Though ultrasound often is the first imaging modality used for the evaluation of adrenal mass in a child, abdominal CT is a valuable modality in the evaluation of the site of origin, extent, and character of renal neoplasms at the time of diagnosis and follow-up. This paper describes the clinical and CT features of a spectrum of benign and malignant renal masses in children, including Wilms' tumor, renal cell carcinoma, and clear cell sarcoma.
The majority of the abdominal masses
occurring in childhood are retroperitoneal in location, and greater
than 50% of these masses arise from the kidney. Most renal masses
are benign in infants less than 2 months of age; the frequency of
malignancy increases with age.1
Ultrasound is the first imaging modality used
for the evaluation of a renal mass in a child. It also can evaluate
extension of malignant tumors into the renal vein, inferior vena
cava, and right atrium. Due to the large size of some malignant
renal tumors, adequate evaluation of the renal veins and IVC may be
difficult because of marked compression and displacement by the
tumors. CT or MRI are required for adequate evaluation when this is
Conditions including hydronephrosis,
ureteropelvic junction obstruction, obstructed duplicated system,
multicystic dysplastic kidney, and polycystic kidney disease can be
diagnosed with ultrasonography. Additionally, abdominal CT is
valuable in the evaluation of the site of origin, extent, and
character of renal neoplasms at the time of diagnosis and
follow-up. It identifies vascular and nodal involvement and hepatic
metastases, as well as images the contralateral kidney. Color coded
3-D surface rendering of renal tumors and their surrounding
structures may be applied to contrast-enhanced helical CT data sets
to improve surgical planning.
Three-dimensional CT imaging may be useful in patients that will
benefit from renal sparing surgery, including patients with a
solitary kidney, bilateral renal tumors, von Hippel-Lindau
syndrome, and compromised contralateral renal function.
MRI is also considered an excellent imaging
modality for the evaluation of renal masses in children due to its
multiplanar capability and excellent inherent contrast. However, as
it is more readily available than MRI in most hospital settings, CT
is more commonly used in this setting. Following resection of renal
tumor, the tumor bed frequently contains bowel loops, which makes
US assessment difficult. Abdominal CT following oral and IV
contrast administration provides adequate evaluation of the tumor
bed for evaluation of residual tumor and recurrence, as well as
contralateral tumor development.
Approximately 87% of solid renal neoplasms in
children are Wilms' tumors; other renal tumors include clear cell
sarcomas (6%), mesoblastic nephroma (2%), rhabdoid tumors (2%),
lymphoma (<0.5%) and renal cell carcinoma (<0.5%).
This paper describes the clinical and CT features of a spectrum of
benign and malignant renal masses in children, including Wilms'
tumor, renal cell carcinoma, clear cell sarcoma, rhabdoid tumor,
renal lymphoma, metastatic renal mass, nephroblastomatosis,
mesoblastic nephroma, and multilocular cystic nephroma.
Wilms' tumor is the most common primary
pediatric malignant abdominal neoplasm; it is the third most common
malignancy in children, after leukemia and brain tumors. It also is
the third most common of all renal masses in childhood, after
hydronephrosis and multicystic dysplastic kidney. Wilms' tumor
occurs equally in males and females.
The peak age of presentation is 3
years; there is, however, earlier presentation in patients with
associated syndromes and bilateral renal tumors. The disorder is
uncommon during the first year of life, though approximately 50% of
children with Wilms' tumor present before 3 years, 80% before 5
years, and 90% before 8 years of age.
Wilms' tumor occurs bilaterally in 5 to 10%
of patients and is multifocal in 10% of patients. Approximately 15%
of children with Wilms' tumor have other clinical problems or
About 33% of patients with sporadic aniridia develop Wilms' tumor
while 10 to 20% of patients with Beckwith-Wiedemann syndrome
(macroglossia, omphalocele, and visceromegaly) develop these
There also are strong associations with hemihypertrophy (figure 3)
and Drash syndrome (pseudohermaphroditism and glomerulonephritis),
and an increased incidence of Wilms' tumor in children with
congenital genitourinary tract anomalies, including cryptorchidism,
horseshoe kidney, ambiguous genitalia, and hypospadias.
