Key words
volvulus - pediatric - acute abdomen - appendicitis - ovary - newborn
Introduction
Acute abdomen is a very common reason for presentation to the emergency department,
particularly in the case of children. The following article aims to provide an overview
of important aspects of the topic for radiologists – in particular for radiologists
who are only occasionally confronted with pediatric radiology cases. The clinical
evaluation of the abdomen during childhood, and in particular in young children, is
complicated by the fact that children are often unable to adequately express their
complaints. As a result, every “stomach pain” in the child or adolescent has a certain
degree of “acuteness”, and imaging plays an important role. Due to age-specific characteristics,
the subdivision into three different age groups appears sensible: neonates, infants
and toddlers, and school age children. From adolescence onwards, adult medicine diagnoses
must be incorporated into the differential diagnostic considerations. Trauma-related
causes of acute abdomen are not included in this paper. An overview of the different
clinical pictures is provided in [Table 1].
Table 1
Age-related causes of acute abdomen.
|
Neonates
|
Infants/toddlers
|
School children/adolescents
|
|
Necrotizing enterocolitis
|
Intussusception
|
Appendicitis
|
|
FIP = focal intestinal perforation
|
Hypertrophic pylorus stenosis
|
Ovarian torsion
|
|
Atresia/stenosis
|
Ingestion of foreign body
|
Testicular torsion
|
|
Meconium ileus
|
Meckel’s diverticulum
|
Gastroenteritis
|
|
Meconium plug syndrome
|
Bowel duplications
|
Cholecystitis
|
|
Hirschsprung’s disease
|
Basal pneumonia
|
Pancreatitis
|
|
Volvulus
|
|
|
Neonatal period
The primary symptoms of an acute abdomen in neonates are a distended abdomen and bilious
vomiting. Causes of ileus in this age group can be congenital, acquired, or a combined
congenital and acquired etiology.
In the neonatal period, both ultrasound and conventional X-ray diagnostics and bowel
fluoroscopy with contrast media (usually water-soluble) are used for the diagnosis.
Abdominal X-ray (AB) is often the first diagnostic imaging tool in neonates with abdominal
problems, if necessary supplemented by imaging in the left lateral position [1]. CT and MRI examinations are not applicable to this age group. Fluoroscopy should
be performed with adequate collimation, pulsed, and using ‘last image hold’. Gastrointestinal
tract and colon contrast enemas are administered [1]. Transient hypothyroidism has been described in premature babies and neonates after
the administration of iodinated contrast media [2]. In our clinic, thyroid levels are therefore followed up 7–10 days after the administration
of contrast media.
Necrotizing enterocolitis (NEC) is the most common and most serious disease in the
neonatal period. It mainly affects physiologically immature preterm infants [3]. NEC is the most common pediatric gastrointestinal surgical emergency in preterm
infants [4] and most frequently occurs at 14 to 21 days of age [5]. There is an increased risk of developing ileus adhesions and short bowel syndrome
[4]. Clinical symptoms manifest in the form of feeding difficulties, vomiting, distended
abdomen with pressure pain, and possibly bloody stool. The abdominal skin is bluish
or reddened [3]. Dilated, distanced intestinal loops, intramural gas, gas in the portal vein, and
free air in pneumoperitoneum can be seen on abdominal overview radiograph ([Fig. 1a–c]) [6]. Ultrasound is more sensitive in experienced hands than X-rays [3].
Fig. 1 a, b premature baby 33 + 6 weeks. a In the right upper abdomen paramedian with bilateral involvement corresponding to
free gas (“football sign” arrows) in NEC. b X-ray in left lateral position (arrows). Free gas above the liver c Premature baby 27 + 2 weeks. Tubular branched air formations projected onto the liver
corresponding to gas in the portal vein system, i. e., pneumatosis hepatis in NEC.
d Premature baby 34 + 3 weeks. Hyperechoic reflexes in the intestinal wall in pneumatosis
intestinalis (arrows).
