Abstract

Primary carcinoid tumor of the kidney is extremely rare ; only 29 previous reports have been described in the world literature, 3 cases of which were known to arise in horseshoe kidneys. Because of the scarcity of primary renal carcinoid tumor, its clinicopathologic features and prognosis are not well characterized, and its histogenesis is unknown. We present a case of primary carcinoid tumor arising in the horseshoe kidney of a 43-year-old man. The lesion is morphologically identical to those of gastrointestinal or respiratory tracts. In addition, this tumor contains clusters of intestinal epithelium with goblet cells and mature bony trabeculae. The cytoplasm of the tumor cells are immunoreactive for keratin, NSE, and synaptophysin, but are negative with Grimelius and Fontana-Masson stains. Membrane-bound cytoplasmic neurosecretory granules are observed by electron microscopic examination. This is the first case of primary renal carcinoid tumor arising in a horseshoe kidney documented in Korea. We describe the gross features, light and electron microscopic, and immunohistochemical findings of renal carcinoid and review the literature, with speculations on the possible histogenesis of this unusual neoplasm.

• Keywords: Carcinoid tumor;Horseshoe Kidney;Histopathogenesis