Renal nephroblastoma in a Green Anaconda (Eunectes Murinus)

Introduction: Nephroblastoma is a renal tumour reported in higher and lower vertebrates. In higher vertebrates, nephroblastoma is more often a paediatric tumour arising from metanephric rests. In contrast, in lower vertebrates, nephroblastoma derives from the opistonephros (mature kidney). Nephroblastomas are rare in snakes. The aim of this report is to document the second case of nephroblastoma in an anaconda. Materials and Methods: A 20-year-old, green, male anaconda was evaluated ultrasonographically in 2012 for severe coelomic distension caused by a bilateral renal mass. The animal was monitored yearly and due to the progressive increase of tumour size and development of anorexia, was humanely destroyed in 2017. Results: The left kidney was replaced by a 3 kg, multilobulated tan-white neoplasm and was surrounded by a large haematoma. Histologically, a triphasic tumour composed of embryonic mesenchyme, primitive glomeruli and nests of polygonal cells (blastema) was observed. A definitive diagnosis of nephroblastoma was made. Conclusions: Nephroblastomas have been reported anecdotally in adult snakes and described only in one anaconda. However, nephroblastoma in snakes is a senile tumour since, contrary to mammals and birds, postembryonic nephrogenesis occurs in reptiles (including Corn snakes). The WT1 pathway is involved in renal development and increased WT1 expression has been associated with the onset of renal neoplasia, such as nephroblastoma, in several mammals and in renal cell carcinoma only in man.