Low torcular Herophili position and large brainstem-tentorium angle in fetuses with open spinal dysraphism at 11-13 weeks' gestation

OBJECTIVE

To evaluate whether in fetuses with open spina bifida (OSB) the tentorium can be seen to be displaced downwards and vertically oriented by the time of the 11-13-week scan and whether this is reflected in an alteration of the brainstem-tentorium (BST) angle.

METHODS

The study population was recruited between 2015 and 2020 from three fetal medicine referral centers and comprised a control group and a study group of pregnancies with OSB. The control group was recruited prospectively and included singleton pregnancies with a normal sonographic examination after first-trimester combined screening for chromosomal abnormalities and normal outcome. The study group was selected retrospectively and included all cases with OSB between 2015 and 2020. All cases underwent detailed ultrasound assessment at 11 + 0 to 13 + 6 weeks' gestation. The position of the torcular Herophili (TH) was identified in the midsagittal view of the fetal brain with the use of color Doppler and was considered as a proxy for the insertion of the tentorium on the fetal skull. The BST angle was calculated in the same view and was compared between the two groups.

RESULTS

Sixty normal fetuses were included in the control group and 22 fetuses with OSB in the study group. In both groups, the BST angle was found to be independent of gestational age or crown-rump length (P = 0.8815, R²  = 0.0003861 in the controls, and P = 0.2665, R²  = 0.00978 in the OSB group). The mean BST angle was 48.7 ± 7.8° in controls and 88.1 ± 1.18°, i.e. close to 90°, in fetuses with OSB. Comparison of BST-angle measurements between the control group and cases with OSB showed a statistically significant difference (P = 0.0153). In all fetuses with OSB, the downward displacement of the TH and tentorium was clearly visible at the 11-13-week scan.

CONCLUSIONS

In fetuses with OSB, the BST angle is significantly larger than in normal controls, with the tentorium being almost perpendicular to the brainstem. This sign confirms the inferior displacement of the tentorium cerebelli with respect to its normal insertion on the occipital clivus as early as the first trimester of pregnancy and is useful in the diagnosis of Chiari-II malformation at this early stage. In fetuses with OSB, the low position of the tentorium and TH is clearly visible, even subjectively, at the 11-13-week scan. © 2021 International Society of Ultrasound in Obstetrics and Gynecology.

Percutaneous fetoscopic spina bifida repair: effect on ambulation and need for postnatal cerebrospinal fluid diversion and bladder catheterization

OBJECTIVE

A trial comparing prenatal with postnatal open spina bifida (OSB) repair established that prenatal surgery was associated with better postnatal outcome. However, in the trial, fetal surgery was carried out through hysterotomy. Minimally invasive approaches are being developed to mitigate the risks of open maternal-fetal surgery. The objective of this study was to investigate the impact of a novel neurosurgical technique for percutaneous fetoscopic repair of fetal OSB, the skin-over-biocellulose for antenatal fetoscopic repair (SAFER) technique, on long-term postnatal outcome.

METHODS

This study examined descriptive data for all patients undergoing fetoscopic OSB repair who had available 12- and 30-month follow-up data for assessment of need for cerebrospinal fluid (CSF) diversion and need for bladder catheterization and ambulation, respectively, from eight centers that perform prenatal OSB repair via percutaneous fetoscopy using a biocellulose patch between the neural placode and skin/myofascial flap, without suture of the dura mater (SAFER technique). Univariate and multivariate logistic regression analyses were used to examine the effect of different factors on need for CSF diversion at 12 months and ambulation and need for bladder catheterization at 30 months. Potential cofactors included gestational age at fetal surgery and delivery, preoperative ultrasound findings of anatomical level of the lesion, cerebral lateral ventricular diameter, lesion type and presence of bilateral talipes, as well as postnatal findings of CSF leakage at birth, motor level, presence of bilateral talipes and reversal of hindbrain herniation.

RESULTS

A total of 170 consecutive patients with fetal OSB were treated prenatally using the SAFER technique. Among these, 103 babies had follow-up at 12 months of age and 59 had follow-up at 30 months of age. At 12 months of age, 53.4% (55/103) of babies did not require ventriculoperitoneal shunt or third ventriculostomy. At 30 months of age, 54.2% (32/59) of children were ambulating independently and 61.0% (36/59) did not require chronic intermittent catheterization of the bladder. Multivariate logistic regression analysis demonstrated that significant prediction of need for CSF diversion was provided by lateral ventricular size and type of lesion (myeloschisis). Significant predictors of ambulatory status were prenatal bilateral talipes and anatomical and functional motor levels of the lesion. There were no significant predictors of need for bladder catheterization.

CONCLUSION

Children who underwent prenatal OSB repair via the percutaneous fetoscopic SAFER technique achieved long-term neurological outcomes similar to those reported in the literature after hysterotomy-assisted OSB repair. © 2021 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.

