Ganglionic Eminence Anomalies and Coexisting Cerebral Developmental Anomalies on Fetal MR Imaging: Multicenter-Based Review of 60 Cases

Fetal Brain MRI Abnormalities in Pyruvate Dehydrogenase Complex Deficiency

BACKGROUND AND OBJECTIVES

Pyruvate dehydrogenase complex deficiency (PDCD) is a disorder of mitochondrial metabolism that is caused by pathogenic variants in multiple genes, including PDHA1. Typical neonatal brain imaging findings have been described, with a focus on malformative and encephaloclastic features. Fetal brain MRI in PDCD has not been comprehensively described. The aims of this study were (1) to further characterize the fetal brain MRI findings in PDCD using comprehensive fetal imaging and genetic testing and (2) to determine whether markers of diagnosis of PDCD could be identified on prenatal imaging.

METHODS

Fetuses with a diagnosis of PDCD related to a genetic etiology that had undergone fetal MRI were included. Fetuses were identified retrospectively from local databases of 4 fetal diagnostic clinics within tertiary pediatric health care centers. Electronic medical records were reviewed retrospectively: demographics, maternal and pregnancy history, fetal outcomes, and neonatal outcomes (if available) were reviewed and recorded. Fetal and neonatal imaging reports were reviewed; source fetal and neonatal brain MRI scans were reviewed by a single pediatric neuroradiologist (J.W.S.) for consistency. Genetic testing strategies and results including variant type, zygosity, inheritance pattern, and pathogenicity were recorded. Deidentified data were combined and reported descriptively.

RESULTS

A total of 10 fetuses with a diagnosis of PDCD were included. 8 fetuses had corpus callosum dysgenesis, 6 had an abnormal gyration pattern, 10 had reduced brain volumes, and 9 had cystic lesions. 1 fetus had intraventricular hemorrhages. 1 fetus had a midbrain malformation with aqueductal stenosis and severe hydrocephalus. 6 fetuses imaged in the second trimester had cystic lesions involving the ganglionic eminences (GEs) while GE cysts were not present in the 4 fetuses imaged in the third trimester.

DISCUSSION

Fetuses with PDCD have similar brain MRI findings to neonates described in the literature, although some of these findings are subtle early in pregnancy. Additional features, such as cystic lesions of the GEs, are noted in the second trimester in fetuses with PDCD. These may represent an early diagnostic marker of PDCD, although more data are needed to validate this association. Early diagnosis of PDCD using fetal MRI may inform genetic counseling, pregnancy decision making, and neonatal care planning.

Characteristic Fetal Brain MRI Abnormalities in Pyruvate Dehydrogenase Complex Deficiency

Pyruvate dehydrogenase complex deficiency (PDCD) is a disorder of mitochondrial metabolism that is caused by pathogenic variants in multiple genes, including PDHA1. Typical neonatal brain imaging findings in PDCD have been described, with a focus on malformative features and chronic encephaloclastic changes. However, fetal brain MRI imaging in confirmed PDCD has not been comprehensively described. We sought to demonstrate the prenatal neurological and systemic manifestations of PDCD determined by comprehensive fetal imaging and genomic sequencing. All fetuses with a diagnosis of genetic PDCD who had undergone fetal MRI were included in the study. Medical records, imaging data, and genetic testing results were reviewed and reported descriptively. Ten patients with diagnosis of PDCD were included. Most patients had corpus callosum dysgenesis, abnormal gyration pattern, reduced brain volumes, and periventricular cystic lesions. One patient had associated intraventricular hemorrhages. One patient had a midbrain malformation with aqueductal stenosis and severe hydrocephalus. Fetuses imaged in the second trimester were found to have enlargement of the ganglionic eminences with cystic cavitations, while those imaged in the third trimester had germinolytic cysts. Fetuses with PDCD have similar brain MRI findings to neonates described in the literature, although some of these findings may be subtle early in pregnancy. Additional features, such as cystic cavitations of the ganglionic eminences, are noted in the second trimester in fetuses with PDCD, and these may represent a novel early diagnostic marker for PDCD. Using fetal MRI to identify these radiological hallmarks to inform prenatal diagnosis of PDCD may guide genetic counseling, pregnancy decision-making, and neonatal care planning.

