A nephroblastoma at renal papilla in a Sprague-Dawley rat

A protruding mass was identified in the papilla of the right kidney of a 10-week-old male Sprague-Dawley rat. Microscopically, the neoplastic tissues were consisted of epithelial elements, where basophilic neoplastic cells displayed a high nucleus-to-cytoplasm ratio and formed tubular growth patterns characterized by small, elongated, or convoluted tubules. Blastemal elements were often arranged in aggregates or nests, composed of tightly packed basophilic polygonal to spindloid primitive cells. The surrounding interstitial tissue appeared loose and myxomatous. Based on these histological features, the diagnosis was nephroblastoma. Nephroblastoma is considered as an embryonic tumor originated from metanephric blastemal elements in the renal cortex and typically displays characteristic triphasic patterns. Also, this tumor seldom arises from or remains localized to the renal pelvis. To our literature review, this is the first nephroblastoma occurred at renal papilla in a rat.