The subarachnoid space: normal fetal development as demonstrated by transvaginal ultrasound

Evidence of brain injury in fetuses of mothers with preterm labor with intact membranes and preterm premature rupture of membranes

BACKGROUND

Brain injury and poor neurodevelopment have been consistently reported in infants and adults born before term. These changes occur, at least in part, prenatally and are associated with intra-amniotic inflammation. The pattern of brain changes has been partially documented by magnetic resonance imaging but not by neurosonography along with amniotic fluid brain injury biomarkers.

OBJECTIVE

This study aimed to evaluate the prenatal features of brain remodeling and injury in fetuses from patients with preterm labor with intact membranes or preterm premature rupture of membranes and to investigate the potential influence of intra-amniotic inflammation as a risk mediator.

STUDY DESIGN

In this prospective cohort study, fetal brain remodeling and injury were evaluated using neurosonography and amniocentesis in singleton pregnant patients with preterm labor with intact membranes or preterm premature rupture of membranes between 24.0 and 34.0 weeks of gestation, with (n=41) and without (n=54) intra-amniotic inflammation. The controls for neurosonography were outpatient pregnant patients without preterm labor or preterm premature rupture of membranes matched 2:1 by gestational age at ultrasound. Amniotic fluid controls were patients with an amniocentesis performed for indications other than preterm labor or preterm premature rupture of membranes without brain or genetic defects whose amniotic fluid was collected in our biobank for research purposes matched by gestational age at amniocentesis. The group with intra-amniotic inflammation included those with intra-amniotic infection (microbial invasion of the amniotic cavity and intra-amniotic inflammation) and those with sterile inflammation. Microbial invasion of the amniotic cavity was defined as a positive amniotic fluid culture and/or positive 16S ribosomal RNA gene. Inflammation was defined by amniotic fluid interleukin 6 concentrations of >13.4 ng/mL in preterm labor and >1.43 ng/mL in preterm premature rupture of membranes. Neurosonography included the evaluation of brain structure biometric parameters and cortical development. Neuron-specific enolase, protein S100B, and glial fibrillary acidic protein were selected as amniotic fluid brain injury biomarkers. Data were adjusted for cephalic biometrics, fetal growth percentile, fetal sex, noncephalic presentation, and preterm premature rupture of membranes at admission.

RESULTS

Fetuses from mothers with preterm labor with intact membranes or preterm premature rupture of membranes showed signs of brain remodeling and injury. First, they had a smaller cerebellum. Thus, in the intra-amniotic inflammation, non-intra-amniotic inflammation, and control groups, the transcerebellar diameter measurements were 32.7 mm (interquartile range, 29.8-37.6), 35.3 mm (interquartile range, 31.2-39.6), and 35.0 mm (interquartile range, 31.3-38.3), respectively (P=.019), and the vermian height measurements were 16.9 mm (interquartile range, 15.5-19.6), 17.2 mm (interquartile range, 16.0-18.9), and 17.1 mm (interquartile range, 15.7-19.0), respectively (P=.041). Second, they presented a lower corpus callosum area (0.72 mm2 [interquartile range, 0.59-0.81], 0.71 mm2 [interquartile range, 0.63-0.82], and 0.78 mm2 [interquartile range, 0.71-0.91], respectively; P=.006). Third, they showed delayed cortical maturation (the Sylvian fissure depth-to-biparietal diameter ratios were 0.14 [interquartile range, 0.12-0.16], 0.14 [interquartile range, 0.13-0.16], and 0.16 [interquartile range, 0.15-0.17], respectively [P<.001], and the right parieto-occipital sulci depth ratios were 0.09 [interquartile range, 0.07-0.12], 0.11 [interquartile range, 0.09-0.14], and 0.11 [interquartile range, 0.09-0.14], respectively [P=.012]). Finally, regarding amniotic fluid brain injury biomarkers, fetuses from mothers with preterm labor with intact membranes or preterm premature rupture of membranes had higher concentrations of neuron-specific enolase (11,804.6 pg/mL [interquartile range, 6213.4-21,098.8], 8397.7 pg/mL [interquartile range, 3682.1-17,398.3], and 2393.7 pg/mL [interquartile range, 1717.1-3209.3], respectively; P<.001), protein S100B (2030.6 pg/mL [interquartile range, 993.0-4883.5], 1070.3 pg/mL [interquartile range, 365.1-1463.2], and 74.8 pg/mL [interquartile range, 44.7-93.7], respectively; P<.001), and glial fibrillary acidic protein (1.01 ng/mL [interquartile range, 0.54-3.88], 0.965 ng/mL [interquartile range, 0.59-2.07], and 0.24 mg/mL [interquartile range, 0.20-0.28], respectively; P=.002).

