Page 140 - Differential Diagnosis in Small Animal Cytology, The Skin and Subcutis

Mesenchymal Tumours and Other Neoplasms

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• Cells are spindle shaped to plump-oval.
• Nuclei are generally large, round to oval and with coarse to granular chromatin.
VetBooks.ir • Nucleoli are often prominent.
The cytoplasm is lightly to moderately basophilic and has poorly defined margins. It can
contain clear vacuoles and/or pink granules.
• Cytological features of atypia can be marked and include anisokaryosis, anisocytosis,
multiple prominent nucleoli (e.g. round, oval, angular or irregular), anisonucleoliosis,
multinucleation and atypical mitotic figures.

Differential diagnoses
• Fibroma:
• Collageneous hamartoma
• Reactive fibroplasia/scar tissue formation
• Keloidal fibroma (rare)
• Fibrosarcoma:
• Reactive fibroplasia/scar tissue formation
• Soft tissue sarcoma of other origin
• Nodular fasciitis (rare)
• Keloidal fibrosarcoma (rare)

Pearls and Pitfalls
• Fibrosarcoma lacks specific morphological features and can mimic other sarcomas. For
this reason, a generic diagnosis of (soft tissue) sarcoma is often made on cytology. A definitive
confirmation of fibrosarcoma relies on histopathology.
• An uncommon variant called canine maxillary well-differentiated sarcoma has been described in
Golden Retrievers and other large-breed dogs. Despite being an extremely well-differentiated
neoplasm with minimal nuclear pleomorphism, this neoplasm is often rapidly growing and
progressive infiltrative. It presents with a swelling of the maxillary or mandibular region.
• A rare hereditary syndrome of multiple fibromas in the dermis and subcutis has been reported
in German Shepherd Dogs. Clinical presentation is characterized by numerous small dermal
nodules, especially on limbs, ears and back. It is important to recognize this syndrome, as it
has often been associated with multiple renal cysts, adenomas or adenocarcinomas and uterine
leiomyomas.