Fetal Anomalies

Doctor Consulting OBGYN patient

Fetal Anomalies

Listed In Order Of Level II Scan / Fetal Anatomy Survey Sequence

illustration of uterus
Cervix
illustration of lungs
Heart / Lung
illustration of fetus and umbilical cord
Placenta
Face
illustration of spine
CNS / Spine
illustraion of baby
Extremities
male and female icons
Genitalia
illustration of stethoscope
Other
bladder icon
Bladder
chromosome icon
Aneuploidy
illustration of fetus
Cord Insertion / Abdominal Wall
illustration of pregnancy
Maternal
illustration of kidneys
Kidneys
illustration of twins in utero
Multiple Pregnancy
illustration of stomach
Stomach

Cervix

Outline

Incompetent Cervix

Patient had a “routine” ultrasound to evaluate fetus at 20 wks gestation. Do to suspicion of cervical dilatation on initial scan (left image), patient was brought back the following day and the second image (right) was obtained. The patient was taken to the O.R. for an emergency cerclage. She delivered at term.

Targeted ultrasound of the cervix is best performed with endovaginal or endovaginal or perineal scanning. Evaluation of patients at risk of incompetent cervix may require serial scanning to identify developing cervical incompetence.

Endovaginal and Perineal Evaluation

Endovaginal and perineal ultrasound are usually performed with an empty bladder. Visualize the cervix in a sagittal plan. It is usually easiest to first identify the internal cervical os, then adjust the probe until the entire cervical canal is visualized. The external os may be difficult to see, but can be identified by following the curve of the posterior lip of the cervix to its intrsection with the cervical canal. Gradually relax pressure on the transducer until the image becomes slightly blurred. Reapply gentle pressure sufficient to establish a sharp cervical image. The length of the closed cervical canal is measured. Funneling of the upper cervical canal, if present is not included in the measurement of cervical length. Funneling may indicate incompetent cervix (depending on gestational age, obstetric history and clinical circumstances).

Perineal scanning is performed with a standard curvilinear probe, covered with a glove and applied to the perineum using a large amount of gel. Place the probe gently between the labia and adjust to get a clear image of the cervix. Perineal scanning is more difficult to learn than endovaginal scanning. The vagina curves and there is frequently shadowing from the pubic bone and from stool in the rectum. Moving the probe slightly to the side or up or down may improve the visualization.

Placenta

Outline

  • Placenta Previa
  • Polyhydramnios (especially note the presence, or absence, of stomach bubble)
    • Excess production
      • Diabetes
      • Macrosomia
    • Decreased swallowing
  • Oligohydramnios
    • Loss (PROM)
    • Decreased Urination
    • Absent kidneys (renal agenesis)

Placenta Previa

Placenta previa occurs when the placenta covers the internal cervical os. Placenta previa occurs in 1/200 to 1/300 pregnancies. The risk of previa increases with increasing parity. Placenta previa should be suspected in any case of second or third trimester bleeding; in particular, previa is associated with painless vaginal bleeding.

Placenta previa is defined by the location of the placenta relative to the internal cervical os. Remember that these definitions were made by digital exams (under double setup conditions) in patients with a cervix dilated 3–4 cm. The definitions of marginal vs. partial previa are of questionable value in patients identified by ultrasound with a closed cervix.

Complete (or total) previa: The placenta completely covers the internal cervical os.

Partial previa: The placenta partially covers the cervical os.

Margina previa: The placental edge is at the edge of the internal cervical os.

Low-lying placenta: The placenta edge is in close proximity to the internal cervical os. By vaginal ultrasound, this is usually defined as a placental edge < 2 cm from the internal cervical os.

Vasa Previa

Vasa previa is best confirmed by endovaginal ultrasound. In this case, endovaginal scan demonstrated fetal vessels coursing over the internal cervical os. Vasa previa can be confusing, as a free loop of cord near the cervix may mimic a vasa previa. I try to identify the placental insertion of the umbilical cord to exclude a vasa previa. In this case the vessels inserted into the lower edge of the placenta, then coursed over the internal cervical os (placenta is low-lying). The clinical pictures as the bottom show the umbilical cord/vessel insertion into the placenta.

