Abnormal cortical plate (polymicrogyria), heterotopias and brain damage in monozygous twins

Incidence and outcome of prenatal brain abnormality in twin-to-twin transfusion syndrome: systematic review and meta-analysis

OBJECTIVES

To evaluate the incidence of antenatally diagnosed brain injury in twin pregnancy complicated by twin-to-twin transfusion syndrome (TTTS) and to quantify the perinatal mortality, morbidity and long-term neurodevelopmental outcome of these fetuses.

METHODS

MEDLINE, EMBASE, ClinicalTrials.gov and The Cochrane Library databases were searched. Inclusion criteria were studies reporting on brain abnormality diagnosed antenatally in twin pregnancies complicated by TTTS. The primary outcome was the incidence of prenatal brain abnormality. The secondary outcomes were intrauterine demise (IUD), neonatal death, termination of pregnancy (TOP) and long-term morbidity. Outcomes were explored in the population of fetuses with antenatal diagnosis of brain abnormality. Subgroup analysis according to the type of treatment, gestational age, Quintero stage at diagnosis and/or treatment, and cotwin death was planned. Meta-analysis of proportions was used to combine data and pooled proportions and their 95% CI were reported.

RESULTS

Thirteen studies including 1573 cases of TTTS and 88 fetuses with an antenatal diagnosis of brain abnormality were included in the systematic review. The meta-analysis included only studies reporting on brain abnormality in twin pregnancy complicated by TTTS cases and treated with laser surgery. Overall, brain injury occurred in 2.2% (52/2410) of fetuses (eight studies). Brain abnormality was reported in 1.03% and 0.82% of recipients and donors, respectively. The most common type of abnormality was ischemic lesions (30.4% (95% CI, 19.1-43.0%)), followed by destructive lesions (23.9% (95% CI, 13.7-35.9%)), ventriculomegaly (19.9% (95% CI, 10.6-31.3%)) and hemorrhagic lesions (15.3% (95% CI, 7.1-25.8%)). Spontaneous IUD occurred in 13.4% (95% CI, 5.1-24.8%) of fetuses, while TOP was chosen by parents in 53.5% (95% CI, 38.9-67.8%) cases. Neonatal death was reported by only three studies, with an incidence of 15.4% (95% CI, 2.8-35.4%). Finally, only two studies reported on composite morbidity, with an overall rate of the outcome of 20.4% (95% CI, 2.5-49.4%) and rates of 29.7% and 20.4% in the recipient and donor fetuses, respectively. Due to the small numbers, only composite morbidity was analyzed and no information on neonatal intensive care unit admission, respiratory distress syndrome or other long-term outcomes, such as neurodevelopmental delay and cerebral palsy, could be retrieved reliably.

CONCLUSIONS

The overall incidence of antenatally diagnosed fetal brain abnormality in twin pregnancy complicated by TTTS treated with laser surgery is around 2% and is mainly ischemic in nature (30.4%). TOP was chosen by parents in more than half of cases (53.5%). No information could be retrieved on morbidity outcomes, highlighting the urgent need for long-term follow-up studies of these children. © 2022 International Society of Ultrasound in Obstetrics and Gynecology.

The spectrum of brain malformations and disruptions in twins

Twins have an increased risk for congenital malformations and disruptions, including defects in brain morphogenesis. We analyzed data on brain imaging, zygosity, sex, and fetal demise in 56 proband twins and 7 less affected co-twins with abnormal brain imaging and compared them to population-based data and to a literature series. We separated our series into malformations of cortical development (MCD, N = 39), cerebellar malformations without MCD (N = 13), and brain disruptions (N = 11). The MCD group included 37/39 (95%) with polymicrogyria (PMG), 8/39 (21%) with pia-ependymal clefts (schizencephaly), and 15/39 (38%) with periventricular nodular heterotopia (PNH) including 2 with PNH but not PMG. Cerebellar malformations were found in 19 individuals including 13 with a cerebellar malformation only and another 6 with cerebellar malformation and MCD. The pattern varied from diffuse cerebellar hypoplasia to classic Dandy-Walker malformation. Brain disruptions were seen in 11 individuals with hydranencephaly, porencephaly, or white matter loss without cysts. Our series included an expected statistically significant excess of monozygotic (MZ) twin pairs (22/41 MZ, 54%) compared to population data (482/1448 MZ, 33.3%; p = .0110), and an unexpected statistically significant excess of dizygotic (DZ) twins (19/41, 46%) compared to the literature cohort (1/46 DZ, 2%; p < .0001. Recurrent association with twin-twin transfusion syndrome, intrauterine growth retardation, and other prenatal factors support disruption of vascular perfusion as the most likely unifying cause.

