Fetal Imaging Flashcards
What is ultrasound used for?
Primary screening modality for obstetric and foetal imaging
What are the advantages of fetal imaging?
- Low cost
- Easy access
- Quicker
What are the advantages of fetal imaging?
- Reduced FOV
- Lower spatial resolution
- Poor soft tissue contrast
- Operator dependent
What is Foetal MRI?
Complementary tool
What are the safety features of foetal imaging?
- Operate within radiological safety guidelines
- Avoid first trimester
- Screen for metal
- Issues with claustrophobia and high BMI
- Minimise heating effects: operate sequences with low SAR (specific absorption rates)
- Minimise noise e.g. add soft tone
- No reported detrimental effects to fetus
What are the features of foetal MR imaging?
- Relatively new technique (1980’s)
- Motion is a major problem
- Initial studies paralysed fetus
- Maternal sedation
Why is foetal MR imaging relatively new technique?
- Complementary to ultraound
- Improve detection rate of abnormalities
- Improve characterisation of known abnormalities
What are the optimal brain sequences essential for optimal clinical scan?
- 3 planes T2 (fast spin echo)
- Axial T1-weighted
- Axial Diffusion weighted (ischaemia)
- T2 GRE (haemorrhage)
What are the body sequences essential for optimal clinical scan?
- T2 (fast spin echo)
- T1 (meconium in the rectum)
- T2 GRE (good for spine)
- T2 TRUFFI (good for spine and placenta)
What are essentials for optimal clinical scan?
- Always have all clinical and ultrasound data available
- Experienced interpreter
- Understanding of relevant pregnancy termination laws
What are the features of foetal motion?
- Single slice fast acquisition - no artefacts unless movement, very quick
- Fetus move in and out of plane during acquisition
- Incomplete coverage of brain and rotated views may make interpretation difficult
What does snap shot image with volume reconstruction (SVR) provide?
- High signal to noise
- High resolution
- 3D volumetric dataset of brain in presence of foetal motion
What does reconstruction allow for?
Non-rotated views with full brain coverage
optimal for clinical interpretation
What are the CNS imaging indications?
- Ventriculomegaly
- Agenesis of corpus callosum
- Cerebellar anomalies
- Congenital infection
- Neural tube defect
What is the consequence of CNS imaging indications?
- Complications of twin pregnancies
2. Acute maternal hypoxic event or illness
When is ventriculomegaly observed?
- 1% pregnancies atrial diameter > 10mm on ultrasound
2. More frequent in males
What are the current practice for ventriculomegaly?
- Detailed fetal ultrasound
- Maternal TORCH screen
- Fetal MRI
- Consider Amniocentesis
MRI in ventriculomegaly
- Most common indication for MR referral
- Detection any obvious cause for ventriculomegaly
- haemorrhage/obstruction - Identification additional anomalies
- Inform further investigations
- Helps on outcome predicition and counselling
When does isolated ventriculomegaly cause neurodevelopmental impairment?
Atrial > 15mm up to 75%
What are the causes of ventriculomegaly?
- Ventricular dilation with evidence of germinal matrix haemorrhage
- Haemorrhage involves basal ganglia
- Posterior limb of internal capsule
Agenesis of corpus callosum
Incidence 0.5 -70 per 10,000
Variable outcome (approx. 30% moderate /severe)
Exclude other abnormalities as outcome worse (increased detection with MRI 22.5%)
Agenesis of corpus callosum
Chromosomal abnormalities in approx. 17% ( More common when other anomalies)
May be referred from US with ventriculomegaly
Occasionally as a parenchymal cyst
Gender of fetus important to exclude possible Aicardi syndrome (females)
What are the cortical anomalies?
- MRI able to assess cortical maturation
- May have early abnormal folding
- Delayed or absent folding
- Markedly abnormal appearance to cortex posteriorly
- Very low signal thickened and abnormally shaped
- Probably early polymicogyria
What are the cerebellar anomalies?
Large cisterna magna Cerebellar hypoplasia Vermis +/- hemispheres Rhomboencephalosynapsis Cerebellar haemorrhage
What are the postnatal examination?
Anorectal anomaly Imperforate anus Micropenis Choanal atresia Normal cardiac echo Normal renal US
What are the other postnatal examination?
Coloboma of the eye, Heart defects, Atresia of the choanae, Retardation of growth and/or development, Genital and/or urinary abnormalities, Ear abnormalities and deafness
What are the neural tube defects?
Myelomeningocele (most common)
Compatible with life but significant morbidity
Prenatal intervention (few centres)
Delivery and neonatal surgical repair
80% ventriculo-peritoneal shunt placement
Complications, lifelong supportive care
Most present with Arnold-Chiari II malformation
