AJR 2005; 184:1010-1016
© American Roentgen Ray Society
Prenatal MRI of Congenital Abdominal and Chest Wall Defects
Pedro Daltro1,
Bradley L. Fricke2,
Beth M. Kline-Fath2,
Heron Werner1,
Leise Rodrigues3,
Tatiana Fazecas3,
Romeu Domingues3 and
Lane F. Donnelly2
1 Clinica de Diagnostico por Imagem, Barra da Tijuca; Instituto Fernandes
Figueira-FIOCRUZ-Rio de Janeiro, Brazil.
2 Department of Radiology, Cincinnati Children's Hospital Medical Center, 3333
Burnet Ave., Cincinnati, OH 45229-3039.
3 Instituto Fernandes Figueira-FIOCRUZ-Rio De Janeiro, Brazil.
Received June 2, 2004;
accepted after revision August 10, 2004.
Address correspondence to L. F. Donnelly.
Introduction
Fetal MRI is being increasingly used in the evaluation of fetal
abnormalities [1]. It is
particularly useful in evaluating the anatomic details of complex anomalies
[1–9].
The additional information beyond that obtained on fetal sonography can be
useful for prenatal counseling, planning for delivery, and planning for
prenatal or postnatal intervention. We describe and illustrate the fetal MRI
appearances of congenital abdominal and chest wall anomalies.
Fetal MRI is performed with a single-shot rapid acquisition sequence with
refocused echoes. This sequence minimizes effects from fetal motion by
producing T2-weighted images in less than a second. Gradient-echo T1-weighted
imaging is used as an adjunct to verify meconium in the bowel, liver anatomy,
or intracranial hemorrhage.
Omphalocele
An omphalocele is an anterior abdominal wall defect encased by parietal
peritoneum that results in the herniation of abdominal contents into the base
of the umbilical cord [2,
3]. Omphalocele occurs in one
of every 4,000 live births [2,
4]. Omphaloceles that contain
liver parenchyma are thought to result from the failure of the lateral
mesodermal body fold to migrate centrally and close the body wall
[2,
3]. Omphaloceles consisting of
mostly bowel with no evidence of liver parenchyma may result from the
persistence of the primitive body stalk beyond 12 weeks' gestation
[2].
Omphaloceles are commonly (54.2%) found to be associated with other
anomalies, which determines prognosis
[2,
3]. Chromosomal abnormalities,
especially trisomy 13 and 18 syndromes, occur in 30–40% of patients
[2,
3]. Beckwith-Wiedemann
syndrome, which includes macrosomia, macroglossia, and organomegaly, is found
in 5–10% of patients born with omphalocele
[2,
3]. Other associated defects
include cardiac, genitourinary, gastrointestinal, musculoskeletal, neural
tube, and head and neck anomalies
[2,
3].
Diagnosing omphalocele on prenatal sonography in the second or third
trimester has varying rates of success (66–93%)
[5,
9]. Additional anatomic detail
can be obtained on MRI. MRI evaluation of the fetus with omphalocele shows a
central abdominal wall defect, with abdominal viscera herniating into a
thin-walled sac separate from the surrounding amniotic fluid (Figs.
1A,
1B, and
1C). The liver can be seen on
MRI as a solid organ of low signal intensity on T2-weighted images (Figs.
2A,
2B, and
2C). The signal of the liver on
prenatal MRI is often lower than that seen in the liver on similar sequences
in children and adults.
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Fig. 1A. —Omphalocele in 31-week fetus. Sagittal MR images show herniation
through anterior abdominal wall defect of bowel and peritoneal covering
(arrows). In B, liver (L) is interior to abdominal wall.
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Fig. 1B. —Omphalocele in 31-week fetus. Sagittal MR images show herniation
through anterior abdominal wall defect of bowel and peritoneal covering
(arrows). In B, liver (L) is interior to abdominal wall.
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Fig. 1C. —Omphalocele in 31-week fetus. Photograph of infant shows omphalocele
protruding through anterior abdominal wall defect. Peritoneal covering
(arrows) has been incised and pulled away to reveal bowel. (Reprinted
with permission from [9])
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Fig. 2A. —Omphalocele in 26.3-week fetus. Sagittal MR images show herniation
through anterior abdominal wall defect of liver and bowel and peritoneal
covering (arrows). In B, stomach (S) is interior to abdominal
wall.
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Fig. 2B. —Omphalocele in 26.3-week fetus. Sagittal MR images show herniation
through anterior abdominal wall defect of liver and bowel and peritoneal
covering (arrows). In B, stomach (S) is interior to abdominal
wall.
