Page 139 - Differential Diagnosis in Small Animal Cytology, The Skin and Subcutis

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9.1 Mesenchymal Tumours
VetBooks.ir Fibroma and fibrosarcoma

Tumours originating from fibrocytes and fibroblasts of dermis and subcutis.

Clinical features
• Fibroma:
• Uncommon in dogs, accounting for less than 2% of all skin tumours. It is rare
in cats.
• It occurs in middle-aged or older animals.
• It may present at any site but legs, head and trunk are preferred locations.
• Masses are generally single, small, round to oval, intradermal or subcutaneous.
• Fibroma is slow‐growing and complete surgical excision is considered curative.
• Over-represented canine breeds: Rhodesian Ridgeback, Dobermann, Boxer.
• Fibrosarcoma:
• Uncommon in dogs; relatively frequent in cats, in which it represents up to 17%
of all skin and subcutaneous tumours.
• Fibrosarcoma belongs to the category of soft tissue sarcomas.
• In cats, fibrosarcoma is often observed as a variant of the injection-site sarcoma.
• Age: mostly seen in adult dogs and cats (average age of 9 years); however, it may
also occur in very young animals.
• Preferred locations include head, legs and trunk. In cats, it commonly occurs in
the interscapular area (injection-site fibrosarcoma) and ear pinnae.
• Masses are often large, well circumscribed or infiltrating. They may be multilobulated,
often cystic and ulcerated.
• Fibrosarcoma has a tendency to be infiltrative and recurrent especially in high-grade
forms, but metastases are uncommon.
• Over-represented canine breeds: mostly large-breed dogs, including Golden Retriever,
Dobermann, Brittany, Gordon Setter, Irish Wolfhound.
• No predisposed feline breeds reported.

Cytological features

• Fibroma:
• Cellularity is very low and aspirates might not be diagnostic.
• Background: clear and variably haemodiluted.
• Cells usually exfoliate individually or in very loose aggregates.
• Cells are small, spindle shaped and fusiform and generally uniform.
• Nuclei are oval, with finely stippled to lacy chromatin.
• The cytoplasm forms one or two slender and pale basophilic tails with poorly demar-
cated margins.
• Fibrosarcoma:
• Cellularity is variable, often high.
• Background: variably haemodiluted.
• Aspirates are composed of mesenchymal cells, which exfoliate individually or in aggregates. Stori-
form patterns may be observed. Neoplastic cells may be embedded in pink amorphous material.