Anterior External Masses of the Fetal Abdomen
· Physiological bowel herniation- Physiological herniation occurs at
10—13 weeks. The best discriminating method for differentiating this from an omphalocele is to perform a repeat sonogram after 15 weeks menstrual age. A large defect with liver exteriorized indicates an omphalocele at any gestation.
· Omphalocele- Omphalocele is herniation of a variable amount of abdominal viscera through a defect (2—10 cm) at the base of the umbilical c9rd. A membrane covers the heri1iation, differentiating it from gastroschisis, and the umbilical vessel inserts into the apex. There is frequent association of liver herniation, ascites, cardiac defects and chromosomal anomalies. Association with holprosencephaly and limb anomalies is occasional. High incidence of chromosomal abnormality — approximately one third. Prognosis related to the karyotype, associated abnormalities and contents of the omphalocele.
· Umbilical hernia- Umbilical hernia is due to a defect in the linea alba; the protruding bowel is covered by subcutaneous tissues and skin.
· Gastroschisis- Gastroschisis results from herniation/evisceration of bowel and occasionally the bladder and adnexa into the amniotic cavity through a small defect (2—5 cm) in the right paraumbilical region. There is no covering membrane. It is thought to result from a vascular event to the omphalomesenteric artery. Vascular compromise may occur from volvulus and may result in obstruction, ischemia and atresia. Bowel wall thickening occurs. Not associated with other abnormalities and the chromosomes are normal. Prognosis good.
· Amniotic bands- ABS is a common cause of abdominal wall defect. Involvement of the abdominal wall may produce appearances similar to gastroschisis. However, an atypical location of the abdominal wall defect should suggest the diagnosis of ABS. Membranes contiguous with such a defect may be identified.
· Extrophy of bladder- Sonographically bladder extrophy may present as an external, well defined, solid or complex mass immediately superior to the fetal genitalia. Prolonged and repeated scans will fail to reveal the fetal bladder. The renal collecting system and ureters need not be dilated, whereas unilateral or horse shoe kidneys may be found. Uterine and adnexal anomalies are relatively frequent. The pubis is abnormally wide and the umbilical cord insertion may be abnormal.
· Thoracoabdominal pentalogy of Cantrell- Ectopia cordis associated with a ventral wall defect should prompt the diagnosis of PC. The syn1ome is often associated with /other anomalies.
· Cloacal extrophy- This consists of a low omphalocele, bladder or cloacal extrophy and frequently other caudal anomalies, including meningomyelocele anal atresia and lower limb anomalies. Most affected fetuses have a single umbilical artery.
· Limb-body wall complex- LBWC is a lethal condition with severe anterior abdominal wall defect, the defect placed laterally, which involves the umbilical cord insertion site. The abdominal contents lie outside within a sac of amnion and mesoderm. There is a frequent association with CHD, cranial anomalies (encephalocele), limb abnormalities and scoliosis. Chromosomal defects are not usually present.
Multiple cavernous hemangiomas- These are most frequently found over the lower body and are often associated with Klippel—Trenaunay—Weber syndrome, which is diagnosed in the presence of multiple surface masses producing limb hypertrophy. Hydrops may occur.
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