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Radiology
Corpus Callosum and Septum Pellucidum Anomalies
Built from Obstetric Imaging
What’s inside
14 sections · 135 slides
Overview
- What this topic is about
- The road ahead
Building the midline
What forms, and when
- The midline is built very early
- Why these two anomalies are grouped together
- The brain's main bridge
- Four parts, front to back
- Normal corpus callosum in the midline view
- The words used for a missing callosum
- 0.3-0.7%
- Reading those numbers honestly
Why the cable fails
Development, and what disturbs it
- A rope bridge for growing axons
- Two segments that meet in the middle
- A myth worth unlearning
- Failure to build versus damage after building
- Two kinds of congenital callosal failure
- Probst bundles: axons that never crossed
- What causes it
- What the family history adds
Naming the anomalies
Classification, and why it matters
- Four ways the callosum can be abnormal
- Which of these you will actually see before birth
- One umbrella term
- Three classes of callosal anomaly
- Class one: hypoplasia
- Class two: hypoplasia with dysplasia
- Class three: complete absence
What it means for the child
Clinical picture and outcome
- The clinical picture is wide
- Does an isolated anomaly do better
- 75.4%
- Where those figures come from
- Problems that surface later
Seeing it with ultrasound
Planes, indirect signs, direct signs
- Why the routine view is not enough
- Getting a window onto the midline
- Three planes at once
- Three-plane navigation of the fetal brain
- The first hint on the routine scan
- Missing cavum and teardrop ventricles
- Colpocephaly, explained
- Ventricles pushed apart and running parallel
- The coronal view and the bull's head
- Normal coronal view beside an absent genu
- Why the diagnosis gets missed
- Direct signs settle it
- Absent callosum early and late in pregnancy
- Why early scans give false reassurance
- The path from suspicion to diagnosis
Partial agenesis
The harder, easier-missed diagnosis
- When only part of the cable formed
- A callosum that stops halfway
- Partial does not mean mild
- A blood vessel that traces the cable
- The pericallosal artery in normal, partial and complete agenesis
- No arterial loop where the callosum should be
- What else may sit in the midline
- A bright fatty mass in the midline
Fetal MRI
Confirming the midline, and finding the rest
- How fetal MRI is done
- The normal callosum on MRI
- Normal callosum and septal leaves on fetal MRI
- The back is always easier to see
- Normal callosum from 21 to 36 weeks
- Measuring the callosum
- Measuring callosal length on the midline image
- Why MRI is added after ultrasound
- Complete agenesis on MRI
- Complete agenesis in four MRI planes
- The bull's head, close up
- Spoke-wheel sulci in the third trimester
- Flat surface early, radiating sulci later
- Seeing the stranded bundles
- Probst bundles lining the lateral ventricles
- Finding a lipoma needs a different sequence
- A fatty lump over a thin splenium
- Partial agenesis on MRI
- Three different degrees of underdevelopment
- MRI's real strength is the cortex
- When cortical problems become visible
- Aberrant folding alongside an absent callosum
- When the pattern names the syndrome
- Asymmetric hemispheres in Aicardi syndrome
Telling look-alikes apart
Differential diagnosis
- Colpocephaly is not plain ventriculomegaly
- An absent cavum is not one diagnosis
- Where a missing cavum can lead
- Four midline appearances between the frontal horns
- The features that separate them
Management and counselling
What can and cannot be offered
- Before birth
- After birth
- What the referring physician needs to know
- Key points on the corpus callosum
- Key points on counselling
The septum pellucidum
A thin wall with heavy consequences
- Where the septum pellucidum sits
- What it is made of
- The cavum and its back recess
- The cavum comes and goes with gestation
- When the septum is absent
- What to look for when the cavum is missing
- Fetal Brain Anomalies Associated With Absent Cavum Septi Pellucidi
- Brain anomalies that go with an absent cavum
- From absent septum to septo-optic dysplasia
- The three arms of septo-optic dysplasia
- SOD-plus
- How common is an absent septum
- What causes septo-optic dysplasia
Living with septo-optic dysplasia
Eyes, hormones, brain
- Severity varies enormously
- 57%
- What the eye figures mean day to day
- The hormones
- The brain and the rest of the body
- What an isolated absent septum means
- The limits of prenatal reassurance
- 90%
- Reading those risk figures
Imaging the septum
Ultrasound, then MRI
- Ultrasound findings of an absent septum
- Classic signs of an absent septum
- Absent septum beside lobar holoprosencephaly
- Downward-pointing frontal horns with a normal genu
- Trying to separate the two before birth
- Optic tract nomograms: useful, not conclusive
- What MRI shows in an absent septum
- Fused frontal horns with a normal callosum
- The fused fornix
- Fused fornices mimicking a septum
- Where MRI runs out of road
- Testing the fetal pituitary
- Absent septum or holoprosencephaly
- Why the coronal view can fool you
- Frontal lobes that never separated
Care and counselling
Septum pellucidum anomalies
- Managing an absent septum
- What the referring physician needs to know
- Key points on the septum pellucidum
- Five things to carry away
- Suggested readings
- References
- References (continued)
- References (continued)
- References (continued)
- References (continued)
- Obstetric Imaging: Fetal Diagnosis and Care, 2nd Edition