Aggressive oncocytic neuroendocrine tumour ('oncocytic paraganglioma') of the cauda equina.

An oncocytic neuroendocrine tumour ('oncocytic paraganglioma') of the cauda equina is reported. The tumour was predominantly intradural, with extension into and destruction of surrounding vertebral bone. The tumour had an organoid pattern, and the tumour cells had abundant non-argyrophilic eosinophilic cytoplasm. Immunocytochemical stains for neurone-specific enolase, S-100 protein, keratin and carcinoembryonic antigen were positive, but stains for glial fibrillary acidic protein were negative. On ultrastructural examination, there were numerous mitochondria and scattered 200 nm dense-core membrane-bound granules, that rarely clustered in small aggregates. Intermediate filaments were focally arranged in long compact bundles. The histogenesis of tumours reported as cauda equina paragangliomas is discussed.