Cortical formation abnormalities on foetal MR imaging: a proposed classification system trialled on 356 cases from Italian and UK centres

OBJECTIVE

To formulate a classification system for foetal cortical formation abnormalities (CFAs) based on in utero magnetic resonance (iuMR) appearances and trial it in 356 cases.

METHODS

This retrospective study included all cases of foetal CFA diagnosed between 2000 and 2017 from seven centres in Italy and UK. All of the studies were reviewed by a panel of paediatric neuroradiologists experienced in iuMR with the aid of an algorithm designed to categorise the abnormalities.

RESULTS

Consensus expert review confirmed 356 foetuses with CFA and the first level of classification distinguished bilateral CFA (229/356-64%) from unilateral CFA (127/356-36%) cases with sub-classification of the bilateral cases into asymmetric (65/356-18%) and symmetric (164/356-46%) involvement. There was a statistically significant excess of foetuses with small head size, e.g. 17% of the cohort had a bi-parietal diameter < 3rd centile. There was a small but statistically significant excess of males in the cohort. Further categorisation was made on fine anatomical structure.

CONCLUSIONS

It is often not possible to classify foetal CFA using the principles and nomenclature used in paediatric neuroradiology. We have created a classification system for foetal CFA based on the analysis of 356 cases and believe that this will assist future research designed to correlate ante-natal and post-natal imaging features and understand the clinical sequelae of CFA described in utero.

KEY POINTS

• We describe a morphological classification system of foetal brain cortical formation abnormalities that can be used in clinical practice. • This classification system can be used in future research studies to evaluate the long-term imaging and clinical outcomes of foetal brain cortical formation abnormalities in 17- to 38-week gestational age range. • The practical value of the work is in providing a framework and language to look for imaging clues that may differentiate between different CFA in further studies.

Subcortical heterotopic gray matter brain malformations: Classification study of 107 individuals

OBJECTIVE

To better evaluate the imaging spectrum of subcortical heterotopic gray matter brain malformations (subcortical heterotopia [SUBH]), we systematically reviewed neuroimaging and clinical data of 107 affected individuals.

METHODS

SUBH is defined as heterotopic gray matter, located within the white matter between the cortex and lateral ventricles. Four large brain malformation databases were searched for individuals with these malformations; data on imaging, clinical outcomes, and results of molecular testing were systematically reviewed and integrated with all previously published subtypes to create a single classification system.

RESULTS

Review of the databases revealed 107 patients with SUBH, the large majority scanned during childhood (84%), including more than half before 4 years (59%). Although most individuals had cognitive or motor disability, 19% had normal development. Epilepsy was documented in 69%. Additional brain malformations were common and included abnormalities of the corpus callosum (65/102 [64%]), and, often, brainstem or cerebellum (47/106 [44%]). Extent of the heterotopic gray matter brain malformations (unilateral or bilateral) did not influence the presence or age at onset of seizures. Although genetic testing was not systematically performed in this group, the sporadic occurrence and frequent asymmetry suggests either postzygotic mutations or prenatal disruptive events. Several rare, bilateral forms are caused by mutations in genes associated with cell proliferation and polarity (EML1, TUBB, KATNB1, CENPJ, GPSM2).

