Magnetic resonance imaging of the brain in Aicardi's syndrome. Report of 20 patients

Brain plasticity following corpus callosum agenesis or loss: a review of the Probst bundles

The corpus callosum is the largest axonal tract in the human brain, connecting the left and right cortical hemipheres. This structure is affected in myriad human neurodevelopmental disorders, and can be entirely absent as a result of congenital or surgical causes. The age when callosal loss occurs, for example via surgical section in cases of refractory epilepsy, correlates with resulting brain morphology and neuropsychological outcomes, whereby an earlier loss generally produces relatively improved interhemispheric connectivity compared to a loss in adulthood (known as the "Sperry's paradox"). However, the mechanisms behind these age-dependent differences remain unclear. Perhaps the best documented and most striking of the plastic changes that occur due to developmental, but not adult, callosal loss is the formation of large, bilateral, longitudinal ectopic tracts termed Probst bundles. Despite over 100 years of research into these ectopic tracts, which are the largest and best described stereotypical ectopic brain tracts in humans, much remains unclear about them. Here, we review the anatomy of the Probst bundles, along with evidence for their faciliatory or detrimental function, the required conditions for their formation, patterns of etiology, and mechanisms of development. We provide hypotheses for many of the remaining mysteries of the Probst bundles, including their possible relationship to preserved interhemispheric communication following corpus callosum absence. Future research into naturally occurring plastic tracts such as Probst bundles will help to inform the general rules governing axon plasticity and disorders of brain miswiring.

Prenatal diagnosis of Aicardi syndrome based on a suggestive imaging pattern: A multicenter case-series

Objectives

To characterize a suggestive prenatal imaging pattern of Aicardi syndrome using ultrasound and MR imaging.

Methods

Based on a retrospective international series of Aicardi syndrome cases from tertiary centers encountered over a 20‐year period (2000–2020), we investigated the frequencies of the imaging features in order to characterize an imaging pattern highly suggestive of the diagnosis.

Results

Among 20 cases included, arachnoid cysts associated with a distortion of the interhemispheric fissure were constantly encountered associated with complete or partial agenesis of the corpus callosum (19/20, 95%). This triad in the presence of other CNS disorganization, such as polymicrogyria (16/17, 94%), heterotopias (15/17, 88%), ventriculomegaly (14/20, 70%), cerebral asymmetry [14/20, 70%]) and less frequently extra‐CNS anomaly (ocular anomalies [7/11, 64%], costal/vertebral segmentation defect [4/20, 20%]) represent a highly suggestive pattern of Aicardi syndrome in a female patient.

Conclusion

Despite absence of genetic test to confirm prenatal diagnosis of AS, this combination of CNS and extra‐CNS fetal findings allows delineation of a characteristic imaging pattern of AS, especially when facing dysgenesis of the corpus callosum.

What is already known about this topic?

Aicardi syndrome (AS) is a rare developmental encephalopathy, characterized by the classic triad of infantile spasms, agenesis of the corpus callosum, and chorioretinal lacunae

As the genetic etiology of AS is unknown and its classic triad cannot be extrapolated to prenatal diagnosis, to establish a prenatal imaging pattern is of major interest

What does this study add?

We confirmed and completed a prenatal imaging pattern highly suggestive of AS, based on the most frequent features encountered in a large series: arachnoid cysts associated with a distortion of the interhemispheric fissure, agenesis of the corpus callosum, cortical malformations and heterotopias, and less frequently extra‐CNS anomaly (ocular anomalies, costal/vertebral segmentation defect)

Palliative epilepsy surgery in Aicardi syndrome: a case series and review of literature

PURPOSE

Aicardi syndrome (AS) is a severe neurodevelopmental disorder characterized by the triad of seizures, agenesis of corpus callosum, and chorioretinal lacunae. Seizures in AS are typically frequent, of various types, and refractory to medical therapy. Optimal treatment of seizures in AS remains undetermined.