The current screening recommendations for
patients at risk for Wilms' tumor include sonography every 4 months
for a year, followed by repeat imaging every 8 months for 2 years,
and then every 12 months until the child is 10 years of age; and CT
scanning every 6 months for a year, followed by every 12 months for
4 years and again at 10 years of age.
Wilms' tumor arises from undifferentiated
metanephric blastema within the renal cortex. Ninety percent of
Wilms' tumors have a favorable histology and contain differentiated
renal tissue which forms primitive glomerular and tubular
structures within a spindle cell stroma. The remaining 10% of
Wilms' tumors, those with an unfavorable histology, contain
Hemorrhage and necrosis occur commonly in
Wilms' tumor. Ninety percent of patients present with an
asymptomatic abdominal mass.
Microscopic and gross hematuria occurs in approximately 20% and 8%
of patients, respectively. Additionally, hypertension may occur due
to renin production by the tumor or vascular compression.
Twenty percent of Wilms' tumor patients may have low-grade fever,
and 25% of patients have abdominal pain. Other less common
presentations include tumor hemorrhage after minor trauma, ascites
due to venous obstruction, and varicocele from left-sided tumor.
CT of Wilms' tumor demonstrates a
heterogenous intrarenal mass with areas of low attenuation due to
necrosis and hemorrhage (figure 1). The tumor is hypodense to
normal renal parenchyma on unenhanced images, and enhances less
than normal renal parenchyma following IV contrast administration
(figure 1). The normal renal parenchyma is compressed and
displaced, forming a small enhancing rim or beak adjacent to the
tumor (figures 1,2,3). The mass distorts the renal collecting
system, which may also be dilated (figure 1). Amorphous or
curvilinear calcification is seen in 10% of tumors, unlike the
stippled and punctate calcification seen in 85% of neuroblastomas.
The tumor may rarely contain fat, which may be diffuse or focal.
Another sign is poor or non-excretion of IV contrast by the kidney
due to invasion or compression of hilar vessels and the collecting
system, or extensive infiltration of the kidney by the tumor.
CT may demonstrate invasion of vessels
(figure 2), rather than displacement or encasement as seen in
neuroblastoma. Five to 10% of Wilms' tumors demonstrate vascular
extension into the renal vein, with variable extension into the
inferior vena cava and right atrium.
There may be invasion of adjacent organs, lymphadenopathy,
contralateral disease, and hematogenous metastatic disease mainly
to the liver and lungs. In evaluation of a possible Wilms' tumor,
chest CT also should be performed, as approximately 20% of patients
develop pulmonary metastases at the time of diagnosis.
Renal cell carcinoma
Renal cell carcinoma accounts for less than
1% of pediatric renal tumors;
its mean age of presentation is 9 years. In studies, patients with
this tumor have been found to present with palpable mass (60%),
abdominal pain (50%), and hematuria (30 to 60%).
Clinical findings include hypertension, polycy-
themia, and bone resorption, which reflect the production of renin,
erythropoietin, and parathyroid hormone, respectively.
Patients with von Hippel-Lindau disease (cerebellar
hemangioblastoma, retinal angioma, pancreatic cysts and tumors,
pheochromocytoma, and renal cysts and tumors) are at increased risk
for renal cell carcinoma.
Imaging studies cannot distinguish renal cell
carcinoma from Wilms' tumor. However, an older presenting age may
suggest a diagnosis of renal cell carcinoma. Such tumors tend to be
smaller than Wilms' tumor at presentation. Twenty-five percent of
renal cell carcinomas have calcification that tends to be more
dense, central, and homogenous than the calcification typically
found in Wilms' tumor.
Contrast-enhanced CT can demonstrate the tumor, as it enhances less
than normal renal parenchyma. Additionally, there may be areas of
low attenuation due to hemorrhage and necrosis (figure 4).
Twenty-five percent of renal cell carcinomas have intravascular
Clear cell sarcoma
Clear cell sarcoma constitutes 6% of
pediatric renal tumors.
