LAUSR

Question 1. The first case was that of a 2-year-old boy with a well-defined retroperitoneal mass (Fig. 1a). On the enhanced computed tomography (CT) image, the tumor (Fig. 1a, black arrows) was of uneven density and showed inhomogeneous enhancement, with a clear border from that of the right kidney and other adjacent tissues. The right ureter had narrowed due to compression by the tumor and right hydronephrosis (Fig. 1a, white arrow). The second case was that of a 2-year-old girl with a mesenteric solid mass (Fig. 2a). The tumor on the enhanced CT image was of uneven density and showed slightly heterogeneous enhancement (Fig. 2a, black arrows), with a clear separation from the right kidney and other surrounding tissues. Question 2. The pathological diagnosis of the first case (Fig. 1b) was retroperitoneal extrarenal nephroblastoma (blastemic type). The pathological diagnosis of the second case (Fig. 2b) was mesentery extrarenal nephroblastoma (mixed epithelial and mesenchymal type).