Learning curves of open and endoscopic fetal spina bifida closure: systematic review and meta-analysis

OBJECTIVE

The Management of Myelomeningocele Study (MOMS) trial demonstrated the safety and efficacy of open fetal surgery for spina bifida aperta (SBA). Recently developed alternative techniques may reduce maternal risks without compromising the fetal neuroprotective effects. The aim of this systematic review was to assess the learning curve (LC) of different fetal SBA closure techniques.

METHODS

MEDLINE, Web of Science, EMBASE, Scopus and Cochrane databases and the gray literature were searched to identify relevant articles on fetal surgery for SBA, without language restriction, published between January 1980 and October 2018. Identified studies were reviewed systematically and those reporting all consecutive procedures and with postnatal follow-up ≥ 12 months were selected. Studies were included only if they reported outcome variables necessary to measure the LC, as defined by fetal safety and efficacy. Two authors independently retrieved data, assessed the quality of the studies and categorized observations into blocks of 30 patients. For meta-analysis, data were pooled using a random-effects model when heterogeneous. To measure the LC, we used two complementary methods. In the group-splitting method, competency was defined when the procedure provided results comparable to those in the MOMS trial for 12 outcome variables representing the immediate surgical outcome, short-term neonatal neuroprotection and long-term neuroprotection at ≥ 12 months of age. Then, when raw patient data were available, we performed cumulative sum analysis based on a composite binary outcome defining successful surgery. The composite outcome combined four clinically relevant variables for safety (absence of extreme preterm delivery < 30 weeks, absence of fetal death ≤ 7 days after surgery) and efficacy (reversal of hindbrain herniation and absence of any neonatal treatment of dehiscence or cerebrospinal fluid leakage at the closure site).

RESULTS

Of 6024 search results, 17 (0.3%) studies were included, all of which had low, moderate or unclear risk of bias. Fetal SBA closure was performed using standard hysterotomy (11 studies), mini-hysterotomy (one study) or fetoscopy by either exteriorized-uterus single-layer closure (one study), percutaneous single-layer closure (three studies) or percutaneous two-layer closure (one study). Only outcomes for standard hysterotomy could be meta-analyzed. Overall, outcomes improved significantly with experience. Competency was reached after 35 consecutive cases for standard hysterotomy and was predicted to be achieved after ≥ 57 cases for mini-hysterotomy and ≥ 56 for percutaneous two-layer fetoscopy. For percutaneous and exteriorized-uterus single-layer fetoscopy, competency was not reached in the 81 and 28 cases available for analysis, respectively, and LC prediction analysis could not be performed.

CONCLUSIONS

The number of cases operated is correlated with the outcome of fetal SBA closure, and the number of operated cases required to reach competency ranges from 35 for standard hysterotomy to ≥ 56-57 for minimally invasive modifications. Our observations provide important information for institutions looking to establish a new fetal center, develop a new fetal surgery technique or train their team, and inform referring clinicians, potential patients and third parties. Copyright © 2019 ISUOG. Published by John Wiley & Sons Ltd.

Percutaneous fetoscopic closure of large open spina bifida using a bilaminar skin substitute

OBJECTIVE

We have described previously our percutaneous fetoscopic technique for the treatment of open spina bifida (OSB). However, approximately 20-30% of OSB defects are too large to allow primary skin closure. Here we describe a modification of our standard technique using a bilaminar skin substitute to allow closure of large spinal defects. The aim of this study was to report our clinical experience with the use of a bilaminar skin substitute and a percutaneous fetoscopic technique for the prenatal closure of large OSB defects.

METHODS

Surgery was performed between 24.0 and 28.9 gestational weeks with the woman under general anesthesia, using an entirely percutaneous fetoscopic approach with partial carbon dioxide insufflation of the uterine cavity, as described previously. If there was enough skin to be sutured in the midline, only a biocellulose patch was placed over the placode (single-patch group). In cases in which skin approximation was not possible, a bilaminar skin substitute (two layers: one silicone and one dermal matrix) was placed over the biocellulose patch and sutured to the skin edges (two-patch group). The surgical site was assessed at birth, and long-term follow-up was carried out.

RESULTS

Percutaneous fetoscopic OSB repair was attempted in 47 consecutive fetuses, but surgery could not be completed in two. Preterm prelabor rupture of membranes (PPROM) occurred in 36 of the 45 (80%) cases which formed the study group, and the mean gestational age at delivery was 32.8 ± 2.5 weeks. A bilaminar skin substitute was required in 13/45 (29%) cases; in the remaining 32 cases, direct skin-to-skin suture was feasible. There were 12 cases of myeloschisis, of which 10 were in the two-patch group. In all cases, the skin substitute was located at the surgical site at birth. In five of the 13 (38.5%) cases in the two-patch group, additional postnatal repair was needed. In the remaining cases, the silicone layer detached spontaneously from the dermal matrix (on average, 25 days after birth), and the lesion healed by secondary intention. The mean operating time was 193 (range, 83-450) min; it was significantly longer in cases requiring the bilaminar skin substitute (additional 42 min on average), although the two-patch group had similar PPROM rate and gestational age at delivery compared with the single-patch group. Complete reversal of hindbrain herniation occurred in 68% of the 28 single-patch cases and 33% of the 12 two-patch cases with this information available (P < 0.05). In four cases there was no reversal; half of these occurred in myeloschisis cases.

