is an Associate Professor of Radiology and Chief of Pediatric
Radiology, SUNY Downstate Medical Center, Brooklyn, NY.
is a Section Chief in the Pediatric Radiology Department and an
Assistant Professor of Radiology at New York University School of
Medicine, New York, NY.
Ultrasonography can play a significant role in the diagnosis and
management of pediatric abdominal and scrotal disorders. This
article will discuss the current imaging concepts with respect to 3
common pediatric abdominal emergencies: pyloric stenosis,
intussusception, and appendicitis. In addition, the role of
ultrasound in acute scrotal pathology in the pediatric population
will also be presented.
Pyloric stenosis (PS) is the most common surgical disorder that
produces nonbilious emesis in infants. Pyloric stenosis is a
developmental problem that is not seen at birth. Infants with
pyloric stenosis can range in age from 1 week to 3 months, with
most presenting at 6 to 8 weeks of age. Pyloric stenosis is much
more common in male infants; males outnumber females by 5 to 1.
Pyloric stenosis may also be familial.
In PS there is hypertrophy of the py-loric muscle and elongation
of the pyloric channel. In addition, there is redundancy of the
pyloric mucosa. The etiology of PS is not known. One theory is that
there is abnormal muscle innervation, as a depletion of some normal
constituents of muscle has been found in the hypertrophied muscle.
Another theory is that some infants may have an abnormal parietal
cell mass within the stomach, which leads to a cycle of
hypersecretion, pyloric contraction, and delayed gastric emptying.
Sonography is the modality of choice in an infant who is
suspected of having pyloric stenosis, with a reported sensitivity
The advantages of sonography for this diagnosis are avoiding the
use of ionizing radiation and directly visualizing the
hypertrophied pyloric muscle. A high-frequency linear transducer
(10 to 15 mHz) is typically used, as the stomach, pylorus, and
duodenum are very superficial in an infant. The patient should be
positioned in the right posterior oblique position, and the
transducer is placed in the transverse plane in the right
epigastric region. If the stomach is empty, sterile water can be
fed to the patient by bottle to allow for the displacement of any
interfering gas in the stomach and also to serve as an acoustical
window. Overdistention, however, can lead to displacement of the
pylorus posteriorly, which may hamper its visualization.
Additionally, scanning the patient in the prone position may aid in
visualization of the pyloric region in an infant in whom there is a
lot of gas.
When PS is present, a thickened py-loric muscle and elongated
pyloric channel are seen (Figure 1). When the muscle thickness is
≥3 mm and the pyloric channel is >1.5 cm, the diagnosis of
pyloric stenosis can be made with confidence. There are a number of
ancillary sonographic signs of pyloric stenosis as well. The
"shoulder" sign (Figure 2) refers to an indentation upon the antrum
of the stomach, which is produced by hypertrophy of the pyloric
muscle. The "nipple" sign is an evagination of redundant pyloric
mucosa into the antrum (Figure 2). Color Doppler evaluation of the
pylorus may reveal hyperemia with-in the muscle and mucosal layers.
Antral dyskinesia, also known as pylorospasm, commonly manifests
as nonbilious vomiting in an infant. Sonographically, pylorospasm
may resemble PS in that there is some pyloric muscle wall
thickening and/or slight elongation of the pyloric channel, but the
thickness usually does not exceed 3 mm, and the length of the
pylorus usually does not exceed 1.5 cm (Figure 3). In addition,
pylorospasm is transient and will subsequently resolve, taking up
to 30 minutes to dissipate. Measurements of the pyloric muscle
thickness and length in pylorospasm may occasionally and
intermittently be compatible with those considered positive for PS,
but such measurements do not persist throughout the examination.
Intussusception represents the telescope-like invagination of
more proximal bowel, known as the intussuseptum, into more distal
bowel, known as the intussuscepiens. In children, 90% of
in-tussusceptions take place at the ileocolic region and are
idiopathic. The remainder are a mixture of ileo-ileocolic and small
bowel intussuceptions. Approximately 10% of intussuceptions have a
lead point, the most common being a Meckel diverticulum, but a
duplication cyst or a mass, such as lymphoma, may also be found.
Most idiopathic intussusceptions are found in association with
lymphoid hyperplasia of the Peyer patches of the terminal ileum.