METHODS

We report a series of four patients with Aicardi syndrome who underwent surgical management of their epilepsy including two with corpus callosotomy (CC) of a partial corpus callosum and three with vagus nerve stimulator implantation.

RESULTS

Seizure outcome was variable and ranged from near complete resolution of seizures to worsening of seizure profile. The most favorable seizure outcome was seen in a patient with partial agenesis of the corpus callosum treated with CC.

CONCLUSIONS

Seizure outcome following CC or vagus nerve stimulation in patients with Aicardi syndrome is variable. Although palliative epilepsy surgery may result in improvement in the seizure profile in some patients, studies on larger patient cohorts are needed to identify the precise role that surgery may play in the multidisciplinary approach to controlling seizures in Aicardi syndrome.

Bilateral subcortical heterotopia with partial callosal agenesis in a mouse mutant

Cognition and behavior depend on the precise placement and interconnection of complex ensembles of neurons in cerebral cortex. Mutations that disrupt migration of immature neurons from the ventricular zone to the cortical plate have provided major insight into mechanisms of brain development and disease. We have discovered a new and highly penetrant spontaneous mutation that leads to large nodular bilateral subcortical heterotopias with partial callosal agenesis. The mutant phenotype was first detected in a colony of fully inbred BXD29 mice already known to harbor a mutation in Tlr4. Neurons confined to the heterotopias are mainly born in midgestation to late gestation and would normally have migrated into layers 2-4 of overlying neocortex. Callosal cross-sectional area and fiber number are reduced up to 50% compared with coisogenic wildtype BXD29 substrain controls. Mutants have a pronounced and highly selective defect in rapid auditory processing. The segregation pattern of the mutant phenotype is most consistent with a two-locus autosomal recessive model, and selective genotyping definitively rules out the Tlr4 mutation as a cause. The discovery of a novel mutation with strong pleiotropic anatomical and behavioral effects provides an important new resource for dissecting molecular mechanisms and functional consequences of errors of neuronal migration.

Laterality of brain and ocular lesions in Aicardi syndrome

This study reports a large case series of children with Aicardi syndrome. A new severity scoring system is established to assess sidedness of ocular and brain lesions. Thirty-five children were recruited from Aicardi syndrome family conferences. All children received dilated ophthalmologic examinations, and brain magnetic resonance images (MRIs) were reviewed. Ocular and brain MRI Aicardi lesion severity scores were devised. A linear mixed model was used to compare each side for the ocular and brain MRI severity scores of Aicardi-associated disease. Twenty-six children met the inclusion criteria for the study. All subjects were female, ages 3 months to 19 years. Rates per child of optic nerve coloboma, severe lacunae, and microphthalmos in one or both eyes (among those with complete fundus examinations available) were 10/24 (42%), 8/22 (36%), and 7/26 (27%), respectively. Ocular and brain MRI asymmetry was found in 18% (4/22) and 58% (15/26) of subjects, respectively, with more right-sided brain lesions than left-sided ones (V = 52, P = 0.028). A significant correlation between sidedness of brain disease and microphthalmos was noted (T = 2.54, P = 0.02). This study substantiates the range and severity of Aicardi syndrome-associated ophthalmologic and brain MRI lesions from prior smaller case series.