CONCLUSIONS

Large OSB defects may be treated successfully in utero using a bilaminar skin substitute over a biocellulose patch through an entirely percutaneous approach. Although the operating time is longer, surgical outcome is similar to that in cases closed primarily. Cases with myeloschisis seem to have a worse prognosis than do those with myelomeningocele. PPROM and preterm birth continue to be a challenge. Further experience is needed to assess the risks and benefits of this technique for the management of large OSB defects. Copyright © 2018 ISUOG. Published by John Wiley & Sons Ltd.

[The standard mid-pregnancy anomaly scan in the Netherlands: what is its effect?]

- The mid-pregnancy anomaly scan was introduced into the Netherlands in 2007. The scan is performed at 18- 21 weeks of pregnancy.- The detection rate of open spina bifida is 94%.- In the Netherlands, 60% of all congenital heart defects are diagnosed prenatally compared with 35-40% in other countries. There is a strong relationship between the severity of the heart defect and the detection rate, as more than 95% of all univentricular heart defects are detected.- The detection rate of isolated cleft lip and cleft palate has increased from 32% to 87%.- The absolute number of abortions has not increased since the implementation of the anomaly scan. However, perinatal morbidity and mortality have decreased.- To further increase the quality of the screening programme, prenatal and postnatal congenital defect registries should be linked and studies into the effect of intensive training of sonographists with modern teaching methods should be performed.

Percutaneous minimally invasive fetoscopic surgery for spina bifida aperta. Part III: neurosurgical intervention in the first postnatal year

OBJECTIVE

To evaluate the need for postnatal neurosurgical intervention after fetoscopic patch coverage of spina bifida aperta (SBA).

METHODS

This was a retrospective analysis of a cohort of 71 fetuses which underwent minimally invasive fetoscopic patch coverage of SBA between 21 + 0 and 29 + 1 weeks of gestation. Postnatal neurosurgical procedures were classified into two types: re-coverage of the SBA within the first 3 months following birth, and shunt placement as treatment of associated hydrocephalus within the first year.

RESULTS

Location of the SBA was lumbosacral in 59 cases, lumbar in seven, thoracic in three and sacral in two. In total, 20/71 (28%) patients underwent early postnatal neurosurgical intervention by means of re-coverage of the SBA. This was performed because of cerebrospinal fluid leakage in seven (35%), adhesions with functional deterioration in three (15%), incomplete coverage in five (25%) and skin defect in five (25%) cases. Ventriculoperitoneal shunt placement within 1 year was required in 32 (45%) cases and was preceded by ventriculostomy in two. Three (4%) infants needed Chiari decompression surgery in the first 12 months following birth, because of syringomyelia or gait disturbance.

CONCLUSIONS

Fetoscopic patch coverage of SBA may require postnatal re-coverage in some cases. In most cases, conservative wound treatment shows good results, without requiring neurosurgical intervention. The low 1-year-shunt rate is comparable to data of the Management of Myelomeningocele Study and lower compared with published data of patients with postnatal only coverage of SBA.

Biparietal/transverse abdominal diameter ratio ≤ 1: potential marker for open spina bifida at 11-13-week scan

OBJECTIVE

In the first trimester of pregnancy, a biparietal diameter (BPD) below the 5(th) percentile is a simple marker that enables the prenatal detection of half of all cases of open spina bifida. We hypothesized that relating the BPD measurement to the transverse abdominal diameter (TAD) might be another simple and effective screening method. In this study we assessed the performance of using the BPD/TAD ratio during the first trimester of pregnancy in screening for open spina bifida.

METHODS

A total of 20,551 first-trimester ultrasound scans (11-13 weeks' gestation), performed between 2000 and 2013, were analyzed retrospectively; there were 26 cases of open spina bifida and 17,665 unaffected pregnancies with a crown-rump length of 45-84 mm and a record of both BPD and TAD measurements.

RESULTS

The mean (± SD) BPD/TAD ratio was 1.00 ± 0.06 for fetuses with spina bifida and 1.13 ± 0.06 for those without (P < 0.0001). A BPD ≤ 5(th) percentile enabled the prenatal detection of 46.2% of spina bifida cases, while a BPD/TAD ratio of ≤ 1.00 detected 69.2%. If we considered cases in which either BPD was ≤ 5(th) percentile or BPD/TAD ratio was ≤ 1, we identified 76.9% of cases. In the latter case, the false-positive rate was 5.1%, while that for using a combination of both BPD ≤ 5th percentile and BPD/TAD ratio ≤ 1 was 0.6%, with a sensitivity of 38.5%. The positive predictive value of using a combination of BPD ≤ 5th percentile and BPD/TAD ratio ≤ 1 for detecting spina bifida was 8.5%.