This lesion generally presents between 1 and 6 years of age and
occurs equally in males and females. Pathologically, the clear cell
sarcoma is characterized by polygonal or stellate cells with clear
cytoplasm, ovoid to round nuclei, and a tendency toward cyst
formation separated by septa.
Clinical features include abdominal mass, lethargy, weight loss,
and hematuria. It is a highly malignant tumor with a worse
prognosis than Wilms' tumor, and has a propensity for skeletal
metastases. Clear cell sarcoma cannot be distinguished from Wilms'
tumor by imaging studies alone.
CT demonstrates a heterogenous solid mass with low attenuation
areas due to necrosis, and water density areas reflecting the
cystic component (figure 5).
Amorphous and linear calcifications occur in 25% of tumors.
Skeletal scintigraphy is useful for staging and follow-up
Rhabdoid tumors constitute 2% of pediatric
They commonly present in early childhood, at a mean age of 17
months, and have a poor prognosis, particularly in the presence of
metastatic disease at presentation.
Rhabdoid tumors usually originate in the renal sinus, unlike Wilms'
tumors, which arise from renal cortex. It commonly metastasizes to
the lungs, liver, and brain. Rhabdoid tumor is associated with
primary brain tumors of neuroectodermal origin, including
medulloblastoma, ependymoma, glioma, and primitive neuroectodermal
As with the other tumors described here, these lesions may not be
distinguished from Wilms' by imaging studies alone, though a
centrally located renal mass with subcapsular fluid collection and
associated posterior fossa mass will suggest the diagnosis. CT
scans will demonstrate a centrally located heterogenous renal mass
(figure 6). There may be thickening of the renal capsule, as well
as subcapsular fluid collection.
A peripheral subcapsular fluid collection adjacent to solid tumor
lobules is present in 70% of malignant rhabdoid tumor.
In studies, this collection has represented subcapsular hematoma in
47% of cases and necrotic cavity in 53%.
Head MRI also is useful for staging and follow up.
Primary renal lymphoma is uncommon, as the
kidney lacks lymphoid tissue. The kidneys may be involved by direct
extension from adjacent pararenal lymphomatous disease or
hematogenous dissemination. Non-Hodgkin's lymphoma more commonly
involves the kidney than does Hodgkin's lymphoma.
Renal involvement in non-Hodgkin's lymphoma usually occurs late in
the disease and often is clinically silent. Occasionally there may
be flank pain, palpable mass, hematuria, hypertension, and renal
failure due to urinary tract obstruction, renal vein compression,
and diffuse infiltration. Bilateral renal involvement is more
common than unilateral disease.
CT findings include hypodense renal mass(es), which enhance less
than normal renal parenchyma following IV contrast administration
(figure 7), and diffuse nephromegaly due to diffuse infiltration,
occurring in 5% of patients.
The CT appearance is non specific; however, the diagnosis should be
suggested in the presence of associated splenomegaly and
Metastatic renal mass
Pediatric renal metastases are uncommon.
The most common form of metastatic disease to the kidney in this
population is local extension of a neuro-blastoma (figure 8).
Hematogenous metastases may arise from a sarcoma, which also
results in diffuse metastatic involvement of other organs and lymph
nodes. The clinical presentation usually reflects the primary tumor
or metastatic site. There may be hematuria due to tumor hemorrhage.
When there is local extension of neuroblastoma to the kidney, CT
findings will include a mass with the epicenter in the adrenal
gland which invades the ipsilateral kidney (figure 8). The CT
features of neuroblastoma include an extrarenal epicenter which may
be suprarenal or paravertebral and of irregular shape and
inhomogeneity due to tumor necrosis, as well as encasement and
displacement of vessels (figure 8). CT demonstrates calcification
in about 85% of cases, which may be dense, stippled, punctate, or
amorphous. Adrenal mass may cross the mid-line, and retroperitoneal
adenopathy and contiguous extension are common. In hematogenous
metastasis to the kidney, CT usually demonstrates multiple renal
masses. The clinical history, lesion's multiplicity, and the
presence of other metastatic disease will suggest the diagnosis.
Nephroblastomatosis is a dysontogenetic
process with persistence of fetal metanephric blastema within the
renal cortex after 36 weeks of gestation. The fetal metanephric
blastema is a precursor of Wilms' tumor.
