Edwards Syndrome: Comprehensive Imaging Guide and Clinical Overview
Overview
Edwards syndrome, also known as trisomy 18, is a chromosomal disorder caused by the presence of an extra copy of chromosome 18.
The name “Edwards syndrome” honors John Hilton Edwards, who first described the disorder. It is the second most common autosomal trisomy after Down syndrome.
Clinically, it presents with multiple congenital anomalies including characteristic facial features such as micrognathia (small jaw), a triangular face, low-set malformed ears, clenched hands with overlapping fingers, and rocker-bottom feet.
This syndrome follows primarily a sporadic inheritance pattern caused by maternal nondisjunction during meiosis, resulting in a 47-chromosome karyotype with trisomy for chromosome 18.
Most affected infants have severe developmental delays, multiple organ malformations, and high perinatal mortality, with less than 10% surviving beyond one year.
Key Imaging Features
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Ultrasound often shows intrauterine growth restriction (IUGR) and a small placenta.
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A strawberry-shaped skull due to a prominent occiput and flattened frontal bones is a typical cranial feature.
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Choroid plexus cysts are common, seen as cystic structures within the lateral ventricles, though often transient.
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Ventriculomegaly may be present, reflecting brain development abnormalities.
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Sonography reveals congenital heart defects such as ventricular or atrial septal defects and atrioventricular septal defects.
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Clenched hands with overlapping fingers visible on fetal ultrasound indicate characteristic limb malformations.
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Limb abnormalities including radial ray defects, absence or hypoplasia of long bones, rocker-bottom feet, and limb reduction defects.
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Fetal MRI may demonstrate brain malformations such as agenesis of the corpus callosum and posterior fossa abnormalities like Dandy-Walker malformation or mega cisterna magna.
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Anomalies of the abdomen including omphalocele and esophageal atresia can be detected prenatally.
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Single umbilical artery is a common finding related to vascular anomalies associated with the syndrome.
Pathophysiology
Edwards syndrome results from nondisjunction leading to an extra chromosome 18 in all or some cells, causing gene dosage imbalance that disrupts normal embryonic development.
The extra genetic material broadly interferes with cellular and organogenesis pathways, resulting in widespread multisystem malformations observed on imaging.
Abnormal brain development manifests as structural anomalies such as ventriculomegaly, corpus callosum agenesis, and posterior fossa defects due to altered neural proliferation and migration.
Cardiac malformations are frequent owing to impaired cardiac septation and morphogenesis, which appear as septal defects or complex congenital heart diseases on imaging.
Limb anomalies including clenched hands, radial ray defects, and rocker-bottom feet occur due to disrupted limb bud patterning and skeletal development caused by gene imbalance.
Vascular abnormalities contribute to findings like a single umbilical artery and influence placental development, correlating with intrauterine growth restriction.
Differential Diagnosis
Key syndromes to consider with overlapping imaging features include:
| Condition | Distinguishing Imaging Features |
|---|---|
| Patau syndrome (Trisomy 13) | Facial midline defects (holoprosencephaly, cleft lip/palate), more prominent cerebral malformations, polydactyly; less frequent clenched hands than trisomy 18 |
| Down syndrome (Trisomy 21) | Nuchal translucency thickening; characteristic heart defects like AV canal defects; less severe limb anomalies; facial profile includes upslanting palpebral fissures |
| Meckel-Gruber syndrome | Occipital encephalocele, cystic renal dysplasia, polydactyly, distinct from Edwards limb features |
| Limb-body wall complex | Severe body wall defects with limb anomalies but lacks typical trisomy 18 brain and craniofacial abnormalities |
Imaging Protocols and Techniques
Ultrasound remains the primary modality for prenatal diagnosis. Perform a detailed anomaly scan between 18 and 22 weeks gestation focusing on:
- Fetal biometry and growth curves to assess intrauterine growth restriction
- Cranial anatomy for skull shape, lateral ventricles, choroid plexus cysts, and posterior fossa
- Cardiac assessment using fetal echocardiography including 4-chamber and outflow tract views for septal and valvular defects
- Limbs and hands to identify clenched hand deformities, radial ray anomalies, and rocker-bottom feet
- Abdominal wall and internal organs, screening for omphalocele and kidney anomalies (horseshoe kidney)
Fetal MRI supplements ultrasound when precise brain anatomy delineation is needed (e.g., corpus callosum agenesis or posterior fossa malformations). T2-weighted single-shot fast spin echo sequences are preferred to reduce motion artifact.
Postnatal imaging includes:
- Chest radiography and echocardiography to characterize cardiac defects thoroughly
- Neuroimaging with brain MRI or ultrasound for ventriculomegaly and structural anomalies
- Skeletal surveys to document limb abnormalities quantitatively and monitor progression
Imaging pearls: Recognize the clenched hand with overlapping index finger over the third digit and pinky over the fourth—this is a hallmark imaging sign. Also, the presence of multiple choroid plexus cysts in a fetus with growth restriction should raise suspicion for trisomy 18, although isolated cysts can be benign.
Imaging pitfalls: Transient choroid plexus cysts occur in normal fetuses; their presence alone is not diagnostic. Limb anomalies can be subtle early on and require careful multiplanar imaging. Distinguishing trisomy 18 from trisomy 13 requires thorough evaluation of craniofacial and brain anomalies.
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