Prenatal diagnostic challenges and pitfalls for schizencephaly

Diagnostic accuracy of ultrasonography and magnetic resonance imaging for the detection of fetal anomalies: a blinded case-control study

OBJECTIVES

To compare the accuracy of two-dimensional ultrasound (2D-US), three-dimensional ultrasound (3D-US) and magnetic resonance imaging (MRI) for the diagnosis of congenital anomalies without prior knowledge of indications and previous imaging findings.

METHODS

This was a prospective, blinded case-control study comprising women with a singleton pregnancy with fetal congenital abnormalities identified on clinical ultrasound and those with an uncomplicated pregnancy. All women volunteered to undergo 2D-US, 3D-US and MRI, which were performed at one institution. Different examiners at a collaborating institution performed image interpretation. Sensitivity and specificity of the three imaging methods were calculated for individual anomalies, based on postnatal imaging and/or autopsy as the definitive diagnosis. Diagnostic confidence was graded on a four-point Likert scale.

RESULTS

A total of 157 singleton pregnancies were enrolled, however nine cases were excluded owing to incomplete outcome, resulting in 148 fetuses (58 cases and 90 controls) included in the final analysis. Among cases, 13 (22.4%) had central nervous system (CNS) anomalies, 40 (69.0%) had non-CNS anomalies and five (8.6%) had both CNS and non-CNS anomalies. The main findings were: (1) MRI was more sensitive than 3D-US for diagnosing CNS anomalies (MRI, 88.9% (16/18) vs 3D-US, 66.7% (12/18) vs 2D-US, 72.2% (13/18); McNemar's test for MRI vs 3D-US: P = 0.046); (2) MRI provided additional information affecting prognosis and/or counseling in 22.2% (4/18) of fetuses with CNS anomalies; (3) 2D-US, 3D-US and MRI had similar sensitivity for diagnosing non-CNS anomalies; (4) specificity for all anomalies was highest for 3D-US (MRI, 85.6% (77/90) vs 3D-US, 94.4% (85/90) vs 2D-US, 92.2% (83/90); McNemar's test for MRI vs 3D-US: P = 0.03); and (5) the confidence of MRI for ruling out certain CNS abnormalities (usually questionable for cortical dysplasias or hemorrhage) that were not confirmed after delivery was lower than it was for 2D-US and 3D-US.

CONCLUSIONS

MRI was more sensitive than ultrasonography and provided additional information that changed prognosis, counseling or management in 22.2% of fetuses with CNS anomalies. False-positive diagnoses for subtle CNS findings were higher with MRI than with ultrasonography. Copyright © 2015 ISUOG. Published by John Wiley & Sons Ltd.

Correlation of prenatal and postnatal MRI findings in schizencephaly

BACKGROUND AND PURPOSE

Schizencephaly is a rare malformation of the brain characterized by a gray matter-lined defect extending from the pial surface to the lateral ventricles. The purpose of this study was to correlate imaging findings of schizencephaly and associated anomalies on fetal and postnatal MR imaging and assess possible changes that may occur from the prenatal-to-postnatal state.

MATERIALS AND METHODS

A retrospective review of subjects with schizencephaly who had both pre- and postnatal MR imaging was performed. Subject age, cleft type, number, location, and features of the defects and associated anomalies were recorded. Normalized dimensions of the defect and ipsilateral ventricle were measured and correlated to changes in the clefts between pre- and postnatal imaging.

RESULTS

Ten subjects with 18 clefts (8 bilateral) were included. Most defects (83%) were open on prenatal MR imaging, but 47% of those were found to have subsequently closed on postnatal imaging. Evidence of prior hemorrhage was seen in 83%. Prenatal MR imaging detected all cases of an absent septum pellucidum but detected a fraction of gross polymicrogyria and missed all cases of optic nerve hypoplasia. The normalized ipsilateral ventricular and inner and middle width dimensions of the defects were significantly decreased at postnatal imaging (P < .05). The widths of the defects, ventricular width, and presence of hemorrhage were not predictors of closure of prenatally diagnosed open defects (P > .05).

