Multifocal Renal Carcinoid Tumor Arising in Horseshoe Kidney with Metastases to the Thyroid

Primary renal carcinoid tumor is a rare tumor of the kidney. Less than 40 cases of primary and metastatic renal carcinoids have been reported. There is a strong association of renal carcinoid tumors with horseshoe kidneys [1, 2]. The radiographic appearance is non-specific and overlaps that of renal cell carcinoma. Histopathologic differentiation between these two entities is essential because the treatment and prognosis are entirely different. We report a unique case of multifocal carcinoid tumor within a horseshoe kidney with metastases to the thyroid gland. It has been postulated that the renal carcinoid horseshoe subtype carried a more favorable prognosis; however, our case with multifocal involvement and distant metastases suggests the possibility for a more aggressive course.