Wilms’ Tumor (Nephroblastoma)
Nephroblastoma is the most common malignant renal tumor in childhood. It accounts for approximately 20% of all abdominal tumors in this age group and for up to 6% of all renal tumors.
The tumor is diagnosed most frequently in children aged 2–5 years. Nephroblastoma is rare in newborns and children of more than 7 years. After a symptom-free initial stage a large palpable mass (mean: 12 cm) is found in 90% of all patients. At the time of diagnosis, there are often metastases in the inguinal lymph nodes, the lungs and the liver.
Infiltration into the renal vein is present in 4–10%. In many cases, a tumor thrombus extending to the right atrium is detected. Often a tumor thrombus that reaches the right atrium can be appreciated. Five to 10% of the tumors are bilateral or even multifocal. Necrosis and hemorrhage (80%) as well as cyst formation and calcifications (15%) may result in an inhomogeneous SI pattern on T1-weighted images. In general, nephroblastoma is slightly hyperintense on T2-weighted images and slightly hypointense on T1-weighted images. In large tumors, central hyperintense signal is present on T1-weighted images, which is due to hemorrhage.
Postgadolinium the tumor enhances heterogeneously. To clearly demonstrate the infiltration of the tumor into the renal vein and the inferior vena cava T2-weighted images with prospective respiratory gating should be acquired.
Nephroblastoma has to be differentiated from hydronephrosis and multicystic kidney disease, which can be achieved easily using MRI due to the higher SI of the latter two diseases on T2-weighted images. Nephroblastoma has to be differentiated from neuroblastoma. This can be easily achieved by determining the origin of the tumor, which is the kidney in case of nephroblastoma.