Ultrastructure of pheochromocytoma: undescribed morphologic features.

We examined samples of human pheochromocytoma from 11 patients aged 30-70 years including one case of malignant pheochromocytoma with a view to identifying previously unreported ultrastructural details.We identified two types of nuclear inclusions consisting of irregularly shaped singular or multiple granulofibrillar formations with a typical concentric halo, on the one hand, and accumulations of egg-shaped structures consisting of granules and microfilaments, on the other. In some of the tumor cells, membrane-covered inclusions containing parallel laminar elements arranged in a paracrystalline, periodic fashion, or mega-mitrochondriae characterized by increased electrodensity of their matrix, and fibrillary material in the spaces between the cristae were present. A frequent finding consisted of typical ciliary formations, while rough/smooth tubular aggregates of different size occurred less frequently. Finally, we were able to demonstrate the uptake of norepinephrine by smooth muscle fibers in the periphery of arterial vessels as evidenced by linear accumulations of membrane-covered granules separating bands of contractile smooth muscle components in the peripheral layers of arterial vessels close to norepinephrine producing neoplastic cells.These findings represent ultrastructural features that contribute to further elucidating the ultrastructural characteristics of the human pheochromocytoma.