Malignant paraganglioma of retroperitoneum. Light, electron microscopic and ultrasonographic study.

A malignant retroperitoneal nonchromaffin paraganglioma in a thirty-four-year-old man was studied by light and electron microscopy. Histologically, the tumor cells displayed a tendency to surround granular, eosinophilic intercellular material and to form nests and pseudo-acini. Ultrastructurally, the tumor was composed of moderately well-differentiated epithelial cells intermixed with sparse sustentacular cells. An organoid pattern, reminiscent of the functional anatomic unit of nonchromaffin paraganglia, was seen occasionally. Epithelial cells formed pseudo-acini around dilated microvillous processes. These morphologic features are consistent with the neurocrestal origin of paragangliomas. The patient died ten months after presentation despite an initial favorable response to irradiation.