CONCLUSION

This study reveals a broad clinical and imaging spectrum of heterotopic malformations and provides a framework for their classification.

Fetal stroke and cerebrovascular disease: Advances in understanding from lenticulostriate and venous imaging, alloimmune thrombocytopaenia and monochorionic twins

Fetal stroke is an important cause of cerebral palsy but is difficult to diagnose unless imaging is undertaken in pregnancies at risk because of known maternal or fetal disorders. Fetal ultrasound or magnetic resonance imaging may show haemorrhage or ischaemic lesions including multicystic encephalomalacia and focal porencephaly. Serial imaging has shown the development of malformations including schizencephaly and polymicrogyra after ischaemic and haemorrhagic stroke. Recognised causes of haemorrhagic fetal stroke include alloimmune and autoimmune thrombocytopaenia, maternal and fetal clotting disorders and trauma but these are relatively rare. It is likely that a significant proportion of periventricular and intraventricular haemorrhages are of venous origin. Recent evidence highlights the importance of arterial endothelial dysfunction, rather than thrombocytopaenia, in the intraparenchymal haemorrhage of alloimmune thrombocytopaenia. In the context of placental anastomoses, monochorionic diamniotic twins are at risk of twin twin transfusion syndrome (TTTS), or partial forms including Twin Oligohydramnios Polyhydramnios Sequence (TOPS), differences in estimated weight (selective Intrauterine growth Retardation; sIUGR), or in fetal haemoglobin (Twin Anaemia Polycythaemia Sequence; TAPS). There is a very wide range of ischaemic and haemorrhagic injury in a focal as well as a global distribution. Acute twin twin transfusion may account for intraventricular haemorrhage in recipients and periventricular leukomalacia in donors but there are additional risk factors for focal embolism and cerebrovascular disease. The recipient has circulatory overload, with effects on systemic and pulmonary circulations which probably lead to systemic and pulmonary hypertension and even right ventricular outflow tract obstruction as well as the polycythaemia which is a risk factor for thrombosis and vasculopathy. The donor is hypovolaemic and has a reticulocytosis in response to the anaemia while maternal hypertension and diabetes may influence stroke risk. Understanding of the mechanisms, including the role of vasculopathy, in well studied conditions such as alloimmune thrombocytopaenia and monochorionic diamniotic twinning may lead to reduction of the burden of antenatally sustained cerebral palsy.

Early formative stage of human focal cortical gyration anomalies: fetal MRI

OBJECTIVE

Limited information is available about the development of focal cortical gyration anomalies in the human brain. Using prenatal MRI, we characterized focal cortical gyration anomalies at an early formative stage and sought clues about the mechanisms of their development.

MATERIALS AND METHODS

From a large prenatal MRI database, 30 cases (gestational age, ≤ 24 weeks) with reported focal distortion of the cortical rim profile were selected. Eight cases were matched with histologic examinations; another seven had prenatal MRI, MRI autopsy, or postnatal MRI follow-up; and 15 had no follow-up but did present analogous abnormal cortical features. Focal cortical gyration anomalies were detectable when the brain was still smooth (i.e., physiological lissencephaly).

RESULTS

Four patterns of cortical plate anomaly were identified: wartlike (11 cases), abnormal invaginating sulcus (11 cases), sawtooth (six cases), and single or multiple bumps (two cases). A thinned or blurred subplate and intermediate zone in the focal cortical gyration anomaly site was detected in 80% of cases. All but two cases had other intracranial anomalies. Seven cases were classified as hypoxic-ischemic, five as genetic, and three as infective. In 15 cases, the cause could not be established. In five fetuses with further intrauterine or postnatal MRI, focal cortical gyration anomalies increased in complexity, fulfilling postnatal imaging criteria of polymicrogyria.

CONCLUSION

Focal cortical gyration anomalies can be detected at the early sulcation process stage. The process leading to abnormal gyration may evolve faster than physiologic ones and seems to be related to alterations of parenchymal layering occurring before 24 weeks' gestation. Most focal cortical gyration anomalies evolve toward what is currently considered polymicrogyria.

