Malignant Abdominal Tumors in Children

Erik Beek, Martine van Grotel, Bart de Keizer, Annemieke Littooij and Rutger Jan Nievelstein

Department of Radiology, Solid tumors and Nuclear Medicine of the University Medical Center Utrecht and Princess Maxima Center for Pediatric Oncology

Abdominal tumors in children are rare.
Treatment is often done in specialized centers. The initial diagnosis, however, is usually made in the hospital where the child initially presents.
It is important that this diagnosis is as accurate as possible. The parents will be very concerned and ask for as much information as is available. The further diagnostic steps are also influenced by the initial diagnosis.

The initial diagnosis is made by history, physical examination, laboratory tests, and imaging. 

The following article aims to provide tools to make the initial imaging diagnosis of the most frequent malignant abdominal tumors as accurate as possible. 

Some benign masses which can easily be mistaken for a malignancy are included.

Clinical presentation

Pediatric abdominal tumors are often very large on initial presentation. It may seem a contradiction but: how larger the tumor, the more difficult it is to ascertain its organ of origin. 

Children with large tumors come to attention because someone noted an increase in abdominal girth. 

Children with nephroblastoma are generally not ill. Nephroblastomas are generally very large at initial diagnosis. Smaller tumors are seen when they are discovered during screening ultrasound in children with predisposition syndromes (see list) or when the tumor causes hematuria.

Children with neuroblastoma generally have complaints of malaise. They can present with metastatic disease. Some children present with opsoclonus myoclonus syndrome. In these cases the tumor can be small.

Laboratory findings

Blood test can help to determine the type of tumor, although sonographic imaging is often completed before the laboratory results are known. 

In neuroblastoma the VanillylMandelic Acid (VMA) and HomoVanillic Acid (HVA) levels in the urine are in most cases elevated.

In hepatoblastoma and hepatocellular carcinoma the serum alpha-fetoprotein (AFP) levels are elevated.

In germ cell tumors AFP, beta-HCG, and CA-125 can be elevated.

Renal tumors

Nephroblastoma of the left kidney in a three-year-old boy. The remnant of the kidney is draped over the tumor (“claw sign” arrow). The tumor is rather homogeneous with some cystic areas.


A renal tumor in children between six months and eight years of age is considered to be a nephroblastoma!

More than 90% of renal tumors in children are nephroblastomas. Nephroblastoma presents mostly in children between one and ten years of age, with 80% before the age of five years and the peak from 2 to 3 years. 

Renal tumors in children are often very large at presentation. Frequently it is diagnosed by a distended painless abdomen. Sometimes hematuria, abdominal pain, or hypertension/headache is the presenting symptom.
Smaller tumors are found during sonographic screening in children with syndromes which predispose to nephroblastoma, like Beckwith-Wiedemann syndrome.
Bilateral nephroblastomas are often syndrome related. 

Nephroblastoma of the left kidney is a three-year-old boy. A bilobar tumor is present in the interpolar region. There is a dilated calyx in the upper pole (arrow).

The lungs are the most frequent site of metastasis. Liver and bone metastasis are rare.

In the US, the kidney is primarily resected, followed by chemotherapy (Children’s Oncology Group, COG approach).
In European countries the patient first receives chemotherapy, after which the kidney is resected, followed by post-operative chemotherapy (International Society of Pediatric Oncology, SIOP approach).
Interestingly, the results of both treatment regimens are about equal.

The prognosis is excellent with a 5-year survival of more than 90%.
Bilateral disease has a less favorable prognosis.

A. The tumor enhances less than the peripheral remnant of normal renal tissue (blue arrow). The left renal vein is open (yellow arrow). Solid parts of the tumor show diffusion restriction (white arrow)

The initial imaging is done by ultrasound. Smaller tumors will be seen to move synchronous with the kidney. Large tumors will not move.

It is often possible to detect a remnant of the kidney draped around the tumor, the claw sign.
The remnant can have a dilated calyx due to obstruction of the pelvis.
The tumor, when small, is usually homogenic echogenic.
Larger tumors are more inhomogeneous with cystic necrotic parts and hemorrhage.
10% of nephroblastomas have fine calcifications.

Left sided nephroblastoma in a two-year-old girl. Note the para-aortal lymph node metastasis (arrow).

Once you are sure of the renal origin of the tumor, scrutinize the other kidney for tumor or nephroblastomatosis (see below).
Search for enlarged para-aortal lymph nodes.
Search with color Doppler for patency of the renal vein and of the inferior caval vein, as a nephroblastoma tends to grow into the renal vein and inferior caval vein. 

Also image the liver for metastasis, although these are rare in nephroblastoma.
The finding of a liver metastasis should urge you to look for an alternative diagnosis.

Video of a nephroblastoma 1

This is a three-year-old girl with a tumor of the left kidney and a large tumor thrombus in the both renal veins and inferior caval vein.
Several liver metastasis are present, which is an unusual occurrence in nephroblastoma.
Also a lung metastasis is seen.

Video of a nephroblastoma 2a

A three-year-old girl with a large tumor in the right flank.

Ultrasound with a high frequency transducer shows that the tumor originates from the right kidney. 

The remnant of the collecting system is dilated, as is often the case.

Video of a nephroblastoma 2b

Same patient.

A tumor thrombus is present in the inferior caval vein.

Video of a nephroblastoma 2c

Same patient.

An axial T2 weighted MR series shows the tumor thrombus extending towards the level of the hepatic veins. Note the dilated remains of the collecting system

Video of a nephroblastoma 3

Two-year-old boy with hemihypertrophy.
A screening ultrasound showed a homogeneous tumor in the upper pole of the left kidney. 

Tumors discovered during screening examinations are usually much smaller than “normal” nephroblastomas.

Classification of Nephroblastoma

The classification of nephroblastomas is done after the kidney is resected.


A kidney can harbor a nephrogenic rest, persisting embryologic tissue. If multiple rests are present it is named nephroblastomatosis. Most nephrogenic rests resolve spontaneously, but they may transform into a nephroblastoma.

Nephroblastomatosis can be perilobar or intralobar. The perilobar form is less likely to transform into a malignancy than the intralobar form. 

The perilobar form is associated with anomalies in the WT2 gene on chromosome 11. Associated syndromes are isolated hemihypertrophy and Beckwith-Wiedemann syndrome.

The intralobar form is associated with a mutation or deletion of the WT1 gene on chromospme 11. Associated syndromes are sporadic aniridia, Denys-Drash syndrome (male, pseudohermaphroditism, nephritis) and 

WAGR syndrome (Wilms tumor, Aniridia, Genital anomalies and mental Retardation).

On ultrasound nephroblastomatosis is difficult to detect as these lesions tend to show similar echogenicities compared to the renal cortex. Microflow imaging can help to identify hypoperfused areas. After chemotherapy nephroblastomatosis generally becomes hyperechoic.

On MRI nephroblastomatosis is best seen on the post contrast images and/or diffusion-weighted images. 

Persistent nephroblastomatosis is a seven-year-old boy who was operated five years ago for a nefroblastoma. 

A peripheral rim of echogenic tissue is seen (arrow).

Two-year-old boy with a nephroblastoma in the left kidney and bilateral nephroblastomatosis. 

With microflow color imaging it is less perfused than normal renal tissue

MRI images of the same patient show hypoperfusion of the pathologic tissue and strong diffusion restriction with low ADC values (arrows).