Page 160 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

CHAPTER 7 Diagnostic Cytopathology in Clinical Oncology 139

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• Fig. 7.25 Fine-needle aspirate of well-differentiated adipocytes from a
lipoma.
• Fig. 7.24 Fine-needle aspirate of a perivascular wall tumor (hemangio-
pericytoma). Note how well the cells exfoliated. Upper left inset: Vessels
are often associated with the tumor cells. Lower right inset: Cells are spin-
dle, stellate, or oval.

vascular tumor. Aspiration of suspected HSA is approached cau-
tiously because of the potential consequence of hemorrhage, but
cellular yields may be sufficient to reach a tentative diagnosis. The
neoplastic cells are often markedly pleomorphic and consist of
spindle, stellate, and oval cells that have deeply basophilic cyto-
plasm containing punctate vacuoles (see Fig. 7.6); some neoplas-
10
tic cells may contain mature red blood cells. Large, irregular, or
indented oval nuclei typically have coarse chromatin and multiple
prominent nucleoli that vary in shape and size. Multinucleated
cells are found occasionally. Anisocytosis and anisokaryosis are
often marked. A small amount of pink extracellular matrix may be
associated with the neoplastic cells. Erythroid precursors and mac-
rophages containing erythrocytes or hemosiderin may accompany
HSA, especially within the spleen. Important markers of vascular • Fig. 7.26 Fine-needle aspirate of a liposarcoma in a dog. Note that the
differentiation are CD31 and von Willebrand factor. HSAs occur polygonal cells contain lipid vacuoles. Inset: A large lipid vacuole in a tumor
primarily in the spleen and right atrium with metastasis to liver cell.
and lung, but also occur in the dermis and subcutis and rarely arise
from bone. Tumor cells are typically not found in hemorrhagic Nuclei are round to oval and often display criteria of malignancy.
effusions that result from rupture of the tumor. Confirming the presence of lipid using Oil Red O stain is best
accomplished on unfixed smears. With inflammation of adipose
Tumors of Adipose Tissue tissue (panniculitis or steatitis), the sample often contains mod-
Tumors of adipose tissue comprise lipomas and liposarcomas. erately pleomorphic fibroblasts and histiocytes that contain lipid
Lipomas are common tumors of dogs, and although the gross or lipid-like vacuoles; these cells are easily mistaken for a neoplas-
appearance and texture of these tumors is characteristic, they often tic population. The presence of even low numbers of neutrophils
are aspirated to rule out other types of tumors that require more within these lesions favors a conservative interpretation, and surgi-
immediate attention. Aspirates of lipomas consist of abundant lipid cal biopsy should be pursued for definitive diagnosis.
that often dissolves during fixation in methanol-based fixatives, Mesenchymal Tumors Composed of Thin Elongate Cells
leaving an acellular smear. Adipose tissue that adheres throughout
the staining procedure consists of clusters of large round cells with Tumors of Smooth Muscle and Stroma
a small nucleus peripheralized by a single clear lipid vacuole (Fig. Tumors of smooth muscle and stroma, such as leiomyoma, leiomyo-
7.25). Supporting stromal strands and capillary vessels are some- sarcoma, and gastrointestinal stromal tumor (GIST), have a similar
times visible within the cluster of adipocytes, and free fat may be cytologic appearance. Aspirates of these tumors, whether benign or
present. Normal subcutaneous adipose tissue cannot be differenti- malignant, often are highly cellular and consist of long thin mes-
ated from a lipoma or infiltrating lipoma cytologically; therefore enchymal cells arranged in aggregates and linear bundles. Nuclei
caution is recommended when making a conclusive cytologic diag- are often elongate or “cigar-shaped” (Fig. 7.27). Pleomorphism is
nosis of lipoma if the gross appearance or texture of the mass is typically mild. The most common sites for these tumors are the
not typical. Liposarcomas are uncommon and can adopt a variety gastrointestinal tract and female reproductive tract, especially the
of cytologic appearances. Cells may be spindle, stellate, or round uterus and vagina. Immunohistochemical detection of smooth
with variable N:C ratios. Clear lipid vacuoles of varying sizes are muscle actin or KIT (CD117) expression in smooth muscle tumors
present within a basophilic or amphophilic cytoplasm (Fig. 7.26). and GIST, respectively, is required to distinguish these tumors.