CNS / Spine

Outline:

Anencephaly

Anencephaly is readily recognized by the absence of calvarium and brain. Typically fetal structures are normal from the level of the orbits down. Neural tube closure normally occurs on postconception day 24 (rostral) and day 26 (caudal). Failure of neural tube closure results in anencephaly (rostral failure of closure) or spina bifida (caudal failure of closure). There is a 2 – 4% risk of recurrence in subsequent pregnancy. Risk of recurrence can be reduced by periconceptional treatment with folic acid. Anencephaly is differentiated from exencephaly by the absence of brain tissue in anencephaly.
Another case: An example of anencephaly also involving cervical spine rachischisis

Exencephaly and Extrathoracic Heart Amniotic Band Syndrome

Exencephaly = acrania

22 y/o G1 P0

EGA 17 wks

Referred due to abnormal ultrasound

Exencephaly (sometimes called acrania) results from failure of the calvarium to develop. It is often (as in this case) due to amniotic band syndrome. If not recognized in early pregnancy, brain tissue may resorb resulting in the appearance of anencephaly. In this case, recurrence is very unlikely as this was due to amniotic band syndrome, a sporadic event.

Anencephaly and Rachischisis Craniorachischisis Cranial Spinal Rachischisis

Initially this was thought to be a possible exencephaly, due to appearance of tissue above the maldeveloped cranial cavity. Autopsy showed only vascular tissues and membrane, confirming anencephaly. Different texts use slightly different terminology to describe this variant of anencephaly. 

Encephalocele

Encephalocele is characterized by herniation of intracranial contents through a defect in the skull. The defect may be anywhere in the midline of the skull, but the majority are occipital. The degree of herniation ranges from meniges and fluid to varying amounts of brain tissue (even including the lateral ventricles). Encephaloceles are often associated with other anomalies (for example, Meckel-Gruber syndrome, an autosomal recessive condition, has polycystic kidneys, polydactyly, cleft lip and encephalocele).

Even isolated encephaloceles are often associated with poor neurological outcome, due to neuronal migration defects in the brain.

Holoprosencephaly (alobar)

Holoprosencephaly results from a failure or midline cleavage of the forebrain. Holoprosencephaly may be alobar, semilobar or lobar. Holoprosencephaly is often associated with Trisomy 13. Autosomal recessive and autosomal dominant forms have also been reported.

The cases shown here are alobar holoprosencephaly. There is a single ventricle anteriorly (first and second images). The cavum septum pellucidum is absent. The thalami are fused (second and third images). The cerebellum may appear normal (fourth image).

Agenesis of the Corpus Callosum

The corpus callosum is an interhemispheric pathway. The majority of cases of agenesis of the corpus callosum (ACC) have other associated CNS anomalies. Approximately 85% of people with isolated agenesis of the corpus callosum are aymptomatic.

Schizencephaly

Schizencephaly is the presence of clefts within the substance of the brain. Pathologic examination shows that the clefts are line with grey-matter. Neurologic impairment is reported to depend on the degree of cerebral mantle involvement.

encephalocele with associated Dandy-Walker malformation

A case of encephalocele with associated Dandy-Walker malformation. As there is no brain tissue in the protruding sac, this may be better identified as a cranial meningocele.

Lumbar Spina Bifida Case 1

Patient was referred due to finding of ventriculomegaly (noted in scan at right). Additional findings included scalloping of the frontal bones (“lemon sign”), second row left, and obliteration of the cisterna magna and compression of the cerebellum (“banana sign”), second row right. Serial transverse images of the spine (third row left) show the splayed laminae in the lumbar region. The defect can also be seen on long axis transverse view of the spine (third row right).

Lumbar Spina Bifida Case 2

MRI images of neural tube defect. First row shows long axis images, sagittal (left) and coronal (right), demonstrating Chiari II malformation. Second set shows a series of transverse images demonstrating the lumbar neural tube defect in images 7 through 9.

Neural Tube Defect (3D)

Genitalia

Ambiguous genitalia

Bladder

  • Absent bladder – confirm expected bladder position by identifying umbilical arteries with color flow doppler
    • renal agenesis
    • infantile polycystic kidney disease
  • Bladder outlet obstruction
  • Other
    • ectopic ureterocele
    • bladder extrophy

Cord Insertion / Abdominal Wall

Omphalocele

Omphalocele is a herniation of intestinal contents, usually at the umbilicus. Size ranges from small, with only bowel herniated to very large, with abdominal contents including stomach and liver herniating into the omphalocele sac. Omphalocele is differentiated from gastroschisis by the presence of a membrane (peritoneum) around the sac. Up to 30% of omphaloceles have associated anomalies, including aneuploidy (chromosome defects). Genetic amniocentesis is recommended in cases of omphalocele. Small omphaloceles are more likely to be associated with aneuploidy than very large defects. Rupture of the membrane may lead to a mistaken diagnosis of gastroschisis; however it should be possible to differentiate the diagnosis by careful examination of the umbilical cord insertion. Case of ruptured omphalocele mistakenly diagnosed as gastroschisis.

Omphalocele identified at 15 wks EGA. Amniocentesis revealed this case to be a Trisomy 13. Color doppler shows that the umbilical cord inserts into the membrane covered mass rather than beside it (although it’s not easy to see at this early GA).