CONCLUSIONS

Between 11 and 13 weeks' gestation, relating BPD to TAD improves considerably the diagnostic performance of using BPD measurement alone in screening for open spina bifida. Screening using this marker is simple and applicable to a large population.

Impact of introduction of mid-trimester scan on pregnancy outcome of open spina bifida in The Netherlands

OBJECTIVE

To examine the impact of introduction of the mid-trimester scan on pregnancy outcome in cases of open spina bifida in two regions of The Netherlands.

METHODS

This was a retrospective cohort study of 190 cases of open spina bifida diagnosed pre- or postnatally, with an estimated date of delivery between 2003 and 2011.

RESULTS

With implementation of the mid-trimester scan the percentage of cases of open spina bifida detected before the 24(th) week of pregnancy increased from 43% to 88%. The rise in prenatal detection rate was associated with a significant increase in the number of terminated pregnancies and a decrease in the rate of perinatal loss; the percentage of children born alive did not change significantly. In the subgroup that underwent a scan between 18 and 24 weeks of pregnancy, cranial signs were present in 94.4% of cases.

CONCLUSION

Introduction of the mid-trimester scan has led to an increase in early identification of pregnancies complicated by open spina bifida. Pregnancies previously destined to end in perinatal loss are now terminated whilst pregnancies with a relatively good prognosis are frequently continued; the number of children with open spina bifida who are born alive has not changed significantly. Our study confirms that prenatal diagnosis is usually triggered by visualization of a lemon-shaped skull or a banana-shaped cerebellum.

Biparietal diameter at 11-13 weeks' gestation in fetuses with open spina bifida

OBJECTIVE

To ascertain the reported association between reduced biparietal diameter (BPD) at 11-13 weeks' gestation and open spina bifida and to investigate its predictive value in a single-center study.

METHODS

This was a retrospective study of fetuses in which BPD was measured at 11-13 weeks' gestation, including 27 fetuses with isolated open spina bifida subsequently diagnosed at 16-24 weeks and 7775 unaffected controls. BPD values were converted into multiples of the expected median (MoM) after adjustment for crown-rump length and maternal characteristics. Multivariable logistic regression analysis was used to determine the maternal characteristics significantly associated with spina bifida. The performance of screening was determined by receiver-operating characteristics curve analysis. BPD values at 11-13 weeks' gestation were compared with those measured in the second trimester using Z-scores.

RESULTS

BPD values at 11-13 weeks' gestation were below the 5(th) centile in 44.4% of cases of open spina bifida. In these fetuses, the median BPD MoM value was significantly smaller than that in the control group (0.930 vs 0.998 MoM; P < 0.0001). Multivariable logistic regression analysis showed a significant contribution from maternal age (P = 0.008) and BMI (P = 0.028) to the association between BPD MoM and spina bifida. The detection rate using BPD measurements in the first trimester was 55.6% with a false-positive rate of 11.6%. In fetuses with open spina bifida, the BPD Z-scores were significantly lower at 16-24 weeks compared to those recorded at 11-13 weeks (median, -1.71 (range, -3.98 to -0.20) vs -1.30 (-3.75 to 2.61); P = 0.006).

CONCLUSION

Fetuses with open spina bifida have a smaller BPD in the first trimester. This observation may be useful in early screening. It is likely that a combination of maternal characteristics such as age and BMI, fetal BPD and maternal serum alpha-fetoprotein measured in the first trimester would provide a clinically useful screening test for open spina bifida.

Fetal surgery for spina bifida: past, present, future

Open spina bifida or myelomeningocele (MMC) is a common birth defect that is associated with significant lifelong morbidity. Little progress has been made in the postnatal surgical management of the child with spina bifida. Postnatal surgery is aimed at covering the exposed spinal cord, preventing infection, and treating hydrocephalus with a ventricular shunt. Experimental and clinical evidence suggest that the primary cause of the neurologic defects associated with MMC is not simply incomplete neurulation, but rather chronic, mechanical and amniotic-fluid induced chemical trauma that progressively damages the exposed neural tissue during gestation. The cerebrospinal fluid leak through the MMC leads to hindbrain herniation and hydrocephalus. In utero repair of open spina bifida is now performed in selected patients and presents an additional therapeutic alternative for expectant mothers carrying a fetus with MMC. In the past, studies in animal models and clinical case series laid the groundwork for a clinical trial to test the safety and efficacy of fetal MMC repair. In the present, a prospective, randomized study (the MOMS trial) has shown that fetal surgery for MMC before 26 weeks' gestation may preserve neurologic function, reverse the hindbrain herniation of the Chiari II malformation, and obviate the need for postnatal placement of a ventriculoperitoneal shunt. However, this study also demonstrates that fetal surgery is associated with significant risks related to the uterine scar and premature birth. In the future, research will expand our understanding of the pathophysiology of MMC, evaluate the long-term impact of in-utero intervention, and to refine timing and technique of fetal MMC surgery using tissue engineering technology.