Children who present with idiopathic intussusception typically
range from 6 months to 2 years of age. Such episodes are usually
postviral in nature and tend to be more common in the winter and
spring. The classic clinical findings are: abdominal pain (drawing
up of the legs), "currant jelly" stool, and a palpable mass, but
these findings are present in <50% of patients. Since the
accuracy of plain radiographs in diagnosing intussusception varies
significantly, so-nography can play a vital role in the de-tection
of this entity. The advantages of ultrasound are that it is
noninvasive, it does not use ionizing radiation, it eliminates
unnecessary enema examinations, it may provide alternative
diagnoses, and it may have some predictive value as to the
reducibility of the intussusception. The sensitivity of ultrasound
for the detection of intussusception is nearly 100%.
As in the diagnosis of PS, a high-frequency (10 to 15 mHz)
transducer is used as well as a small-parts algorithm, with focal
zones set in the midfield and depth set for a large field of view.
Scanning in both the longitudinal and transverse planes begins in
the right lower quadrant and continues until the entire colon is
scanned. Most of the time, intussuceptions are encountered in the
right upper quadrant or at the level of the mid transverse colon.
If the scan does not reveal an intussusception, a repeat scan using
a probe with a larger field of view is suggested. The appearance of
intussusception in the transverse plane is a large mass with a
"swiss-roll" ap-pearance, representing the various layers of bowel,
which are trapped in the pro-cess (Figure 4). The outer hypoechoic
layer represents the intussuscipiens, and the hypoechoic inner
layer represents the intussusceptum. In the longitudinal plane, the
intussusception displays a "sandwich" sign (Figure 5). The center
of the intussusception is hyperechoic, which represents the
mesenteric fat that is pulled in. Additionally, mesenteric vessels
within the center of the intussusception should be identified
(Figure 6). One may also see lymph nodes within the process (Figure
Free fluid within the abdomen may be seen as a transudative
phenomenon but is not necessarily an ominous sign of bowel
necrosis. The absence of color Doppler flow within the
intussusception may indicate necrotic bowel. Trapped fluid within
the layers of the intussusception may be associated with an
Occasionally, a lead point may be seen, such as a duplication cyst
(Figure 8). It should be noted that the documentation of a lead
point does not necessarily predict that the intussusception is
There are pitfalls in the sonographic diagnosis of
intussusception. A thickened bowel wall may have the appearance of
an intussusception, except that the central mesenteric fat and
vessels are not present, which are essential to the diagnosis
(Figure 9). The psoas muscle can also have the appearance of an
intussusception in the transverse plane if the incorrect choice of
transducers is made. A false-negative diagnosis can be avoided by
making sure that the field of view is not too small as to produce
"tunnel vision." This pitfall can be avoided by rescanning with a
curvilinear probe, if the initial scan with the high-frequency
linear transducer appears to be normal.
There has been much debate in the literature between the use of
ultrasound or computed tomography (CT) in the de-tection of
appendicitis. The decision as to which modality to use largely
depends on the institution. In a recent meta-analysis that studied
the accuracy of both modalities in >9000 pediatric patients,
ultrasound was found to be nearly as sensitive and as specific as
Some of the disadvantages of ultrasound are that it is
operator-dependent, it requires patient cooperation, and the
appendix may not be visualized if there is a lot of bowel gas
present in the right lower quadrant. The major advantages of
ultrasound are the lack of ionizing radiation and the speed with
which the examination can be performed. In our institution, we
start with sonography, and if positive, the patient goes to
surgery. If the examination is negative or equivocal, the pediatric
surgeons decide whether or not to observe the patient or to further
evaluate with CT.
A sonogram performed for appendicitis requires a linear
high-frequency transducer (10 to 15 mHz) and a field of view that
is set so that the psoas muscle is clearly visualized. A graded
compression technique is used and thus there is a gradual but
steady pressure on the region examined with the transducer. The
graded compression technique allows for the determination of
compressible, normal appendix versus noncompressible, abnormal
appendix. We find it useful to have the patient point with 1 finger
to the area in pain and then first scan in that area. However, it
has been advocated that a complete survey of the right lower
quadrant be performed in searching for a normal or abnormal
Most often, the appendix is in the superior aspect of the pelvis,
draped over the psoas muscle, or is retrocecal in position.
