Pigmented ("black") extraadrenal paraganglioma.

A pigmented ("black") extraadrenal paraganglioma was discovered incidentally in a 57-year-old woman during ultrasonography. The tumor was located in the retroperitoneum near the superior border of the right kidney. Results of preoperative fine-needle aspiration and intraoperative frozen sectioning of the resected jet-black tumor (13 cm in diameter, 225 g) were both interpreted as suspicious for malignant melanoma. Histomorphology and immunohistochemistry were diagnostic for paraganglioma. Electron microscopy showed numerous dense-core neurosecretory-type granules, as well as abundant, larger pleomorphic electron-dense granules; most were consistent with lipofuscin or neuromelanin. No melanosomes or premelanosomes were identified. Histochemical stains showed that the pigment most likely is neuromelanin, a nonenzymatic or oxidative waste product of catecholamine metabolism. Eighteen other examples of pigmented paragangliomas have been reported in various sites in the English literature during the last 12 years; most indicate the presence of melanosomes or premelanosomes using electron microscopy, whereas in a minority of cases the pigment has not been characterized rigorously. Common embryogenesis from neural crest may help explain the overlapping phenotype of melanocytes and cells of paraganglioma.