Cerebral ventricular system in fetuses with open spina bifida at 11-13 weeks' gestation

OBJECTIVE

To determine if in fetuses with open spina bifida at 11-13 weeks' gestation there are alterations in the cerebral ventricular system.

METHODS

In this study we selected 10 cases of open spina bifida and 410 normal singleton pregnancies which subsequently resulted in the delivery of phenotypically normal neonates. In all cases transvaginal sonography was carried out at 11-13 weeks' gestation and three-dimensional (3D) brain volumes were acquired. The fetal head was systematically assessed in a series of transverse views and measurements were obtained of the area of the lateral ventricles, the diameter of the roof of the third ventricle, the diameter of the aqueduct of Sylvius and the diameter of the fourth ventricle. The measurements obtained on the normal and affected fetuses were compared.

RESULTS

In normal fetuses the area of the lateral ventricles and the diameter of the roof of the third ventricle increased, the diameter of the aqueduct of Sylvius decreased and the diameter of the fourth ventricle did not change significantly with biparietal diameter (BPD). In fetuses with open spina bifida, compared with normal fetuses, the measurements of the lateral ventricle area, the diameter of the roof of the third ventricle, the diameter of the aqueduct of Sylvius and the diameter of the fourth ventricle were significantly decreased (P < 0.01).

CONCLUSION

In fetuses with open spina bifida at 11-13 weeks' gestation the intracranial collection of cerebrospinal fluid is substantially reduced.

Prospective detection of open spina bifida at 11-13 weeks by assessing intracranial translucency and posterior brain

We describe a case series of six fetuses with open spina bifida (OSB) from four different prenatal units, where the anomaly was detected at the routine 11-13-week ultrasound examination. Crown-rump length ranged from 49 to 78 mm. All cases were first suspected during nuchal translucency thickness measurement in the mid-sagittal plane of the face. OSB was lumbosacral in five fetuses and cervical in one. The intracranial translucency (IT) was obliterated in two cases, but some fluid was found in the other four cases. However, in all cases the typical landmarks of a normal posterior brain and normal IT were absent. In all six cases the ratio of brainstem diameter to brainstem-occipital bone distance was increased (≥ 1). This detection of an abnormal posterior brain led to a targeted examination and detection of the spinal lesion during the same examination in five cases, whereas in one suspicious case the patient was recalled at 17 weeks, when the abnormality was detected. Two fetuses had both multiple anomalies and trisomy 18. These prospective cases demonstrate the feasibility of using the standard mid-sagittal plane commonly used for NT measurement to assess the IT and the posterior brain and to determine the presence of OSB during NT screening.

The aqueduct of Sylvius: a sonographic landmark for neural tube defects in the first trimester

OBJECTIVES

To describe a new first-trimester sonographic landmark, posterior displacement of the midbrain and aqueduct of Sylvius, which may be useful in early screening for neural tube defects.

METHODS

This was a prospective study of 457 normal fetuses at 11 + 0 to 13 + 6 weeks' gestation. We measured the distance from the posterior border of the aqueduct of Sylvius to the anterior border of the occiput (AOS-to-occiput distance) in the axial plane and created a reference range. In the nine fetuses with abnormal midbrain position identified in the first trimester and with neural tube defect subsequently confirmed, we analyzed ultrasound images to determine the position of the aqueduct of Sylvius.

RESULTS

The lower limit of normal AOS-to-occiput distance (mean minus 2 SD) ranged from 1.7 mm at a crown-rump length (CRL) of 45 mm to 3.7 mm at a CRL of 84 mm. In the nine cases with abnormal position of the midbrain and confirmed neural tube defect, juxtaposition of the midbrain to the occiput was the clue to diagnosis of the spinal abnormality. In all nine cases, the AOS-to-occiput distance was below the established normal range.

CONCLUSIONS

Examination of the midbrain in an axial plane may prove a reliable marker for the first-trimester diagnosis of neural tube defects. In contrast to recently reported subtle changes in the mid-sagittal view of the posterior cranial fossa, axial imaging of the midbrain reveals striking displacement of this structure, with virtual juxtaposition to the occiput, in fetuses with confirmed open spina bifida. This anatomical distortion of the midbrain can be quantified by measurement of the AOS-to-occiput distance.

Retrospective review of diagnostic performance of intracranial translucency in detection of open spina bifida at the 11-13-week scan

OBJECTIVES

To evaluate diagnostic performance of intracranial translucency (IT) for detection of open spina bifida and interobserver agreement for visualization of IT during the 11-13-week scan.

METHODS

A retrospective study was undertaken in a tertiary referral center. Two hundred 11-13-week scans for nuchal translucency, performed by sonographers certified by The Fetal Medicine Foundation, U.K., were reviewed independently for IT by two expert observers. When IT was not seen, the observers determined whether this was due to poor IT image quality or the presence of spina bifida. Discordant cases were reviewed by a third observer and the majority decision was used for analysis. All observers were blinded to individual pregnancy outcome and the number of cases with spina bifida.