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The mortality rate is 80% when any associated defect is present and
increases to near 100% when chromosomal or cardiovascular anomalies exist
[2]. However, if an omphalocele
is found in isolation, then the mortality rate decreases to 10%
[2]. Therefore, detection of
associated abnormalities on fetal imaging has great prognostic significance.
In uncomplicated cases, the size of an omphalocele does not affect prognosis
[4]. Accurate diagnosis is
essential for parental counseling to avoid misclassification between
omphalocele and gastroschisis, which may influence elective termination rates
[3].
Gastroschisis
Gastroschisis is the herniation of fetal bowel loops into the amniotic
cavity through a typically right-sided paraumbilical abdominal wall defect
[2,
6]. This anomaly does not have
a surrounding membrane and has an incidence of 1–6 per 10,000 live
births [6]. The cause of
gastroschisis is unclear but likely is heterogenous
[2,
3,
6, 10]. One theory states that
premature atrophy or abnormal persistence of the right umbilical vein results
in rupture of the anterior abdominal wall at a point of weakness
[2,
6]. Another speculates the
defect is caused by ischemic damage to the anterior abdominal wall by
premature interruption of the omphalomesenteric artery
[2,
6].
Associated anomalies are rare in gastroschisis except related bowel
abnormalities, usually intestinal atresia or stenosis from vascular compromise
[2,
5,
6]. Other bowel complications
include obstruction, perforation, peritonitis, motility dysfunction,
necrotizing enterocolitis, short-gut syndrome, and fistulas
[6]. The intrauterine mortality
rate is 10–15%, and the condition of the bowel at birth is the single
most important prognostic factor
[6].
MRI evaluation shows bowel loops herniating through an abdominal wall
defect adjacent to an intact umbilical cord. The bowel loops are not
surrounded by a membrane and can be seen freely floating in the amniotic fluid
(Fig. 3). Bowel loops may be
dilated and fluid-filled with a thickened bowel wall, indicative of bowel
abnormalities [2,
5,
6] (Figs.
4A,
4B, and
4C). The presence of
free-floating extracorporeal solid organs may indicate a ruptured omphalocele
is present rather than gastroschisis
[5]. Overall survival rates are
good (85–97%) [6], but a
mortality rate of up to 28% has been reported, usually from prematurity,
sepsis, and associated bowel abnormalities
[4]. Antenatal diagnosis of
gastroschisis may facilitate planned delivery in a specialized unit, parental
counseling, and surgical planning.
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Fig. 4A. —Gastroschisis in 30-week fetus. Sagittal MR image shows bowel loops
(arrows) outside abdominal cavity. Bowel is dilated and fluid-filled,
indicative of bowel abnormality. No peritoneal covering is seen.
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Pentalogy of Cantrell
In 1958, Cantrell described a syndrome consisting of defects of the midline
supraumbilicus, the lower sternum, the anterior diaphragm, the diaphragmatic
pericardium, and the heart [2,
4,
7,
9]. Pentalogy of Cantrell is
rare, with fewer than 60 cases reported in the literature
[4]. The cause is thought to
result from incomplete ventral migration of sternal anlage and myotomes at
14–19 days of gestation
[7]. The sternal and abdominal
wall defects are thought to arise from this abnormal mesodermal migration
[4]. Failure of the transverse
septum to develop and abnormal development of the myocardium result in
diaphragmatic and cardiac defects, respectively
[4].
The abdominal wall defect is commonly an omphalocele, but diastasis recti
abdominis, epigastric hernia, and umbilical hernia have also been reported
[7]. An inferior sternal cleft
usually constitutes the sternal defect, with the heart external to the defect
[7]. The anterior diaphragmatic
defect is present in 91% of cases, and continuity between the pericardial and
peritoneal cavities is not rare
[7]. Ventricular septal defect
is almost universal, with pulmonic stenosis, atrial septal defect, and
tetralogy of Fallot occurring less commonly
[7]. Patients may also have
diverticula of either ventricle, with left diverticula occurring more
frequently [7]. This syndrome
may be associated with chromosomal anomalies, including trisomy 13 and 18
syndromes and Turner's syndrome
[4]. Other associated anomalies
include ascites, a two-vessel cord, scoliosis, and craniofacial abnormalities
[4].
Imaging findings usually show omphalocele, ectopic heart, and pericardial
or pleural effusions [4] (Figs.
5A,
5B,
5C,
6A,
6B, and
6C). The diaphragmatic defects
may be difficult to characterize on MRI
[4]. The prognosis of pentalogy
of Cantrell depends on the severity of associated abnormalities but is
generally poor, with a high infant mortality rate
[2,
4,
7]. Cardiac diverticula should
be repaired early to prevent rupture, and staged repair may help alleviate
high intraabdominal and intrathoracic postoperative pressures
[7].
