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 a slightly. The image consists of few red blood cells, very few small lymphocytes and a 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 sppled chroman paern. 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 differenate these tumors from poorly differenated plasma cell tumors and degranulated mast cell tumors.