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Cerebellar Anomalies

Introduction The fetal cerebellum develops throughout pregnancy and may be visualized starting from the first trimester. By the seventh week of gestation, the rhombencephalic vesicle, the precursor of the fourth ventricle and cisterna magna, is the most prominent structure of the brain. By the eighth week, the cerebellar hemispheres may be seen lateral to the fourth ventricle; the choroid plexus of the fourth ventricle is also…

Cortical Development and Disorders

Introduction Cortical neuronal cell development starts at about 7 weeks' gestation from stem cells in the germinal matrix that line the ventricles. The stem cells proliferate and differentiate into glial cells and neurons. The glial cells migrate radially to the brain surface and create a scaffold for the neurons to follow to the outer cortex, where the neurons organize connections and commissures. Other neurons derived from…

Septooptic Dysplasia

Introduction Septooptic dysplasia (SOD), also known as de Morsier syndrome, is a rare heterogeneous disorder. It is characterized by optic nerve hypoplasia and midline forebrain abnormalities, such as agenesis of the corpus callosum, absence of the cavum septi pellucidi, and pituitary hypoplasia with consequent panhypopituitarism. It has been proposed that the terms SOD and de Morsier syndrome should be abandoned, as they are not independent entities.…

Corpus Callosum and Septum Pellucidum Anomalies

Introduction Anomalies of the corpus callosum and septum pellucidum are disorders of prosencephalic midline development. Midline prosencephalic development peaks at 7 to 12 weeks' gestation and includes the formation of the chiasmatic, commissural, and hypothalamic plates, enabling formation of the corpus callosum (12 to 20 weeks) and septum pellucidum. Corpus callosum and septum pellucidum anomalies are often associated with other brain abnormalities. Corpus Callosum Anomalies Definition…

Choroid Plexus Anomalies: Cysts and Papillomas

Introduction The choroid plexus is a vascular convolute, consisting of epithelial cells (a type of microglia), fenestrated blood vessels, and stroma, which lie in the ventricular system of the brain. It is the main source of cerebrospinal fluid (CSF) and actively regulates the constituents in CSF. The choroid plexus epithelial cells and the tanycytes, special ependymal cells located in the floor of the third ventricle, constitute…

Fetal Spleen

Introduction The fetal spleen is an important center of hematopoiesis until the late fetal period. In postnatal life, the function of the spleen is mainly as an immune organ, with lymphocyte and monocyte production continuing throughout adult life. During fetal development, the spleen appears between the fifth and eighth gestational weeks as an aggregation of reticular mesenchymal cells in the dorsal epigastrium of the stomach. The…

Sacrococcygeal Teratoma and Fetus in Fetu

Introduction Sacrococcygeal teratoma (SCT) is the most common tumor in newborns. Fetal SCT diagnosed in utero is associated with a 50% risk of preterm delivery, a mortality rate of 15% to 35%, and a morbidity rate of 12% to 68%. Perinatal mortality and morbidity are high because of high-output cardiac failure, fetal hydrops, preterm delivery, anemia, dystocia, and tumor rupture. The intrapelvic and intraabdominal extent of…

Megacystis-Microcolon-Intestinal Hypoperistalsis Syndrome

Introduction Megacystis-microcolon-intestinal hypoperistalsis syndrome (MMIHS) is a rare and severe condition that is characterized by functional intestinal obstruction with dilated small intestine, microcolon, malrotation, decreased or absent bowel movement, and, prenatally, a massively enlarged nonobstructive urinary bladder often associated with hydroureteronephrosis. The anomaly was first described by Berdon et al. in 1976 and is also termed neonatal hollow visceral myopathy . Female fetuses are affected four to…

Intraabdominal Masses

Introduction Intraabdominal solid masses and cystic lesions are not commonly identified during the routine 20-week anomaly ultrasound (US) scan and are uncommon findings at later gestations. However, intraabdominal masses occasionally are seen as an incidental finding during a third-trimester US scan assessing fetal growth and wellbeing. Potential differential diagnoses are numerous, but the differential diagnosis typically can be restricted through a detailed assessment of the site…

Hepatic Anomalies

Introduction Structural fetal hepatic anomalies include tumors (usually primary, rarely metastatic), calcifications, cysts, hepatomegaly, and biliary anomalies. Fetal biliary anomalies are discussed in Chapter 25 . Many of these conditions can be diagnosed prenatally by ultrasound (US). Hepatic Tumors, Calcifications, and Cysts Solid hepatic tumors are rare, accounting for approximately 5% of perinatal neoplasms. They include benign and malignant primary neoplasms and metastases of nonhepatic cancers.…

