Fetal imaging
Spina-bifida screening in the first quarter
Neural tube closure abnormalities (AFTN) are serious pathologies that cause, in the vast majority of cases, a major handicap. The estimated frequency in France is 1/1,000. FNTDs of the Acraine Sequence type are easy to identify and are the subject of a recommendation of the National Technical Committee for Prenatal Screening (CNTEDP) in its 2005 report. Advances in ultrasonic technology and our knowledge, particularly early anatomy of the fetus, should allow us to consider the possibility of screening for open spina-bifida (SB) anomalies in the first quarter. This screening is based on the existence of indirect signs of spina-bifida present from the 1st quarter. These signs have been widely described for these diseases when they are discovered in the 2th quarter and when these malformations are reported to be open, which is true in 90% of cases. All of these indirect signs are, of course, due to the leakage of cerebrospinal fluid resulting in changes in brain structures.
In 1997, changes in the shape of the fetal skull were shown on an axial cross-section of the head tip: the prominent aspect of the anterior contrasted with the flattened aspect of the posterior bet, which could be compared to that of a "gland"(5) (Figure 1), and then in 2002 the parallel aspect of the Bichat slits in the case of open SB was described(4)(Figure 2). The advent of nucal clarity for chromosome abnormalities testing, and thus the "obligation" to achieve a strict sagital plan, showed that the 4th ventricle was visualizable on this cutting plane; thus was born the "intracerebral clarity" (IT) (Figure 3)(1,2). This intracerebral clarity, which corresponds to the future 4th ventricle, disappears in the case of open spina-bifida(6), the realized aspect being that of an enlarged cerebral trunk (Figure 4). Of course, IT remains normal in the case of a closed SB(21). It is usually visualized with a fetus positioned in front of the probe, but visualization is also possible when the fetus presents its back to the probe(2). Unfortunately, several teams have shown that IT visualization is often difficult to achieve(7,8), while operators’ training in recognizing the precise markers of brain anatomy seems to have a beneficial effect on the possibilities of IT(7) highlighting. Moreover, it is quite surprising that in recent literature there is only one article relating to an axial plane study(3). This paper, published in 2002, does not directly address the anatomical markers of the posterior pit(4). Indirect signs based on biometrics seem much easier to use. In the case of open SB, the decrease in volume of cerebrospinal fluid in the cranial box(10.11) leads to a reduction in diameter, as demonstrated by J.-P. Bernard in his study published in the American Journal in 2012. For example, for a false positive rate of 5%, the screening rate for open SBs was 50%.
Figure 1: Sign of the "gland".
Figure 2: Parallel Bichat slits. Right normal control.
Figure 3: * Intracerebral clarity; Large tank; green arrow: V4 choroid plexus; TC: brain stem.
Figure 4: Disappearance of intracerebral clarity.
Numerous publications corroborated these initial findings(12,13). This is all the more interesting because the finding of an isolated biparietal diameter (BIP) below the 5th percenile in the 1st quarter does not appear to be due to anomalies other than SBs(14). The evidence of a small BIP in relation to a measure of the normal abdominal diameter further increases sensitivity(15). The use of other biometric parameters such as the measurement of the large tank(16), the distance between the Sylvius aqueduct and the occipital shell was also suggested. The search for SB’s direct signs by visualizing the rachis is almost never discussed, except perhaps in a "discreet" way in the ISUOG’s recommendations for the 1st quarter review(20). Therefore, as a synthesis, we propose to conduct a screening of SBs in the first quarter based on the following tripod:
- Presence of an isolated biometric anomaly at the BIP level in relation to cranial length and possibly abdominal biometry.
- Finding the disappearance of intracerebral clarity in the sagital plane of measurement of nucal clarity, but also and above all in an axial plane of the posterior pit (Figure 5), plane which is very easy to obtain from the plane of the BIP by slightly "bend" the probe to the caudal pole of the fetus. Figure 6 illustrates the loss of IT in this plan.
- Search for direct signs at the spine level: it is perfectly possible to visualize the rachis in the 1st quarter by paying particular attention to the integrity of the skin (figure 7).
Figure 5: Intracerebral Clarity (IT): *: IT; °: large tank; green arrow: V4 choroid plexus.
Figure 6: Yellow Arrow: disappearance of IT (open SB); °: large small tank.
Figure 7: Rachis in the sagittal cup.
However, it should be noted that the visualization of a defect in the lombo-sacred spine may be difficult to highlight, as illustrated in the two cases in Figure 8.
Figure 8: SB open. a: green arrows: major spinal defect, b: defect with erosion of the legacies.
