1195: The fetal abdomen from end to end

Abstract

[Embryology and ultrasound evaluation]. Fetal structures develop very rapidly in early pregnancy. Unmistakable human characteristics are obvious by 10 weeks menstrual age. By 12 weeks swallowing starts and the stomach becomes visible. By 15 to 16 weeks, meconium starts accumulating and peristalsis can be noted by ultrasound. The standard AIUM/ACR views of the abdomen include abdomen circumference, stomach, kidneys, urinary bladder and umbilical cord insertion site and intactness of the anterior abdominal wall. [Hollow gut]. The esophagus is visible even in the early second trimester as a slightly echogenic line in its expected location in the chest. [Stomach]. The stomach is usually visible by the end of the first trimester. Failure to see the stomach is suspicious for abnormality. Small bowel excessive bowel echogenicity occurs in about 0.2 to 1.8 percent of pregnancies and about 35% have problems including aneuploidy, anomalies 11%, cystic fibrosis 8%, infection 3% and others. Bowel obstruction may not be evident until after 20 to 24 weeks. Meconium peritonitis causes chemical peritonitis but often does not need surgery. [Large bowel]. The colon becomes visible in some by 18 weeks and in all by 25 weeks. Contained meconium may be hypoechoic or echogenic. [Liver]. The liver and its vessels are readily identified. Vascular variants occur and are not a functional problem but there is high association of associated anomalies. Calcifications of the liver are common but often not recognized. Isolated calcification after exclusion of infection and aneuploidy has good outcomes. Tumors are unusual. [Gallbladder and bile ducts]. The gallbladder is virtually always visible. Gallstones can be seen and virtually always resolve spontaneously. Bile duct dilations are rare. [Adrenals]. Normal adrenal glands are visible. Masses in the adrenal area include extralobar pulmonary sequestration (these are usually left sided), hemorrhage and neuroblastoma. Prenatally diagnosed cases have a good prognosis and may regress spontaneously. [Ascites]. Ascites commonly occurs with generalized hydrops due to multiple etiologies. Isolated ascites is more commonly due to obstructive urinary disease and urine leak than gastrointestinal disorders with perforation. A surprisingly common cause of ascites in our lab has been fetal infection due to Parvovirus B19. [Miscellaneous]. Cystic masses are frequently seen in the abdomen, especially ovarian cysts in females. Other cystic masses include mesenteric cysts, duplication cysts and urachal cysts. Mixed and solid abdominal tumours are rare and include lymphangiomas, liver adenomas and hemangiomas, hepatoblastomas and hemoangioendotheliomas. Summary: prenatal ultrasound can find numerous abdominal abnormalities. Some of these do not become apparent until after 20 weeks. This is especially true for obstructive lesions of the bowel. As with other fetal anomalies, there is a high association with additional abnormalities.