Non-random X chromosome inactivation in Aicardi syndrome

Most females have random X-chromosome inactivation (XCI), defined as an equal likelihood for inactivation of the maternally- or paternally-derived X chromosome in each cell. Several X-linked disorders have been associated with a higher prevalence of non-random XCI patterns, but previous studies on XCI patterns in Aicardi syndrome were limited by small numbers and older methodologies, and have yielded conflicting results. We studied XCI patterns in DNA extracted from peripheral blood leukocytes of 35 girls with typical Aicardi syndrome (AIC) from 0.25 to 16.42 years of age, using the human androgen receptor assay. Data on 33 informative samples showed non-random XCI in 11 (33%), defined as a >80:20% skewed ratio of one versus the other X chromosome being active. In six (18%) of these, there was a >95:5% extremely skewed ratio of one versus the other X chromosome being active. XCI patterns on maternal samples were not excessively skewed. The prevalence of non-random XCI in Aicardi syndrome is significantly different from that in the general population (p < 0.0001) and provides additional support for the hypothesis that Aicardi syndrome is an X-linked disorder. We also investigated the correlation between X-inactivation patterns and clinical severity and found that non-random XCI is associated with a high neurological composite severity score. Conversely, a statistically significant association was found between random XCI and the skeletal composite score. Correlations between X-inactivation patterns and individual features were made and we found a significant association between vertebral anomalies and random XCI.

Cerebellar migration defects in aicardi syndrome: an extension of the neuropathological spectrum

The Aicardi syndrome is characterized by infantile spasms, corpus callosum agenesis, and chorioretinal lacunae and almost exclusively affects females (very rarely, 47, XXY males). The crucial genetic mishap likely occurs in the postzygotic stage, but the variable clinical phenotype among the approximately 450 known cases has not been explained. No consistent mutations or deletions exist among patients. We encountered a baby girl with early onset infantile spasms. She had left-sided cleft lip/palate, costovertebral defects, scoliosis, callosal agenesis, and microphthalmia. She expired at the age of 3 months of respiratory infection. On autopsy she had thoracic hemivertebrae with rib defects, bilateral microphthalmia, microcornea, posterior colobomata, abnormalities of the retinal pigment epithelium, absence of normal ganglion cells in the retina, gross asymmetry of the brain with cerebral polymicrogyria, total callosal agenesis, cerebral subcortical and subependymal nodular heterotopias, cerebellar nodular heterotopias, and tegmental/basal unilateral brainstem hypoplasia. Cerebellar and retinal migration defects have not been described before in Aicardi syndrome and may have had a bearing on this patient's eventual outcome.

Neuroimaging aspects of Aicardi syndrome

Aicardi syndrome is a rare neurodevelopmental disorder characterized by congenital chorioretinal lacunae, corpus callosum dysgenesis, seizures, polymicrogyria, cerebral heterotopias, intracranial cysts, and costovertebral defects. Cerebellar abnormalities have been described occasionally. Aicardi syndrome is sporadic and has been observed only in females and 47,XXY males. Therefore, it is thought to result from a mutation in an X-linked gene. Improved definition of the clinical phenotype should focus the selection of functional candidate genes for mutation analysis. Because central nervous system abnormalities are the most prominent component of the phenotype, we performed a detailed characterization of abnormalities identified on magnetic resonance neuroimaging studies from 23 girls with Aicardi syndrome, the largest cohort to undergo such review by a single group of investigators. All patients had polymicrogyria that was predominantly frontal and perisylvian and often associated with underopercularization. Periventricular nodular heterotopias, present in all patients, were more frequent than previously reported; 10 had single and 11 had multiple intracranial cysts. Posterior fossa abnormalities were also more frequent than previously described. Cerebellar abnormalities were noted in 95% of studies where they could be evaluated. As a novel finding, we noted tectal enlargement in 10 patients. Since mildly affected girls with variable callosal dysgenesis have now been reported, the constellation of frontal-dominant and perisylvian polymicrogyria, periventricular nodular heterotopias, intracranial cysts, and posterior fossa abnormalities, including tectal enlargement, should prompt consideration of the diagnosis of Aicardi syndrome. We further propose that improved characterization of the neurological phenotype will benefit the selection of candidate genes for mutation analysis.

