4. Obstetrics p102-107 (Congenital Fetal Anomalies)

Question 1

Concerning US findings for Downs (4)

Answer 1

Congenital heart disease
- More than half of Downs have congenital heart disease, most commonly AV canal and VSD.
Echogenic focus in cardiac ventricle - non specific but increases Downs risk x4

Duodenal atresia
- Commonest intra-abdominal pathology associated with Downs
Echogenic bowel - non specific (can be due to obstruction, CF, infection, ischaemia)

Short femur length - non specific
Choroid plexus cyst - Non specific, more common in trisomy 18

Nuchal translucency - translucency >3mm in first trimester
Nuchal fold thickness - >6mm in second trimester, also seen with Turners

Question 1

Nuchal lucency (2)

Answer 1

Measured between 9-12 weeks, anechoic area between neck/occiput and skin should be <3mm.
Also associated with other chromosomal anomalies.
Positioning of the neck is important to avoid false positives.

Question 2

Amniotic band syndrome (3)

Answer 2

If amnion gets disrupted, foetus can get into chorionic cavity and get caught in sticky fibrous septa. Can cause decapitation or limb amputation.
X-ray of hand or baby showing amputated fingers or arm, remaining exam normal.
Foetal US with bands entangling arms or legs of a foetus.

Question 3

Hydrops (3)

Answer 3

Can be immune or non-immune causes.
Commonest cause is Rh sensitisation from prior pregnancy, others include TORCH, turners, twin related, Alpha thalassaemia.
US: presence of 2: Pleural effusion, pericardial effusion, subcutaneous oedema.

Question 4

Lemon sign (2)

Answer 4

Indented frontal bone, classically seen in Chiari II, and also spina bifida.
Seen before 24 weeks, usually disappears after 24 weeks.

Question 5

Banana sign (4)

Answer 5

Cerebellum wraps around the brainstem due to spinal cord tethering and migrates downward, looking like a banana.
Cisterna magna is obliterated and cerebellum looks like a banana.
Seen with Chiari II and spina bifida.
Anterior curving of cerebellar hemispheres with obliteration of cisterna magna is called banana sign.
Other findings in spina bifida include small biparietal diameter and ventricular enlargement.

Question 6

Choroid plexus cyst

Answer 6

Incidental, but more likely in trisomy 18, trisomy 21, turners, Klinefelters.

Question 7

Facial clefts (3)

Answer 7

Commonest foetal facial anomaly.
30% associated with chromosome anomaly.
80% have cerebral palsy.
Can see cleft lips, but cleft palate in isolation is difficult to see.

Question 8

Cystic hygroma (2)

Answer 8

Complex cystic mass in posterior neck in antenatal period.
Associated with Downs and Turners

Question 9

Ventriculomegaly (4)

Answer 9

Multiple causes (Hydrocephalus (communicating and non communicating), cerebral artophy included.
Aquaductal stenosis is commonest cause of non communicating hydrocephalus in neonate.
Ventricular atrium diameter >10mm = too big.
“Dangling choroid” hanging off the wall by more than 3mm.

Question 10

Anencephaly (2)

Answer 10

Most common neural tube defect, total absence of cranial vault and brain above the level of the orbits.
Not compatible with life.

Question 11

Pleural effusion

Answer 11

Often caused by Hydrops in neonate, multiple other causes exist.

Question 12

Congenital diaphragmatic hernias (3)

Answer 12

Usually left sided.
Causes high mortality due to association with pulmonary hypoplasia.
Causes gut malrotations.
Usually shown on newborn CXR or 3rd trimester MRI.

Question 13

Echogenic Intracardiac Focus (3)

Answer 13

Calcification seen in papillary muscle, usually left ventricle.
Seen more commonly in trisomy 21 and trisomy 13.
Also occurs in normal population (5% vs 12% in Downs).

Question 14

Abnormal heart rate

Answer 14

Tachycardia defined as >180bpm. Bradycardia is <100bpm.

Question 15

Double bubble (2)

Answer 15

Shown on antenatal US or MRI.
Suggests duodenal atresia.

Question 16

Echogenic bowel (5)

Answer 16

Can be normal variant, but associated with:
- CF
- Downs
- Trisomies
- Viral infections
- Bowel atresia.
Normal bowel is isoechoic to liver. If equal to iliac crest bone, it’s too bright.

Question 17

Sacrococcygeal teratoma (6)

Answer 17

Commonest tumour of foetus or infant.
Solid or cystic masses, usually large, found on prenatal imaging or at birth.
Can cause mass effect on GI system, hip dislocation, nerve compression causing incontinence and high output cardiac failure.
Can cause issues with premature delivery, dystocia and haemorrhage of the tumour.
Usually benign (80%). Higher malignant potential when presenting in older infants.
Located wither external to pelvis (47%P, internal to pelvis (9%) or dumbbell protruding inside and out.

Question 18

Autosomal recessive polycystic kidney disease

Answer 18

Massively enlarged bilateral kidneys with oligohydramnos.

Question 19

Posterior urethral valves

Answer 19

Bilateral hydro on either foetal US or 3rd trimester MRI.

Question 20

Short femur

Answer 20

Short femur (below 5th centile) suggests skeletal dysplasia.