Adrenal and extra-adrenal pheochromocytomas: an ultrastructural and formaldehyde-induced fluorescence study with catecholamine content.

Twenty-one adrenal and 6 extra-adrenal pheochromocytomas were studied by light and electron microscopy, and formaldehyde-induced fluorescence (FIF). These morphological findings were compared to the content of tumor catecholamines. Based on predominancy of the cell types, pheochromocytomas were classified into three groups: basophilic, chromophobic and oxyphilic (oncocytic) types. The basophilic type was characterized by basophilic cytoplasm of the tumor cells with hematoxylin and eosin (H & E) stain, green cytoplasmic fluorescence with FIF and numerous epinephrine type of electron dense granules with electron microscopy. Its epinephrine content was compatible to the normal adrenal medulla. The basophilic type was only of adrenal origin. Chromophobic and oxyphilic tumors contained predominantly norepinephrine, and showed yellow-green or light brown cytoplasmic fluorescence by FIF. By electron microscopy, various granules of different sizes and shapes of the norepinephrine type were noted. Extra-adrenal pheochromocytoma cells demonstrated dark brown cytoplasmic fluorescence by FIF. Morphological findings of the extra-adrenal tumor corresponded to those of chromophobic type adrenal pheochromocytoma. The tumors contained only norepinephrine.