Primary carcinoid tumor of the kidney with special reference to its histogenesis.

A case of primary carcinoid tumor of the kidney occurring in a 66-year-old woman is reported. The tumor was 10 x 10 x 9 cm in size, solid, yellowish-white in color, and associated with massive hemorrhagic necrosis. Histologically, it was composed of trabecular and anastomosing ribbon-like nests. The tumor cells showed argyrophilicity with the Grimelius stain and cytoplasmic positivity for neuroendocrine markers, (including chromogranin A, neuron-specific enolase, synaptophysin and Leu-7), prostatic acid phosphatase, keratin and vimentin. Numerous cytoplasmic neurosecretory granules were demonstrated ultrastructurally. These histologic and immunohistochemical findings are consistent with the theory that this tumor has a common phenotype with that of carcinoid tumor arising from the hindgut or cloaca.