L12 Fetal and Maternal Imaging

Question 1

Structure of the uterus:

Answer 1

• Hollow, muscular (contractility important)
• 7.5cm under normal circumstances (uteruses which have housed pregnancies to term will become less compact)
• Neck and fundus (upper rounded part) with os (opening) at bottom (internal os marks start of cervix)
• Joins to tubes at horn
• Supported in the pelvic cavity by various long ligaments

Question 2

When will a transvaginal ultrasound be used?

Answer 2

• Viewing endometrium (thickness), ovaries or myometrium

Question 3

What may a sonohysterography/hysterosalpingography be used for?

Answer 3

• In-depth investigations of uterine cavity (X-ray with contrast medium in uterus)
• e.g. uterine anomalies, scar tissues, polyps and fibroids, cancer (especially in patients with abnormal uterine bleeding)

Question 4

Give a brief explanation of ultrasound imaging:

Answer 4

• Reflection of ultrasound waves from probe is read by the transducer in the probe
• Intensity of the signal determines tissue density (based on changes to the pitch and direction of the sound as they bounce off internal surfaces)
  *e.g. bone is white, fluid shows as white
• Will use a catheter with a balloon to better visualise cavity
• Imaging is real time

Question 5

Briefly outline the principles of doppler ultrasound:

Answer 5

• Special application of USS that measures direction and speed of blood cells as they move through vessels
• Movement causes a change in pitch of refleced sound waves (a.k.a. the doppler effect)
• Allow a graph to be computed showing flow of blood -> circulation through umbilical artery

Question 6

Benefits of uterine imaging using USS:

Answer 6

• Real-time imaging
• Minimally invasive (compared to procedures like needle biopsies and aspiration)
• Doesn’t involve X-ray exposure
• No known harmful effects for standard diagnostic ultrasound

Question 7

What is a hysterosalpingography?

Answer 7

• Catheter inserted into uterine cavity
• Contrast medium injected into cavity under pressure
• Contrast tracked along tubes by quick flashes of X-ray -> watching progress of medium

Question 8

Downsides of imaging during pregnancy:

Answer 8

• NHS costs of widespread screening programmes
• Patient expectations -> unexpected distress
• However, history has shown that cessation of screening programmes has serious and widespread impact on pregnancy outcomes

Question 9

What scans are typically administered during a pregnancy?

Answer 9

• 12-week dating scan and nuchal thickness
• 20-week anomaly scan
• Additional scans (including early scans) depending on clinical need (risk factors e.g. smoker, advanced age)

Question 10

What is checked at the 12-week dating scan?

Answer 10

• Crown-rump length (dating the pregnancy)
• Heartbeat (viability!)
• Number of fetuses
• Nuchal translucency (too thick indicates further tests for chromosomal abnormality and neural tube defects)

Question 11

What is checked at the 20-week anomaly scan?

Answer 11

• Full checklist for whole body scan (including anatomy and doppler)
• If abnormal, assessing nature and extent of abnormality -> viable? -> gathering evidence for referral to fetal maternal specialist
• Assessing placenta and its location -> immediate further investigation if issues found

Question 12

Potential extra measures following adverse outcomes at 20-week scan:

Answer 12

• Second detailed USS
• Counselling
• Blood test (some CAs/CMV)
• Amniocentesis (genetic testing of skin cells)
• MRI

Question 13

What is the risk of miscarriage associated with amniocentesis?

Answer 13

• 0.5 - 1%

Question 14

When may MRI be used for maternal imaging?

Answer 14

• Following tertiary referral after 20 week scan
• Thought to be generally safe but follow-up data lacking -> never in first trimester (evidence for safety based on animal studies)
• Limited availability in the UK, based in Sheffield
• KEY: Useful in post-mortem imaging subject to parental consent

Question 15

Benefits and drawbacks of maternal MRI:

Answer 15

• Expensive
• Limited availability
• Limited experience (not trained universally)
• Not routine for NHS -> one centre in UK -> logistical issues for patients
• Images easier for patients to understand
• More informative -> better definition of brain and soft tissues
• Less informative -> limbs, heart, movement
• Uncomfortable for patients (claustrophobia, lying still, long duration)

Question 16

When can MRI be useful in autopsies?

Answer 16

• MRI can direct autopsy -> where to excise
• Informative (e.g. vermian development)
• Directing autopsy to particular areas