CONCLUSIONS

In our series, nearly half of prenatally open schizencephaly defects had closed on postnatal imaging. Prenatal MR imaging was only able to demonstrate some of the associated anomalies.

Prenatal and Postnatal Schizencephaly Findings by 2D and 3D Ultrasound: Pictorial Essay

Schizencephaly is a brain-destructive lesion relating to clefts in the fetal brain that usually communicate with the ventricular system, subarachnoid space, or both. It presents as two types: Type I (closed) and Type II (open). During pregnancy, it may be suspected in the course of ultrasonography, which highlights ventricular dilatation and brain abnormalities. Usually, the diagnosis is confirmed postnatally using trans-fontanel ultrasonography. The etiology of schizencephaly is still unknown, but it may be derived from a primary disorder of brain development or from bilateral middle cerebral artery occlusion. Many causative agents including vascular insult, infections, toxins, and medications have been associated with this malformation. We present a pictorial essay of six cases of schizencephaly that were suspected on prenatal ultrasound scans and confirmed postnatally by trans-fontanel, two-dimensional and three-dimensional ultrasonography.

Schizencephaly prevalence, prenatal diagnosis and clues to etiology: a register-based study

OBJECTIVES

To establish the prevalence and antenatal diagnosis of schizencephaly in the UK.

METHODS

Data on schizencephaly were extracted from six regional congenital anomaly registers.

RESULTS

Thirty-eight cases of schizencephaly were identified in 2 567 165 livebirths and stillbirths, giving a total prevalence of 1.48/100 000 births (95% CI, 1.01-1.95). Eighteen (47% (95% CI, 31-63%)) of the 38 cases were identified antenatally. No affected fetus had an abnormal karyotype identified. A high proportion of cases of schizencephaly occurred in younger mothers: 63% were aged 24 years or less, significantly higher (P < 0.0001) than the corresponding proportion (26%) of mothers in England and Wales. The majority of cases were not identified until after 22 weeks of pregnancy. Additional anomalies associated with vascular disruption sequences were found in eight cases which had septo-optic dysplasia or absent septum pellucidum, one of which also had gastroschisis.

CONCLUSIONS

Schizencephaly occurs more frequently in the fetuses of younger mothers. It is often associated with septo-optic dysplasia, suggesting that the two conditions may share a common origin, arising as a result of destructive processes that cause changes in the brain which only become apparent on ultrasound in the second half of pregnancy.

The cavum septi pellucidi: why is it important?

OBJECTIVE

The cavum septi pellucidi (CSP) is routinely imaged in the fetal brain during obstetric sonography; in fact, for well over a decade, assessment of the CSP has been considered part of the required elements of a standard examination of fetal morphology in guidelines developed by multiple specialty societies. Our objective is to present the 4 reasons why all practicing sonologists and sonographers should be familiar with this anatomic structure.

METHODS

Prenatal sonograms and magnetic resonance imaging examinations are used to review the following topics: terminology, embryology, and anatomy of the CSP; pitfalls in its identification; and a wide variety of abnormalities (predominantly relating to nonvisualization) associated with the CSP.

RESULTS

Embryologic development of the CSP is intimately associated with the corpus callosum (CC); thus, correct identification of the CSP essentially excludes complete agenesis of the CC. Absence of the CSP is associated with an extremely wide spectrum of neuroanatomic malformations: these range from the lethal entities of hydranencephaly and alobar holoprosencephaly; to the potentially serious but nonlethal entities of schizencephaly, porencephaly, basilar encephaloceles, severe hydrocephalus, and the less severe prosencephalic cleavage disorders (including syntelencephaly); to the normal variant, the rare and somewhat controversial entity of isolated septal deficiency. The value of noting that the absent CSP allows diagnosis of very subtle and easily overlooked abnormalities such as septo-optic dysplasia is presented.

CONCLUSIONS

Correct recognition of the CSP provides welcome reassurance of proper development of the central forebrain.