Page 143 - Differential Diagnosis in Small Animal Cytology, The Skin and Subcutis

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Myxoma and myxosarcoma
VetBooks.ir Tumours originating from fibrocytes and fibroblasts of the dermis and subcutis and distin-
guished by their abundant myxoid matrix rich in polysaccharides (mucin).

Clinical features
• Rare neoplasms observed in middle-aged or older dogs and cats. They account for less
than 1% of all skin tumours.
• Myxosarcoma belongs to the category of soft tissue sarcomas.
• Lesions are usually single, variably sized, soft, grey-white and poorly defined. They
may exude a clear mucoid fluid.
• It is most commonly observed in the subcutis of the trunk and limbs.
• Myxosarcoma is locally infiltrative and metastases are rare.
• Over-represented canine breeds: Basset Hound and Dobermann.

Cytological features
• Cellularity is variable, often low, especially in benign forms.
• Background: variable amount of viscous, eosinophilic amorphous material containing
abundant mucin (Alcian blue positive). It may be variably haemodiluted and red blood cells
are often lined in rows because of the viscous background.
• Neoplastic cells are fusiform to stellate and loosely arranged in aggregates. They are often
embedded in abundant pink matrix.
• Nuclei are oval and the chromatin is granular to coarse. Prominent nucleoli may be seen in
myxosarcoma.
• The cytoplasm is lightly basophilic, often forming one or two tails projecting away from the
nucleus.
• Cytological features of atypia, multinucleation and mitoses are often observed in myxosarcoma.
• The distinction between myxoma and myxosarcoma can be difficult on the basis of
cytology alone.

Differential diagnoses
• Soft tissue sarcoma of other origin
• Liposarcoma (myxoid variant)

Pearls and Pitfalls
Cytological smears of these tumours may be difficult to prepare because the slimy texture of
the sample may prevent the specimen from adhering to the slide.