The abdominal mass in an infant or child is most commonly an
incidental finding first observed by a parent or at the time of
a pediatric screening examination. Over 50% of abdominal
masses detected by physical examination are actually cases of organomegaly.1,2 The
remaining 43% of masses require surgical evaluation and
comprise neoplasms, developmental anomalies, and inflammatory or
infectious disease. Ninety percent of this group are retroperitoneal
masses, approximately half of which derive from the urinary tract.2 In
neonates, multicystic dysplastic kidney and hydronephrosis occur
in equal frequency and comprise 75% of abdominal masses.2 Older
children are more likely to have neoplastic processes.2Table 388-1 lists the most likely diagnoses
that vary by location of the mass and age group.
Most masses are asymptomatic, so the history is rarely diagnostic.
Signs and symptoms concerning for malignancy include increased abdominal
girth, associated abdominal pain, pain with movement or palpation,
constipation, or change in pattern of urination.1 Other
helpful elements in the history include signs or symptoms of intestinal
obstruction, jaundice, fever, and weight loss. The approximate location
of the mass; its mobility, size, and consistency; and any associated
developmental anomalies should be noted on physical examination
and may be helpful when discussing initial imaging modalities with
the radiologist. Ultimately, the age of the patient and physical examination
findings narrow the differential diagnosis prior to radiologic imaging.
The radiologic evaluation of the neonatal abdominal mass should
begin with abdominal plain films to rule out gastrointestinal obstruction.
In contemporary practice, an increasing number of neonatal masses
are discovered on prenatal maternal ultrasound. If an obstructive
pattern is seen, an upper gastrointestinal series should be obtained
to rule out malrotation and volvulus. In the absence of an obstructive
pattern, ultrasound is a very useful noninvasive imaging modality
in the neonate.3 Ultrasound can be completed without
sedation and does not expose the child to ionizing radiation. Resolution
provided by modern studies allows for description of origin, vascular
supply, calcification, homogeneity, and cystic or solid nature of
the mass.1,4-6 The incidence of radiation-induced
cancer is increased to approximately 1:1200 with a single computed
tomography (CT) scan of the abdomen. When coupled with a 20-fold
increase in the number of CT scans ordered in the last 25 years,
this poses a substantial risk to the pediatric population.7-9 Magnetic
resonance imaging (MRI) provides similar axial anatomic information
and is preferred to evaluate midline masses, which may involve the
spinal canal or invade vascular structures. However, in the neonatal
population, this study requires general anesthesia.
In older infants and children, ultrasound should be attempted
first in the absence of apparent intestinal obstruction. The origin
of a very large abdominal mass is unlikely to be resolved on axial
imaging and will likely require surgical exploration and biopsy.
CT scan is most helpful in older children with nondiagnostic ultrasound
or for staging tumors. In the case of hepatic tumor, MRI provides
much more diagnostic information.3,4,10 Adjunctive
laboratory tests are often helpful in differentiating tumor types
in older children.1 These may include serum or
urine catecholamines, β-human chorionic gonadotropin
(β-HCG), α-fetoprotein (AFP),
and other relatively specific markers as well as general tests of
renal, hepatic, and other physiologic states (Table
Neonatal oncologic lesions are further discussed in Chapter 447. Renal masses are the most common causes
of flank masses in neonates and include hydronephrosis and multicystic
dysplastic kidney. Multicystic dysplastic kidney is believed to
result from renal outflow obstruction in utero. Its ultrasonographic
features include abnormal contour of the kidney and the presence
of multiple disconnected cysts throughout the organ. The presence
of a single cyst in a neonatal kidney is most likely an obstructed
unit of a duplex system.11,12 Bilateral renal involvement
with diffuse cystic changes is most likely autosomal recessive polycystic
kidney disease, a severe progressive course of renal failure requiring
dialysis and eventual transplant (see Chapter 470).
Hydroureter, ureterocoele, and caliceal dilation do not accompany
any of the previously mentioned diagnoses and should prompt careful
evaluation of the collecting system with a voiding cystourethrogram to
assess ureterovesical junction obstruction, vesicoureteral reflux,
or ureteropelvic junction obstruction (see Chapter 476). A solid mass in the kidney of a newborn is most likely
mesoblastic nephroma, a tumor resembling Wilms tumor with excellent
prognosis (95% benign). These tumors show concentric rings
of echogenicity on ultrasound and should be removed.6 Renal
vein thrombosis may result from dehydration or low flow state and
is evident as a congested kidney with an incompressible renal vein
and lack of flow on Doppler examination.12
Perirenal masses such as adrenal hemorrhage
and adrenal neuroblastoma are relatively uncommon in newborns and
can be followed with serial ultrasound to discriminate them. Additionally,
90% of neuroblastoma tumors secrete measurable urinary
catecholamines.6Fetus in fetu is
an extremely rare abnormality with a partially developed twin enveloped
in the retroperitoneum. Plain films and ultrasound demonstrate intact
skeletal elements, and removal can be a surgical challenge.
Sacrococcygeal teratoma is the most common abdominal
neoplasm in neonates, affecting 1 in 35,000 live births.2 In
utero, this lesion can be found on screening ultrasound. It can
lead to significant arteriovenous shunting, hydrops, and fetal demise.
This germ cell tumor is classified into 4 groups based upon abdominal
and extrapelvic position, and classification correlates with malignant
potential (see Chapter 459). Approximately
85% of these tumors have an external portion that is readily
visible at the base of the coccyx on physical examination. These
are easily diagnosed at birth and are relatively favorable in terms
of malignant risk. Those with little or no exophytic component may
be delayed in diagnosis, presenting with rectal or urinary obstruction
in a toddler. These are likely to be malignant when discovered.