Ultrasound may identify
-
largely hyperechoic bowel walls
-
intestinal wall thickening (> 3 mm)
-
thinning of the intestinal wall
-
dilated intestinal loops
-
the absence of peristalsis
-
intramural gas in the form of increased echogenicity of the intestinal wall ([Fig. 1 d])
-
focal hyperperfusion or the segmental absence of perfusion
-
increased flow velocity in the mesenteric vessels
-
decreased flow velocity in the portal vein
-
mobile punctate echogenic enhancements on B-scan, short bidirectional spikes on spectral
Doppler superimposed on normal portal vein flow.
A colon contrast enema is not indicated, especially in NEC [4]. Many complex ascites or air bubbles are suggestive of a perforation [3].
A differential diagnosis is focal intestinal perforation (FIP), which can occur in
very physiologically immature preterm babies without signs of inflammation during
the first days of life. The perforation site is often localized to the terminal ileum.
Clinically, FIP is characterized by sudden onset, livid discoloration of the abdomen,
and radiologically by the presence of air bubbles on conventional X-rays [7]. Congenital malformations include atresia. Atresia is the most common cause of ileus in neonates. Duodenal atresia results
from an absence of canalization [8]. Duodenal atresia manifests as vomiting with or without bilious gastric contents.
It occurs pre- or post-papillary. The annular pancreas is a special form. On the X-ray
image, it presents as a typical “double bubble sign” (air in the stomach and duodenum
in the context of an otherwise gas-free abdomen) ([Fig. 2a]) [1]. If it is caused by a duodenal membrane, air can be observed in the intestine in
addition to the double bubble. Small intestinal atresia is a consequence of intrauterine
infarcts, volvulus, or intussusception [8]. In small intestinal atresia, conventional radiography shows a distended stomach
and dilated small intestinal loops without air in the colon ([Fig. 2b]). The microcolon can also be seen by sonography. In the context of atresia, anal
atresia may also result in ileus.
Fig. 2 a Mature newborn, first day of life. Double bubble with air in the stomach and duodenum
in the annular pancreas. b Premature baby 36 weeks. Stomach slightly filled with air when the gastric tube is
in place, proximal small bowel loops dilated, no air in the colon. Small bowel atresia.
Additional findings: Umbilical clamp projected c Premature baby 33 + 6 weeks, first day of life. Almost gas-free abdomen with reduced
transparency and discrete calcifications in meconium peritonitis. NB: Malposition
of umbilical vein catheter with half-loop formation. d 1 year and 5 months. Constipation since beginning complementary feeding. Colon contrast
enema. X-ray in left lateral position. Narrowed, aganglionic rectosigmoid, transition
zone and prestenotic dilatation in Hirschsprung disease.
Meconium ileus is caused by thickened meconium in the distal ileum. Cystic fibrosis is causative
in 80–90 % of cases [9]. Abnormally hard and sticky meconium leads to a retention of meconium into the significantly
enlarged proximal ileum. By sonography, a normal wide terminal ileum can be seen,
filled with a homogeneous mass, dilated in the oral direction, also filled with meconium,
an atone ileum, and a narrow colon. The microcolon can also be visualized by means
of a colon contrast enema; this often also allows the terminal ileum to be flushed
out. The cause of meconium plug syndrome is immature bowel function [1]. A dense meconium plug in the descending colon and rectum leads to the clinical
picture of a deep intestinal obstruction. There is no spontaneous meconium excretion.
In contrast to meconium ileus, the colon is filled. In this case, the colon contrast
enema is both diagnostic and frequently also therapeutic. Meconium peritonitis ([Fig. 2c]) is a consequence of intrauterine intestinal perforation.
Hirschsprung’s disease is an aganglionosis of the myenteric and submucosal plexus in a segment of the distal
bowel of varying length with consecutive permanent contracture and narrowing of the
bowel. The process of meconium excretion is delayed. 80 % of affected individuals
present with anomalies during the neonatal period [1]. The diagnosis is made by fluoroscopy with a colon contrast enema. Here we can see
the distally narrowed segment, the transition zone, and the prestenotic enlarged colon
([Fig. 2 d]). The radiological diagnosis and exact extent should be verified by rectal suction
biopsies.
