Ultrasound signs of fetal abnormalities

Fetal pathology

Fetal developmental abnormalities

Anomalies of neural tube development

• Anencephaly.
• Hydrocephalus.
• Microcephaly.
• Encephalocele.

Spinal anomalies

• Myelomeningocele.
• Spina bifida.

Cystic hygroma.

Heart anomalies

• Anomalies of the position of the heart.
• Ventricular septal defect.
• Hypoplasia.

Developmental anomalies of the gastrointestinal tract

• Atresia of the duodenum.
• Atresia of the jejunum.
• Cardiac atresia.

Developmental anomalies of the anterior abdominal wall

• Omphalocele.
• Gastroschisis.
• Fetal ascites.

Renal malformations

• Hypoplasia.
• Obstructions.
• Polycystic kidney disease.

Anomalies in the amount of amniotic fluid

• Low water content.
• Polyhydramnios.

Death of the fetus

Anomalies of neural tube development

Anencephaly, the congenital absence of the cranial vault and brain, is the most common abnormality of the fetal central nervous system. This abnormality is recognized at 12 weeks of pregnancy: hydramnios and other abnormalities will also be detected. Elevated levels of alpha-fetoprotein will be detected in the amniotic fluid and maternal serum.

Hydrocephalus can be recognized at 18 weeks of pregnancy. The dilation of the anterior and posterior horns of the lateral ventricles will be determined.

Hydrocephalus against the background of Arnold-Chiari syndrome is combined with lumbar meningocele. The enlargement of the frontal tubercles gives the head a characteristic shape, the detection of which requires a thorough examination of the head and spine, especially in the presence of an increase in alpha-fetoprotein in the mother's blood serum.

If hydrocephalus is secondary to brain atrophy, the fetal head is usually reduced in size.

Microcephaly. Abnormal undersize is defined as the biparietal diameter being less than three standard deviations below the established mean. The biparietal diameter of the fetal head should be determined, but the head-to-body ratio should also be calculated to exclude intrauterine growth retardation. Isolated microcephaly is rare, and diagnosis in borderline cases is always difficult. Serial studies and careful interpretation are necessary. Unless the fetal head is severely undersized, avoid making a diagnosis of microcephaly unless other abnormalities are present.

Be very careful with the diagnosis of microcephaly. Serial studies are necessary.

Encephalomeningocele. This neural tube defect is usually seen as a rounded bulge in the cranial vault containing fluid or brain matter. Occipital encephalomeningocele is most common, but anterior encephaloceles are seen in some ethnic groups. If an asymmetric encephalocele is present, amniotic bands will also be seen. The most common cause of error is a similar shadow caused by a fetal ear or limb near the head. Repeat the examination in different planes and at different times. Errors may also occur with cystic hygroma, but the cranial vault will be intact. Encephalocele may be associated with polycystic kidney disease or polydactyly.

Recognizing neurological abnormalities can be extremely difficult and should always be confirmed by repeated examinations, preferably by another specialist.

Anomalies of the spine

Spinal developmental anomalies most often affect the cervical and lumbar spine. It is necessary to examine the soft tissues above the spine to determine the continuity of their contour, as well as the spine for the presence of additional formations. The fetal spine can be clearly differentiated starting from 15 weeks of pregnancy.

Myelomeningocele is visualized as a fluid-containing saccular formation located at the back, often having elements of the spinal cord in the cavity. Open myelomeningocele may not have a superficial "sac" - in this case, only a prolapse of soft tissues through the defect will be determined: myelomeningocele without a bulging contour is especially difficult to detect. Bone anomalies are usually determined. Normally, the posterior ossification centers are visualized as two hyperechoic linear, almost parallel echostructures, but in spina bifida , they will diverge. On normal transverse sections, the ossification centers at the back appear parallel; in the presence of spina bifida, the posterior elements are displaced laterally, are not parallel, and diverge outward. Longitudinal sections are used to identify the hernial sac.

Not all stages of spina bifida can be detected by ultrasound.

Cystic hygroma

Cystic hygroma is a developmental abnormality of the lymphatic system, in which a cystic formation with septa is detected, located in the posterior cervical region. This formation can spread laterally and anteriorly, in some cases septa or structures resembling the spokes of a wheel are detected in the center. Unlike encephalocele or cervical meningocele, the skull and spinal cord are intact.