Causal Hypothesis for Some Congenital Anomalies

Congenital anomalies are a major cause of fetal and neonatal death and of childhood morbidity. Chromosomal and other genetic abnormalities, environmental teratogens and some nutritional deficiencies account for some congenital anomalies but the majority are of unknown etiology. The hypothesis is here proposed that a significant proportion of congenital anomalies and cerebral palsy of unknown etiology are attributable to a monozygotic multiple conception with monochorionic placentation and that these anomalies, even in singletons, may be explained by early, unrecognized or unrecorded loss of one conceptus in a monochorionic monozygotic conception. The pathological mechanism is hemodynamic instability with episodes of acute feto–fetal transfusion that produce ischemic organ impairment in either or both twins. The resultant clinical abnormality will depend on range of severity (fetal death, infant death, congenital anomaly, normal infant), site or combination of sites (which organ[s] present[s] with the congenital anomaly) and timing (early, middle or late in gestation as shown by variation in brain pathology that is observed).

Malformations of cortical development: current concepts and advanced neuroimaging review

Malformations of cortical development (MCD) result from disruptions in the complex process of the human brain cortex formation and are highly associated to severe epilepsy, neurodevelopmental delay and motor dysfunction. Nowadays, magnetic resonance imaging (MRI) is the cornerstone of the work-up of patients with epilepsy and modern advanced imaging techniques have improved not only our ability to detect and characterize cortical malformations, but also in identifying associated functional abnormalities that are far beyond the structural visualized lesions. Herein, we address the most currently used classifications of MCD and make a concise review of the embryological process of cortical development. Our main goal is to summarize recent advances and new trends in diagnostic imaging techniques concerning MCD. Thereafter, follows a brief discussion of specific disorders and their radiological features.

Bridging the gene-behavior divide through neuroimaging deletion syndromes: Velocardiofacial (22q11.2 Deletion) and Williams (7q11.23 Deletion) syndromes

Investigating the relationship between genes and the neural substrates of complex human behavior promises to provide essential insight into the pathophysiology of mental disorders. One approach to this inquiry is through neuroimaging of individuals with microdeletion syndromes that manifest in specific neuropsychiatric phenotypes. Both Velocardiofacial syndrome (VCFS) and Williams syndrome (WS) involve haploinsufficiency of a relatively small set of identified genes on the one hand and association with distinct, clinically relevant behavioral and cognitive profiles on the other hand. In VCFS, there is a deletion in chromosomal region 22q11.2 and a resultant predilection toward psychosis, poor arithmetic proficiency, and low performance intelligence quotients. In WS, there is a deletion in chromosomal region 7q11.23 and a resultant predilection toward hypersociability, non-social anxiety, impaired visuospatial construction, and often intellectual impairment. Structural and functional neuroimaging studies have begun not only to map these well-defined genetic alterations to systems-level brain abnormalities, but also to identify relationships between neural phenotypes and particular genes within the critical deletion regions. Though neuroimaging of both VCFS and WS presents specific, formidable methodological challenges, including comparison subject selection and accounting for neuroanatomical and vascular anomalies in patients, and many questions remain, the literature to date on these syndromes, reviewed herein, constitutes a fruitful "bottom-up" approach to defining gene-brain relationships.

Prenatal stroke

The main focus of this chapter is the comprehensive description of the neuropathology, the imaging correlates and underlying mechanisms of prenatal stroke. We describe established prenatal stroke in subgroups similar to postnatal stroke: arterial (forebrain or hindbrain) infarction, venous thrombosis, primary lobar haemorrhage. This longitudinal classification should facilitate the study of risk factors and mechanisms. Forebrain lesions of arterial type present as porencephaly, (hemi)hydranencephaly, multicystic encephalopathy or schizencephaly. Venous prenatal forebrain stroke presents as simple porencephaly (in some of genetic nature) and sinus thrombosis. A list of rare porencephaly-like conditions is added for differentiation from arterial and venous porencephaly. Hindbrain infarctions (so far the only reported variants seem to be of arterial nature) present as brainstem disconnection, focal brainstem destruction, uni- or bilateral cerebellar destruction and focal spinal cord ischaemia. Prenatal intracranial haemorrhage and congenital brain infection should be considered in the differential diagnosis of prenatal stroke.

