15.1 Introduction

Lymph node samples generally exfoliate extremely well for cytological evaluation so examination of lymph node aspirates can often provide an expedient and fairly simple way to elucidate a causative pathological process for lymphadenopathy or lymph node enlargement. Cytology can frequently provide a diagnosis (i.e., lymphoma, infectious agents, metastatic neoplasia, etc.) or it may point to various disease processes (i.e., lymphadenitis, hyperplasia, etc.).

Lymphadenopathy can be localized or generalized and primary or secondary in nature. Differentials for lymphadenopathy include hyperplasia or reactive lymphadenopathy, lymphadenitis (neutrophilic, macrophagic, eosinophilic, mixed), lymphoma, and metastatic neoplasia. An algorithmic approach to lymph node aspirate evaluation and interpretation is presented in Figure 15.1.

15.2 Sample Collection and Preparation

When one is aspirating peripheral lymph nodes, the site of aspiration is prepared as for an injection. Suitable fine needle aspirate can be collected using a 21–25 gauge needle attached to a 5 mL or larger syringe or holding the hub of the needle without a syringe (nonaspiration technique). Small (5 mL) syringes can be used when aspirating lymph nodes because lymph node cells exfoliate more easily than those of many other body tissues and the cells are often fragile as well.

For collection, the lymph node is isolated between the collector’s thumb and forefinger. Remember that lymphoid tissue can be fairly heterogeneous, and sampling many areas of the node is ideal [1]. Holding either the syringe with needle attached or the hub of the needle directly, insert the needle into the node and apply gentle suction (if syringe attached). Then redirect the needle inside the node without removing completely from the tissue. If using a syringe method (active suctioning technique), the plunger should be mostly pulled out before the tip of the needle exits the node. Forceful suction often lyzes the cells and may cause blood contamination or hemodilution. After collection, place a 5 mL syringe on the hub (if using nonaspiration technique) and gently expel onto the slide at a close distance. Smear the sample like a blood film or place a glider slide on top of the sample and gently pull perpendicularly to the sample. Heat fixing is not necessary and may rupture cells; air drying is the ideal method of “fixing” the cells to the slide prior to staining. If multiple lymph nodes are enlarged, collection from all affected nodes may increase the chances of a diagnosis.

15.3 Lymph Node Cell Types

Several cell types will be seen in normal lymph node aspirates: small lymphocytes, intermediate sized lymphocytes, large lymphocytes (lymphoblasts), plasma cells, and Mott cells. Inflammatory cells such as neutrophils, macrophages, eosinophils, and mast cells can be identified when the lymph node is inflamed or draining an area of inflammation. Primary and metastatic cancer cells can also populate a lymph node.

15.3.1 Small Lymphocytes

Small lymphocytes are <9 μm in diameter (smaller than a neutrophil, equal to or slightly larger than an erythrocyte) with round to oval nuclei, dense chromatin, and a scant amount of pale to mildly basophilic cytoplasm.