When cystic hygroma is combined with a generalized anomaly of the lymphatic system, fluid is detected in the abdominal cavity and pleural cavities, and fetal survival is unlikely.

Fetal cardiac anomalies

Detection of most cardiac anomalies requires specialized equipment, with the ability to perform Doppler ultrasound examination, as well as specialized knowledge. Anomalies of the position of the heart, hypoplasia of one half, defects of the interventricular septum can be detected, but in any case, if there is a suspicion of cardiac anomalies, an additional expert opinion is required. If the final diagnosis is difficult, it is necessary to warn clinicians about possible complications so that they are ready to provide specialized care at the birth of the child.

Fetal intestinal malformations

Congenital intestinal obstructions most commonly occur in either the duodenum or the jejunum or ileum.

1. Duodenal atresia is the most common anomaly of the gastrointestinal tract. In this case, round cystic structures will be visualized in the upper part of the fetal abdomen. The cystic structure located on the left is the dilated stomach, the cystic structure on the right is the duodenum. This is the echographic sign of the "double bladder". In 50% of cases, this anomaly is combined with polyhydramnios in Down syndrome, and anomalies in the development of the heart, kidneys, and central nervous system are also common.
2. Atresia of the jejunum and ileum. Diagnosis can be difficult. Multiple cystic structures may be visualized in the upper abdomen of the fetus; these are overstretched loops of intestine. This anomaly is usually detected during the second routine ultrasound examination in the third trimester of pregnancy. Polyhydramnios usually occurs with high intestinal obstruction; with obstruction localized in the lower parts, polyhydramnios is not observed. Combined anomalies are much less common than with duodenal atresia.
3. Obstruction or atresia of the colon. This malformation is rare, and it is almost impossible to make an accurate diagnosis based on ultrasound examination.

Anomalies in the development of the anterior abdominal wall of the fetus

The most common developmental anomaly is a defect of the anterior abdominal wall in the midline (omphalocele); omphalocele is often combined with other congenital anomalies. Depending on the size of the defect, the hernial sac may contain part of the intestine, liver, stomach, and spleen, covered externally by the amniotic membrane and internally by the parietal peritoneum. The vessels of the umbilical cord usually penetrate the hernial sac and extend inside the wall of the hernial sac.

Other defects are mainly determined in the right umbilical region (gastroschisis) and are usually isolated. Only intestinal loops not covered by the amniotic membrane usually prolapse through this defect. Echography reveals intestinal loops floating in the amniotic fluid outside the anterior abdominal wall. The umbilical cord enters the abdominal wall normally.

Ascites in the fetus

Free fluid in the fetal abdominal cavity is defined as an anechoic zone surrounding the fetal internal organs. In the presence of true ascites, the fluid surrounds the falciform ligament and umbilical vein. A hypoechoic rim around the abdomen, caused by the presence of muscular and fatty layers of the abdominal wall, may be mistaken for ascites.

If ascites is suspected, a thorough examination of the fetal anatomy is necessary to exclude associated anomalies. The most common causes of ascites are renal obstruction or hydrops. Since ascitic fluid may be present as urine, a thorough examination of the kidneys is necessary. Hydrops cannot be diagnosed unless there is thickening of the skin or the presence of fluid in at least two cavities (e.g., ascites with pleural or pericardial effusion). The most common causes of hydrops are:

• Rhesus conflict or incompatibility of other blood factors;
• cardiac anomalies;
• cardiac arrhythmia (usually tachyarrhythmia);
• vascular or lymphatic obstruction (eg, in cystic hygroma).

Developmental abnormalities of the fetal urinary system

Some anomalies of kidney development are incompatible with life, and if detected before 22 weeks, indications for termination of pregnancy may be determined (where permitted). Recognition of anomalies at later stages of pregnancy may also affect the tactics of management of the pregnant woman.

The presence of echographically unchanged (in size, shape, echogenicity) kidneys does not exclude the possibility of the presence of developmental anomalies of the urinary system.

