Malignant cauda equina paraganglioma in a cat.

An 11-year-old spayed female domestic long-haired cat presented for surgical removal of a slowly growing and deeply invasive 2.5 x 3.5-cm mass cranial to the base of the tail. Light microscopic examination of surgical biopsy specimens revealed an encapsulated mass composed of packets of polygonal cells of various sizes separated by a delicate fibrovascular stroma. Gömöri's reticulum stain revealed a characteristic endocrine or "Zellballen" pattern. Tumor cells contained diffuse positive reactivity to synaptophysin and neuron-specific enolase, reactions consistent with a neuroendocrine neoplasm. S-100 protein-positive cells reminiscent of sustentacular (support) cells occurred singly or in small clusters within tumor packets. At postmortem examination 3 months later, a 9- x 5- x 4-cm multinodular raised tan mass involving the caudal pelvis, sacrum, and tail-head regions was found. The base of this neoplastic mass originated within the cauda equina region and involved approximately five caudal nerve roots. Numerous 1-3-mm metastatic nodules were identified disseminated throughout the pulmonary parenchyma. The tumor was diagnosed as a malignant paraganglioma of the cauda equina region with pulmonary metastasis.