[Primary metastatic renal metastatic carcinoid tumor in a young male patient: a contribution to the differential diagnosis of neuroendocrine tumors].

Primary renal carcinoid tumors originating in normal kidney are extremely rare. We report a case of primary renal carcinoid tumor with an aggressive clinical course and multiple metastases in the paraaortal lymph nodes and the liver as well as a pulmonary metastasis, in a 30-year-old patient. A CT scan of the abdomen revealed a large mass in the right kidney and multiple tumor suspect areas in the liver and paraaortal lymph nodes. The patient did not have clinical manifestations of carcinoid syndrome. Histologically, the tumor was composed of trabecular, solid or anastomosing ribbon-like nests, identical to the features of neuroendocrine tumors from other locations. Immunohistochemical staining was positive for cytokeratin, neurospecific enolase, and chromogranin. Electron microscopically, tonofibrils, primitive desmosomes, and dense-core granules with a neuroendocrine appearance were present. The pathological features of this case are briefly reviewed in comparison with those of previously reportet in terms of certain clinical aspects, prognostic factors and the WHO-classification (2004) of this rare neoplasia.