Renal agenesis syndrome (absent kidneys). There is no amniotic fluid and ultrasound diagnosis is difficult. In the last few weeks of pregnancy, the presence of kidneys may be falsely apparent due to the significant enlargement of the adrenal glands, which take on the bean-shaped form of kidneys. The urinary bladder is usually small or absent. It is necessary to make sections in different planes.

Renal hypoplasia (small kidneys). Measuring the kidneys will show that they are smaller.

Renal obstructions; hydronephrosis. It should be taken into account that transient dilation of the renal pelvis is acceptable. Such dilations are usually bilateral, but can be unilateral and persist for some time. Repeat the examination in 2 weeks. If the dilation of the renal pelvis is physiological, the diameter of the renal pelvis will either remain the same or the dilation will disappear.

In case of pathological dilatation, negative dynamics will be observed. Bilateral renal obstruction (bilateral hydronephrosis) is usually combined with oligohydramnios and has an unfavorable prognosis. Unilateral obstruction is not combined with oligohydramnios, since the opposite kidney takes over the function of both kidneys.

In some cases, polyhydramnios is present. Echography reveals a cystic formation in the central part of the kidneys with smaller cystic structures located outward. These smaller cysts (up to 1 cm) in the projection of the parenchyma of the hydronephrotic kidney may be a sign of rare renal dysplasia. Increased echogenicity and decreased parenchyma thickness are fairly accurate signs of renal dysfunction.

If there is obstruction at the level of the ureteropelvic junction, the renal pelvis is rounded and the ureter is not visualized. If there is obstruction of the internal opening of the urethra (usually in the presence of a urethral valve in male fetuses), there is distension of the bladder, as well as dilation of both ureters and the renal pelvis. Sometimes, distension of the posterior urethra can be determined as a bulging of the urethral contour.

Multicystic kidney. Echography will reveal several cysts of varying diameters, usually located diffusely, less often in one part of the kidney. Bilateral defect is incompatible with life. Kidney tissue can be determined between the cysts, although the parenchyma is not clearly differentiated, since the tissue will be significantly more echogenic than normal renal parenchyma.

Autosomal recessive polycystic kidney disease is usually recognized only in the third trimester of pregnancy. There is usually a family history and oligohydramnios due to a sharp decline in renal function. Both kidneys may be so enlarged that they can be mistaken for the liver, but the shape of the kidneys is preserved. Individual cysts are not visible, since their diameter is too small to differentiate them, but the presence of multiple reflective surfaces gives a sharp increase in the echogenicity of the kidneys.

Amniotic fluid

Increased amniotic fluid (polyhydramnios, hydramnios). Increased amniotic fluid may be observed in various fetal pathologies. The most common causes of polyhydramnios are:

• gastrointestinal obstruction (high jejunal obstruction or higher);
• central nervous system anomalies and neural tube defects:
• hydrops fetalis;
• small defects of the anterior abdominal wall;
• skeletal dysplasia of the chest (microsomia) - defects that are usually incompatible with life;
• multiple pregnancy;
• diabetes in the mother.

Decreased amount of amniotic fluid (oligohydramnios).

The production of fetal amniotic fluid, starting from 18-20 weeks of pregnancy, is mainly due to renal secretion. In the presence of bilateral renal obstruction, renal dysplasia or non-functioning kidneys, the amount of amniotic fluid is greatly reduced or absent. This can lead to pulmonary hypoplasia.

Oligohydramnios develops as a result of:

• damage to the membranes with fluid leakage;
• bilateral renal anomalies or urinary tract malformations (abnormalities of the kidneys, ureters, or urethra);
• intrauterine growth retardation;
• post-term pregnancy;
• intrauterine fetal death.

Most formations in the abdominal cavity of the fetus are of renal origin.

Multicystic disease can be unilateral or bilateral, with cysts that are not connected to each other being detected.

Autosomal recessive (infantile type) polycystic disease is determined echographically as “large white kidneys”: individual cysts are not differentiated.

Oligohydramnios is a poor prognostic sign in the presence of renal anomalies, since it leads to the development of pulmonary hypoplasia.

Intrauterine fetal death

The diagnosis is made when there is no fetal heartbeat. A normal fetus may have transient bradycardia or syncopal absence of heartbeat, so observation for several minutes is necessary. Other signs of fetal death include oligohydramnios and damage to the skull bones with overlapping bone fragments (Spalding's sign).