Gastroschisis Imaging

Updated: Nov 28, 2016
  • Author: Ali Nawaz Khan, MBBS, FRCS, FRCP, FRCR; Chief Editor: Eugene C Lin, MD  more...
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Overview

Overview

Gastroschisis represents a herniation of abdominal contents through a paramedian full-thickness abdominal fusion defect. The abdominal herniation is usually to the right of the umbilical cord. No genetic association exists. A gastroschisis usually contains small bowel and has no surrounding membrane. The herniated bowel is not rotated and is devoid of secondary fixation to the posterior abdominal wall. [1, 2, 3]

Gastroschisis occurs 1 in 2000 births and is ordinarily detected during prenatal ultrasound scans. Fetal outcome varies from uncomplicated surgical correction to stillbirth or neonatal death. Early markers on ultrasound indicating increased mortality include abdominal circumference less than 5th percentile and an abnormal gastric bubble. [4]

(See the images below.)

Axial sonogram through the mid to upper abdomen. T Axial sonogram through the mid to upper abdomen. This image shows free-floating exteriorized bowel in relation to the anterior abdominal wall. S = stomach; V = spine.
Diagram of the transverse section of the fetal abd Diagram of the transverse section of the fetal abdomen showing gastroschisis. Note the bowel herniation in the right paramedian/paraumbilical region. The cord is inserted in the normal location to the left of the herniation. No membranous covering exists over the herniated bowel.
Ultrasound of fetal abdomen showing anterior wall Ultrasound of fetal abdomen showing anterior wall defect.

Because the herniated bowel is bathed by amniotic fluid, both maternal serum and amniotic fluid alpha-fetoprotein (AFP) levels are elevated, more so than in exomphalos. Thus, gastroschisis is found incidentally or because of an elevated maternal AFP level, a finding in 77-100% of cases. Rarely, polyhydramnios may prompt an antenatal sonographic examination. Fetal growth restriction is a frequent association. Oligohydramnios is rare. Chromosomal anomalies are not associated with gastroschisis, and familial occurrence is exceptionally rare.

Gastroschisis usually is detected in the second trimester using antenatal sonography. [5, 6, 7, 8, 9, 10, 11, 12, 13] The diagnosis can often be made by using antenatal sonography before 20 weeks' gestation. With transvaginal sonograms, the diagnosis has been made as early as 12 weeks' gestation.

In early pregnancy, the bowel loops can be seen floating in the amniotic fluid. The thickness and the diameter of the bowel are normal. Later in pregnancy, bowel obstruction, peritonitis, bowel perforation, and fetal growth restriction may occur. Intrauterine growth restriction (IUGR) occurs in 38-77% of fetuses and is usually secondary to nutrient loss through exposed bowel. Approximately 48% of infants with gastroschisis are small for their gestational age. [14]

A bowel diameter greater than 17 mm usually represents significant bowel dilatation, and diameters greater than 11 mm are usually associated with a greater number of postnatal bowel complications. Sonographic findings of bowel abnormalities are associated with difficult abdominal wall repair and an increased incidence of complications.

Approximately 50% of fetuses with gastroschisis are small for their gestational dates. Fetal abdominal circumference, which is regarded as a standard reference for assessment of fetal size, does not apply to this group of fetuses; therefore, obstetric management may be difficult.

The mortality rate of gastroschisis is approximately 17%. Surgical repair should be offered within the first day after delivery to avoid infection. The outcome is no different in infants delivered in tertiary obstetric centers than in infants delivered in smaller peripheral hospitals, although delivery within easy access of a neonatal surgical unit is advised. Cesarean delivery is performed in many mothers of fetuses with gastroschisis, although this does not convey any advantage over vaginal delivery.

