Metanephric adenoma in a 2-year-old child: case report and immunohistochemical observations.

Renal metanephric adenoma (MA) is an extremely rare benign tumor, especially in children under the age of 12 years old. In this article, we report a case of MA that was incidentally discovered in a 2-year-old girl by ultrasound. Magnetic resonance scan revealed a mass of right kidney that was hypointense and hyperintense on T1- and T2-weighted images, respectively. Laparoscopic nephron-sparing surgery was carried out to remove the lesion. Histopathologic examination of the specimen revealed MA with clear surgical margins. Immunohistochemically, the tumor cells showed focal reactivity for CD56, pan-cytokeratin (AE1/AE3), and epithelial membrane antigen, and negative reactivity for Wilms' tumor 1 gene product. Meanwhile, the tumor stroma was diffusely positive for vimentin. We also review the literature regarding the clinical, imaging, and histopathologic features of this lesion in the pediatric population.