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Gastroschisis


Gastroschisis / Non-dilated extra-abdominal bowel

Dilated intra-abdominal bowel in fetus with gastroschisis

Gastroschisis with herniated bowel (arrow) to right of the cord

Findings:

Non-dilated bowel (arrowheads) is seen adjacent to the anterior abdominal wall in this patient with gastroschisis. In the same patient evidence of dilated intra-abdominal bowel is seen. This may be due to atresias or volvulus.

Discussion:

Gastroschisis is an anterior abdominal wall defect in which the fetal intestines herniate through a paraumbilical defect involving all layers of the abdominal wall. The defect is invariably on the right side and usually measures between 2 to 4 cm. There is no covering membrane or membrane remnant. The small intestine always herniates through the abdominal wall defect and lacks normal rotation and fixation to the posterior abdominal wall. In addition to the small intestine, the large intestine, stomach, portions of the genitourinary system and liver may herniate through the defect as well. For reasons which will be discussed below, the defect is virtually always on the right side but in rare cases may be to the left of the umbilical cord insertion. The overall prevalence of gastroschisis is 1 to 2 per 10,000 births, but it may occur as frequently as 7 per 10,000 in births to mothers under 20 years of age. Although the vast majority of cases are sporadic, several cases of familial occurrence have been reported. A male preponderance is often observed.

A number of theories have been proposed to explain the occurrence of gastroschisis. The common thread of most of the plausible explanations for this abnormality is a compromise of vascular supply to the area in the abdominal wall adjacent to the umbilicus. The three most common explanations for the pathophysiology of gastroschisis are: 1) abnormal involution of the right umbilical vein, 2) an intravascular accident of the omphalomesenteric artery and 3) early intrauterine rupture of an omphalocele with complete resorption of the sac. Most investigators believe that premature atrophy or persistence of the right umbilical vein are the most likely explanations for this condition. In both instances, the abnormalities of the right umbilical vein result in a failure of normal collateral circulation from the aorta and result in ischemia of the umbilical ring. While rupture of an omphalocele sac was, at one time, an attractive explanation for gastroschisis, it is unlikely to be the case.

Gastroschisis is frequently accompanied by fetal abnormalities that are known to be directly related to problems in vascularity such as intestinal stenosis and atresia. There is a low incidence of associated abnormalities ranging from 7% to 30%. This is significantly less than occurs with an omphalocele. Most centers do not recommend that either an amniocentesis or formal fetal echocardiogram be performed when this condition is diagnosed.

Fetuses with gastroschisis often have intrauterine growth restriction (IUGR). In a series by Fries et al, 48% of fetuses had IUGR. The etiology of IUGR in these fetuses is uncertain as most of the nutrition occurs as a result of either diffusion or active transport of nutrients across the chorionic villi. It is possible that transmural loss of some nutrients occurs across the bowel wall into the amniotic fluid resulting in decreased growth. Despite the fact that large amounts of bowel are eviscerated in this condition, sonographic biometry, particularly measurement of the abdominal circumference still appears to be useful in the diagnosis of IUGR in these patients. The abdominal circumference is largely determined by the presence and size of the liver which is rarely herniated in patients with gastroschisis. The prognosis of gastroschisis is largely dependent upon the condition of the intestines, ranging from either normal bowel to edematous matted bowel with a fibrous coating and multiple atresias. The etiology of damage to the intestines is thought to be due either to prenatal contact with the amniotic fluid or vascular compromise and ischemia due to constriction at the site of the defect. Over 88% of patients with gastroschisis are liveborn. Most infants are treated surgically on the first day of life with survival rates ranging from 87% to 100%. Unfortunately, such infants may display prolonged intestinal motility dysfunction, bowel atresias or necrosis, necrotizing enterocolitis or hyperalimentation hepatitis, necessitating long hospitalizations with the potential of chronic short-gut complications. Post-surgical death may rarely occur due to infarction and or sepsis.

There has been much interest in the possibility of the antenatal diagnosis of early intestinal damage in fetuses with gastroschisis. Early studies suggested that when the bowel was dilated (either >10 mm or > 17 mm in diameter) infants were at significant risk for neonatal complications including delayed enteral feeding, prolonged hospital stay and significant surgical complications. Two studies, by Babcook et al and Alsulyman et al have questioned the ability of prenatal sonography to predict neonatal outcome in fetuses with gastroschisis. In the study by Babcook et al, interestingly enough there was poor interobserver correlation of findings of abnormal bowel. In the study by Alsulyman et al there was no significant difference in complication rate of those groups with prenatal sonographic bowel measurements less than or greater than 17 mm. Even if sonography were accurate in the diagnosis of intestinal complications in patients with gastroschisis there are two major criticisms of attempts to use sonographic information to alter obstetrical management of these patients: 1) many investigators believe that at the time when sonography can unequivocally detect damaged intestine it may be irreversibly affected and 2) at the time at which sonography might detect damage to the intestine, the fetus may be too premature for delivery (a more critical factor in determining overall complications). There are two potential pitfalls when one is attempting to evaluate the bowel sonographically for damage: the normal colon may be quite prominent particularly in the third trimester and the normal mesentery may create the appearance of thickened bowel.