Fetal magnetic resonance imaging of acquired and developmental brain anomalies

During the last decade, increasing interest in magnetic resonance imaging has emerged for the evaluation of fetal abnormalities detected on ultrasound. The advent of single-shot rapid acquisition sequences has greatly facilitated our ability to obtain detailed imaging information of the fetal brain. To date, fetal magnetic resonance imaging has shown to have an important role in the investigation of cerebral abnormalities suspected by sonography, and in the detection of subtle brain anomalies associated with high-risk pregnancies. Magnetic resonance imaging has proved to be a useful adjunct to sonography during the prenatal period of development, especially for the detection of acquired disorders.

Incidence, mechanisms, and patterns of fetal cerebral lesions in twin-to-twin transfusion syndrome

OBJECTIVE

To determine the incidence of fetal cerebral lesions and their characteristics in twin-to-twin transfusion syndrome (TTTS).

DESIGN AND SETTING

This was a retrospective analysis at a single center for the period 1999 to 2004 in which 299 cases of severe TTTS at 15-28 weeks of gestation were reviewed.

METHODS

Only cerebral injuries diagnosed during pregnancy or ischemic lesions diagnosed within the first week of life were considered in order to exclude those related to prematurity. We only included cases resulting in at least one survivor at one week after delivery, as well as fetuses that were terminated because of severe cerebral abnormalities. We excluded all fetuses delivered at <24 weeks of gestation that died prior to undergoing postnatal cranial ultrasonography. The main outcome measures were fetal cerebral lesions, intrauterine death, survival, and neonatal death.

RESULTS

Two hundred and ninety-nine pregnancies were evaluated. Three hundred and fifteen fetuses were reviewed. Cerebral abnormalities developed antenatally in 26/315 fetuses (8.25%). All lesions but one were diagnosed prenatally. Prenatal diagnosis of these lesions was achieved primarily by ultrasound (US) and magnetic resonance imaging (MRI), in 20/25 (80%) and in 5/25 (20%) fetuses, respectively. Cerebral abnormalities developed following primary laser coagulation in 12/222 (5.40%), following serial amnioreduction in 9/66 (13.63%), and following expectant management in 3/14 (21.4%) fetuses. Abnormalities developed after single intrauterine fetal death (IUFD) in 14 cases.

CONCLUSIONS

Cerebral morbidity in TTTS mainly occurs following vascular disruptive lesions. Both donors and recipients are at risk of developing either ischemic or hemorrhagic lesions. The risk of developing cerebral lesions in single survivors is significantly lower following laser treatment. Combined use of a targeted US and fetal MRI could detect most cerebral abnormalities antenatally. Timing of the triggering event is critical for planning serial US and MRI follow-up examinations.

Intracranial magnetic resonance imaging findings in the surviving fetus after spontaneous monochorionic cotwin demise

OBJECTIVE

This study was undertaken to evaluate intracranial magnetic resonance imaging abnormalities in the surviving fetus after a cotwin demise.

STUDY DESIGN

This is a retrospective observational study evaluating the intracranial findings of surviving twins after demise of a monochorionic cotwin. A total of 47 cases of cotwin demise were identified from an magnetic resonance imaging database consisting of all fetal magnetic resonance imagings performed at the University of California San Francisco. Twenty-one of these cases were monochorionic twins who had not undergone an intervention (fetal radiofrequency ablation and placental laser ablation) and these comprised the study group. The magnetic resonance imagings were reviewed by a pediatric neuroradiologist who was blinded to the ultrasound and clinical findings.