Fetal macrocephaly: Pathophysiology, prenatal diagnosis and management

Macrocephaly means a large head and is defined as a head circumference (HC) above the 98th percentile or greater than +2SD above the mean for gestational age. Macrocephaly can be primary and due to increased brain tissue (megalocephaly), which in most cases is familial and benign or secondary. The latter may be due to various causes, including but not limited to communicating or non-communicating hydrocephalus, cerebral edema, focal and pericerebral increased fluid collections, thickened calvarium and brain tumors. Megalocephaly can be syndromic or non-syndromic. In the former, gyral and structural CNS anomalies are common. It is important to exercise caution when considering a diagnosis of megalocephaly due to limitations in the accuracy of HC measurement, lack of nomograms for specific populations, inconsistencies between prenatal and postnatal HC growth curves and progression over time. The degree of macrocephaly is important, with mild macrocephaly ≤2.5SD carrying a good prognosis, especially when one of the parents has macrocephaly and normal development. Cases in which the patient history and/or physical exam are positive or when parental HC are normal are more worrisome and warrant a neurosonogram, fetal MRI and genetic testing to better delineate the underlying etiology and provide appropriate counseling.

Normal and abnormal appearance of fetal ganglionic eminence on second-trimester three-dimensional ultrasound

OBJECTIVES

To describe the appearance and size of the ganglionic eminence (GE) in normal fetuses on midtrimester three-dimensional (3D) neurosonography and to report on the association between GE alterations (cavitation or enlargement) and malformation of cortical development (MCD).

METHODS

This was a prospective multicenter cohort study of normal fetuses and a retrospective analysis of pathological cases with MCD. From January 2022 to June 2022, patients attending our tertiary centers for an expert fetal brain scan were recruited for the purpose of the study. A 3D volume of the fetal head, starting from the sagittal plane, was acquired in apparently normal fetuses using a transabdominal or transvaginal approach. Stored volume datasets were then evaluated independently by two expert operators. Two measurements (longitudinal diameter and transverse diameter) of the GE in the coronal view were obtained twice by each operator. Intra- and interobserver measurement variation was calculated. Reference ranges for GE measurements were calculated in the normal population. A previously stored volume dataset of 60 cases with MCD was also analyzed independently by the two operators using the same method in order to assess if GE abnormalities (cavitation or enlargement) were present. Postnatal follow-up was obtained in all cases.

RESULTS

In the study period, 160 normal fetuses between 19 and 22 weeks of gestation were included in the study. The GE was visible in the coronal plane on 3D neurosonography in 144 (90%) cases and was not clearly visible in the remaining 16 (10%) cases. The intra- and interobserver agreement was almost perfect for the longitudinal diameter, with an intraclass correlation coefficient (ICC) of 0.90 (95% CI, 0.83-0.93) and 0.90 (95% CI, 0.86-0.92), respectively, and substantial for the transverse diameter, with an ICC of 0.80 (95% CI, 0.70-0.87) and 0.64 (95% CI, 0.53-0.72), respectively. A retrospective analysis of 50 cases with MCD in the second trimester showed that GE enlargement was present in 12 cases and GE cavitation was present in four cases.

CONCLUSIONS

Systematic assessment of the GE in fetuses at 19-22 weeks of gestation is feasible on 3D neurosonography, with good reproducibility in normal cases. Cavitation or enlargement of the GE can be demonstrated in fetuses with MCD. © 2023 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.

Ganglionic eminence: volumetric assessment of transient brain structure utilizing fetal magnetic resonance imaging

OBJECTIVE

To provide quantitative magnetic resonance imaging (MRI) super-resolution-based three-dimensional volumetric reference data on the growth dynamics of the ganglionic eminence (GE) relative to cortical and total fetal brain volumes (TBV).

METHODS

This was a retrospective study of fetuses without structural central nervous system anomalies or other confounding comorbidities that were referred for fetal MRI. Super-resolution reconstructions of 1.5- and 3-Tesla T2-weighted images were generated. Semiautomatic segmentation of TBV and cortical volume and manual segmentation of the GE were performed. Cortical volume, TBV and GE volume were quantified and three-dimensional reconstructions were generated to visualize the developmental dynamics of the GE.

RESULTS

Overall, 120 fetuses that underwent 127 MRI scans at a mean gestational age of 27.23 ± 4.81 weeks (range, 20-37 weeks) were included. In the investigated gestational-age range, GE volume ranged from 74.88 to 808.75 mm3 and was at its maximum at 21 gestational weeks, followed by a linear decrease (R2  = 0.559) throughout the late second and third trimesters. A pronounced reduction in GE volume relative to cortical volume and TBV occurred in the late second trimester, with a decline in this reduction observed in the third trimester (R2  = 0.936 and 0.924, respectively). Three-dimensional rendering allowed visualization of a continuous change in the shape and size of the GE throughout the second and third trimesters.