Dilatation of small and large bowel (greater than normal) in a fetus with gastroschisis

Thickening of non-dilated bowel in a fetus with gastroschisis

Normal blood flow to the bowel in a fetus with gastroschisis

The major differential diagnoses of a gastroschisis include : omphalocele, amniotic band syndrome (body stalk abnormality) and normal midgut herniation. In gastroschisis the umbilical cord inserts normally into the anterior abdominal wall and the defect is to the right of the insertion site. There is no covering sac and the liver is normally within the abdominal cavity. In an omphalocele, the umbilical cord inserts centrally into the eviscerated sac. Liver is almost always herniated into the sac and the incidence of associated anomalies is high. Amniotic band syndrome or limb-body wall complex are almost always non-anatomic defects. The defect is often more lateral and associated anomalies are common, particularly of the spine or extremities. Perhaps the most common diagnostic dilemma is differentiating either a gastroschisis or omphalocele from the presence of normal embryonic midgut herniation between the 6th and 10th week of gestation. An interesting study by Bowerman evaluated the size of the normal midgut herniation as a way to differentiate it from abdominal wall defects. In his study all fetuses with a crown-rump length of 38 mm or less, and two of six fetuses with a crown-rump length of 40 to 42 mm, demonstrated midgut herniation. No fetuses with a crown-rump length greater than 44 mm had this finding. The cord containing midgut increased roughly from 4 to 7 mm, in maximum dimensions, for crown-rump length of 19 to 41 mm. An anterior abdominal wall mass greater than 7 mm at any crown-rump length , or of any size in a fetus of crown-rump length greater than 44 mm, is suggestive of a fetal anomaly. Alternatively, a cord base "mass" within the 4 to 7 mm range for a crown-rump length of 19 to 44 mm can be considered normal and not to require any follow-up.

Physiologic normal herniation of the midgut in an embryo

Non-Sonographic Diagnosis and Management:

The antenatal diagnosis of abdominal wall defects, particularly gastroschisis is being made with increasing frequency with the advent of maternal serum AFP screening programs. Maternal serum AFP screening sensitivity will be greater for gastroschisis than for omphalocele at any given cutoff. This is almost certainly due to the free diffusion of AFP from the fetal circulation because of the exposed viscera in gastroschisis, not covered by a membrane. The management of gastroschisis is still controversial. Some investigators advocate elective cesarean section, whereas others have found that vaginal delivery does not appear to adversely affect fetal outcome.

References:

van de Geijn EJ, van Vugt JMG,Sollie JE, van Geijn HP. Ultrasonographic diagnosis and perinatal management of fetal abdominal wall defects. Fetal Diagn Therapy 6:2-10, 1991

Goncalves LF, Jeanty P. Ultrasound evaluation of fetal abdominal wall defects In Ultrasonography in Obstetrics and Gyncecology, Ed Peter W. Callen, MD, WB Saunders and Co., 3rd Edition, 1994, Philadelphia

McMahon MJ, Kuller JA, Chescheir NC. Prenatal ultrasonographic findings associated with short bowel syndrome in two fetuses with gastroschisis. Obstet Gynecol 88:676-678, 1996

Alsulyman OM, Monteiro H, Ouzounian JG, Barton L, et al. Clinical significance of prenatal ultrsonographic intestinal dilatation in fetuses with gastroschisis. Am J Obstet Gynecol 175:982-4, 1996

Langer JC, Khanna J, Caco C, Dykes EH et al. Prenatal diagnosis of gastroschisis:development of objective sonographic criteria for predicting outcome. Obstet Gynecol 81:53-6, 1993

Bond SJ, Harrison MJ, Filly RA, Callen PW, Anderson RA et al. Severity of intestinal damage in gastroschisis: correlation with prenatal sonographic findings. J Pediatr Surg 23:520-5, 1988

Babcook CJ, Hedrick MH, Goldstein RB, Callen PW et al. Gastroschisis: can sonography of fetal bowel accurately predict post-natal outcome? J Ultrasound Med 12:701-6, 1994

Gorczyca DP, Lindfors KK, Giles KA, McGahan JP et al. Prenatally diagnosed gastroschisis in monozygotic twins. J Clin Ultrasound 12:216-218, 1989

Fries MH, Filly RA, Callen PW, Goldstein RB et al. Growth retardation in prenatally diagnosed cases of gastroschisis. J Ultrasound Med 12:583-588, 1993

Kushnir O, Izquierdo L, Vigil D, Curet LB. Early transvaginal sonographic diagnosis of gastroschisis. J Clin Ultrasound 18:194-197,1990

Bowerman RA. Sonography of fetal midgut herniation: Normal size criteria and correlation with crown-rump length. J Ultrasound Med 5:251-254, 1993

Palomaki GE, Hill LE, Knight GJ, Haddow JE, Carpenter M. Second-trimester maternal serum alpha-fetoprotein levels in pregnancies associated with gastroschisis and omphalocele. Obstet Gynecol 71:906, 1988

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Peter W. Callen, M.D.
Professor of Radiology, Obstetrics, Gynecology and Reproductive Science
University of California Medical Center, San Francisco, California

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