A recent meta-analysis by South and associates has shown that the overall incidence of intrauterine fetal death (IUFD) in gastroschisis is much lower than previously reported. The largest risk of intrauterine IUFD occurs before routine and elective early delivery would be acceptable. The analysis has concluded that the risk for IUFD should not be the primary indication for routine elective preterm delivery in pregnancies that are affected by gastroschisis. [15]

Preferred examination

Antenatal sonography is the key imaging examination available, with detection rates of 70-72%. Prenatal sonography is the primary imaging modality in pregnancy because it is noninvasive, is rapid, and allows real-time fetal examination. Plain radiographs and bowel contrast studies may be indicated in the postnatal postoperative period to assess bowel complications.

In studies exploring the association between antenatal ultrasound signs and outcomes in gastroschisis,  significant positive associations were identified between intra-abdominal bowel dilatation (IABD) and bowel atresia, polyhydramnios and bowel atresia, and gastric dilatation and neonatal death. No other ultrasound sign was significantly related to any other outcome. [3]

With the use of antenatal sonography, the diagnosis of a surgically treatable malformation is made before birth in an increasing number of fetuses. This allows fetal intervention, in utero transfer, planned delivery in a specialized unit, and antenatal counseling of the parents regarding the likely prognosis and outcome. [16]

Limitations of techniques

Sonography remains operator dependent, and artifacts are a problem. Despite the straightforward nature of the defect, a diagnosis of gastroschisis can be missed.

Misdiagnosis of exomphalos as gastroschisis has occurred in 5% of patients. This misdiagnosis has serious implications because exomphalos is often associated with chromosomal and other severe anomalies and karyotyping is not performed in patients with gastroschisis.

In one case series, gastroschisis was misdiagnosed as exomphalos at a rate of 14.7%. This misdiagnosis results in unnecessary amniocentesis, which exposes the fetus to the risks involved in amniocentesis and which also exposes the mother to psychological trauma.

Assessment of fetal size by using abdominal circumference measurements is difficult in the presence of gastroschisis. Postnatal plain radiographs and bowel-contrast studies lack specificity and expose the infant to a radiation burden. However, Siemer et al have developed a sonographic weight formula for fetuses with abdominal wall defects. [14] The authors evaluated their formula in a group of 97 fetuses with either gastroschisis or omphalocele and concluded that it provided a significantly greater accuracy in estimating fetal weight than a more commonly used formula. More data will be necessary to determine the utility of Siemer et al's formula.

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Radiography

Conventional radiography is no longer used in the assessment of fetal abnormalities because this imaging modality exposes both the mother and fetus to an unnecessary radiation burden. However, conventional radiology does have a role in postnatal evaluations, particularly in infants in the postoperative period.

A minority of infants develop complications, such as necrotizing enterocolitis, short-bowel syndrome, persistent bowel dysfunction, and cholestatic jaundice. Investigation by means of plain imaging, contrast studies, and sonographic examinations are necessary and helpful in these patients.

Plain images reveal bowel-wall thickening, luminal dilatation, and generalized abdominal distention. A small-bowel enema is considered superior to conventional follow-through in distinguishing mechanical obstruction from functional obstruction in infants with persistent bowel dilatation. [17]

Degree of confidence

Conventional radiographs demonstrate poor resolution between maternal parts and fetal parts, and they have no place in antenatal management.

Plain-film and contrast radiography are excellent noninvasive procedures for use in the investigation of the postoperative persistent gaseous distention in infants, and plain radiography remains the most useful noninvasive procedure in the radiographic diagnosis of small bowel obstruction despite its limited sensitivity (50-66%). When plain radiographic findings are combined with the clinical history and results of physical and laboratory examinations, a confident diagnosis of small bowel obstruction can usually be made.

False positives/negatives

Plain radiographs cannot always be used to differentiate mechanical obstruction from functional obstruction. Differentiating an adynamic ileus from a mechanical small bowel obstruction may be particularly difficult, especially in the immediate postoperative period.

Eventually, most intestinal obstructions (especially when strangulation is present) may lead to an adynamic ileus, which is associated with perforation and peritonitis. Under these circumstances, gas may appear in the small bowel proximal to the obstruction or may be retained in the atonic colon, leading to diagnostic confusion.