RESULTS

There were 191 normal fetuses, eight fetuses with open spina bifida and one with closed spina bifida (this case was excluded from analysis). IT was seen in 150 fetuses and all were normal. In six of the 49 cases in which IT was not seen, IT non-visibility was attributed to open spina bifida; among these cases, four fetuses had open spina bifida and two were normal. In the remaining 43 cases (including 39 normal fetuses), IT non-visibility was attributed to inadequate image quality. Sensitivity was 50% (4/8) and specificity was 99% (150/152). Concordance between the two observers concerning IT visibility was 79%, (κ = 0.47, representing moderate agreement).

CONCLUSION

There was moderate interobserver agreement for visualization of IT on images obtained for nuchal translucency measurement at 11-13 weeks. When IT was confidently seen, open spina bifida could be excluded. However, non-visibility of IT correctly diagnosed only 50% of fetuses with open spina bifida.

Three-dimensional sonography of the posterior fossa in fetuses with open spina bifida at 11-13 weeks' gestation

OBJECTIVES

To investigate the posterior fossa of normal fetuses and fetuses with open spina bifida in stored three-dimensional (3D) volumes and to describe signs that might allow early detection of this defect.

METHODS

A prospective study of 3D volumes of the fetal brain obtained from 10 normal fetuses and three fetuses with open spina bifida was undertaken. Measurements of the anteroposterior diameters of the cisterna magna and fourth ventricle were taken in the tilted axial view. In the mid-sagittal plane the brainstem (BS) diameter and the brainstem-occipital bone (BSOB) distance were measured. The BS/BSOB ratio was calculated. All measurements were expressed as Z-scores. Structural analysis of the differences in the posterior fossa between normal fetuses and fetuses with open spina bifida was undertaken.

RESULTS

In normal fetuses all measurements were within ±2.5 Z-scores. In three fetuses with open spina bifida the BS Z-scores were 2.7, 2.8 and 2.8; the BSOB scores were -3.4, -2.8 and -2.9; the cisterna magna scores were -5.6, -3.7 and -4.2; and the BS/BSOB ratio scores were 4.1, 9.7 and 8.9. In normal fetuses the cisterna magna was posterior to the fourth ventricle and extended along its entire length. In fetuses with open spina bifida the cisterna magna was partially or completely obliterated.

CONCLUSIONS

Assessment of the cranial posterior fossa is feasible at 11-13 weeks' gestation. There are distinct signs in fetuses with open spina bifida which can be evaluated by ultrasonography.

Visualization of intracranial translucency at the 11-13-week scan is improved after specific training

OBJECTIVE

To evaluate the ability to confidently identify intracranial translucency (IT) in a clinical practice and following specific training of 10 operators.

METHODS

Two experienced observers reviewed 11-13-week nuchal translucency (NT) images for IT visibility in (1) a series of 50 randomly selected images obtained by 10 skilled operators certified by the Collège Français d'Echographie Foetale (CFEF) (retrospective analysis) and (2) a series of 315 images obtained by 10 different operators following specific training for IT visualization (prospective analysis). We calculated proportions of images for which IT was deemed visible and the agreement between the two observers. Data were also stratified by Herman and CFEF quality-score intervals.

RESULTS

In the retrospective analysis, IT was visualized by both reviewers in 52% of images, with a moderate level of agreement (κ = 0.63). The rate of IT visualization by both reviewers increased very slightly to 56-58% when only considering images with the best NT quality-control scores. Following specific training of the operators the proportion of images for which both reviewers could identify the fourth ventricle increased to 85%, but the level of agreement remained moderate (κ = 0.66). When considering images with the best NT quality-control scores, IT visualization by both reviewers increased to 91-92%.

CONCLUSIONS

In a clinical practice that focuses on NT measurement IT cannot be visualized in a substantial proportion of the images obtained, which limits the utility of this approach for the early prenatal diagnosis of open spina bifida. However, the ability to identify the fourth ventricle significantly increases following specific training.

Muscle ultrasound density in human fetuses with spina bifida aperta

BACKGROUND

In fetal spina bifida aperta (SBA), leg movements caudal to the meningomyelocele (MMC) are transiently present, but they disappear shortly after birth. Insight in the underlying mechanism could help to improve treatment strategies. In fetal SBA, the pathogenesis of neuromuscular damage prior to movement loss is still unknown. We reasoned that prenatal assessment of muscle ultrasound density (fetal-MUD) could help to reveal whether progressive neuromuscular damage is present in fetal SBA, or not.

AIM

To reveal whether prenatal neuromuscular damage is progressively present in SBA.

PATIENTS/METHODS

In SBA fetuses (n=6; 22-37 weeks gestational age), we assessed fetal-MUD in myotomes caudal to the MMC and compared measurements between myotomes cranial to the MMC and controls (n=11; 17-36 weeks gestational age). Furthermore, we intra-individually compared MUD and muscle histology between the pre- and postnatal period.