Ninety to 100% of kidneys with bilateral Wilms' tumor (figure 3)
and up to 40% of kidneys with unilateral Wilms' tumor have foci of
metanephric blastema present on pathologic examination.
Nephroblastomatosis is associated with hemihypertrophy, sporadic
aniridia, Beckwith-Wiedemann syndrome, and Drash syndrome.
Most cases of nephroblastomatosis are seen in
patients under 2 years of age. Nephroblastomatosis may be diffuse
or multifocal. In the diffuse form, there is circumferential
subcortical tissue associated with bilateral nephromegaly and
distortion of the collecting system and renal parenchyma. On
unenhanced CT the subcortical rind is seen which is hypodense to
normal renal parenchyma; following intravenous administration of
contrast it enhances less than normal renal tissue.
In the multifocal form, small rests of metanephric blastema are
scattered throughout the renal parenchyma. Those rests large enough
to be demonstrated on CT may be indistinguishable from small Wilms'
Due to the malignant potential of the persistent nephrogenic
blastema, patients with nephroblastomatosis should be followed at
close intervals with sonography and CT scanning to exclude the
development of Wilms' tumor.
Mesoblastic nephroma is the most common renal
neoplasm in infancy. It typically presents as a flank mass; less
commonly it may present with hematuria, hypertension, and anemia.
Pathologically, it is solid, unencapsulated, and grows by
infiltrating through the renal parenchyma.
Mesoblastic nephroma is considered a benign lesion; there are,
however, several reports in the literature of metastatic disease
Contrast-enhanced CT scans of a mesoblastic nephroma demonstrate an
intrarenal mass with uniform enhancement but less than normal renal
parenchyma. In large lesions there may be areas of low attenuation
due to hemorrhage or necrosis (figure 9). Tumor calcification is
rare, and it does not invade vessels or the collecting system.
Nephrectomy is usually curative for this type of lesion. If there
is no concern for residual disease after nephrectomy and histology
does not appear aggressive, no imaging follow up is necessary.
However, if there is extensive necrosis, extrarenal extension,
hypercellular or immature histology, or the patient is greater than
3 months of age, clinical surveillance and follow-up CT scanning is
recommended to exclude recurrence or metastasis.
Multilocular cystic nephroma (MLCN)
MLCN is a benign cystic tumor with biphasic
age and sex distribution. It occurs in children aged 2 months to 4
years with a 75% male predilection, and in adults over 40 years of
age with a 95% female predilection.
MLCN usually presents as an asymptomatic mass, though there may be
hematuria due to prolapse of the mass into the renal pelvis.
Pathologically, the lesion is well encapsulated and consists of
multiple well-circumscribed, noncommunicating locules; there also
may be fibrous stroma containing septations.
There are two distinct histologic entities of
MLCN: cystic nephroma without blastema elements within the septa,
and cystic, partially differentiated nephroblastoma, which has
blastema elements in the septa. These two entities are
indistinguishable on the basis of imaging characteristics. The
relationship between cystic nephroma, cystic partially
differentiated nephroblastoma, and Wilms' tumor is controversial.
Contrast-enhanced CT scans demonstrate a well defined intrarenal,
multi-locular mass which compresses or displaces the adjacent renal
parenchyma, forming a rim or beak adjacent to the mass. The
septations enhance, but the cysts do not (figure 10). The
attenuation of an individual cyst depends on the protein content
and the presence or absence of hemorrhage.
There may be linear calcification within the septations or
Benign and malignant renal neoplasms comprise
a large proportion of childhood tumors. Wilms' tumor is the most
common primary malignant abdominal neoplasm in children, and
mesoblastic nephroma is the most common renal neoplasm in infancy.
Other important causes of renal masses in childhood include renal
cell carcinoma, clear cell sarcoma, rhabdoid tumor, renal lymphoma,
metastatic neuroblastoma, nephroblastomatosis and multilocular
cystic nephroma. Although the CT features of most pediatric renal
masses are not specific, it is, however, a useful modality in the
evaluation of renal masses and postoperative/therapy follow up.