Page 164 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

CHAPTER 7 Diagnostic Cytopathology in Clinical Oncology 143

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• Fig. 7.33 Fine-needle aspirate of a lymph node from a dog with T-cell • Fig. 7.34 Fine-needle aspirate of a mesenteric lymph node from a cat
lymphoma. Note that most of the cells are about two times the diameter of with large granular lymphoma. Note the prominent coarse eosinophilic
an erythrocyte and that nucleoli are indistinct in many cells. granules in the tumor cells.

polyclonal (nonneoplastic) populations of lymphocytes. When a
diagnosis of lymphoma is not obvious from the cytologic speci-
men, additional procedures should be performed, including sur-
gical biopsy with histologic evaluation, immunophenotyping,
assessment of clonality, or a combination of these (see Chapter
33, Sections A and B).
Lymphoma can be diagnosed cytologically when large or inter-
mediate lymphocytes comprise the majority of the nodal popu-
lation. Large and intermediate lymphocytes are defined as those
larger than or the same size as a neutrophil, respectively, or that
are greater than two times or one and a half to two times the
diameter of an erythrocyte, respectively. Cytologic types include
immunoblastic or centroblastic types, composed of large cells with
visible nucleoli and deeply basophilic cytoplasm (see Fig. 7.1A),
and lymphoblastic types composed of medium-sized cells often
having indistinct nucleoli (Fig. 7.33). Mitotic figures and tingible-
body macrophages, which are macrophages containing nuclear
debris from tumor cells, may be increased, but this is not a defin- • Fig. 7.35 Fine-needle aspirate of a histiocytoma. Note the discrete round
ing characteristic. Cytologic diagnosis of small-cell lymphoma is cells with a variable appearance. A few small lymphocytes also are pres-
more challenging, especially in tissues such as lymph node and ent.
spleen with a resident population of small lymphocytes or in tis-
sues such as liver and small intestine in which lymphocytic inflam-
mation is common. In these cases, additional diagnostic testing phenotype. In large granular lymphoma, the lymphocytes contain
is required for confirmation and may include one or more of the large, coarse, pink granules and are thought to be cytotoxic T or
following: histologic examination, preferably of a whole node or NK cells (Fig. 7.34).
full-thickness piece of intestine; immunophenotyping by immu-
nocytochemical/histochemical staining or flow cytometry; and Tumors of Histiocytic Origin
polymerase chain reaction for antigen receptor rearrangement
(PARR) to detect clonality (see Chapter 8). Because lymphocytes Cutaneous Histiocytoma
are fragile, free nuclei and cytoplasmic fragments frequently are Cutaneous histiocytoma originates from epidermal dendritic
observed in aspirates of lymphoma (see Fig. 7.1A); however, these or Langerhans cells and is typically found on the head or limbs
features can be found in samples from reactive lymphocytic popu- of young dogs. The cells are round and have pale blue to col-
lations and are not criteria for neoplasia. orless cytoplasm and a round, sometimes indented, central
Infrequently, neoplastic lymphocytes are highly pleomor- nucleus with fine to reticular chromatin and indistinct nucleoli
phic and exhibit moderate to marked anisocytosis, indented or (Fig. 7.35). Occasionally, the cytoplasm is more basophilic, and
deeply clefted nuclei, ameboid nuclei, multinuclearity, cytoplas- the nucleus more eccentrically located; in these cases, the cells
mic vacuoles, and aberrant phagocytic behavior. When present, may be mistaken for immature plasma cells and the mass called
a few, some, or most of the neoplastic lymphocytes in a given a plasmacytoma. Finding a few mitotic figures is common, but
tumor may have these features and may be mistaken for neoplastic binuclearity is infrequent. Often the tumor cells are highlighted
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histiocytes. Sometimes neoplastic lymphocytes contain fine or by a pale purple proteinaceous background. In mature lesions,
coarse pink cytoplasmic granules, suggestive of a T- or NK-cell there may be an infiltrate of small lymphocytes representing the