Determining the intra-abdominal extent and anterior involvement
once detected is critical to surgical planning and is best delineated
with MRI. The presence of a sacral mass should be investigated in
any neonate with imaging that depicts a sacral bony abnormality.
Other intra-abdominal masses include gastrointestinal
tract abdominal masses in neonates that are uncommon, such as meconium
disease, mesenteric cyst, and abdominal lymphangioma. Hypertrophic
pyloric stenosis presents with a mass, but the typical history generally
allows straightforward diagnosis (see Chapter 398).
Palpable pelvic masses in young female babies should prompt an inspection
of the vagina to look for cause of hydrocolpos or hydrometrocolpos.
Additionally, an ultrasound of the uterus and adnexa should be performed.
Ovarian cysts are relatively common in neonates, routinely noted
on prenatal ultrasound, and are rarely malignant. The loss of maternal
hormonal influence on the baby’s ovaries results in spontaneous
regression of most cysts by 6 months of age, and these can generally
be followed with ultrasound. Failure of regression by 6 months,
complex cysts, necrotic cysts, or any solid ovarian mass should
receive prompt surgical evaluation and removal.
Hepatobiliary masses in the neonate include
hemangioma (most common), hamartoma, and, rarely, hepatoblastoma
(see Chapter 458). Following an initial ultrasound,
MRI and serum tumor markers provide the most information. In cases
of uncertain diagnosis, surgical biopsy may be completed. Choledochal
cysts are congenital bile duct malformations that place children
at markedly increased lifetime risk of cholangiocarcinoma as well
as infection, obstruction, biliary stone formation, and acute pancreatitis.
These cysts require excision and may be a cause of persistent conjugated
hyperbilirubinemia (see Chapter 427).
Congenital abnormalities associated with the abdominal
wall, such as umbilical hernia, inguinal hernia, hydrocele,
urachal remnant, omphalomesenteric duct remnant, and falciform ligament
abscess, may be palpated as abdominal masses. Ultrasound elucidates their
anatomy and likely origin.
Masses in Infants
Stool in the colon is the most frequently palpated abdominal
mass, particularly in the toddler and preschool-aged child. Wilms
tumor and neuroblastoma are the most common solid abdominal tumors
in children beyond infancy (details of diagnosis and management
are provided in Chapters 456 and 457).
Wilms tumor is the most common solid tumor in the first year of
life2,4 and is the most common abdominal malignancy
in children. Wilms tumor typically presents between 1 and 5 years
of age. Neuroblastomas generally arise from the adrenal gland or
paraspinal ganglia. They are the most common neoplasms that cause
abdominal enlargement in childhood overall.13 Median
age at diagnosis of neuroblastoma is 22 months, and 90% of
newly diagnosed cases are under 5 years of age.1 Ultrasound
or MRI of neuroblastoma demonstrates calcium and often encasement
of major abdominal vessels, including the aorta, celiac, and superior
mesenteric arteries.13 Wilms tumor typically displaces
rather than envelopes major vessels and rarely calcifies (15%).13 Because
90% of neuroblastomas secrete catecholamines, measurement
of urinary catecholamines and/or metabolites is useful
for most patients with an undiagnosed abdominal mass. Axial imaging
of some type is required for neuroblastoma staging, and liver function
tests are a useful screening study.
Masses within the liver should prompt careful history regarding
recent illness and travel. Initial evaluation with ultrasound will
differentiate abscess from tumor. Liver tumors are discussed in
detail in Chapter 458. MRI allows narrowing
of the differential diagnosis on the basis of radiologic characteristics.
Mesenchymal hamartoma of the liver is a developmental lesion, often
cystic or mixed solid/cystic, presenting in patients under
2 years of age with hepatomegaly or right upper quadrant mass. Both
ultrasound and MRI demonstrate simple cysts without debris. Hepatoblastoma
is the most common primary malignant hepatobiliary tumor in children.
Children typically present at between 18 and 24 months. Serum α-fetoprotein
is often elevated and thus should be obtained in all children with
a liver mass. MRI is less helpful in differentiating this tumor
from a hemangioma, occasionally requiring surgical biopsy for definitive
diagnosis and treatment. Hepatocellular carcinoma typically occurs
in older children, with peak incidences at ages 2 to 4 and 12 to
14 years of age. It is the second-most common primary malignancy
of the liver. Approximately half of these children have intrinsic
liver disease (hereditary tyrosinemia, biliary atresia, Alagille
Pelvic masses in females should prompt vaginal examination. Hydrometrocolpos
may be present in postmenarcheal females with imperforate hymen.
Ovarian masses in girls are neoplastic in 64% of cases.14 Initial
evaluation of a pelvic mass should begin with an ultrasound study.
Simple cysts in children under 1 year of age should be monitored
with ultrasound every 3 months, as outlined previously. Larger cysts
that do not resolve by 1 year of age should be removed surgically
with preservation of the ovary (cystectomy or fenestration). In
the event of pain accompanying an ovarian mass, prompt surgical assessment
should be obtained to correct ovarian torsion and salvage the ovary
if possible. Solid or mixed-consistency masses are worrisome for
malignancy, particularly if larger than 8 cm, and should prompt
surgical consultation. The differential diagnosis includes both
germ cell and epithelial neoplasms. Staging chest and abdominal
CT scan, β-human chorionic gonadotropin, α-fetoprotein,
and CA-125 levels should be obtained as diagnostic markers for germ
cell tumor and epithelial cancer of the ovary (see Chapter 459). In the case of precocious puberty preoperative follicle-stimulating
hormone, luteinizing hormone, estradiol, and lactate dehydrogenase
levels should be obtained.