Page 158 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

CHAPTER 7 Diagnostic Cytopathology in Clinical Oncology 137

Thyroid Carcinomas
Thyroid carcinomas in dogs are highly vascularized, and aspirates
may yield abundant blood as well as some hemosiderophages. In
VetBooks.ir addition to displaying general features of endocrine tissue, cells
from thyroid tumors may contain blue-black cytoplasmic gran-
ules (see Fig. 7.17, inset), believed to represent tyrosine granules,
and amorphous pink material that may represent colloid. In the
absence of these features, thyroid tumors cannot be differentiated
cytologically from C-cell tumors and parathyroid tumors that
occur in the same location. Most thyroid tumors in dogs are non-
functional carcinomas, whereas in cats thyroidal masses or nodules
are functional adenomas or adenomatous hyperplasia. Ectopic
thyroid tissue may undergo transformation and be found in unex-
pected locations, such as the thoracic inlet and mediastinum.
Parathyroid Tumors
Parathyroid tumors are typically adenomas but are often func-
tional and result in hypercalcemia through the systemic actions • Fig. 7.19 Fine-needle aspirate of a myxosarcoma in a dog. Note the indi-
of parathyroid hormone. Parathyroid tumors have the typical vidualized spindle cells.
features of endocrine tissue. Occasionally, eosinophilic spiculate
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inclusions are found in the cytoplasm.
Chemodectomas or Paragangliomas
Chemodectomas or paragangliomas are neuroendocrine tumors of
chemoreceptor cells found in the carotid or aortic bodies located in
the submandibular region and at the base of the heart, respectively.
In some tumors, the cells have numerous small pink granules. Oth-
erwise, they do not have cytologic features that distinguish them
from other endocrine tumors, such as ectopic thyroid tumors.

Adrenal Cortical and Medullary Tumors
Adrenal cortical and medullary tumors are cytologically similar
and have a typical neuroendocrine appearance. Adrenal cortical
tumors of the zona glomerulosa and fasciculata often contain few-
to-many discrete clear vacuoles. Pleomorphism is minimal and
differentiation between adrenal adenoma and adenocarcinoma
is not always possible cytologically. Pheochromocytomas of the
adrenal medulla lack distinct cytoplasmic vacuoles but may con- • Fig. 7.20 Imprint of granulation tissue composed of pleomorphic fibro-
tain pink granules and will stain positively with silver stains and blasts.
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express synaptophysin and chromogranin A.
Insulinomas (Fig. 7.19); however, in cases in which cellularity is high or when
Insulinomas, or beta-cell tumors, have typical neuroendocrine scraping and imprint methods are used to prepare slides, cells may
features without additional defining characteristics except for the be found in dense noncohesive aggregates that are disorganized.
clinical presentation of hypoglycemia. Insulinomas may metasta- Cell shape is typically oval, spindle, or stellate, and the tumors are
size to liver, regional lymph nodes, mesentery, and omentum, and often grouped according to the most common shape. Cytoplasmic
these metastatic sites may be the first place the tumor is recognized. margins are characteristically indistinct, and nuclei are generally
round, oval, or elongate. Some mesenchymal tumors lack further
Carcinoids of Lung, Liver, Intestine, and Colon distinguishing features, and knowledge of the location and other
Carcinoids of lung, liver, intestine, and colon are rare neuroen- clinical information is necessary to formulate a list of differen-
docrine tumors. They must be distinguished from other neuroen- tial diagnoses in anticipation of the definitive diagnosis based on
docrine tumors that have metastasized based on history, clinical histologic and immunohistochemical staining. Even then, some
presentation, presence of other primary tumors, and histologic of these tumors may be reported as soft tissue sarcomas without
examination. identifying the specific lineage of origin.
Reactive or hyperplastic mesenchymal cells that accompany
Tumors of Mesenchymal Tissues inflammatory and neoplastic lesions present a diagnostic dilemma
because these cells may have criteria of malignancy (Fig. 7.20).
Tumors derived from mesenchymal or connective tissues can be When a mass is composed of heterogeneous cell populations,
diverse in their cytologic appearances, but they have some com- caution is advised in making a definitive cytologic diagnosis of a
mon features. Cells are often embedded in extracellular matrix mesenchymal tumor; this is especially true when concurrent neu-
produced by tumor cells and exfoliate poorly. Thus cytologic sam- trophilic inflammation is present. Additional diagnostic measures
ples tend to have low cellularity, although exceptions occur. Cells should be taken to confirm the presence of a neoplasm before
do not have intercellular junctions and are arranged individually making major treatment decisions.