Page 162 - Differential Diagnosis in Small Animal Cytology, The Skin and Subcutis

Mesenchymal Tumours and Other Neoplasms
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• Storiform pleomorphic type:
• This is the most common form in dogs.
VetBooks.ir • Neoplastic cells are spindle shaped (fibroblast-like cells) and arranged in storiform patterns.
There are also histiocytoid cells, which often display karyomegaly and multinucleation.
•
• Mixed inflammatory cells are often present.
• Giant cell type:
• This is the most common variant in cats.
• It exfoliates multinucleated giant cells admixed with mononuclear histiocytoid elements.
• Inflammatory cells are not a consistent feature of this variant.

Differential diagnoses
• Histiocytic sarcoma
• Sarcoma of other origin

Pearls and Pitfalls
• Initially thought to be one neoplasm with different variants, recent studies have shown this
likely represents an umbrella, descriptive and more general term that includes anaplastic
versions of several mesenchymal and histiocytic tumours. This includes a tumour of myofi-
broblast origin that is analogous to the human malignant fibrous histiocytoma (MFH).
• When the tumour arises at the level of a joint, immunohistochemistry is required to dif-
ferentiate it from other neoplasms typical of this location, including histiocytic sarcoma
and synovial sarcoma.

Fig. 9.20. Cat. Anaplastic sarcoma with giant cells. Wright-Giemsa.