Ultrasonographic and pathologic study of schwannoma in a Goldfish (Carassius auratus)

An adult Goldfish (Carassius auratus) developed an exophitic,multinodular, mass in the dorsal region involving the fin. The clinical andpathologic approach included ultrasonography, cytology, histopathology,immunohistochemistry, and ultrastructural evaluation. B-mode and colorDoppler ultrasonographic findings showed an oval, well-defined mass withslightly inhomogeneous parenchymatous echotexture associated with anintense intralesional vascularization. Cytology and histology revealed neo-plastic pleomorphic spindle cells arranged in a storiform pattern or in pal-isades typical of Antoni A pattern schwannoma. Moderate anisocytosis andanisokaryosis and occasional binucleation were also present. The neoplastictissue deeply infiltrated the skeletal muscle of the dorsal region. Immuno-histochemistry showed a diffuse cytoplasmic immunoreactivity of neoplas-tic cells to S100 protein and proliferating cell nuclear antigen (PCNA); glialfibrillary acidic protein was negative. The PCNA proliferation rate was23.5% (calculated as the mean of 10 fields). Ultrastructurally, neoplasticcells were juxtaposed with parallel nuclei forming the typical palisade pat-tern and sharing cytoplasmic and nuclear features with human schwan-noma. This is the first cytologic description supplied with echographicinvestigation of a malignant schwannoma in a fish species.