A “physiologic” omphalocele may be noted prior to 11-12 weeks gestation. The intestine initially develops outside the abdominal wall and retracts into the abdomen at about 10.5 weeks EGA. This is demonstrated in the following two scans (of the same patient) at 10 and 11 weeks EGA.

This massive omphalocele was part of a limb-body-wall complex. The anomaly occurred in a twin gestation; twin A was normal.

Gastroschisis

Gastroschisis is an abdominal wall defect, usually right paramedian, resulting in bowel freely floating in the amniotic cavity. It is more common in women <20 y/o and may be associated with smoking and drug use. Gastroschisis is differentiated from omphalocele by the absence of a membrane containing the herniated bowel. Unlike omphalocele, gastroschisis is rarely associated with other anomalys or with chromosomal aneuploidies; however, a ruptured omphalocele may appear similar to a gastroschisis. Fetuses with gastroschisis are frequently growth restricted and are at increased risk of intrauterine fetal demise.

Route of delivery is controversial – there is no substantial published evidence to suggest that outcomes are better with cesarean delivery, but cesarean delivery is frequently recommended due to concern for protecting the bowel.

Pentalogy of Cantrell

Pentalogy of Cantrell is a complex anomaly involving 5 findings:
  • ectopia cordis (extrathoracic heart)
  • omphalocele (specifically an epigastric omphalocele)
  • disruption of distal sternum
  • diaphragmatic defect
  • pericardial defect(Cantrell, 1958)
Other findings may include neural tube defects, facial defects, clubbed feet, cardiac defect (tetralogy of Fallot). This anomaly is almost always lethal. The etiology is not clear but this anomaly seems to be part of a spectrum of complex anomalies involving disruption of the body wall (see Limb-Body-Wall complex). They are sometimes also called body stalk anomalies. The first sonographic clue may be a large omphalocele; often these fetuses have so many anomalies that the picture is very confusing. It’s important to work systematically through each system to identify the structures and the abnormalities.

The clinical pictures demonstrate the multiple, and somewhat confusing, complex of anomalies. Note that the umbilical cord is essentially absent with the umbilical region connected to the placenta. Intestine and liver are out of the abdominal cavity. The lower extremities are malpositioned. There is a large meningocele. The heart is extrathroacic, although it is covered by a membrane. There was some debate as to whether to call this a pentalogy of Cantrell or a Limb-Body-Wall complex.

Limb-Body-Wall Complex (Body Stalk Anomaly) (Amnion Rupture Sequence)

Limb-Body-Wall complex involves a number of anomalies, although I find it easiest to think of this as the result of a short or absent umbilical cord. The anterior abdominal wall is adherent to the placenta and the embryo, and later fetus, must fold backwards during development. The abdominal contents are pulled completely out of the body and the spine is usually severely deformed, in some cases bent almost like a hairpin. The lower extremities are often rotated posteriorly. Limb-Body-Wall complex appears to be synonomous with Body Stalk Anomaly and in some texts is called Amnion Rupture Sequence. The etiology is described differently in different texts. Some believe it results from a vasular disruption early in embryogensis. Others describe it as a variation of amniotic band sequence. The ultrasound findings are often confusing and these patients of commonly referred with the comment that “something is wrong because I can’t find any normal structures.” Other complex anomalies that appear related include pentalogy of Cantrell and bladder extrophy There is a series of clinical pictures in pentalogy section of a fetus that has features of Limb-Body-Wall complex as well as pentalogy of Cantrell.

Kidneys

  • Absence (renal agenesis) – bilateral or unilateral
  • Obstruction
    • uretero-pelvic junction (UPJ)
    • ureteral
    • ectopic ureterocele
    • bladder outlet obstruction (posterior urethral valve in male)
  • Pyelectasis (dilated renal pelvis)
    • aneuploidy
    • obstruction
  • Abnormal morphology
    • multicystic dysplastic kidney
    • polycystic kidney disease
    • Prune-belly syndrome

Renal Agenesis (Bilateral)

Bilateral renal agenesis, sometimes called Potter’s Syndrome, is a complete failure of development of the kidneys. It is suspected when there is severe, or absolute, oligohydramnios (anhydramnios). It is important to differentiate from premature rupture of membranes and from other renal abnormalities that result in severe oligohydramnios (such as infantile polycystic kidneys).

Bilateral renal agenesis is lethal due to oligohydramnios sequence—pulmonary hypoplasia, dysmorphic facial features (flat nose, low set ears), and limb deformities. It may not be diagnosed until well into the second trimester, as amniotic fluid is generated by skin transudation until second trimester, when fetal urine production is the primary source of amniotic fluid. Most cases are sporadic, so the risk of recurrence is low.

