Today's Veterinary Practice

MAY-JUN 2014

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| LymPh Node CyToLogy Today's Veterinary Practice May/June 2014 20 tvpjournal.com Categories of Neoplasms After evaluating lymphocyte cell size, the next step in success- ful cytologic evaluation is to determine whether any other types of cells that represent metastasis to the node are pres- ent. If present, these cells can be categorized as mesenchymal, epithelial, or round/discrete. In addition, uncommon catego- ries, such as neuroendocrine or histiocytic, may be relevant. Criteria of Malignancy Finding cells where they do not belong, such as the presence of epithelial cells in a lymph node, is a sign of neoplasia. Malignant cells are bizarre, and may not immediately resemble their cell of origin. While atypia can be seen in diseased tissue, the presence of cytologic changes outlined in Table 2, combined with lack of inflammation, is a strong indication of malignancy: • When inflammation is prominent, it can be difficult to commit to a diagnosis of cancer. • However, very bizarre cells support a diagnosis of malig- nancy even if some inflammation is present. Fibroblasts can be mislead- ing—tumors can elicit a scirrhous response in which reactive fibro- blasts are present among an atyp- ical population, potentially creat- ing the impression of a mesenchy- mal neoplasm, when the primary malignant process has a different origin, such as carcinoma or mast cell tumor. Mitotic figures can be seen in both normal and reactive lymph nodes as part of the normal renew- al of lymphocytes. Mitotic figures that are concerning include those: • Accompanied by cells that display other cytologic criteria of malignancy • With bizarre chromatin patterns, including polar asym- metry, distraction of chromatin to more than 2 poles, and chromatin lagging and bridging. 3 In some cases, a biopsy is needed to confirm the pres- ence of a neoplasm, and it is often needed to confirm type of cancer. DIAgNOSES BASED ON LYMPH NODE CYTOLOgY Lymphoma The most common finding on fine-needle aspiration and cytology of lymph nodes that are enlarged due to lympho- ma is a monomorphic population of lymphoblasts (Figure 2). Characteristics of lymphoma identified by lymph node cytology are listed in Table 3. Comparison to RBCs or neutrophils can help with size determination. It is tempting to suspect lymphoma when a large population of lymphoblasts is seen; however, use cau- tion and spend some time evaluating all the cells—there may be more small lymphocytes present than appreciated initially. If an enlarged lymph node is reactive, there should be a population of plasma cells and inflammatory cells, and more variety to the lymphoid population (Figure 3). Biopsy may be needed to confirm the diagnosis if only lymphoid cells—most of similar size (and intermediate or small)—are seen; however, lymphoma should be strongly suspected. This is especially true when multiple peripheral TaBLe 3. Lymphoma Characteristics Identified by Lymph Node Cytology • all (or almost all) cells in the aspirate will be lymphoblasts characterized by: » high nuclear:cytoplasmic ratio » Loose chromatin pattern » discrete cell pattern: abundant cellular yield, round cells and nuclei, and no obvious clustering (although number/close proximity of cells may initially resemble clustering) • anisocytosis and anisokaryosis may be present • The sample often lacks any indication of inflammation • monomorphic cells (roughly the same size and shape) that are intermediate or small in size should arouse suspi- cion of lymphoma—a normal or reactive lymph node contains lymphocytes and lymphoblasts of many different sizes, though smaller in proportion to mature lymphocytes TaBLe 1. Lymphocyte Size & appearance TYPE SIZE APPEARANCE Lymphocytes: Small Mature Same size or smaller than neutrophil or RBC • dense chromatin in nucleus (more deeply basophilic appearance) • high nuclear:cytoplasmic ratio (very little cytoplasm) Lymphocytes: Intermediate Similar to, or only slightly larger than, neutrophil • Interpret in light of total cell population (Table 3) Lymphoblasts: Large Immature Larger than neutrophil or RBC • Looser chromatin in nucleus (lighter blue appearance) • Lower nuclear:cytoplasmic ratio (more cytoplasm) TaBLe 2. malignancy Criteria • mitotic figures, especially if bizarre, with hap- hazardly arranged, instead of orderly, chromatin • multiple nuclei, especially if an odd number • multiple nucleoli, especially if they vary in size • anisocytosis • anisokaryosis TVP_2014-0506_Lymph Node Cytology.indd 20 5/24/2014 10:39:00 AM

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