Page 87 - Differential Diagnosis in Small Animal Cytology, The Skin and Subcutis

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7.8 Nodular Fasciitis
VetBooks.ir Non-neoplastic proliferation, also known as pseudosarcoma in human literature. Characterized

by exuberant proliferation of fibroblasts and myofibroblasts.

Clinical features

• Rarely described in dogs. Not reported in cats.
• The cause of nodular fasciitis is unknown, but it is seems that local trauma might
be a trigger. Some cytogenetic studies performed in people demonstrated a clonal
proliferation.
• Masses are variably sized, poorly delineated and deep in the derma or subcutis.
• Most common anatomical sites include trunk and legs.
• Mass growth can be rapid; however, the behaviour is benign and surgical excision is
curative. Masses can spontaneously regress or reduce in size.
• Collie breeds may be over-represented.

Cytological features
• Cellularity: generally high.
• Background: often characterized by the presence of a large amount of granular to fibrillar,
pink amorphous material scattered throughout the slides and admixed with the cells. Haemo-
dilution is variable and windrowing of the erythrocytes may be observed.
• Aspirates often contain numerous spindle cells arranged in medium-large aggregates or
occasionally individualized.
• Nuclei are medium-large, round to oval. They have coarsely stippled to granular chromatin
and may contain one to multiple, small to medium-sized, round and variably prominent
nucleoli.
• The cytoplasm forms one or two tails that project away from the nucleus. It is pale to moder-
ately basophilic and can contain small clear vacuoles or pink granules. Cell margins are
generally poorly defined.
• Cellular pleomorphism is variable. Anisokaryosis and anisocytosis can be moderate.
Occasional binucleation can be observed and rare mitoses found.
• In spite of the name that implies inflammation, inflammatory cells are not always observed.
When present, they mostly consist of lymphocytes, plasma cells and histiocytes–
macrophages.

Differential diagnosis
Sarcoma