Combined congenital and acquired ileus etiologies include volvulus and bowel duplications.
“Midgut” volvulus generally occurs during the neonatal period, most commonly during the first week
of life [1], but can also manifest later. It is caused by abnormal positioning of the bowel.
The incompletely rotated and atypically fixed bowel has a small mesenteric adhesion.
This carries the risk of torsion of the bowel, the mesentery, and the superior mesenteric
vein surrounding the superior mesenteric artery, with narrowing of the vessels. The
obstruction arises from an extrinsic peritoneal adhesion, from the midgut volvulus,
or a combination of both [1]. The X-ray can show normal or nonspecific gas distribution in the stomach and intestine,
but also a double bubble as a sign of duodenal obstruction. Distended intestinal loops
may also occur in the context of decreased perfusion. Ultrasound reveals a whirlpool
sign at the level of the mesenteric root with atypical locations of the artery and
superior mesenteric vein ([Fig. 3a], [Video 1]). Persistent ischemia results in loops of thickened small intestinal wall packed
closely together in the mid-abdomen devoid of peristalsis. In terms of the gastrointestinal
tract, the stomach and proximal duodenum are dilated. Distal to the obstruction, a
corkscrew-like contrast enhancement is observed [1]. In general, ultrasound is the first choice examination method as a rapid bedside
or emergency room examination method. The feasibility of reconstituting the continuity
of the gastrointestinal tract needs to be investigated or established immediately
depending on the patient’s condition.
Fig. 3 a Newborn. Transverse color Doppler upper abdomen. “Whirlpool sign” by twisting of
the mesenteric root (different position). b 13-month-old child. Transverse mid-abdominal sonography. Small target sign in ileoileal
intussusception. c 8-month-old infant. Transverse sonography of the right lower abdomen. Persistent
vomiting. Dehydration, later bloody stools. Pathological intestinal target sign in
ileocolic intussusception. “crescent in doughnut” sign – corresponding to mesenteric
fatty tissue (arrows). d 12-month-old child. Transverse mid-abdominal sonography, longitudinal section of
invaginate showing perfusion on color Doppler.
Video 1
Another cause of an acute abdomen is an incarcerated inguinal hernia. Ultrasound can detect intestinal loops in the inguinal canal of boys. The hernial
sac can extend into the scrotum. In girls, the ovary may prolapse in addition to the
bowel. High-resolution sonographic examination may provide evidence of ischemia of
the herniated contents, if appropriate.
Infants and toddlers
An intussusception is the most common abdominal emergency in children younger than two years of age.
Classic symptoms include: spasmodic pain, bloody stool, palpable mass (found only
in approximately 50 % of all cases but in 80–90 % of children younger than 2 years
of age) [10]. It generally involves an ileocolic intussusception, commonly following a viral
infection, and there is a suspected causal association with pathological intestinal
motility and enlargement of lymph nodes or Peyer’s patches. Other forms of intussusception
are rarer and most commonly involve small intestinal intussusception ([Fig. 3b]); These forms are usually transient, and often occur in the context of gastroenteritis.
Ultrasound evidence of the typical cocard phenomenon has a very high sensitivity and
specificity ([Fig. 3c, d], [Video 2]) [11]. Further imaging is generally not required; If perforation in particular is suspected,
an abdominal overview image is required to exclude free intra-abdominal gas accumulation
(the prolapse may be visible as a dense soft tissue mass). The reduction procedure
is usually image-guided either by fluoroscopy or increasingly by sonography in recent
decades. Hydrostatic reduction with a saline solution warmed to body temperature is
used most frequently (pneumatic reduction has the disadvantage of reduced clarity,
particularly with respect to successful monitoring). In our clinic, together with
colleagues from the pediatric surgery department, even in the case of a longer medical
history (as long as there is no evidence of perforation), a reduction procedure is
attempted. We perform this with analgesia, but without sedation (disadvantages of
sedation: extra time and personnel required for monitoring, potential complications)
[12]. Even a partial reduction makes it easier to perform any additional operation. The
reduction procedure is invariably performed under fluoroscopic guidance (pneumatic
or with water-soluble contrast media); Safety and the effectiveness of both methods
is equivalent [13] – the main disadvantage compared to ultrasound is the use of ionizing radiation.
