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A seven-year-old neutered male Jack Russell Terrier presented with an interdigital mass of several weeks’ duration. Smears were made from an aspirate of the mass.
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What features are illustrated in these photomicrographs (both Wright–Giemsa, ×50 oil)?
There are a few erythrocytes and moderate to high nucleated cellularity.
The nucleated cells include many neutrophils, a moderate number of foamy, active macrophages and a few spindle cells.
The spindle cells have granular, evenly distributed chromatin and the nuclei contain one to several small but distinct nucleoli.
The cytoplasm is wispy and often has bipolar extensions.
The cytological features are consistent with moderate to marked pyogranulomatous inflammation with spindle cell proliferation, most likely fibroplasia.
What comments do you have regarding these findings?
The cytological finding of pyogranulomatous inflammation may be nonspecific, but the possibility of a reaction to a foreign body or penetrating wound of the interdigital area should be considered.
This type of inflammation may or may not be easily resolved.
The spindle cells are consistent with a proliferative population, most likely a fibroplastic response.
Atypical spindle cells with nucleoli and increased numbers typical of proliferation represent a diagnostic problem for all cytologists.
When present in small numbers and accompanied by the type of inflammation found in this specimen, they are most likely due to fibroplasia.
However, in some cases, spindle cell proliferations may be difficult to differentiate and it may be difficult or impossible to separate fibroplasia from an actively growing benign tumour or a malignant one.
Cellularity, degree of atypia and other concurrent features all have to be considered. In some cases, cytological evaluation can help separate these conditions with a high degree of confidence.
In others the differential diagnoses cannot be differentiated on the basis of cytology alone and a biopsy will be needed to determine the definitive diagnosis.