The abnormal appendix is enlarged, measuring >6 mm in
transverse diameter, noncompressible, blind-ending, and hyperemic.
Ancillary sonographic findings consist of: heterogeneity of the
surrounding periappendiceal fat secondary to inflammation (Figure
10), an appendicolith (Figure 11), free fluid (Figure 12), and a
frank abscess in cases of perforation. Harmonic imaging has also
been advocated for better delineation of the periappendiceal
findings in appendicitis, especially in patients who are of less
than optimal body habitus for sonography.
The best Doppler sonographic sign of appendiceal rupture is a
hyperemic periappendiceal fluid collection.
Lymphadenopathy may also be present in cases of appendicitis, but
is a nonspecific finding.
Lymphoid hyperplasia of the appendix may produce a
sonographically enlarged appendix, but the morphology of the
appendix in such cases is that of a tubular structure with a
central echogenic stripe sandwiched by hypoechoic layers.
Scrotal pain and swelling
The 3 most common entities that present in the pediatric patient
with scrotal pain and swelling are: torsion of the appendix testis,
testicular torsion, and epididymitis.
Torsion of the appendix testis
Torsion of the appendix testis is the most common cause of
scrotal pain in children. The etiology of a torsed ap-pendix testis
is not known, but it is a self-limiting condition and does not
require surgery. A normal appendix testis is generally not visible
unless a hydrocele is present or it is torsed. As in all of scrotal
imaging, a high-frequency transducer is used. In the transverse
plane, a torsed appendix testis presents as a heterogeneous
structure medial to the testicle (Figure 13). The torsed appendix
generally has a "swiss cheese" appearance. Since the epididymis
lies along the lateral surface of the testicle, a "Mickey Mouse"
sign is produced when a torsed appendix is present (Figure 13). The
epididymis and testis may also be enlarged and hyperemic; on color
Doppler, the testis may resemble a detorsed testis. The key to the
diagnosis is the visualization of the enlarged, avascular appendix
testis. In subacute torsion, the appendix testis can become
progressively echogenic, (Figure 14) calcify, or undergo
There are 2 age peaks for testicular torsion in children:
newborn and adolescence. There are 2 types of testicular torsion:
extravaginal and intravaginal. With extravaginal torsion, which is
more common in the neonate, the testicle, epididymis, vascular
plexus, and tunica undergo torsion. With intravaginal torsion,
which is most common in the adolescent, all of the intravaginal
contents torse except for the tunica. Sonography has a high
sensitivity and specificity for testicular torsion in young
children and adolescents.
Color Doppler detection of blood flow to the neonatal testes may be
difficult, even in a normal state. The gray-scale findings in
testicular torsion depend on the duration of the torsed state. In
early torsion, the abnormal testicle may have a normal appearance
on gray-scale imaging (Figure 15). However, decreased or no blood
flow to the torsed testicle will be found on color Doppler imaging.
Ancillary signs of acute torsion include an abnormal position of
the testicle (Figure 16), enlarged epididymis, reactive hydrocele,
and scrotal skin thickening (Figure 17). After 4 to 6 hours, the
torsed testicle is enlarged and hypoechoic because of edema. In
late testicular torsion, the testicle is enlarged and heterogeneous
because of hemorrhage, vascular congestion, and ischemia (Figure
18). The torsed testicle may undergo spontaneous detorsion. In such
cases, color Doppler ultrasound will show a reactive hyperemia to
the epididymis and testicle and may be indistguishable from
epididymitis (Figure 19).
Epididymitis represents an infectious inflammation of the
epididymis and is most common in pubertal males. Prior to puberty,
epididymitis may be the result of an ectopic ureter or from chronic
bladder obstruction. We have had several cases of epididymitis in
boys as a result of a recent history of trauma to the scrotum. In
cases of epididymitis, gray-scale images will reveal an enlarged
epididymis and testicle if there is con- comitant orchitis. A
reactive hydrocele and thickening of the scrotal wall and tunica
may also be seen (Figure 20). Color Doppler sonography reveals
marked hyperemia to the epididymis (Figure 20).
Sonography can play a vital role in the diagnosis of pediatric
abdominal and scrotal emergencies. As sonography provides rapid
diagnoses, without the use of ionizing radiation, it has become the
"workhorse" of anyone involved with imaging of children.