Wilms tumor is a cancerous tumor of the kidney. This tumor occurs in children.

Wilms tumor is one of the most common childhood tumors of the abdomen, and the most common type of kidney tumor. The exact cause of this tumor in most children is unknown.

The tumor is associated with certain birth defects, including urinary tract abnormalities, absence of the iris (aniridia), and hemihypertrophy (enlargement of one side of the body). It is more common among some siblings and twins, which suggests a possible genetic cause.

The tumor may become quite large, but usually remains encapsulated (self-enclosed). It may spread to other body tissues, especially the lungs.

The disease is estimated to occur in about 1 out of 200,000 to 250,000 children. The peak time of occurrence is at 3 years old, and Wilms tumor is rare after the age of 8 years.

• Abdominal pain
• Swelling in the abdomen (abdominal hernia or mass)
• Blood in the urine (occurs in less than 1/4 of children)
• Fever
• Loss of appetite
• Nausea
• Vomiting
• General discomfort or uneasiness (malaise)
• High blood pressure
• Constipation
• Increased growth on only one side of the body (hemihypertrophy)

Note: Abnormal urine color may also be associated with this disease. A missing iris of the eye (aniridia) is a birth defect that is sometimes associated with Wilms tumor.

CAUTION: Avoid palpation (prodding or pushing) of the abdomen, and use care during bathing and handling to avoid injury to the tumor site.

Special emphasis is placed on the history and physical exam -- looking for a family history of cancer and for associated birth defects in the child. The physical examination reveals an abdominal mass. High blood pressure may also be present.

Tests include:

• CBC (may show anemia)
• BUN
• Creatinine
• Creatinine clearance (may be decreased)
• Urinalysis (blood or protein in urine)
• Abdominal ultrasound
• Abdominal x-ray
• Chest x-ray (may demonstrate metastasis)
• Intravenous pyelogram (distortion of the kidney)
• CT scan of the abdomen (abdominal mass arising from kidney)

Other tests may be required to determine if the tumor has spread.