Little or no gas within the small bowel may lead to a false-negative diagnosis.

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Computed Tomography

The computed tomography (CT) scan appearance of fetal gastroschisis discovered as an incidental finding was reported in a 25-year-old woman who was pregnant and who underwent CT scanning for blunt abdominal trauma. [18] However, the high radiation burden makes CT scanning unsuitable for use in the assessment of fetal anomalies.

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Magnetic Resonance Imaging

In general, magnetic resonance imaging (MRI) has not been used in the diagnosis of gastroschisis, partly because MRI is time consuming, expensive, and limited in availability. Moreover, to date, the image quality has been poor. Some of these problems have been overcome with the use of ultrafast sequences; therefore, MRI can be used as an adjunct to sonography, especially in patients in whom sonographic findings are unclear or degraded as a result of obesity or oligohydramnios. [5, 19, 20, 21, 22, 23, 24]

MRI findings frequently add information beyond that available with sonograms. This information commonly changes patient counseling and, at times, patient treatment. [5, 19, 20, 21, 22, 23] MRI does provide a global view of the fetus and analysis of the anatomy in multiple planes. This imaging modality is useful in the diagnosis of intestinal obstruction and detection of microcolon, malrotation, and volvulus.

Degree of confidence

Fetal MRI during the first trimester remains controversial secondary to biosafety issues, and its use is limited because of the diminutive fetal size. However, fetal abdominal masses are well depicted on MRIs, and the performance of MRI is not affected by diminished amounts of amniotic fluid.

False positives/negatives

Sufficient experience has not yet been gained in the diagnosis of anterior abdominal wall defects with MRI to determine the existence of false-positive findings.

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Ultrasonography

Prenatal sonography is the primary imaging modality in pregnancy because it is noninvasive and rapid, and because it allows real-time fetal examination. [3, 25, 26, 27, 4]

The anterior abdominal wall and umbilical cord insertion are readily recognized on antenatal scanning because the wall provides a direct interface between itself and the amniotic fluid. The anterior abdominal wall is best demonstrated by axial scans. Assessment of the lower anterior abdominal wall is occasionally made difficult by flexed fetal limbs. The inner aspect of the anterior abdominal wall is difficult to see because its echodensities are identical to the remainder of the abdominal viscera unless fetal ascites is present. [28, 29]

Gastroschisis results from herniation/evisceration of small bowel into the amniotic cavity through a small defect (2-5 cm) in the right paraumbilical region. Reportedly, the defect can be located in the left paraumbilical region, but this site is extremely rare. No covering membrane exists. The large bowel (common), pancreas, stomach, liver (rare), spleen, bladder, uterus, ovaries, and fallopian tubes may also be herniated. The attachment of the umbilical cord is normal.

Sonographic features that suggest gastroschisis

Findings include exteriorized bowel in relation to the anterior abdominal wall (see image below), multiple loops of bowel, and a thickened bowel floating freely in the amniotic fluid. The bowel can be identified by its characteristic sonographic pattern.

Axial sonogram through the mid to upper abdomen. T Axial sonogram through the mid to upper abdomen. This image shows free-floating exteriorized bowel in relation to the anterior abdominal wall. S = stomach; V = spine.

Because no covering is present around the bowel loops, the bowel loops of a gastroschisis result in a mass with irregular edges (see image below).

Axial sonogram through the mid abdomen of a fetus. Axial sonogram through the mid abdomen of a fetus. This image shows exteriorized bowel in relation to the anterior abdominal wall. Multiple loops of bowel are depicted. Because the bowel loops are not covered, they have irregular edges. L = liver.

Usually, the small and large bowels are herniated, but, occasionally, the stomach, liver, gallbladder, spleen, uterus, adnexa, and urinary bladder may be herniated.

Signs of intestinal obstruction may be depicted; examples of these include multiple distended loops of bowel (both intraperitoneal and extraperitoneal), bowel loops greater than 17 mm in diameter, and increased peristalsis. Polyhydramnios may ensue in high intestinal obstructions. A bowel diameter of greater than 17 mm usually represents significant bowel dilatation, and diameters greater than 11 mm are usually associated with a greater number of postnatal bowel complications.

