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Radiology
Trisomy 18
Built from Obstetric Imaging
What’s inside
10 sections · 66 slides
Overview
- What this session covers
What trisomy 18 is
One extra chromosome, and what it does to a fetus
- Start with the normal chromosome count
- Three copies of chromosome 18 in a karyotype
- How common is it?
- 2nd
- Where the extra chromosome comes from
- Why it happens
What it means for the baby
Survival, heart surgery, and the limits of treatment
- The outcome is almost always lethal
- ~50%
- Heart defects drive much of the outcome
- Where the feature list comes from
- Clinical features and how often they occur
- Common Clinical Features in Trisomy 18
- Common Clinical Features in Trisomy 18 (continued)
- Common Clinical Features in Trisomy 18 (continued)
- What to take from the feature list
How well ultrasound finds it
Detection rates, the genetic scan, and timing
- Ultrasound is the front-line test
- The genetic ultrasound scan
- “
- Do the whole anatomy scan, not a quick look
- Timing changes what you can see
- The same fetuses, scanned later
- What else blunts the scan
What to look for
Major structural anomalies, system by system
- Findings split into two families
- Major versus minor findings
- Organ systems to sweep on the scan
- The heart: the commonest major defect
- A hole in the wall between the ventricles
- The brain: seen in about 8 in 10 fetuses
- More brain findings to name
- Fluid at the back of the fetal brain
- Bones, joints, hands and feet
- Clenched hand with overlapping fingers
- The face
- The gut and the abdominal wall
- Abdominal contents bulging at the umbilicus
- The kidneys and genitals
Minor anomalies and soft markers
Small signs that shift the risk
- Why the small signs matter
- The choroid plexus cyst
- Fluid pockets inside the brain's choroid plexus
- A cyst on its own is not a diagnosis
- How the risk climbs when the cyst has company
- 50-70%
- Counting the markers in 70 pregnancies
- Most Common Minor Abnormalities Found in Fetuses with Trisomy 18
Other imaging tools
Three- and four-dimensional ultrasound, and MRI
- 3D, 4D and MRI as add-ons
Conditions that look similar
Four differential diagnoses on imaging
- Trisomy 13
- Sorting trisomy 13 from trisomy 18
- Trisomy 21
- Pena-Shokeir I syndrome
- Pena-Shokeir I against trisomy 18
- Pseudotrisomy 18
Screening, confirming, counselling
From a positive screen to an agreed care plan
- The path from suspicion to diagnosis
- Screening before birth
- Confirming the diagnosis
- Managing the pregnancy
- Planning care after delivery
- What surgery can and cannot do
What to carry away
For the referring clinician and for revision
- What the referring physician needs to know
- Key points: outcome
- Key points: what the scan shows
- References
- References (continued)
- References (continued)
- References (continued)
- Obstetric Imaging: Fetal Diagnosis and Care, 2nd Edition