Ultrasonographic Findings in Fetal neck and chromosomal aberrations



S.Degani

Nuchal translucency

  1. Langdon Down (1866): “... The skin of affected individuals appear to be too large for their bodies”.
  2. Fraser & Mitchelle (1876): Association with advanced maternal age.
  3. Increased nuchal translucency at 10-14 weeks of gestation is a common phenotypic expression of :Trisomies, Turner & Triploidy.

    Nuchal translucency

    Fluid accumulation behind fetal neck

    Nuchal translucency

    Physiological basis

  1. Bony components of posterior fossa are not fully differentiated in 1st trimester.
  2. Cervical “window” to protect from overperfusion during rapid placental growth.
  3. Relation to specific {e.g. cardiovascular} malformations in human and animal model.

    4.  

    Nuchal Translucency

    Pathology:

  4. Chromosomally abnormal fetuses with NT- Narrow aortic isthmus (Hyette et al).
  5. Trisomy 18+NT: No endothelial lining (exclude lymphatic origin), and no cardiac malformation.

    6.  

    Nuchal translucency

    Measurement:

  6. Sagittal section (CRL).
  7. Max. thickness : skin to supraspinal soft

    8. tissue.

  8. Distinguish amn. membrane/fetal skin.
  9. Mean of two good measurements.
  10. Inter/Intra observer < 0.5 mm in 95%.

    11. Nuchal translucency

    To determine significance of ultrasonographic marker : prevalence of the abnormality at different gestational age and maternal age.

    2nd trimester fetus with Down Syndrome

  11. Nuchal fold: 80% of neonate with Down .

    12.  

  12. 42% (9/21) of trisomy 21 - thickened nuchal fold [> 6mm] (Benaceraf 1987).

    13. Sensitivity=42% , Specificity 99.9%

    Nuchal fold (2nd trimester)

    Prospective studies:

  13. Detection rate 38-50% (Watson 94, Grandjean 95, Crane 91&94)
  14. selected population.
  15. false positive:1.4-3%

    16. Crane et al: >5 mm (14-18 wks)

    >6 mm (19-24 wks)

    Nuchal fold thickening:

  16. The most sensitive & specific sonographic finding for the detection of 2nd trimester fetus with Trisomy 21. (Benaceraf 1992).

    17.  

  17. Insufficient data on low risk population (<35 year, normal levels of markers).

Lateral neck cysts

  1. “Non septated cystic hygroma”
  2. “Nuchal blebs”

    3.  

  3. Bronshtein (1989,1993): 5% Abnormal karyotype (septated vs non-septated).
  4. Achiron (1995): Chromosomal anomalies when nuchal thickness > 4mm, Spontaneous resolution in euploides.

    5.  

    Etiology?? Histology??

    Nuchal translucency

    20 small series (early 90s):

     

  5. Mean Prevalence (1968 patients) : 29% (range 19-88%).
  6. Variations reflect:
  7. Different maternal age distribution.
  8. Different definition of abnormal NT (2-10mm).
  9. Different gestational ages.

    10. Nuchal translucency

    Screening studies in high risk pregnancies:

    (before karyotyping, mainly for maternal age)

     

  10. 1273 pregnancies: NT> 95 percentile of normal range , in 80% trisomy 21. (Nicolaides/ Comas/ Szabo/Savoldelli/Shulte).

    11.  

  11. 1819 pregnancies (Brambati) : NT>3mm identified only 30% of chromosomal aberrations (not only Down).

    12.  

    Nuchal translucency

    The prevalence of chromosomal aberrations is dependant on both NT thickness

    &

    maternal age.

     

    Nuchal translucency

    Screening unselected population:

    Frimley Park Hosp. & St Peter’s Hospital:

  12. 1993: only 2/11 Down were detected (maternal age > 35)
  13. 1994: NT + Maternal age
  14. Invasive procedure : 5%
  15. All 4 cases of Down Syndrome were detected.

    16. Nuchal translucency

    Austrian study:

  16. 1972 women; 10-13 wks
  17. NT> 2.5mm in 1.3%

    18.  

  18. 73% 0f fetuses with chromosomal abnormalities.

    19. Nuchal translucency

    The multicenter screening study:

    20,804 pregnancies; 164 chromosomal aberrations:

  19. In normal pregnancies : NT increased with gestation.
  20. In chromosomally abnormal pregnancies: NT thickness is increased.

    21. Nuchal translucency

  21. The multicenter sdtudy (II):
  22. In 5% of pregnancies, estimated risk for Trisomy 21: 1/100 80% of Down syndrome fetuses and 77% of other chromosome anomalies.
  23. Because the maternal age of screened population was higher than average: estimated cut-off risk :1/300 (to include 80% of trisomy 21).

    24. Nuchal translucency

    The multicenter study (III):

    “Combining maternal age with fetal NT thickness is currently the most sensitive method of screening for chromosomal abnormalities”.

    Nuchal translucency

    University College study:

    (1704 women , TAS at 8-14 weeks)

  24. “NT measurement is feasible and promising ... but to warrant its introduction for screening:
  25. Insufficient data.
  26. Poor reproducibility.