Diagnostic ultrasound ( PDFDrive )

CHAPTER 38 The Fetal Gastrointestinal Tract and Abdominal Wall 1323
A
B
C
FIG. 38.27 Physiologic Midgut Herniation (Illustrations).
(A) Physiologic gut herniation into the coelomic
outpouching of the umbilical cord insertion at 9 weeks. (B)
Ninety-degree rotation of the bowel at the axis of the superior
mesenteric artery. (C) At 12 weeks the bowel reverts to its
intraabdominal placement, undergoing an additional 180-degree
rotation along the axis of the superior mesenteric artery.
20- to 25-year-old women. 188 Other factors associated with
gastroschisis include use of tobacco, illicit drugs, and pseudoephedrine.
187,188,191-196 More recently, a possible association of
gastroschisis with agricultural chemicals such as atrazine has been
suggested. 197-199
FIG. 38.28 Physiologic Midgut Herniation. Sagittal image at 10
weeks shows echogenic loops of bowel (arrowhead) in the base of the
normal umbilical cord (UC). The lower extremities (LE) are visible and
the amnion (arrow) has not yet expanded suficiently to ill the chorionic
cavity. These are all normal observations at this gestational age.
per 10,000 up to 1.4 to 4 per 10,000 live births during the
past 35 years. 187-191 here is no gender predilection in the
afected fetuses. he incidence is higher in teenage mothers,
with the largest population-based study showing a 10-fold
higher incidence in 15- to 19-year-old women compared with
Pathogenesis
he pathogenesis of gastroschisis is unclear. One hypothesis
is that the abdominal wall defect is the result of an isolated
vascular compromise of the abdominal wall in the irst trimester.
his hypothesis is supported by the risk factors for gastroschisis
listed in the previous paragraph, as well as by the association
of gastroschisis with other fetal abnormalities that are thought
to have an underlying vascular cause. Other proposed causes
include failed development of the mesoderm and the lateral
mesodermal enfolding, 200 rupture of the amniotic membrane
at the base of the umbilical cord, disruption of the right vitelline
artery with subsequent body wall damage, and abnormal
extension of apoptosis patterns during regression of the right
umbilical vein. 184
Prenatal Diagnosis
he diagnosis of gastroschisis is relatively straightforward when
the defect is limited, and free-loating loops of bowel are identiied
intraamniotically; in these cases the diagnosis can already be
made as early as the irst trimester. 188,201 Most oten the defect is
located at the right paraumbilical region (Fig. 38.29, Video 38.12).
he free-loating bowel has a characteristic caulilower-like
appearance. he bowel may appear echogenic due to edema
and inlammation of the wall secondary to long-standing exposure