It is now entirely feasible to be able to test spina bifida opened in the first trimester of pregnancy. For example, the verification of biometrics alone will enable the detection of one in two cases, the search for the disappearance of intracerebral clarity (IT), in particular in an axial plane, to improve the performance of this first level of screening; finally, the slightest doubt, both biometric and anatomical, at the posterior pit level will lead to an active examination of the rachis, which will be carried out at best by vaginal means using high frequency probes.
Finally, it should be remembered that an effort to inform women who are considering pregnancy has yet to be made in order to promote the prevention of AFTNs(22) par administration of folic acid before pregnancy at sufficient doses.
References
Click on the references and access the Abstracts on
1. Chaoui R, Benoit B, Mitkowska-Wozniak H, Heling KS, Nicolaides KH. Ultrasound Obstet Gynecol 2009 ; 34 : 249-52. Search the abstract2. Chaoui R, Nicolaides KH. Ultrasound in Obstetrics & Gynecology First Published: 25 January 2010. Search the abstract3. Chaoui R, Nicolaides KH. Ultrasound in Obstetrics & Gynecology First Published: 28 November 2011. Search the abstract4. Buisson O, de Keersmaecker B, Senat MV, Bernard JP, Moscoso G, Ville Y. Ultrasound in Obstetrics and Gynecology 2002 ; 19 (3) : 290-2. Search the abstract5. Bernard JP, Suarez B, Rambaud C, Muller F, Ville Y. Ultrasound in Obstetrics & Gynecology First Published: December 1997. Search the abstract6. Chaoui R, Benoit B, Heling KS, Kagan KO, Pietzsch V, Sarut Lopez A, Tekesin I, Karl K. Ultrasound in Obstetrics & Gynecology First Published: 11 November 2011. Search the abstract7. Mangione R, Lelong N, Fontanges M et al. Ultrasound in Obstetrics & Gynecology First Published: 22 November 2011. Search the abstract8. Fong KW, Toi A, Okun N, Al-Shami E, Menezes R.J. Ultrasound in Obstetrics & Gynecology First Published: 11 November 2011. Search the abstract9. Bernard JP, Cuckle HS, Sirnemann JJ et al. Am J Obstet Gynecol 2012 ; 207 : 306.e1-2. Search the abstract10. Bernard JP, Cuckle HS, Bernard MA, Brochet C, Salomon LJ, Ville Y. Am J Obstet Gynecol 2013 Sep ; 209 : 223. Search the abstract11. Loureiro T, Ushakov F, Montenegro N, Gielchinsky Y, Nicolaides KH. Ultrasound in Obstetrics & Gynecology First Published: 28 May 2012. Search the abstract12. Karl K, Benoit B, Entezami M, Heling KS, Chaoui R. Ultrasound in Obstetrics & Gynecology First Published: 30 July 2012. Search the abstract13. Khalil A, Coates A, Papageorghiou A, Bhide A, Thilaganathan B. Ultrasound in Obstetrics & Gynecology First Published: 22 August 2013. Search the abstract14. Socolov D, Deloison B, Bernard JP, Ville Y, Salomon LJ. Ultrasound in Obstetrics & Gynecology First Published: 23 September 2013. Search the abstract15. Simon EG, Arthuis CJ, Haddad G, Bertrand P, Perroin F. Ultrasound in Obstetrics & Gynecology First Published: 3 March 2015. Search the abstract16. Garcia-Posada R, Eixarch E, Sanz M, Puerto B, Figueras F, Borrell A. Ultrasound in Obstetrics & Gynecology First Published: 11 April 2013. Search the abstract17. Finn M, Suton D, Atkinson S et al. Ultrasound in Obstetrics & Gynecology First Published: 1 November 2011. Search the abstract18. Mangione R, Dhombres F, Lelong N et al. Ultrasound in Obstetrics & Gynecology First Published: 23 September 2013. Search the abstract19. Scheier M, Lachmann R, Pětroš M, Nicolaides KH. Ultrasound in Obstetrics & Gynecology First Published: 11 November 2011. Search the abstract20. ISUOG Pracice Guidelines: performance of first-trimester fetal ultrasound scan. Ultrasound in Obstetrics & Gynecology First Published: 25 December 2012. Search the abstract21. Fuchs I, Henrich W, Becker R, Albig M,Chaoui R. Ultrasound in Obstetrics & Gynecology First Published: 30 July 2012. Search the abstract22. Dehe S, Elefant E, Goujard J, Potier de Courcy G, Boog G, Horovitz J, Masnou P, Philippe HJ. Recommandations pour la prévention des anomalies de la fermeture du tube neural. Groupe de travail réuni par la Direction générale de la santé DGS - 8, avenue Search the abstract
Articles on the same theme
- 1 of 2
- >
