Metastatic extra-adrenal sympathetic paraganglioma in a horse.

Post-mortem examination was performed on a horse that died after exhibiting signs of colic. Gross findings included haemoperitoneum and a large round encapsulated mass located in the sublumbar area cranial to the left kidney. On sectioning the mass was solid red to brown and small nodules of similar tissue were noted at the periphery of the mass. The spleen was firm and three nodules were found in one thyroid gland. Microscopically, the abdominal mass, adjacent nodules, the spleen and one thyroid nodule consisted of clusters and cords of round to oval neoplastic cells, separated by a fine collagen and reticulin fibre network. Immunohistochemically, tumour cells expressed chromogranin A, synaptophysin and neuron-specific enolase, but did not express cytokeratin. The findings were consistent with a metastatic extra-adrenal sympathetic paraganglioma.