CONCLUSION

Fetuses with preterm labor with intact membranes or preterm premature rupture of membranes had prenatal signs of brain remodeling and injury at the time of clinical presentation. These changes were more pronounced in fetuses with intra-amniotic inflammation.

Fetal wide subarachnoid space and its outcome in cases of macrocephaly without ventriculomegaly

Objective: To examine the occurrence and outcomes of fetuses with wide subarachnoid space (WSS) without ventriculomegaly in pregnant women with fetal macrocephaly as a sole diagnosis.Study design: A retrospective study was performed, analyzing patients with fetal macrocephaly between the years 2008 and 2018. All these patients underwent MRI, in order to detect brain anomalies. In the absence of any other brain abnormality, they were evaluated for WSS and their offspring's database was followed for at least two years after birth.Results: Ten patients were found to be carrying fetuses with macrocephaly, nine of them were diagnosed with WSS without ventriculomegaly prior to delivery. Following at least two years of follow up, all patients did not present significant neurodevelopmental abnormalities, apart from one child that had a genetic mutation of 15q21.2-22.31 deletion with other anomalies that were not diagnosed prenatally.Conclusions: We present herein for the first time in the literature a cohort of patients with a prenatal diagnosis of WSS without ventriculomegaly in fetuses with macrocephaly. Our data show that, in the presence of normal anomaly scan and normal chromosomal study, there is a low chance for significant neurodevelopmental abnormalities in fetuses with WSS without ventriculomegaly.

Congenital aqueduct stenosis: Progressive brain findings in utero to birth in the presence of severe hydrocephalus

PURPOSE

To evaluate the effects of progressive hydrocephalus on the developing brain in a cohort of fetuses diagnosed with congenital aqueduct stenosis by comparing prenatal magnetic resonance imaging and postnatal imaging.

METHODS

This IRB approved single center retrospective review of prenatally diagnosed children with congenital aqueduct stenosis interrogated changes in the brain between prenatal and postnatal imaging and analyzed statistics using SAS software package version 9.3.

RESULTS

Thirty fetuses imaged at a mean gestational age of 26 weeks had aqueduct obstruction confirmed by postnatal imaging. Progressive hydrocephalus required shunting in all but one patient (97%). Those patients with increasing hydrocephalus showed increase in ventricular rupture (60%), loss of septal leaflets (47%), and reduction in white matter and corpus callosum volume (43%). Cerebellar ectopia developed in 27% with 6% meeting the criteria for Chiari I malformation.

CONCLUSION

Hydrocephalus in the fetus results in enlarging ventricular rupture, loss of the septum pellucidum leaflets, volume reduction of brain parenchyma including corpus callosum, and risk for Chiari I anomaly. Given advances in fetal surgery and imaging in the last 3 decades, there may be cause to revisit the idea of in utero cerebral spinal fluid diversion as a means to potentially ameliorate progressive loss of the developing brain.

Evaluation of fetal subarachnoid space using transabdominal ultrasonography and normal values during pregnancy

Objectives

To determine the feasibility of evaluating the subarachnoid space by measuring two novel sonographic parameters in axial section using transabdominal ultrasound, in addition to the parameters previously defined in coronal section, and to construct a normal range for the subarachnoid space width in singleton healthy fetuses.

Methods

Healthy pregnant women between 20 and 29 weeks were scanned using transabdominal ultrasound. Four variables were measured for the evaluation of subarachnoid space width; sinocortical width and anterior craniocortical width in coronal plane, and lateral and posterior craniocortical width in axial plane.

