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Radiology
Thymus
Built from Obstetric Imaging
What’s inside
7 sections · 69 slides
Overview
- What this topic covers
- The story in one slide
What the thymus is
Its job, what it is made of, and how it forms
- A gland that trains the immune system
- Made of two tissues at once
- Where it sits in the chest
- How the thymus forms
- Where it comes from in the embryo
- Filling up, then moving down
- Two zones inside the gland
Normal anatomy
Two lobes, what surrounds them, and normal variation
- Two lobes side by side
- What lies around it
- The thymus between the lungs, in front of the heart
- Normal variation you should not over-read
Finding it on ultrasound
The views that show it, and how its brightness changes
- What the gland looks like on a scan
- The three-vessel view
- The three-vessel-trachea view
- Thymus in front of the three vessels and trachea
- How bright it looks changes with age
- Early second trimester against later pregnancy
- Thymus brighter than the lungs at twenty weeks
- Thymus darker than the lungs at twenty-eight weeks
- The same darker appearance at twenty-four weeks
- Seen from the side instead
- Teardrop-shaped thymus on a side-on slice
Measuring the thymus
From simple diameters to 3D volume and MRI
- Why measure it at all
- Published ways to size the fetal thymus
- The thy-box: use the vessels as the box
- The walls of the thy-box
- How well the thy-box works
- Comparing the gland with the chest around it
- Rebuilding the whole gland from stacked slices
- Thymus volume rebuilt from three planes at twenty-two weeks
- A larger thymus volume at twenty-six weeks
- The same thymus in transverse, sagittal and coronal planes
- What magnetic resonance imaging adds
- 97%
When the gland is small or missing
What it points to, and the evidence behind each link
- Two words to know
- Two routes to a small thymus
- Conditions reported with a small or absent gland
- Genetic and immune conditions
- Pregnancy and environmental causes
- The chromosome 22 deletion
- How well an absent thymus flags the deletion
- at least 90%
- What autopsy studies found
- Poor growth shrinks the gland
- 58 / 60
- Does a small gland change the outcome?
- When inflammation reaches the fetus
- Why inflammation shrinks the thymus
- Predicting infection in the newborn
- Diabetes in pregnancy
- Preeclampsia, and a first-trimester idea
- Measuring thymus volume at 11 to 14 weeks
Using it in the clinic
When to look, and what a small thymus should change
- When assessing the thymus may be indicated
- If the gland is small or absent on the anatomy scan
- When a heart defect is already suspected
- When the pregnancy is inflamed or the fetus is small
- What is still unsettled
- Key points
- Take-home summary
- References
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- Suggested reading
- Obstetric Imaging: Fetal Diagnosis and Care, 2nd Edition