In small animal medicine, mass lesions are routinely identified on palpation and ultrasonography. These masses can arise from 2 general processes in dog and cats: inflammation or cellular proliferation. Differentiating these processes is an important first step in cytologic evaluation of fine-needle aspirates or impression smears.
Question & Answer
Q • What types of inflammation cause cutaneous masses or lesions?
A • Suppurative and pyogranulomatous inflammation are common causes of cutaneousmasses or open draining lesions. In aspirates where the primary process is suppurative inflammation, neutrophils are the most common cell type; they can be degenerative or nondegenerative. It is important to closely examine the nucleus of these cells for evidence of karyolysis—typified by a pale and swollen nucleus that has begun to lose its filamentous segments—because this is a hallmark feature of degenerative neutrophils. The presence of degenerative neutrophils is commonly associated with bacterial infection. Pyogranulomas consist of a mixed inflammatory population, including neutrophils, macrophages, multinucleated giant cells, and lesser numbers of lymphocytes and plasma cells. Infections with higher-order bacteria or fungi such as Blastomyces dermatitidis are a common cause of this type of inflammation (Figure 1, above).