Renal agenesis may be associated with other fetal anomalies such as VATER or VACTERL.

Renal Collecting System Dilatation Pyelectasis, Hydronephrosis

Stomach

  • Absent stomach (especially if associated with polyhydramnios)
    • esophageal atresia or T-E fistula
  • Excessively large stomach (“double-bubble”)
    • duodenal atresia
  • Abnormal location

Diaphragmatic Hernia

Diaphragmatic hernia is a defect in the diaphragm that allows abdominal contents to herniate into the chest. Left sided, posterolateral defects are most common, but the defect can occur anywhere. Diaphragmatic hernia results in compression of the lung, often leading to pulmonary hypoplasia. 1/3 to 1/2 of fetuses with diaphragmatic hernia have other associated anomalies and chromosome abnormalities are common. Survival of infants with diaphragmatic hernia is reported as anywhere from 50% to 80%, depending on the location of the hernia, presence of poor prognostic factors and postnatal treatment. In-utero surgery for diaphragmatic hernia has been described. Poor prognostic factors include herniation of liver into the chest, polyhydramnios and effusions.

Diaphragmatic hernia in Twin B at 22 weeks EGA. Note the stomach in the same picture as the 4 chamber heart view. On long axis stomach and intestine herniate through the diaphragm into the chest. The heart is moved into the right side of the chest (dextrocardia).

Diaphragmatic hernia at 29 weeks EGA

Heart / Lung

  • Abnormal position
  • Abnormal axis
    • dextrocardia, situs inversus
  • Abnormal 4 chamber view
  • Abnormal outflow tracts
  • Abnormal rhythm
    • premature atrial contractions
    • tachycardia
    • bradycardia
  • Pericardial effusion (component of hydrops)
    • isoimmunization
    • viral infection
  • Lung

Face

  • Cleft lip
  • Hypertelorism
  • Hypotelorism

Extremities

Polydactyly

Polydactyly may occur as an isolated autosomal dominant disorder (more common in African-Americans), but most cases that are sonographically identified are associated with other anomalies. Trisomy 13 is the most common chromosome aneuploidy associated with polydactyly.

Clubfoot

Isolated clubfoot. Clubfoot may be associated with a wide variety of conditions, including chromosome aneuploidy.

Other

Aneuploidy

46, XY, der(13)t(3;13)(q11.2;p11.2) – Unbalanced translocation with monosomy 13p and trisomy 3q

Second Trimester Markers of Aneuploidy*

  • Nuchal thickening (>5 mm — Likelihood ratio for Down Syndrome 25x)
  • Cardiac anomalies (increased risk – varies with anomaly observed)
  • Femur length (<0.91 of expected — Likelihood ratio for Down Syndrome 2.2x)
  • Humerus length (<0.89 of expected — Likelihood ratio for Down Syndrome 2.5x)
  • Renal pyelectasis (>3 mm AP diameter — Likelihood ratio for Down Syndrome 1.6x)
  • Echogenic bowel (echogenicity matches iliac wing — Likelihood ratio for Down Syndrome 5.5x)
  • Echogenic intracardiac focus (discrete bright focus within the heart — Likelihood ratio for Down Syndrome 2x)*Likelihood ratios for Down Syndrome from Nyberg DA, et al, Ultrasound Obstet Gynecol 1998; 12:8-14

 

Occasional Findings associated with aneuploidy

Second Trimester Markers

Occasional findings in cases of aneuploidy

Nuchal Translucency

First Trimester Aneuploidy Screening

Aneuploidy Unbalanced Translocation 46, XY, der(13)t(3;13)(q11.2;p11.2)

Unbalanced chromosome rearrangement, with a derivative chromosome 13 in all cells examined. This chromosome appears to be derived from a translocation involving the long arm of one chromosome 3 and the short arm of one chromosome 13, resulting in partial monosomy for 13p and partial trisomy for 3q.

Monosomy for 13p is not expected to be clinically significant. Trisomy 3q in one reported case had severe brain and cardiac malformations, renal abnormalities, omphalocele, and neonatal death.

Maternal

Multiple Pregnancy

Determining zygosity

Multiple Pregnancy

An effort should be made to distinguish the type of twinning (monozygotic or dizygotic) as monozygotic twins have an increased risk of specific complications, such as twin-twin transfusion syndrome. Many high-order multiple pregnancies result from assisted reproductive technologies (ovulation induction, IVF, etc.), but dizygotic twinning still may occur. The best time to identify the type of membranes (dichorionic, diamnionic or monochorionic, diamnionic) is probably in late first trimester.

 Unusual twinning situations:

Monoamniotic Twins

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