RESULTS

The mean gestational age at the time of cotwin demise was 19(6/7) weeks (range 12(4/7) weeks-26(5/7) weeks) with an average interval of 4(3/7) weeks between the time of cotwin demise and fetal magnetic resonance imaging (range 0-12(1/7) weeks). Nine cases (41%) were associated with diagnosed twin-twin transfusion syndrome. Abnormal findings, including polymicrogyria, germinolytic cysts, intracranial hemorrhage, ventriculomegaly, and delayed sulcation were identified by fetal magnetic resonance imaging in 7 (33%) cases, the majority of which had a normal ultrasound.

CONCLUSION

Prenatal magnetic resonance imaging is a valuable tool in evaluating the fetal brain after a cotwin demise.

Polymicrogyria and deletion 22q11.2 syndrome: window to the etiology of a common cortical malformation

Several brain malformations have been described in rare patients with the deletion 22q11.2 syndrome (DEL22q11) including agenesis of the corpus callosum, pachygyria or polymicrogyria (PMG), cerebellar anomalies and meningomyelocele, with PMG reported most frequently. In view of our interest in the causes of PMG, we reviewed clinical data including brain-imaging studies on 21 patients with PMG associated with deletion 22q11.2 and another 11 from the literature. We found that the cortical malformation consists of perisylvian PMG of variable severity and frequent asymmetry with a striking predisposition for the right hemisphere (P = 0.008). This and other observations suggest that the PMG may be a sequela of abnormal embryonic vascular development rather than a primary brain malformation. We also noted mild cerebellar hypoplasia or mega-cisterna magna in 8 of 24 patients. Although this was not the focus of the present study, mild cerebellar anomalies are probably the most common brain malformation associated with DEL22q11.

Postnatal onset cortical dysplasia associated with infarction of white matter

On MRI at 35 weeks of a boy born at 25 weeks, focal disorganization of the cortex was observed near a frontal venous infarct developed in the first week. Disruption of the final steps of cell migration, injury to the subplate and/or disruption of corticospinal axons are possible mechanisms behind it. Preterms with white matter lesions at or below 25 weeks postconceptional age should be scrutinized for cortical dysplasia.

Risk of cerebral palsy in multiple pregnancies

Multiple compared with singleton gestations have a five- to tenfold increased risk of CP. The increased risk associated with MC placentation has been variously ascribed to transfer of thromboplastin or thromboemboli from the dead to the surviving fetus, exsanguination of the surviving fetus into the low pressure reservoir of the dead fetus, or hemodynamic instability with bidirectional shunting of blood between the two fetuses. An increased risk of CP in assisted reproductive technology gestations is to be expected because of the higher proportion of preterm births. The increase in risk of CP associated with monochorionic placentation will not be observed except for the minority of assisted reproductive technology gestations that undergo monozygotic splitting.

[Neurological outcome of children from twin pregnancies]

The neurological outcome is an important issue regarding twin pregnancies. In fact, twin pregnancy is clearly associated with an important neurological morbidity, roughly 4 times higher than singleton pregnancy. It is possible to distinguish some high-risk situations, making it possible to calculate more accurately the individual risk. The different aetiologies are analysed: hypotrophy, prematurity, malformations, prenatal occurrence of anoxic and ischemic lesions, and particularly the link with monochorionicity. The neurological outcome is mainly depending on hypotrophy and prematurity. However, the rate of long-term neurological complications is not different between twins and singletons after adjustment for term and birth weight. An increased risk of malformation is associated with twin pregnancies, essentially a high rate of abnormal neural tube closing (RR=2). Monochorionic pregnancies have a specific morbidity, not related to these aetiologies, with characteristic anoxic and ischemic lesions. Cerebral palsy is observed in 10-20% of the monochorionic pregnancies, vs 3.7% of the bichorionic ones. These complications are linked to the constant vascular anastomoses, between the circulations of the two monochorionic twins. When the twin-to-twin transfusion syndrome is severe, a poor neurological outcome is observed in 4 to 18% of the surviving children. However, this rate depends on studies, treatments, and methods of neurological evaluation. The laser destruction of anastomoses could decrease this morbidity. The stillbirth rate, either associated or not with twin to twin transfusion syndrome, is increased by monochorionicity. The death of one of the twins is associated with a 20% higher risk of neurological sequelae for the surviving co-twin.