Result

The data of 154 patients were recorded. SCW could be measured in 87.6 % (135) of fetuses, while the same figure was 77.9 % (120), 96.1 % (151) and 98.1 % (148) for anterior, lateral and posterolateral CCW, respectively. The SCW and anterior CCW did not display a significant correlation with gestational age and head circumference. The mean of SCW was 1.55 ± 0.41 mm with a range of 0.85–3.87 mm. The mean anterior CCW was 1.63 ± 0.39 mm with a range of 0.85–2.82 mm. A linear regression line was plotted between gestational age and lateral CCW (r = 0.707; p < 0.0001) and posterolateral CCW (r = 0.437; p < 0.0001), and nomograms for these parameters are constructed.

Conclusion

This study presents a novel approach for the in utero evaluation of the subarachnoid space with two measurements in axial plane using transabdominal ultrasound. The nomograms will be helpful when there is a suspicion of subarachnoid space dilatation during routine cranial scan.

Cerebral measurements made using cranial ultrasound in term Ugandan newborns

BACKGROUND

Few cUS studies of cerebral measurements are available for normal term infants. Normative data is important for evaluating cerebral structure size in symptomatic term infants and assessing preterm brain growth by term age.

OBJECTIVES

To (i) make linear measurements using cranial ultrasound (cUS) for major cerebral structures and intracranial spaces in normal newborn term infants, (ii) correlate these measurements with gestational age (GA), birth weight (BW), head circumference (HC), gender and within one infant (iii) examine inter/intra-observer variation, and (iv) compare these data with those currently available.

DESIGN, SETTING AND PATIENTS

Linear cUS measurements of major cerebral structures were made in well term-born Ugandan infants at Mulago University Hospital, Kampala. Correlations between the measurements and gender, HC, BW and GA were calculated. Intra- and inter-observer agreements were assessed.

RESULTS

Data from 106 infants (mean GA 39.20±1.4SD weeks) were analysed. Intra/inter-observer agreement was substantial/excellent. Significant correlations were found between HC and pons anterior-posterior diameter (p<0.01), corpus callosal (CC) length (p=0.02) and transverse cerebellar diameter (TCD, p<0.01) and between BW and CC length (p=0.02), vermis height (<0.01) and thalamo-occipital distance (p=0.03); no significant correlation was found with GA. Within infants CC length and TCD correlated significantly (p=0.019). Males had larger left ventricular indices than females (p=0.04). The data was similar to those from other populations.

CONCLUSIONS

These data provide reliable reference values for linear measurements of many cerebral structures made using cUS. The data agree well with those from other populations suggesting that cerebral size is similar in different ethnic groups.

Can syndromic macrocephaly be diagnosed in utero?

OBJECTIVES

To compare the outcomes of fetuses with apparently isolated macrocephaly and those with associated findings, and to compare prenatal findings with postnatal diagnoses in children with syndromic macrocephaly.

METHODS

We reviewed the files of all patients referred for suspected fetal macrocephaly, during a 10-year period from 2000, to a large prenatal diagnosis unit with expertise in fetal neurology counseling. Macrocephaly was defined as head circumference (HC) > 2 SDs of the norm. Patients with confirmed HC > 2 SD were identified and contacted, and their development was evaluated.

RESULTS

Adequate data for analysis were available for 98 patients, in 82 of whom the fetal macrocephaly was considered isolated (Group A), and in 16 of whom associated fetal anomalies were identified (Group B). Macrocephaly was diagnosed earlier in Group B patients (28.4 vs. 32.3 weeks, P = 0.069), and the HC in Group B patients was larger (Z-score 2.95 vs. 2.3, P < 0.001). From Group A there were 81 liveborn; one of whom was diagnosed as having infantile autism. From Group B, there were nine liveborn. The associated central nervous system findings, as demonstrated by ultrasound and magnetic resonance imaging, included mild ventriculomegaly, malformations of cortical development, callosal abnormalities, overdeveloped sulcation, large cavum septi pellucidi, large subarachnoid spaces, mega cisterna magna, periventricular pseudocyst, open operculum and vermian dysgenesis. Syndromic diagnosis was made in utero in five fetuses and after birth in three. In eight patients, associated malformations were confirmed after birth but a specific diagnosis was not reached.