RESULTS

Despite persistently present fetal leg movements caudal to the MMC, fetal-MUD was higher caudal to the MMC than in controls (p<0.05). Fetal-MUD caudal to the MMC did not increase with gestational age, whereas fetal-MUD in controls and cranial to the MMC increased with gestational age (p<0.05). In 5 of 6 patients assessed, comparison between pre- and postnatal MUD and/or muscle histology indicated consistent findings.

CONCLUSIONS

In fetal SBA, persistent leg movements concur with stable, non-progressively increased fetal-MUD. These data may implicate that early postnatal loss of leg movements is associated with the impact of additional neuromuscular damage after the prenatal period.

Fetal open spina bifida: a natural history of disease progression in utero

OBJECTIVE

To determine the natural history of the prenatal development of ventriculomegaly and talipes in fetuses with open spina bifida.

STUDY DESIGN

All fetuses with isolated open spina bifida and managed at our center between January 1996 and March 2000 were retrospectively evaluated. Ultrasonographic images and reports were reviewed from examinations performed every 3 to 4 weeks from the time of diagnosis to delivery for lesion level and type, ventriculomegaly (defined as an atrial width of > or =10 mm), and lower extremity appearance.

RESULTS

Of the 53 pregnancies identified, 20 (38%) were electively terminated. In the 33 ongoing gestations, the lesions ranged from lower thoracic to sacral; 79% were characterized as meningomyeloceles and 21% as myeloschises. Fifty-five percent (n = 18) had ventriculomegaly at diagnosis (early onset, mean gestational age at diagnosis 22 +/- 5 weeks), 33% (n = 11) subsequently developed ventriculomegaly (late onset, mean 29 +/- 6 weeks), and 12% (n = 4) had normal ventricle size at the last sonogram before birth (mean 38 +/- 1 weeks). The ventricular size prior to delivery was significantly smaller with late-onset ventriculomegaly than with early-onset: 15 +/- 4 mm versus 28 +/- 10 mm, (p = 0.001). Only 6% (n = 2) had talipes at the initial sonogram, and 18% (n = 6) were subsequently determined to have talipes (mean 30 +/- 6 weeks).

CONCLUSION

Most fetuses with open spina bifida develop ventriculomegaly, and the majority do so by 21 weeks' gestation. Fetuses that develop ventriculomegaly later in gestation have less severe ventricular dilation at birth. In contrast, a minority of fetuses have congenital talipes, and because most cases develop after 20 weeks, they are not predicted by early midtrimester sonographic evaluation.

Assay precision of serum alpha fetoprotein in antenatal screening for neural tube defects and Down's syndrome

OBJECTIVES

To assess the impact of current serum alpha fetoprotein (AFP) assays on the performance of screening for open neural tube defects and Down's syndrome.

METHODS

Maternal serum samples, collected between weeks 15 and 22 from 470 singleton pregnancies without neural tube defects or Down's syndrome, were assayed for AFP using an automated fluorometric immunoassay. The samples had been assayed for AFP using an in house radioimmunoassay with a lower precision ten years before. The variance of AFP using the radioimmunoassay was compared with that using the current fluorometric assay and then used to estimate the detection rates and false positive rates for neural tube defect and Down's syndrome screening.

RESULTS

Current serum AFP assays are more precise. Using a cut off level of 2.5 multiples of the median, the false positive rate in screening for anencephaly and open spina bifida was 0.8% with the new assay compared with 2% using the previous assay. When screening for Down's syndrome, the false positive rate is reduced by about one percentage point without loss of detection.

CONCLUSION

Improvements in the precision of maternal serum AFP measurement have led to small but useful improvements in screening for open neural tube defects and Down's syndrome. Published estimates of screening performance using such modern assays can be revised accordingly.

The case for and against intrauterine surgery for myelomeningoceles

The case for and against intrauterine surgery on a myelomeningocele depends on how and in what order the malformations in the spinal cord and brain are thought to develop. If the brain defects arise in the embryonic period and undergo no further change and if the spinal cord is so deformed that it is functionless from the start, then operative intervention before birth will have no significant effect on the ultimate neurological defect. If, on the other hand, the brain lesions evolve during gestation and the deformed spinal cord has some useful function that can be lost by contact with the amniotic fluid or is susceptible to mechanical damage, then intrauterine surgery may have a beneficial role. Long-term follow-up of children who have already undergone intrauterine surgery should answer whether this novel form of treatment imparts significant benefit to justify the risks it imposes on the mother and fetus.

Experimental model: change in the posterior fossa with surgically induced spina bifida aperta in mouse

On the basis of experimental studies on mouse embryos in which spina bifida development of the brain ventricular system. Mouse embryos were exposed and surgically treated at gestation day 12 to produce spina bifida aperta, and operated embryos were cultured exo utero in the peritoneal cavity of the pregnant dam. Embryos were harvested at gestation day 14. Open neural tube defects resulted in 7 out of 10 embryos surviving surgery. Histological examination revealed that the sizes of ventricles in both the supra- and infratentorial compartments were greatly reduced in embryos with spina bifida aperta compared with control embryos. This result supports the hypothesis that leakage of cerebrospinal fluid through the opening of the caudal spine may be a major cause of brain abnormalities in patients with myelomeningocele.