Assessment of cortical maturation with prenatal MRI: part II: abnormalities of cortical maturation

The fetal cortical maturation is a long process with predefined steps. Abnormalities can occur at different stages of cortical maturation, resulting in various malformations. They can result from disturbance in cell proliferation, cell differentiation, cell migration and in organization of the cortex. Analysis of the different abnormalities of cortical maturation is given with illustrations of the principal malformations encountered in utero and accessible to MRI.

Risk of cerebral palsy in multiple pregnancies

Multiple compared with singleton gestations have a five- to tenfold increased risk of CP. The increased risk associated with MC placentation has been variously ascribed to transfer of thromboplastin or thromboemboli from the dead to the surviving fetus, exsanguination of the surviving fetus into the low pressure reservoir of the dead fetus, or hemodynamic instability with bidirectional shunting of blood between the two fetuses. An increased risk of CP in assisted reproductive technology gestations is to be expected because of the higher proportion of preterm births. The increase in risk of CP associated with monochorionic placentation will not be observed except for the minority of assisted reproductive technology gestations that undergo monozygotic splitting.

Experimental cortical dysplasia following ibotenate administration in hamsters: pathogenesis of microgyria and associated gray matter heterotopia

The study presented here investigated the pathogenetic relationship among different types of neuronal migration disorders occurring simultaneously in the brain using an experimental model induced by ibotenate in hamsters. In the cerebral cortex, abnormal neuronal arrangement was induced 1 day after ibotenate injection. This brain lesion resulted in microgyria in the rostral portion, focal subcortical heterotopia in the mid-portion, and focal subependymal heterotopia in the caudal portion in the same specimen. Vimentin-immunoreactive radial glial fibers were lacking in the area of disorganized neuronal arrangement, but were detected around the microgyria and the intermediate zone surrounding focal subcortical heterotopia. The focal subependymal heterotopia did not include radial glial elements. Glial fibrillary acidic protein (GFAP)-positive glial reaction was weak in these cortical lesions. We suggest that the occurrence of each type of migration disorder depends on the depth of the cortical lesion, that is, the production of microgyria, focal subcortical heterotopia and focal subependymal heterotopia are closely related to the lesions including the cortical plate, subplate and ventricular zone, respectively.

Fetal brain injury

Improvements in MRI techniques widen the indications for fetal brain imaging and fetal brain injury represents the third indication of fetal brain magnetic resonance imaging (MRI) after the evaluation of suspected central nervous system (CNS) malformations and ventricular dilatation. Optimal MR imaging technique is necessary in order to collect as much data as possible about the fetal brain. Diffusion images can be used routinely in addition to the standard protocol of fetal brain MRI that consists of T1 and T2 weighted images of the fetal brain. Monovoxel proton magnetic resonance spectroscopy can also be performed in utero, but this technique is still more part of research protocol than of routine clinical protocol. Fetal brain injury includes hypoxia-ischemia, congenital infections (especially toxoplasmosis and cytomegalovirus infections), brain damage due to malformation such as vascular brain malformation and heart malformation, pregnancies at risk of fetal brain damage, and even inherited metabolic diseases, especially mitochondrial diseases. MRI findings in fetal brain injury consist of acute or chronic lesions that can be seen alone or in combination. Acute response of the fetal brain is less commonly seen than the chronic response compared to the brain response encountered in the postnatal period.

Prenatal ultrasound detection of bilateral focal polymicrogyria

OBJECTIVES

Prenatal diagnosis by ultrasound of fetal polymicrogyria has been reported only once.

METHODS

We describe an additional case of polymicrogyria in a fetus from a monozygotic twin pair, probably the consequence of twin-to-twin transfusion syndrome.