A right paramedian paraumbilical abdominal wall defect is revealed, usually of 2-5 cm.

Insertion of the umbilical cord is normal.

Typically, no ascites is noted.

Bowel perforation can cause calcification and an intramesenteric extra-abdominal pseudocyst.

Unlike with omphalocele, associated anomalies are uncommon, but if present, most are detectable on antenatal sonography.

A 13-year retrospective analysis of ultrasound images in 59 pregnancies affected by fetal gastroschisis found that the only statistically significant predictor of complex cases of gastroschisis was extra-abdominal bowel dilatation. However, approximately 75% of the infants with gastroschisis with associated extra-abdominal bowel dilatation had simple gastroschisis. [25]

In an 11-year retrospective study of of prenatal ultrasound markers for complex gastroschisis in the first 10 days of life,  third-trimester intra-abdominal bowel dilatation (IABD) adjusted for gestational age appeared to be the prenatal ultrasound marker most strongly associated with adverse outcome. [27]

Other considerations

Color Doppler and Doppler velocimetry of the mesenteric circulation have been used in the diagnosis of gastroschisis, but findings add little to the clinical outcome and are not predictive of a poor neonatal outcome. [30]

Addition of 3-dimensional (3-D) sonography in patients with abdominal wall defects can help in family counseling and in planning postnatal therapy. [7]

Sonography can be used in the postoperative neonatal period when images may demonstrate features of intestinal obstruction, volvulus, perforation, ascites, and other fluid collections.

Degree of confidence

The sensitivity of abnormality detection using sonography is 75% for gastroschisis and 77.3% for omphalocele. Ultrasound sensitivity in the diagnosis of gastroschisis has improved considerably over the past 2 decades.

False positives/negatives

Other anterior abdominal wall defects may mimic gastroschisis, but with the use of modern ultrasound equipment, confusion should not arise. When the liver is intra-abdominal in an omphalocele, a false diagnosis of gastroschisis may be entertained; however, the many anomalies associated with omphalocele should indicate the correct diagnosis. [14, 31] Bladder extrophy, body-stalk anomaly, and periumbilical blood clots are other mimics of gastroschisis.

Differentiation from physiologic bowel herniation: Physiologic bowel herniation occurs at 10-13 weeks. The best method for differentiating this from an omphalocele is to obtain a repeat sonogram after 15 weeks' menstrual age. A large defect with the liver exteriorized indicates an omphalocele at any gestational age.

Differentiation from umbilical hernia: Umbilical hernia results from a defect in the linea alba; the protruding bowel is covered by subcutaneous tissues and skin. Umbilical hernia is common in the first months in 20% of black neonates and in 3% of white neonates, as well as common in premature infants, namely, in more than 5% of premature infants weighing less than 1500 g. Sonographic findings include a prominent bulge of the anterior abdominal wall that may contain omentum and/or bowel, which may protrude into the umbilical cord. Amniotic fluid AFP levels may be elevated when the bowel is herniated into the umbilical cord.

Differentiation from bladder extrophy: Sonographically, bladder extrophy may present as an external, well-defined, solid or complex mass immediately superior to the fetal genitalia. Prolonged and repeated scans fail to reveal the fetal bladder. The renal collecting system and ureters need not be dilatated, and unilateral or horseshoe kidneys may be found. Uterine and adnexal anomalies are relatively frequent. The pubis is abnormally wide, and the umbilical cord insertion may be abnormal.

Differentiation from cloacal extrophy: Cloacal extrophy consists of a low omphalocele; bladder or cloacal extrophy; and, frequently, other caudal anomalies. These other conditions may include meningomyelocele anal atresia and lower limb anomalies. Most affected fetuses have a single umbilical artery. Sonographic findings include a low anterior abdominal mass below the umbilical cord that is associated with an absent urinary bladder.

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