When malignant abdominal tumors are considered in the differential diagnosis of abdominal masses in pediatric patients,
two conditions come to mind immediately: the nephroblastoma and the neuroblastoma.
Nephroblastoma,
also known as Wilms’ tumor after Max Wilms who first described it in 1899,
is the most common pediatric renal tumor that arises from immature renal parenchyma.
It accounts for approximately 6% of all pediatric malignancies in children.
Its peak incidence occurs between 3 and 4 years of age,
with approximately 80% of cases detected under 5 years of age.
The vast majority are unilateral with less than 5% occurring bilaterally.
Although most cases of Wilms tumor occur in otherwise normal children,
there is an association between the development of Wilms tumor and overgrowth disorders (congenital hemihypertrophy,
Beckwith-Wiedemann syndrome),
sporadic aniridia and other malformations.
Early diagnosis can be difficult due to its slow grown without causing any symptoms.
Presentation is usually with a large,
painless abdominal mass that may arise in any portion of the kidney and expands within the renal parenchyma distorting the pelvicalyceal system and displacing surrounding structures.
Approximately 20-30% of patients refer abdominal pain,
malaise and hematuria; hypertension may be present due to an increase in renin secretion by the tumor or from displaced kidney or renal artery by tumor growth.
Nephroblastomas are usually quite large when diagnosed,
but they very rarely infiltrate adjacent organs.
On computed-tomography imaging scan (CT),
Wilms tumors are heterogeneous soft-tissue density masses with infrequent areas of calcification (~15%) and fat-density regions.
Enhancement is also patchy,
and allows for better delineation of the relationship between the mass and the kidney.
20% of cases have lung metastases at the time of diagnosis.
Neuroblastoma,
first described by Virchow in 1863,
is the most common extra-cranial childhood tumor,
that arises from primordial neural crest cells along the sympathetic nervous system chain.
The incidence of neuroblastoma is between 0 and 14 years of age,
with a slight male predominance; the tumor typically occurs in infants and very young children (mean age of presentation being approximately 22 months) with 95% of cases diagnosed before the age of 10 years.
Because of its aggressive nature and late staging at presentation,
it accounts for approximately 15% of childhood cancer deaths.
There are a wide number of conditions that have been associated with neuroblastoma: Neurofibromatosis type 1,
Beckwith-Weidemann syndrome,
Hirschsprung’s disease and DiGeorge syndrome.
Neuroblastomas are most commonly located within the adrenal gland,
so typically present as palpable abdominal masses causing pain and distension.
However,
affected children may have various clinical presentations as a result of disseminated metastatic disease or associated paraneoplastic syndromes at the time of diagnosis.
Common places for neuroblastoma to metastasize to are cortical bone,
bone marrow,
and lymph nodes.
CT reveals a large,
heterogeneous mass in the adrenal bed or paravertebral area in the region of the sympathetic trunk.
Up to 50% of the lesions contain areas of hemorrhage and necrosis,
and 30–70% contain calcifications.
The tumor morphology is often helpful,
with the mass seen insinuating itself beneath the aorta and lifting it off the vertebral column.
It tends to encase vessels and may lead to compression.
Unlike nephroblastoma,
the tumor deforms the kidneys without causing renal destruction (fig.
1).
Giving the fact that both these tumors occur in early childhood and typically present as large abdominal masses in close proximity to the kidneys,
it is therefore important to review the imaging features that could provide a valuable tool to distinguish them.
Medical imaging,
especially CT,
is essential for positive diagnosis,
pretherapeutic staging and monitoring of treatment.
Hence the need to know the semiological elements of the positive and distinctive diagnosis of Wilms tumor compared to its main differential diagnosis- neuroblastoma (table 1).