As in other cases, the method used should be the one that the examiner is most familiar
with. After a successful reduction, a sonographic follow-up is necessary as up to
10 % of recurrences occur within 24 hours of the reduction procedure [14]
[15]. In children older than 3 years of age, investigating a causal pathology is warranted.
A pathological lead point is often identified in these cases e. g., Meckel’s diverticulum,
intestinal duplication, polyps, and lymphoma [12] ([Fig. 4a]). In Henoch–Schönlein purpura, intussusceptions (predominantly small intestinal
intussusceptions) have been described as a result of intestinal wall hemorrhage [16].
Video 2
Fig. 4 a 8-year-old boy – ultrasonography of the transverse mid-abdomen. Significant thickening
of the intestinal wall in multifocal Burkitt lymphoma. b 2-month-old infant. Transverse ultrasound of the upper abdomen. Projectile vomiting.
Elongated pyloric canal with increased diameter and thickened muscular wall. Increase
in wall thickness from the prepyloric antrum to the pyloric canal c, d 5-year-old boy, abdominal cramps and therapy-resistant constipation. On the following
day clinical deterioration and bilious vomiting. c Intraoperative site d X-ray ileus. Evidence of 5 small bowel perforations caused by 7 ultra-magnets and
an attached nail.
Non-bilious vomiting in an infant between 3 and 6 weeks of age (also observed in premature
neonates, even in later infancy) is a classic presentation for hypertrophic pyloric stenosis. Weight loss and dehydration occur if the disease is left untreated, and in the longer
term a palpable mass can form in the upper abdomen. The incidence in boys is significantly
higher than in girls (4–5: 1). Ultrasound is the imaging gold standard [17]. With some experience, the pylorus in the infant can be reliably imaged [18]. If gastric air interferes in the pyloric region, imaging from a right-sided position
is generally successful. If this is not the case, the stomach can be used as a sound
window after the administration of a clear liquid. The thickened and elongated pyloric
canal can usually be easily delineated (normal value for muscle thickness up to 3–4 mm,
length of pylorus canal up to 15–19 mm) ([Fig. 4b]) [17]. The passage of fluid through the pyloric canal excludes a pyloric stenosis. Complementary
examinations, specifically a gastrointestinal transit examination are only indicated
in the case of inconclusive findings or an atypical presentation [18].
Meckel’s diverticulum (incomplete occlusion of Ductus omphaloentericus, occurs in approximately 2 % of
the population) is usually asymptomatic. There is low sensitivity of imaging for visualization
of a non-inflammatory Meckel’s diverticulum. Symptoms of Meckel’s diverticulum can
occur at any age. However, 25–50 % of symptomatic Meckel’s diverticulum cases have
been described in children under 10 years of age, most commonly involving an obstruction.
As mentioned above, an inverted Meckel’s diverticulum can be a pathological sign of
an intussusception. In the case of inflammation, differentiation from appendicitis
can be difficult [19]
[20]. The ingestion of foreign bodies is most commonly observed in children between 6 months and 3 years of age. This is
generally asymptomatic [21]; however, when batteries or magnets are ingested, caution is warranted. Ingestion
of a button battery is an emergency, as necrosis occurs very quickly, especially in
the esophagus. Magnetic foreign bodies may be problematic especially in the case of
the ingestion of multiple magnets, which may induce peristaltic disorders and subsequently
intestinal wall necrosis if the magnets are positioned in different regions of the
tract, e. g., the small intestine ([Fig. 4c, d]). Generally, other foreign bodies that have passed through the stomach do not cause
problems. Exceptions have been described [21]. X-ray dense foreign bodies such as magnetic and button batteries are easily detected
with X-ray projection techniques; To reduce the radiation dose, we use a low-dose
technique on the fluoroscopy device (documentation using the “last image hold” function).
