26 Sep Cutaneous Histiocytoma
Aspirate from a 1cm, circular, raised pink dermal mass on the pinna of a 3-year-old spayed female Bull terrier. The mass has been present for 1-2 weeks and has grown slightly. The image consists of few red blood cells, very few small lymphocytes and neutrophil, and several individual round cells with abundant light gray cytoplasm, which is highlighted by the moderately proteinaceous background. These cells have a round nucleus that is predominantly centrally located and exhibits a finely stippled chromatin pattern. Anisokaryosis and anisocytosis are mild. The diagnosis is a cutaneous hisocytoma.
These are common, benign dermal tumors that are most commonly found in dogs less than 4 years of age but can be found in dogs older than 10 years. They usually regress spontaneously in a few weeks to months; if aspirated during regression, small lymphocytes can outnumber the hisocytes. It is important to differentiate these tumors from poorly differentiated plasma cell tumors and degranulated mast cell tumors.