Open myelomeningocele

This article defines open myelomeningocele and describes its development in the embryo. The anatomic features of the neural placode, pia-arachnoid, and dorsal versus ventral roots are well described. The surgical technique and prenatal and postnatal care are detailed. Anomalies associated with open myelomeningocele are also described. The concept of a team approach to treating children with myelomeningocele and their families is addressed.

Experimental study of the embryogenesis of open spinal dysraphism

This article discusses the experimental studies that have been performed to make clear the embryogenesis of myeloschisis or spina bifida. Some of these theories include: Simple nonclosure; overgrowth and nonclosure; so-called reopening; overgrowth and reopening; and primary mesodermal insufficiency. The authors also discuss recent investigations and give a view into the future.

Ultrasound evaluation of prenatal and neonatal spina bifida

Interest in studying the role of sonography in the evaluation of newborns and infants with spinal dysraphism waned with the advent of MR imaging. Sonographic evaluation of the neonatal spine, however, can be performed portably, is relatively inexpensive when compared with MR imaging, and does not require sedation. Its recognized utility in evaluating the neonatal spine in both open and occult spinal dysraphisms makes sonography an ideal diagnostic modality for this patient population. Its most valuable contribution probably lies in screening for closed dysraphisms, but comparative studies with MR imaging are necessary to clarify sonography's role.

Surgical complications of open spinal dysraphism

The embryogenesis, closure technique, and preoperative preparation of open myelomeningocele are described in this article. Both early and late complications of myelomeningocele closure are discussed with respect to predisposing factors, diagnosis, treatment, and prevention. These complications include worsened neurological level, wound dehiscence, wound infection, cerebrospinal fluid leak, postoperative ileus, symptomatic Chiari malformation, shunt infection, necrotizing enterocolitis, and problems related to kyphectomy.

Evidence for multi-site closure of the neural tube in humans

Four separate initiation sites for neural tube (NT) fusion have been demonstrated recently in mice and other experimental animals. We evaluated the question of whether the multisite model vs. the traditional single-site model of NT closure provided the best explanation for neural tube defects (NTDs) in humans. Evidence for segmental vs. continuous NT closure was obtained by review of our recent clinical cases of NTDs and previous medical literature. With the multi-site NT closure model, we find that the majority of NTDs can be explained by failure of fusion of one of the closures or their contiguous neuropores. We hypothesize that: Anencephaly results from failure of closure 2 for meroacranium and closures 2 and 4 for holoacranium. Spina-bifida cystica results from failure of rostral and/or caudal closure 1 fusion. Craniorachischisis results from failure of closures 2, 4, and 1. Closure 3 non-fusion is rare, presenting as a midfacial cleft extending from the upper lip through the frontal area ("facioschisis"). Frontal and parietal cephaloceles occur at the sites of the junctions of the cranial closures 3-2 and 2-4 (the prosencephalic and mesencephalic neuropores). Occipital cephaloceles result from incomplete membrane fusion of closure 4. In humans, the most caudal NT may have a 5th closure site involving L2 to S2. Closure below S2 is by secondary neurulation. Evidence for multi-site NT closure is apparent in clinical cases of NTDs, as well as in previous epidemiological studies, empiric recurrence risk studies, and pathological studies. Genetic variations of NT closures sites occur in mice and are evident in humans, e.g., familial NTDs with Sikh heritage (closure 4 and rostral 1), Meckel-Gruber syndrome (closure 4), and Walker-Warburg syndrome (2-4 neuropore, closure 4). Environmental and teratogenic exposures frequently affect specific closure sites, e.g., folate deficiency (closures 2, 4, and caudal 1) and valproic acid (closure 5 and canalization). Classification of NTDs by closure site is recommended for all studies of NTDs in humans.(ABSTRACT TRUNCATED AT 400 WORDS)

Upper and lower neural tube defects: an alternate hypothesis

It has been suggested that neural tube defects (NTDs) of the upper type (anencephaly, encephalocele, and thoracic spina bifida) may have a pathogenesis different from those of the lower type (lumbosacral spina bifida), since recurrent cases within a sibship were said always to be concordant with respect to NTD type. Also, spontaneous abortion, additional malformation, and recurrence rate were observed to be higher in the upper group, and there was an excess of females in upper NTD probands. To test this hypothesis, we measured the above variables in upper and lower NTDs in a sample from Quebec. We found less than full concordance (50%) of NTD type in 18 sib pairs. Recurrence rate was not significantly lower in the lower NTD group (5.6 v 5.8%). The other variables were in general agreement with previous studies, inconsistent findings possibly attributable to different NTD population incidences. These findings can be accounted for if upper and lower NTDs share a similar pathogenesis and the embryo is more susceptible during early than late neural tube formation.