Bowel duplication (or cyst duplication) is a less common incidental finding on abdominal
ultrasound. It typically presents as a cyst formation with a multilayered wall adjacent
to a bowel structure. Intra-abdominal duplications are found in 53 % of cases in the
ileum [22]. Symptomatic duplications can present very differently (e. g., as a palpable mass,
intussusception, obstruction).
Acute abdominal pain symptomatology is not uncommon in basal pneumonias! We see this
repeatedly in the context of primary diagnostics, usually in connection with the initial
sonographic examination. Therefore, when taking X-ray abdominal overview images, it
is important to carefully inspect the basal lung sections included in the image. As
a rule, imaging is not required for the diagnosis of uncomplicated gastroenteritis.
School children and adolescents (6–18 years)
School children and adolescents (6–18 years)
The most common pathologies causing an acute abdomen in school children and adolescents
include appendicitis and, in girls, ovarian torsion.
The most important differential diagnoses include:
The frequency peak for appendicitis is 9–14 years of age. In younger children, the
clinical picture can appear completely normal [23]
[24]. The clinical picture of appendicitis is described as right-sided abdominal pain,
which may begin in the epigastric or periumbilical region [24]. As the disease progresses, the pain migrates to the right abdomen. Concomitant
findings include muscular tension, one-time vomiting, fever, leukocytosis, and CRP
elevation, although not all of the above symptoms may be present. Ultrasound is leading
the way in diagnostic imaging. In experienced hands, a sensitivity between 74 % and
100 %, and specificity of 88 % to 99 %, has been reported [25]. An abdominal overview image is only necessary if there are indications of complications
(e. g., obstruction, perforation). If the appendix cannot be detected sonographically
and in the absence of other inflammatory changes, acute appendicitis is less likely,
and a follow-up the next day is the recommended course of action [26]. If the clinical and sonographic findings are unclear, supplementary cross-sectional
imaging may be necessary. High sensitivity and specificity have been reported for
computed tomography [25]. Recent data do not show any disadvantages in terms of using MRI to address this
question ([Fig. 5a]) [27]. This is why the current German guidelines only recommend CT for children and adolescents
in exceptional cases to minimize exposure to radiation [28].
Fig. 5 a 11-year-old child. Acute symptoms and abnormal laboratory parameters, with an appendix
that cannot be demonstrated sonographically. MRI abdomen STIR cor 4 mm. Round low-signal
appendicolith in the right lower quadrant with surrounding free fluid and tissue edema.
b 15-year-old boy. Transverse sonography of the right lower abdomen. Elevated temperature
for 3 days. Last vomited 2 days ago. Inflamed, thickened appendix pictured twice with
marked hyperechoic surrounding reaction. Laparoscopic findings: ulcerophlegmonous
appendicitis. c 8-year-old boy. Transverse sonography of the right lower abdomen. Abdominal pain
and vomiting since the previous day. Hyperechoic structure with acoustic shadows due
to appendicolith. Intraoperative findings: ulcerphlegmonous appendix. d 12-year-old boy. Transverse sonography of the right lower abdomen. Nausea and vomiting.
Subfebrile. Cross-section through the inflamed appendix in the right lower abdomen
(ventrally inconspicuous terminal ileum). Intraoperative findings: perforated appendicitis.
Ultrasound allows the appendix to be visualized as a blind-ended tubular structure
localized to the right abdomen. It identifies the typical wall layers of the intestinal
wall, but without discernible peristalsis [29]. Indicative of appendicitis is an increase in transverse diameter > 6 mm, abolition
of wall stratification, hyperechogenic environmental reaction, hyperemia, and locoregional
lymph node enlargement. Free fluid may occur locally or in the pouch of Douglas. In
addition, the clear indication of pain on deep sonopalpation in the right lower abdomen
is suggestive of an inflammatory altered appendix vermiformis. In most cases, an appendicolith
can be detected [30]. Depending on the stage of inflammation, not all symptoms are present here ([Fig. 5b–d]). It ranges from tip appendicitis to perityphlitic abscess with four-quadrant peritonitis.