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Fig. 5A. —Pentalogy of Cantrell in 32-week fetus. Frontal chest radiograph on
day 1 of life (after 32 weeks' gestation) shows heart (arrows)
outside thoracic cavity. Rim of increased radiolucency (arrowheads)
is seen around liver, suggesting liver is outside abdominal cavity.
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Fig. 5B. —Pentalogy of Cantrell in 32-week fetus. Sagittal MR image obtained
at 20 weeks' gestation shows heart (arrows) outside thoracic cavity.
Liver (arrowhead) is seen protruding through anterior abdominal wall
defect.
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Fig. 6B. —Pentalogy of Cantrell in 27-week fetus. Axial MR image shows heart
(H) and liver (L) protruding from defect in anterior body wall of fetus.
Bilateral pleural effusions (P) are evident. (Reprinted with permission from
[9])
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Limb–Body Wall Complex
Limb–body wall complex consists of a variable group of congenital
limb and body wall defects of the chest and abdomen
[4]. Reported defects include a
large, usually left-sided, abdominoschisis; a thoracic wall defect; rotational
anomalies of the lower limbs; clubfoot; brachydactyly; polydactyly;
syndactyly, absent limbs; and scoliosis
[4,
8]. This syndrome is rare, with
a reported incidence of one in more than 14,000 live births
[4]. The etiology is
controversial; the proposed mechanisms are amnion rupture, early vascular
disruption, and embryologic malformation with abnormal development of the body
folds [4,
8].
Associated craniofacial anomalies include exencephaly, encephalocele, and
facial defects [4,
8]. Myelomeningocele may be
present, leading to Arnold-Chiari malformation and hydrocephalus
[8]. In addition, the internal
organs are frequently affected with a high incidence of cardiac and
diaphragmatic defects, bowel atresia, renal agenesis, and hydronephrosis
[4,
8]. The umbilical cord is
typically short or absent, with the placenta attached to the fetal trunk and
viscera herniated [4] (Figs.
7A,
7B,
7C, and
7D). Amniotic bands are
present in up to 40% of cases
[4].
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Fig. 7A. —Limb–body wall complex in 19-week fetus. Coronal (A)
and sagittal (B) MR images show large anterior abdominal wall defect
(arrows) with liver (L) and bowel (B) attached to placenta (P).
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Fig. 7B. —Limb–body wall complex in 19-week fetus. Coronal (A)
and sagittal (B) MR images show large anterior abdominal wall defect
(arrows) with liver (L) and bowel (B) attached to placenta (P).
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Imaging findings may show an abnormally located placenta without evidence
of an umbilicus [8]. The
abdominal, thoracic, limb, craniofacial, and internal organ anomalies are
variably displayed on imaging evaluation
[4]. Often, herniated abdominal
organs are seen entangled in membranes and forming a complex mass
[4] (Figs.
7A,
7B,
7C, and
7D). Amniotic bands, when
present, may be seen as linear structures but can be nonvisualized as a result
of volume averaging [4].
Limb–body wall complex is universally fatal
[4]. Thus, the prenatal
diagnosis and differentiation of limb–body wall complex from other
abdominal wall defects are crucial for parental counseling
[8].
Bladder Exstrophy
Bladder exstrophy is the herniation of the urinary bladder through an
infraumbilical anterior abdominal wall defect
[4]. The incidence of bladder
exstrophy is one in every 33,000 live births
[2,
4]. This defect occurs during
cloacal development, with abnormal retraction of the cloacal membrane
resulting in eversion of the bladder
[2,
4].
Associated genitourinary findings include extension of the bladder defect
into the urethra, incomplete testicular descent, and bilateral inguinal
hernias [2]. Bladder exstrophy
is also associated with OEIS complex (omphalocele, extrophy [bladder],
imperforate anus, spinal defects)
[4]. This complex can be
differentiated from limb–body wall complex by the placental involvement
and scoliosis seen with limb–body wall complex in OEIS complex
[4]. Complications of bladder
exstrophy include urinary incontinence, infertility, and pyelonephritis
[2].
Imaging findings of bladder exstrophy include a soft-tissue mass extending
from a large infraumbilical anterior wall defect
[2,
4] (Figs.
8A and
8B). The absence of a normal
urinary bladder and a low-lying umbilical cord insertion may also indicate the
diagnosis [4]. Prognosis is
good for bladder exstrophy, with surgical intervention required for primary
closure or excision with urinary diversion
[2,
4].
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Fig. 8A. —Bladder exstrophy in 32-week fetus. Sagittal MR image shows bladder
(white arrow) outside anterior body wall. Umbilical cord
(arrowheads) with low-lying insertion (black arrow) is also
seen.
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Introduction
Omphalocele