Phenotype and management of Aicardi syndrome: new findings from a survey of 69 children

Aicardi syndrome is a rare neurodevelopmental disorder characterized by agenesis of the corpus callosum, other developmental brain abnormalities, chorioretinal lacunae, and severe seizures. Current clinical knowledge is derived from small series that focus on these major defects. The authors performed a health survey on a large number of affected children to expand this knowledge and to uncover previously unrecognized features of Aicardi syndrome. Responses received from caregivers of 69 children with Aicardi syndrome met inclusion criteria for data analysis. Ages ranged from 5 months to 32 years (mean, 88 months). All subjects were girls, except for 1 boy with a 47,XXY karyotype. The authors found that the growth rate in Aicardi syndrome slows at age 10 years to below the 5th percentile and that weight gain slows at age 7 years to below the 25th percentile. The median age of survival was estimated at 18.5 (+/-4) years, more favorable than previously reported. The most common complication aside from seizures was gastrointestinal dysfunction, present in >90%. The results from this survey contribute new information on Aicardi syndrome that will benefit clinical management, and collected data will benefit phenotype-driven research toward its underlying cause.

Anomalies of the Corpus Callosum: An MR Analysis of the Phenotypic Spectrum of Associated Malformations

OBJECTIVE

We sought to categorize the structural brain anomalies associated with abnormalities of the corpus callosum and anterior and hippocampal commissures in a large cohort.

MATERIALS AND METHODS

Brain MR images of adult and pediatric patients from our institution and from a national support organization (the ACC Network) were retrospectively evaluated for the type and severity of commissural anomalies and the presence and type of other structural abnormalities.

RESULTS

Of 142 cases that were reviewed, 82 patients had agenesis of the corpus callosum (ACC), while 60 had hypogenesis of the corpus callosum (HCC). Of the overall cohort, almost all had reduced white matter volume outside the commissures, the majority had malformations of cortical development (most commonly heterotopia or abnormal sulcation), many had noncallosal midline anomalies (including abnormal anterior or hippocampal commissures and interhemispheric cysts and lipomas), and several patients had abnormalities of the cerebellum or brainstem. Sixty-six patients had Probst bundles, which were more common in patients with ACC than in those with HCC. Probst bundles were present in all four patients who had ACC or HCC but no other midline, cortical, or posterior fossa anomalies.

CONCLUSION

Isolated commissural anomalies were rare in the populations of patients examined. Most cases of ACC and HCC were associated with complex telencephalic, diencephalic, or rhombencephalic malformations. Reduced cerebral hemispheric white matter volume and malformations of cortical development were seen in more than half of the patients, suggesting that many commissural anomalies are part of an overall cerebral dysgenesis. ACC and HCC appear to lie along a dysgenetic spectrum, as opposed to representing distinct disorders.

Callosal anomalies with interhemispheric cyst: expanding the phenotype

AIM

To determine the frequency and clinical features of corpus callosum hypoagenesis, dysgenesis or hypoplasia in conjunction with extraparenchymal interhemispheric cyst.

METHODS

A retrospective study of clinical files and imaging records of all 2500 children referred to the University Department of Paediatrics, Catania, Italy, who underwent neuroimaging by ultrasound, computerized tomography or magnetic resonance imaging in 1992-2003. Five children (all girls, aged 2-18 y) were found to have abnormalities of the corpus callosum associated with interhemispheric cyst.

RESULTS

Three cases were type 2b, one type 2c and one mixed type 2b and 2c according to the classification proposed by Barkovich et al. The onset of clinical symptoms was very early, with severe neurological involvement, seizures that were difficult to treat and profound psychomotor retardation.

CONCLUSIONS

In callosal anomalies with cysts, a prevalence in females is not confined to type 2b cysts, the spectrum of abnormalities of the corpus callosum is more varied than previously recorded, and the natural history and outcome of the condition are poor with profound developmental delay and drug-resistant seizures. The finding that all the cases were of type 2 suggests that the overall phenotype is more widespread than previously thought and may present in association with other complex syndromes.

