Both occur in early childhood and typically present as large abdominal masses closely related to the kidneys. Distinguishing between the two is impoant, and a number of features are helpful. Neuroblastoma calcification very common: 90% encases vascular structures but does not invade them younger age group (<2 years of age) poorly marginated elevates the aoa away from the veebral column more commonly crosses the midline, especially behind the aoa 2 more common to have extension into the chest bony metastasis are common (Hutchinson syndrome) extension into spinal canal can be seen. retroperitoneal lymph nodes are more often seen. Wilms tumor calcification uncommon: 10-15% (10% rule of Wilm&;s tumor) displaces adjacent structures without insinuating between them slightly older age group: peak 3-4 years of age well circumscribed