A lump or swelling in a child's abdomen — what it means and what to do

Finding a lump in your child's abdomen is understandably frightening. Most abdominal lumps in children are not cancer — they can be caused by constipation, enlarged lymph nodes, a hernia, a cyst, or other benign causes. However, some abdominal masses in children are serious and require prompt evaluation. You should not try to diagnose this at home.

Take your child to a doctor within 24–48 hours if the lump feels firm or hard, if it has appeared suddenly or is growing, if your child has fever, unexplained weight loss, or fatigue alongside it, or if the lump is painless (painless lumps are sometimes more concerning than painful ones). A physical examination and an ultrasound are the starting point.

The most common cancers that present as an abdominal mass in children are Wilms tumour (nephroblastoma), which arises in the kidney and is most common between ages 3 and 5; neuroblastoma, which arises from nerve tissue near the adrenal glands or along the spine; hepatoblastoma, a liver tumour seen mainly in children under 5; and non-Hodgkin lymphoma, which can present as an abdominal mass particularly in older children.

These are distinct from adult cancers. Diagnosis requires an ultrasound, followed by CT or MRI, and a biopsy for tissue confirmation. No doctor can tell from a physical exam alone whether a mass is cancerous — imaging and pathology are always needed.

Asymmetric abdominal swelling — where one side appears larger than the other — is one of the classic ways Wilms tumour and neuroblastoma first come to the attention of parents, often noticed during bath time or when dressing the child. It does not mean cancer is confirmed, but it does mean your child needs an urgent medical assessment.

Do not press on the abdomen repeatedly as this can cause discomfort and, in the case of certain tumours, is best avoided until a diagnosis is in hand. Show the doctor exactly what you have noticed. An abdominal ultrasound is usually the first investigation.

The standard evaluation starts with a careful physical examination and an ultrasound of the abdomen, which is painless, uses no radiation, and gives the doctor a first look at the mass and which organ it involves. If the ultrasound shows something that needs further characterisation, the next step is usually a contrast-enhanced CT scan or MRI, which gives a detailed three-dimensional picture of the mass, its relation to surrounding structures, and whether it has spread.

Blood and urine tests — including urinary catecholamines for neuroblastoma — are also done. A biopsy (taking a small sample of tissue) gives the definitive diagnosis. Your child's team will explain every step before it happens.

Act quickly — within 24 to 48 hours. You do not need to go to an emergency room unless your child is in severe pain, has a high fever, is vomiting uncontrollably, or the abdomen is rigid and tender. But do not wait weeks for a routine appointment.

Call your child's paediatrician today and describe what you have found. A good paediatrician will arrange an abdominal ultrasound within days. If you are already seeing a specialist, call their office directly. Early evaluation means earlier diagnosis, which matters for treatment outcomes in the cancers that cause abdominal masses in children.

Yes, many abdominal lumps in children are harmless. A common cause is a faecal mass from constipation, which feels like a firm lump in the left side of the abdomen and goes away once the bowel is cleared. Enlarged lymph nodes after an infection, umbilical hernias, ovarian cysts in girls, and benign kidney cysts can all present as lumps.

However, because some abdominal masses are serious, every lump should be evaluated by a doctor. The difference between a benign and a serious cause cannot be determined without an examination and an ultrasound. Please do not delay this assessment.