If appendicitis is already perforated, the appendiceal wall is no longer delineable, at least in most cases. Free fluid
can often be detected. In some cases, the appendix itself is no longer detectable.
Instead, there is a mostly anechoic mass located in the right abdomen and surrounded
by hyperechoic tissue. Centrally, no perfusion can be detected in the formation; hyperperfusion
is found in the surrounding area. Free perforation into the peritoneal cavity often
reveals interenteric echogenic fluid as evidence of peritonitis [24]. Another important cause of acute abdomen in girls (with a peak during puberty)
is ovarian torsion. This involves a torsion of the ovarian vessels and/or the tube
with subsequent interruption of arterial blood supply and a decrease in venous outflow.
Patients usually report a sudden onset of abdominal pain on the right or left side.
Sometimes nausea or vomiting are also reported [29]
[30]. Ultrasound usually gives a clear picture [31]
[32] of a unilateral organ enlargement (at least up to twice the normal organ size) and
a displacement of the affected ovary to the midline ([Fig. 6]). Typically, follicles may be lined up at the edges. The Doppler sonographic evidence
of perfusion does not exclude torsion (dual vascular supply: ovarian and uterine artery)
[24]. In rare cases, further diagnostic confirmation by MRI is required; In particular,
if an ovarian tumor is suspected to cause the torsion or if it is sonographically
difficult to differentiate from an ovarian cyst hemorrhage. Large ovarian cysts can
also occasionally cause symptoms, hemorrhage, or rupture. In this case, there is usually
plenty of fluid in the pouch of Douglas [32]. In boys, testicular torsion can lead to sudden onset of lower abdominal pain and
also vomiting. Testicular torsion is the rotation of the testicle in the longitudinal
axis of the Funiculus spermaticus. The age peak is between 12 and 18 years [24]. Here, too, the realm of diagnostic imaging primarily centers on sonography, followed
by Doppler sonography. The affected testis may appear enlarged and more anechoic compared
to the other side. At the same time, a lateral comparison may also no longer detect
central vessels by Doppler sonography, and a scrotal edema may occur ([Fig. 7]) [24]. Torsion of the spermatic cord can be documented by imaging ([Video 3]). Increasingly heterogeneous testicular tissue suggests a necrotic zone. Both ovarian
torsion and testicular torsion are a real emergency, as the time to detorsion is crucial
for the subsequent functional capacity of the affected organ. Therefore, in the case
of a strong clinical suspicion of torsion, treatment should not be delayed by performing
diagnostic imaging.
Fig. 6 a, b 14-year-old girl a B-mode b Color Doppler, abdominal pain in right lower abdomen for 4 days. Right ovary significantly
enlarged, multiple cysts in the periphery, lack of perfusion. Intraoperative findings:
360° ovarian torsion.
Fig. 7 a, b 15-year-old boy a B-mode b Color Doppler sonography 4 hours after the onset of symptoms on the left side of
the scrotum, significantly enlarged left testicle, extensive loss of perfusion in
comparison to the right testicle. Intraoperative findings: 720° torsion.
Video 3
In the testis, nearly 100 % functional capacity can be preserved after a maximum of
6 hours of ischemia. After approx. 12 hours of ischemia, only approximately 20–70 %
of testicular function is retained [23]. The differential diagnoses that are well-established in adult medicine will not
be discussed further here.
Summary
The causes of acute abdomen during childhood and adolescence differ greatly from those
in adulthood. Ultrasound is the primary diagnostic imaging tool for diagnosing an
acute abdomen. Sonographic diagnosis is often sufficient to establish the diagnosis;
in the case of intussusception, it is also helpful for treatment/therapy. Additionally,
conventional X-ray and fluoroscopy examinations are necessary, depending on the issue.
Cross-sectional imaging on large equipment (preferably MRI for reasons of radiation
hygiene) is indicated only in selected cases – usually in larger children and adolescents.
Close interdisciplinary cooperation between the different specialties involved is
essential for good patient care.
