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Lymph node cytology: sampling and interpretation (Proceedings)


Lymph nodes are most often aspirated only if they're enlarged, but they may also be sampled to determine if there's metastasis of a tumor. Peripheral lymph nodes are one of the easier tissues to obtain a fine needle aspirate from as this can be done relatively painlessly. In many cases, a diagnosis can be made very quickly and relatively inexpensively. However, interpretation of lymph node cytology is somewhat complicated by the fact that there is overlap in the types of cells seen in the differing conditions that can cause lymph node enlargement. Sometimes, the fine needle aspirate findings could be explained by either of several processes, and histologic review of a lymph node is needed to examine the architecture of the node for a definitive diagnosis.

Obtaining the sample

Lymph node aspiration and slide preparation should be performed gently as lymphocytes, especially the less mature lymphocytes, are fragile and easily rupture. It's not at all uncommon to view lymph node cytology preparations that contain 100% ruptured cells, with naked nuclei and sometimes with streaming chromatin.

Aspiration is most often performed with a 22 gauge needle and a 6 or 12 ml syringe. While the lymph node is stabilized with one hand, the other hand performs either a suction-type aspiration or the non-suction, "tattooing" type of aspiration which may prevent the problem of too much peripheral blood contamination of the sample.

The needle is then removed from the syringe, air is drawn into the syringe, the needle is re-attached, and the sample is gently blown out onto a glass slides. Another slide is used to very gently spread out the cells without rupturing them. Slides should be air-dried and may be submitted to a laboratory or stained with an in-house stain.

Slides should be first viewed on low magnification to determine whether there are adequate cell numbers without too much peripheral blood and whether there are enough intact cells that are spread out well enough for evaluation. When good areas are identified, further microscopic examination is carried out at high power or oil immersion.

Normal lymph nodes

Aspirates from normal lymph nodes will have a heterogenous lymphocyte population. Small, mature lymphocytes will make up about 85-95% of the cells observed. These are roughly between the size of an erythrocytes and a neutrophil and they have a round nucleus that almost fills the whole cell, with only a small rim of blue cytoplasm present. Medium-sized lymphocytes are typically about 5-10% of the population. These are somewhat larger than the small, mature lymphocyte. Large lymphoblasts, that contain a distinct nucleolus typically comprise 5% or less of the cells.

Normal lymph nodes may also contain a small number of neutrophils, plasma cells, macrophages and occasional eosinophils and mast cells. Lymph node aspirates often have numerous lymphoglandular bodies, which are small, irregular but often round, granular fragments of lymphocyte cytoplasm that are characteristic of lymphoid tissue. The presence of these lymphoglandular bodies is often helpful in determining cytologically whether it is actually lymphoid tissue that has been aspirated.

Reactive or hyperplastic lymph nodes

Lymphoid reactivity or hyperplasia occurs when lymph nodes are antigenically stimulated. These nodes will also have a heterogenous lymphoid population with small, mature lymphocytes also predominating. However, the percentage of medium-sized to large lymphocytes is increased and may comprise up to 50% of the lymphoid cells, though they are usually less than 30-35%. There is also commonly an increase in the number of plasma cells. Increased numbers of mitotic figures may be seen. Reactive lymph nodes may also contain macrophages, neutrophils eosinophils and mast cells.