First-Trimester Cranial Ultrasound Markers of Open Spina Bifida

Comparison between MRI and the Combination of 2D and 3D US in the Prenatal Diagnosis of Closed Spina Bifida

INTRODUCTION

Closed spina bifida (CSB) is a rare condition with a challenging prenatal diagnosis. Herein, we assess the conventional two-dimensional (2D) ultrasound (US) combined with three-dimensional (3D) ultrasound (US) and magnetic resonance imaging (MRI) in the prenatal diagnosis of CSB.

METHODS

In this retrospective study, we included 20 cases of fetal CSB confirmed by postnatal MRI, post-mortem pathological examination, or postpartum surgery. Prenatal 2D US complemented with the 3D US was performed in all fetuses to evaluate the characteristics of the conus, vertebral arch, and scoliosis. Moreover, MRI was performed to establish the split vertebrae, with or without a bulging mass. Thereafter, we compared the performance of the US and MRI.

RESULTS

Diagnosis accuracy of US was comparable with MRI (70% vs. 75%, κ = 0.62); US detected more cases with interpediculate distance ≥95% (55% vs. 35%, κ = 0.22) than MRI. On the other hand, MRI had a superior capacity for identifying vertebral arch fissures (20% vs. 35%, κ = 0.39). MRI and ultrasound had good agreement in the conus medullaris (65% vs. 70%, κ = 0.42) and scoliosis (45% vs. 35%, κ = 0.59). Both US and MRI detected 1 (5.0%) case with "lemon sign" and "banana sign." The missed diagnosis rates of US and MRI were 15% (3/20) and 5% (1/20), respectively. The misdiagnosis rates of US and MRI were 15.0% (3/20) and 20.0% (4/20), respectively.

CONCLUSION

Both MRI and 2D US combined with the 3D US had excellent performance in prenatal diagnosis of CSB.

Advances in Fetal Surgical Repair of Open Spina Bifida

Spina bifida remains a common congenital anomaly of the central nervous system despite national fortification of foods with folic acid, with a prevalence of 2-4 per 10,000 live births. Prenatal screening for the early detection of this condition provides patients with the opportunity to consider various management options during pregnancy. Prenatal repair of open spina bifida, traditionally performed by the open maternal-fetal surgical approach through hysterotomy, has been shown to improve outcomes for the child, including decreased need for cerebrospinal fluid diversion surgery and improved lower neuromotor function. However, the open maternal-fetal surgical approach is associated with relatively increased risk for the patient and the overall pregnancy, as well as future pregnancies. Recent advances in minimally invasive prenatal repair of open spina bifida through fetoscopy have shown similar benefits for the child but relatively improved outcomes for the pregnant patient and future childbearing.

First Trimester Ultrasound Detection of Fetal Central Nervous System Anomalies

OBJECTIVE

To evaluate the potential of the first-trimester ultrasound (US) features for the detection of central nervous system (CNS) anomalies. Methods/Methodology: This is a prospective one-center three-year study. Unselected singleton pregnant women were examined using an extended first-trimester anomaly scan (FTAS) that included the CNS assessment: the calvaria shape, the septum (falx cerebri), the aspect of the lateral ventricles, the presence of the third ventricle and aqueduct of Sylvius (AS) and the posterior brain morphometry: the fourth ventricle, namely intracranial translucency (IT), brain stem/brain stem-occipital bone ratio (BS/BSOB) and cisterna magna (CM). The spine and underlying skin were also evaluated. The cases were also followed during the second and third trimesters of pregnancy and at delivery. FTAS efficiency to detect major CNS abnormalities was calculated.

RESULTS

We detected 17 cases with CNS major abnormalities in a population of 1943 first-trimester (FT) fetuses, including spina bifida with myelomeningocele, exencephaly-anencephaly, holoprosencephaly, hydrocephaly, cephalocele and Dandy-Walker malformation. The CNS features in the abnormal group are presented. In the second trimester (ST), we further diagnosed cases of corpus callosum agenesis, cerebellar hypoplasia, vein of Galen aneurysm and fetal infection features (ventriculomegaly, intraventricular bands, intraventricular cyst and hyperechoic foci), all declared normal at the FTAS. During the third trimester (TT) scan we identified a massive fetal cerebral haemorrhage absent at previous investigations. We report a detection rate of 72.7% of fetal brain anomalies in the FT using the proposed CNS parameters. The sensitivity of the examination protocol was 72.7%, and the specificity was 100%.

CONCLUSION

A detailed FT CNS scan is feasible and efficient. The majority of cases of major CNS abnormalities can be detected early in pregnancy. The visualization rates of the CNS parameters in the FT are great with short, if any, additional investigation time. FT cerebral disorders such as haemorrhage or infections were missed in the FT even when an extended evaluation protocol was used.

Systematic Classification of Spina Bifida

Spina bifida (SB) is an umbrella term for multiple conditions characterized by misclosure of vertebral arches. Neuropathologic findings in SB cases are often reported with imprecise and overlapping terminology. In view of the increasing identification of SB-associated genes and pathomechanisms, the precise description of SB subtypes is highly important. In particular, the term "myelomeningocele" is applied to various and divergent SB subtypes. We reevaluated 90 cases with SB (58 prenatal; 32 postnatal). The most frequent SB phenotype in our cohort was myeloschisis, which is characterized by an open neural plate with exposed ependyma (n = 28; 31.1%). An open neural plate was initially described in only in two-thirds of the myeloschisis cases. An additional 21 cases (23.3%) had myelomeningocele; 2 cases (2.2%) had a meningocele; and 21 cases (23.3%) had an unspecified SB aperta (SBA) subtype. Overall, the SB phenotype was corrected in about one-third of the cases. Our findings highlight that "myelomeningocele" and "SB aperta" cannot be used as synonymous terms and that myeloschisis is an underreported SB phenotype. Based on our findings and a review of literature we propose a classification of SB subtypes in SB occulta and the 3 SBA subtypes, meningocele, myelomeningocele, and myeloschisis.