Abstract
Renal Mesenchymal Tumor (RMT) and Nephroblastoma (NB) represent two diagnostically challenging neoplasms of the rat kidney. Both are uncommon tumors reported less frequently than tubule epithelial neoplasms. Excellent guideline criteria exist for both neoplasms. However, in some cases, the diagnosis between RMT and NB may be difficult and occasionally controversial. The most important feature of RMT is the presence of a fibroblastic-like cell which proliferates between tubules and glomeruli. RMT may contain heterogenous tissue such as fibrous, vascular, smooth or striated muscle, cartilage and even bone. On the other hand, NB are usually characterized by the presence of varying patterns of deeply basophilic blastemal cells which are pathognomic for NB. Organoid epithelial differentiation into glomeruloid or epithelial-lined tubules further characterizes NB. The observation of “altered” renal tubule structures in RMT are often a point of confusion with respect to NB diagnosis. In addition, attempts to compare human NB to the rat RMT and NB may be problematic.