Neuroimaging in disorders of cortical development

Malformations of cortical development are important causes of developmental delay and epilepsy. They are classified by the presumed stage during which normal development is interrupted: neuronal proliferation and differentiation, neuronal migration, and late migration/cortical organization. This article discusses the important malformations in each of these groups, how and why the malformations develop, and their imaging findings. A better understanding of these disorders helps in genetic counseling of the parents and may help in the treatment of associated epilepsy.

An atypical case of Aicardi syndrome with favorable outcome

Aicardi syndrome is a severe congenital disorder characterized by infantile spasms, chorioretinal lacunae, and agenesis or hypogenesis of the corpus callosum. A 6 month old female had developed abnormal eye movement and seizures of the complex partial type and myoclonic type. MRI pictures of the patient revealed the presence of genu associated with agenesis of the rest of corpus callosum. A funduscopic examination revealed bilateral small, solitary, pale areas with sharp borders, some of which had minimal surrounding pigmentation (chorioretinal lacunae), especially clustered around the disc, and they were more prominent on the left side. We report here on the unusual findings of a complex partial seizure, myoclonic seizure and the atypical EEG finding in addition to the well-known characteristic clinical and imaging findings of a patient with Aicardi syndrome.

Malformations of cortical development

Malformations of cortical development are an important cause of developmental delay and epilepsy. Proper identification of these malformations can greatly help in accurately counseling affected families and, in some cases, in the treatment of the epilepsy. Modem neuroimaging is an important tool in the diagnosis of these malformations.

Persistance et hyperplasie du vitré primitif et syndrome d’Aicardi

INTRODUCTION

Aicardi syndrome is characterized by infantile spasms, agenesis of the corpus callosum and chorioretinal lacunae. This disorder affects mostly females, with early embryonic lethality in males. Numerous general and ocular disorders may be associated with this affection. We present here a case of persistent hyperplastic primary vitreous (PHPV) in association with Aicardi syndrome in a 30-year-old woman.

CASE REPORT

The authors report a case of a 30-year-old woman with Aicardi syndrome associated with persistent hyperplastic primary vitreous.

DISCUSSION

Aicardi syndrome is a polymalformative disease occurring at an early period of embryogenesis. It can affect many ocular structures. This syndrome is essentially described in female children, who rarely reach an adult age. The observation we report is particular because of the patient's age (30-years-old) and the association with a persistent hyperplastic primary vitreous, exceptional in this context.

CONCLUSION

With a review of the literature, the Authors discuss the clinical neuroradiological and prognostic aspects of this polymalformative syndrome and different associated general and ocular abnormalities, emphasizing particularly those of persistent hyperplastic primary vitreous in this affection.

Aicardi syndrome: spectrum of disease and long-term prognosis in 77 females

Aicardi syndrome is an X-linked-dominant condition characterized by infantile spasms, agenesis of the corpus callosum, and chorioretinal lacunae. We reviewed the Aicardi Syndrome Foundation's compilation of family-based, self-reported questionnaires for the year 2000. Information was obtained from 77 females with Aicardi syndrome regarding developmental milestones, seizure frequency, seizure classification, antiepileptic drug use, and medical problems. Patient ages ranged from 1 to 25 years (mean = 7.2 years). All patients were significantly developmentally delayed with milestones ranging from 2 to 36 months. Of the patients, 91% attained milestones no higher than 12 months. Seizures were reported in 92% of patients and occurred daily in 67%. Infantile spasms were the most common seizure type observed in 17%, although a variety of other seizure types were also reported. Multiple antiepileptic drugs were used in these patients with 73% of patients taking two or more antiepileptic drugs. Five patients had a vagal nerve stimulator implanted, and one patient underwent a hemispherectomy. The most common medical problems cited included scoliosis, constipation, gastroesophageal reflux, aspiration pneumonia, and otitis media, but overall health was perceived to be good. Our review demonstrates the spectrum of developmental disabilities, epilepsy severity, and prognosis in a large group of Aicardi patients.