Congenital Diaphragmatic Hernia

Introduction Incomplete formation of the fetal diaphragm early in gestation results in a diaphragmatic defect allowing abdominal organs to herniate into the chest. These organs compete for space with the growing lungs, leading to inadequate pulmonary development and to respiratory failure and pulmonary hypertension at birth. Even with the advances made in the neonatal management of congenital diaphragmatic hernia (CDH), the postnatal mortality of this condition…

Intestinal Obstruction

Introduction The fetal intestinal tract can be altered by numerous pathologic processes. Typical ultrasound (US) findings of bowel obstruction are dilated bowel loops in the fetal abdomen proximal to the obstruction. Although large bowel dilatation occasionally can be observed, most cases of bowel dilatation are in the small intestine. Early diagnosis is possible for some proximal obstructions, such as duodenal atresia and esophageal atresia. In this…

Biliary Anomalies

Introduction The diagnosis and detection of some forms of bile duct disease have become possible with routine prenatal ultrasound. However, it remains difficult to offer a specific diagnosis or even prognosis in most cases. The most common finding is probably cystic dilatation of the biliary tree, mainly because of choledochal cysts or biliary atresia. In this chapter, biliary atresia, choledochal cysts, and gallstones will be discussed,…

Abdominal Cysts

Introduction Different organ systems can give rise to abdominal cysts that can be detected on prenatal ultrasound (US) ( Table 24.1 ). Depending on the location, gestational age, gender, and US appearance of the cyst, a limited differential diagnosis or the correct diagnosis can often be achieved. Intraabdominal cysts may develop from many organs. The most frequent origins are the urinary system (hydronephrosis, multicystic dysplastic kidneys,…

Fetal Hepatic Calcification

Introduction Fetal hepatic calcifications are divided into three categories: peritoneal, parenchymal, and vascular. This chapter addresses parenchymal hepatic calcifications and, to a lesser degree, vascular calcifications, which may be included in the differential diagnosis of parenchymal calcifications. Disorder Definition Fetal hepatic calcifications are single or multiple echogenic areas of various sizes (usually small, punctate) within the fetal hepatic parenchyma detected by ultrasound (US). They can be…

Echogenic Bowel

Introduction Fetal echogenic bowel (FEB) is typically seen during second trimester prenatal ultrasound. FEB occurs when the fetal bowel appears with the same or greater echogenicity than do surrounding bony structures. When seen in the second trimester, FEB has been associated with increased risk for fetal cystic fibrosis, aneuploidy, gastrointestinal abnormalities, growth restriction, and viral infections. However, it is important to realize that the majority of…

Omphalocele

Introduction Omphalocele is classified as a ventral wall defect in which there is midline herniation of abdominal viscera into the base of the umbilical cord. Before the 1950s, gastroschisis was considered a variant of omphalocele. It is now known that each entity has a separate etiology, unique risk factors, and distinct outcomes. As a result of widespread use of prenatal screening with maternal serum alpha-fetoprotein (MSAFP)…

Gastroschisis

Introduction Gastroschisis, a full thickness paraumbilical defect in the abdominal wall that results in herniation of the fetal midgut, has been considered an entity embryologically distinct from omphalocele since the mid-1950s. The widespread availability of prenatal ultrasound (US) and of maternal serum alpha-fetoprotein screening allows for routine antepartum diagnosis of gastroschisis with high accuracy. For reasons not well defined, the prevalence of gastroschisis has continued to…

Cloacal Abnormalities

Introduction Cloaca is derived from the Latin word for sewer or drain. Anatomically, it is used to describe a confluence of the urinary, genital, and gastrointestinal (GI) tracts. While this is the norm in birds, reptiles, and amphibians, most mammals have separate outlets for each system. In humans, there is a wide range of cloacal abnormalities. Mild forms may involve only a persistent urogenital sinus opening…

Ambiguous Genitalia

Introduction While not of primary focus for the medically minded sonographer or sonologist, sex determination is often the most important question for parents during a fetal ultrasound (US) examination. Sex determination, however, can be medically important in the diagnosis of zygosity or chorionicity in multiple gestations, for counseling regarding X-linked diseases, and in cases of ambiguous genitalia. The diagnosis of ambiguous genitalia, which has various causes,…