Ultrasound examination during should include a systematic evaluation of fetal anatomy. Apart from anencephaly, the fetal organs cannot be accurately measured before 17-18 weeks of gestation. After 30-35 weeks, evaluation becomes increasingly difficult. Hence level-two ultrasound scan is done at 18 to 20 weeks of gestation.
CLASSIFICATION OF FETAL SONOGRAPHIC EXAMINATIONS
1. First-Trimester Ultrasound
2. Standard Second- or Third-Trimester Ultrasound
a. Fetal presentation, amniotic fluid volume,
b. Cardiac activity, placental position
c. Fetal biometry, anatomic survey
d. Maternal cervix, adnexae
3. Limited Examination
a. Fetal cardiac activity
b. Fetal presentation
4. Specialized Examination (also called a Level 2 or Targeted Examination) a. Detailed anatomic study
b. Fetal Doppler, biophysical profile, echocardiogram
RECOMMENDED FETAL ANATOMY
1. Head: Cerebral ventricle, Cerebellum, Cisterna magna, Midline falx, CSP Lips. 2. Chest: 4 chamber heart and great vessels.
3. Abdomen: Stomach, Kidneys. Urinary bladder, echogenicity. 4. Umbilical cord: Insertion and vessels.
5. Limbs: upper and lower.
6. Spine: Cervical, Thoracic, Lumbar, Sacral, Spina bifida, Meningomyelocoele
ADDITIONAL VIEWS IN A TARGETED OR DETAILED EXAMINATION
1. Skull: Configuration, mineralization, contiguity
2. Brain: Cerebral hemispheres, third ventricle, fourth ventricle, trans-cerebellar diameter 3. Face: Profile, nasal bridge, oral cavity/tongue, ears, outer orbital diameter 4. Neck: Soft tissues and external contours
5. Thorax: Configuration of bony thorax, thoracic circumference 6. Heart: Four chamber, outflow tracts, descending aorta, septa, valves 7. Abdominal cavity / bowel / liver / spleen: Any mass, calcification, dilatation 8. Umbilical Cord: Assess insertion.
9. Spine: assess for Spina Bifida
10. Long bone lengths: Severity and distribution of shortening, check clavicles 11. Extremities: Limb reductions, demineralization, number of digits, deformations 12. Amniotic Fluid assessment
SKULL. Ultrasound can demonstrate the fetal head by the eighth week of gestation, but intracranial anatomy becomes visible only after 12 weeks. BRAIN
Start with biparietal diameter view and rotate transducer 20-30 degrees Still transects thalamus
Now transect cerebellum
Now transect ventricle
1. Head shape
2. Bone density
4. Cerebellum and Vermis
5. Choroid plexus
6. Cisterna magna
7. Lateral Ventricles
8. Cavum septum pellucidum
9. Assess for meningomyelocele
Assessment Planes for Intracranial Anatomy
1. Transthalamic plane
2. Transventricular plane
3. Transcerebellar plane:
This is the plane which has been traditionally used to measure the BPD and the HC. The three structures which have to be looked for in this plane are • Falx cerebri, which is interrupted by
• Cavum septum pellucidum
• Thalami, forming an arrow pointing to the occipt
The occipital horn of the lateral ventricle must be imaged clearly. The far field lateral ventricle is seen more clearly as the near hemisphere is obscured by reverberation artifacts. A coronal view is needed. The three structures seen in the transventricular plane are • The lateral ventricles
• Choroid plexus
• Cavum septum pellucidum
Imaged by rotating the probe posteriorly from the BPD plane till a clear view of the posterior fossa and the occipital bone is obtained. The tree structures that are to be identified in the posterior fossa are: • Rounded cerebellar hemispheres (dumb bell shaped) • Vermis of the cerebellum (there should be no space between the 2 cerebellar hemispheres) • Cisterna magna (seen as a...