Abstract

Pigmented extraadrenal paraganglioma is an unusual neoplasm that has rarely been reported in the literature. Based on histochemical staining or electron microscopy, pigment has been classified as lipofuscin, neuromelanin or true melanin. We report a case of pigmented extraadrenal paraganglioma in the posterior mediastinum of a 70-year-old woman. Histologically, the tumor had a characteristic organoid architecture of "zellballen" pattern with rich delicate microvasculature. Tumor cells contained numerous coarse brown-black pigment granules. Ultrastructurally, the tumor showed abundant large electron-dense pigment granules that vary in size and shape and smaller membrane-bound neurosecretory granules. The larger granules were consistent with neuromelanin or lipofuscin. Histochemically, the pigment is most likely neuromelanin, which is a waste product of catecholamine metabolism.

• Keywords: Paraganglioma;Mediastinum;Neuromelanin;Melanin