RESULTS

On ultrasound, there were bilateral cortical hyperechogenic spots, and prenatal magnetic resonance imaging demonstrated the typical features of bilateral focal polymicrogyria.

CONCLUSION

Polymicrogyria can be considered in the differential diagnosis of hyperechogenic brain lesions on fetal ultrasound. We also confirm the risk of brain damage in monochorionic twins pregnancies and the likely hypoxic-ischemic etiology of polymicrogyria.

Experimentally-induced microencephaly: effects on cortical neurons

Genetic and epigenetic factors may alter the normal development of cerebral cortex, producing laminar and cellular abnormalities and heterotopiae, major causes of juvenile, drug-resistant epilepsy. Experimentally-induced migration disorders provide interesting insights in the mechanisms of the determination of neuronal phenotype and connectivity, of congenital cortical dysgenesis and the pathophysiology of associated neurological disorders, such as epilepsy. We investigated the effects of E14 administration of methylazoxymethanol acetate (MAM), which induces microencephaly by ablating dividing cells. Brains from newborn and adult rats were reacted for NADPH-d and CO histochemistry. Moreover, callosally-projecting neurons were retrogradely labeled with DiI at P9 or with BDA in adults. MAM-treated rats displayed a remarkable reduction in cortical thickness, mainly due to reduction in layer IV and in supragranular layers. Heterotopic nodules appeared in the supragranular layers and in the hippocampus. CO-positive barrels in somatosensory cortex were almost absent. The distribution of NADPH-d-positive neurons was regular, but they were rare in heterotopic nodules. Callosally-projecting neurons displayed abnormal orientation of the apical dendrite and increase in the basal dendritic length. Alterations in the dendritic arborization of pyramidal neurons may be one of the substrates for the increased sensitivity to drugs which induce epileptic seizures in these animals.

Neonatal neurologic characteristics of preterm twin infants <1,250 gm birth weight

The study objectives were to determine the incidence, time of onset, and clinical characteristics of neonatal neurologic injury in preterm twin infants <1,250 gm birth weight. Forty-one twin infants of birth weight 929 gm +/- 160 and 27.3 +/- 1.96 weeks gestation were evaluated and compared to 225 singleton infants <1,250 gm. Seventeen infants were monozygotic and 24 dizygotic. Six of the 9 monozygotic pregnancies were complicated by the polyhydramnios/oligohydramnios syndrome; a weight discordancy of >20% was observed in 8 of the monozygotic twin sets and polycythemia (hematocrit >65%) in 3 infants. Nine (22%) of the 41 infants died. Periventricular-intraventricular hemorrhage (PV-IVH) developed in 11 (27%) of 41 infants and was severe in 9 (22%) infants. IVH was noted on day 1 (n = 2), day 2 (n = 3), and day 3 (n = 6). IVH developed in 69 (30%) of the 225 singletons and was severe in 28 (12%) infants. Twin infants were more likely to have been delivered via cesarean section, to have required intubation in the delivery room, and to have been administered surfactant as compared with singletons (P < .01). It was concluded that preterm twin infants <1,250 gm are at high risk for developing severe IVH, and that the onset of IVH was within the first 3 postnatal days in all cases.

Congenital bilateral perisylvian syndrome in a monozygotic twin with intra-uterine death of the co-twin

Congenital bilateral perisylvian syndrome was diagnosed in a two-year- old boy with signs of pseudobulbar and diplegic cerebral palsy presenting on MRI a polymicrogyric appearance of the perisylvian regions. He was born from a monochorionic bi-amniotic twin pregnancy complicated by twin-twin transfusion syndrome and death of the co-twin between the 16th and 18th weeks of gestation. Ventricular enlargement and hepatic hyperechogenic lesions were seen during his sonographic intra-uterine follow-up. The authors suggest that ischaemic injury occurred in this patient as a consequence of acute haemodynamic changes induced by the death of his co-twin.