CONCLUSIONS

When fetal macrocephaly is associated with other brain or systemic anomalies, syndromic macrocephaly can be diagnosed in utero. Fetuses with syndromic macrocephaly have a significantly larger HC, usually > 2.5 SD above the mean. Isolated macrocephaly, particularly when the HC is < 2.5 SD above the norm, may be clinically benign.

Abnormalities of the foetal cerebral cortex

Prenatal ultrasound has concentrated on readily visible cerebral structures including head size, shape, ventricles, CSP (cavum septi pellucidi), cerebellar size/vermian presence and cisterna magna. However, apart from these easily visible structures it is important to evaluate the brain itself. Patients who initially appear to have mild isolated findings such as borderline ventriculomegaly in fact can have many more subtle findings that significantly alter prognosis and management that can be detected on detailed examination of the brain. There has been rapid evolution in imaging these foetuses, especially with neurosonography and MRI, and a revolution in understanding the underlying genetic and biochemical mechanisms. There is increasing emphasis to detect cortical abnormalities as early as possible. This article reviews development of the cerebral cortex, the classification, aetiologies and clinical manifestations of cortical disorders, normal and abnormal appearances at ultrasound and MRI, and approaches to investigation.

Fetal brain monitoring: future applications

Future application of fetal brain monitoring is explored by selecting and analysing articles for information on types of brain damage that can be monitored, where in the brain this can be done, how long after the risk exposure, and with what method of investigation. A limited number of--mainly--case histories reported that early (cell death and oedema) and late (gliosis) effects of brain damage can be demonstrated before birth with multiplanar ultrasound and magnetic resonance imaging, and that hypoxic ischaemic injury or infection can induce local or widespread brain injury, occurring as transient or longer-lasting changes in age-related predilection areas for which normal features are known. The antenatal role of risk factors inducing abnormal brain development can be studied longitudinally with ultrasound and magnetic resonance imaging. A multidisciplinary approach will facilitate the introduction of various techniques with adequate know-how of underlying processes, to evaluate the predictive value on neurological outcome and prevent premature introduction into clinical application.

Assessment of fetal intracranial pathologies first demonstrated late in pregnancy: cell proliferation disorders

A considerable number of central nervous system pathologies remain undiagnosed during the first two trimesters of pregnancy. This group of disorders includes anomalies of brain proliferation, migration and cortical organization. Due to the fact that a detailed ultrasound examination of the fetal brain is usually not performed during the third trimester the diagnosis of these disorders is usually only made in families with a previously affected child or in many cases be mere chance. In this article we review the feasibility of prenatal diagnosis of disorders of brain proliferation: microcephaly, macrocephaly, hemimegalencephaly and neoplastic and non-neoplastic abnormal cell types. We discuss the differential diagnosis and offer a stepwise approach to the diagnosis of the more common disorders.

A normal second-trimester ultrasound does not exclude intracranial structural pathology

OBJECTIVE

To report the prenatal diagnosis and management of 34 fetuses with various intracranial structural pathologies diagnosed following a normal second-trimester ultrasound examination.

METHODS

We retrospectively reviewed the images of 203 abnormal central nervous system ultrasound examinations performed between 13 and 37 weeks of gestation at our prenatal diagnosis unit. In 34 (16.7%) of them at least one previous second-trimester ultrasound examination had been performed and considered normal. These 34 fetuses represent the study group.

RESULTS

The following intracranial pathologies were diagnosed: dysgenesis of the corpus callosum, ventriculomegaly, cerebral cysts or hemorrhage, migrational disorders, vermian dysgenesis, arachnoid cysts, macrocephaly, enlarged subarachnoid space, brain calcifications and microcephaly.

CONCLUSION

A normal second-trimester ultrasound scan does not rule out significant intracranial anomalies. Parents and physicians should be informed about the limitations of second-trimester sonography as far as brain diagnosis is concerned. A repeat third-trimester scan may enable more accurate diagnosis and counseling.