Why does Wilms Tumour cause abdominal swelling?

Wilms Tumour develops in a kidney, often in a young child. As it grows, it can make one side of the abdomen look fuller or feel firm. The swelling may be noticed while dressing, bathing or cuddling the child, and it may not cause pain. Pressure from the mass can sometimes affect appetite, bowel comfort or movement. A swollen abdomen has many possible causes, including constipation, trapped gas or other conditions, so its appearance alone cannot identify the cause. Do not press, massage or repeatedly examine a suspected mass.

Arrange medical assessment for a new, persistent or enlarging swelling. Note when it was first seen, whether it changes during the day, and any associated fever, vomiting, poor appetite, constipation, blood in urine or changes in urination. Avoid rough play or pressure over the abdomen until a clinician has assessed the child. Bring a list of medicines and describe changes in eating, drinking, energy and sleep. Imaging and other tests may be used to understand the kidney and surrounding tissues.

Seek urgent medical advice for abdominal swelling with severe or increasing pain, repeated vomiting, a hard or rapidly enlarging abdomen, difficulty breathing, marked drowsiness, fainting, inability to pass urine or blood in the urine. A child who becomes suddenly very unwell needs emergency assessment. Do not wait for a routine appointment when these changes occur.

Could the swelling be related to the kidney or another cause? Which examination or scan is appropriate? Should my child avoid contact sports or pressure on the abdomen? Which changes should prompt an urgent call?