CONCLUSIONS

Even small compartments of the fetal brain, which are not easily accessible by standardized two-dimensional modalities, can be assessed precisely by super-resolution processed fetal MRI. The inverse growth dynamics of GE volume compared with TBV and cortical volume reflects the transitory nature and physiological involution of this (patho-)physiologically important brain structure. The normal development and involution of the GE is mandatory for normal cortical development. Pathological changes of this transient organ precede impairment of cortical structures, and their detection may allow an earlier diagnosis of such anomalies. © 2023 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.

Second trimester fetal MRI of the brain: Through the ground glass

Fetal MRI is an important tool for the prenatal diagnosis of brain malformations and is often requested after second-trimester ultrasonography reveals a possible abnormality. Despite the immature state of the fetal brain at this early stage, early suggestive signs of the presence of brain malformations can be recognized. To differentiate between the normal dynamics of the growing brain and the developing pathological conditions can be challenging and requires extensive knowledge of normal central nervous system developmental stages and their neuroradiological counterparts at those different stages. This article reviews the second-trimester appearances of some commonly encountered brain malformations, focusing on helpful tricks and subtle signs to aid in the diagnosis of such conditions as rhombencephalosynapsis, various causes of vermian rotation, molar tooth spectrum anomalies, diencephalic-mesencephalic junction dysplasia, ganglionic eminence anomalies, and the most common malformations of cortical development.

Transcranial Magnetic Stimulation and Neocortical Neurons: The Micro-Macro Connection

Understanding the operation of cortical circuits is an important and necessary task in both neuroscience and neurorehabilitation. The functioning of the neocortex results from integrative neuronal activity, which can be probed non-invasively by transcranial magnetic stimulation (TMS). Despite a clear indication of the direct involvement of cortical neurons in TMS, no explicit connection model has been made between the microscopic neuronal landscape and the macroscopic TMS outcome. Here we have performed an integrative review of multidisciplinary evidence regarding motor cortex neurocytology and TMS-related neurophysiology with the aim of elucidating the micro–macro connections underlying TMS. Neurocytological evidence from animal and human studies has been reviewed to describe the landscape of the cortical neurons covering the taxonomy, morphology, circuit wiring, and excitatory–inhibitory balance. Evidence from TMS studies in healthy humans is discussed, with emphasis on the TMS pulse and paradigm selectivity that reflect the underlying neural circuitry constitution. As a result, we propose a preliminary neuronal model of the human motor cortex and then link the TMS mechanisms with the neuronal model by stimulus intensity, direction of induced current, and paired-pulse timing. As TMS bears great developmental potential for both a probe and modulator of neural network activity and neurotransmission, the connection model will act as a foundation for future combined studies of neurocytology and neurophysiology, as well as the technical advances and application of TMS.

The Fetus with Ganglionic Eminence Abnormality: Head Size and Extracranial Sonographic Findings Predict Genetic Diagnoses and Postnatal Outcomes

BACKGROUND AND PURPOSE

Ganglionic eminence abnormalities on fetal MR imaging are associated with cerebral malformations. Their presumed genetic basis and associated postnatal outcomes remain largely unknown. We aimed to elucidate these through a multicenter study.

MATERIALS AND METHODS

Between January 2010 and June 2020, seven hospitals in 2 countries performing fetal MR imaging examinations identified fetal MR imaging studies demonstrating ganglionic eminence enlargement, cavitation, or both. Cases with no genetic diagnosis, no whole exome sequencing, or no outcome of a liveborn child were excluded. Head size was classified as large (fronto-occipital diameter > 95th centile), small (fronto-occipital diameter <5th centile), or normal.

RESULTS

Twenty-two fetuses with ganglionic eminence abnormalities were identified. Of 8 with large heads, 2 were diagnosed with MTOR mutations; 1 with PIK3CA mutation-producing megalencephaly, polymicrogyria, polydactyly, hydrocephalus (MPPH) syndrome; 3 with TSC mutations; 1 with megalencephaly capillary malformation syndrome; and 1 with hemimegalencephaly. Cardiac rhabdomyoma was present prenatally in all cases of TSC; mutation postaxial polydactyly accompanied megalencephaly capillary malformation and MPPH. Of 12 fetuses with small heads, 7 had TUBA1A mutations, 1 had a TUBB3 mutation, 2 had cobblestone lissencephaly postnatally with no genetic diagnosis, 1 had a PDHA1 mutation, and 1 had a fetal akinesia dyskinesia sequence with no pathogenic mutation on trio whole exome sequencing. One of the fetuses with a normal head size had an OPHN1 mutation with postnatal febrile seizures, and the other had peri-Sylvian polymicrogyria, seizures, and severe developmental delay but no explanatory mutation on whole exome sequencing.

CONCLUSIONS

Fetal head size and extracranial prenatal sonographic findings can refine the phenotype and facilitate genetic diagnosis when ganglionic eminence abnormality is diagnosed with MR imaging.