory test results. [ABSTRACT FROM AUTHOR]

Ancillary tests are critically important tools in the assessment of lymph node aspirates, as they can help establish the etiology of infectious lymphadenopathies, determine the type and primary site of metastatic malignancies, diagnose and subclassify lymphomas, and exclude malignancy in reactive lymphadenopathies. In addition, ancillary tests can also be used to provide prognostic information in certain neoplasms and help predict treatment response. [ABSTRACT FROM AUTHOR]

Lymph nodes are some of the most common targets for fine needle aspiration (FNA) as persistent lymphadenopathy is a common finding. It is therefore not surprising that the first description of what we now call FNA biopsy was made in 1904 by two British marine officers, Captain E.D.W. Greig and Lieutenant A.C.H. Gray who reported their findings on the aspiration of lymph nodes in sleeping sickness. They could demonstrate motile trypanosomes in the ˵node juice″ obtained by aspirating from swollen neck lymph nodes of patients in Uganda with hypodermic needles. The following year, German physicians Fritz Schaudinn and Erich Hoffmann, were able to identify Treponema pallidum, which they had previously identified as the causative agent of syphilis, in inguinal lymph node aspirates by using dark-field microscopy. [ABSTRACT FROM AUTHOR]