Large-scale functional network dynamics in human callosal agenesis: Increased subcortical involvement and preserved laterality

In the human brain, the corpus callosum is the major white-matter commissural tract enabling the transmission of sensory-motor, and higher level cognitive information between homotopic regions of the two cerebral hemispheres. Despite developmental absence (i.e., agenesis) of the corpus callosum (AgCC), functional connectivity is preserved, including interhemispheric connectivity. Subcortical structures have been hypothesised to provide alternative pathways to enable this preservation. To test this hypothesis, we used functional Magnetic Resonance Imaging (fMRI) recordings in children with AgCC and typically developing children, and a time-resolved approach to retrieve temporal characteristics of whole-brain functional networks. We observed an increased engagement of the cerebellum and amygdala/hippocampus networks in children with AgCC compared to typically developing children. There was little evidence that laterality of activation networks was affected in AgCC. Our findings support the hypothesis that subcortical structures play an essential role in the functional reconfiguration of the brain in the absence of a corpus callosum.

Bilateral epileptic networks in congenital and acquired corpus callosum defects: EEG-fMRI study

OBJECTIVES

Electroencephalography-correlated functional magnetic resonance imaging (EEG-fMRI) allows imaging of brain-wide epileptic networks, and demonstrates that focal interictal epileptic activity is sometimes accompanied by bilateral functional activations. The corpus callosum (CC) facilitates bilateral spread of epileptic activity and at times targeted surgically for drug-resistant epilepsy (DRE). We hypothesized that focal epileptic networks are more unilateral in patients lacking intact CC.

METHODS

We included focal DRE patients who underwent pre-surgical EEG-fMRI and had CC agenesis (group A, n = 5), patients who previously underwent anterior callosotomy as treatment for drop attacks and continued having seizures (group B, n = 6), and control group of patients with focal epilepsy and intact CC (group C, n = 9). Blood-oxygenation-level-dependent (BOLD) signal maps were generated for interictal epileptic discharges. To quantify bi-hemispheric distribution of epileptic networks, laterality indices were compared between groups. Anatomical and diffusion-weighted imaging demonstrated white matter pathways.

RESULTS

96% of studies demonstrated bilateral activations. Laterality indices were similar in groups A and C, whereas group B demonstrated a more bilateral network than group C (p = 0.028). Diffusion-weighted and anatomical imaging showed aberrant white matter pathways and larger anterior commissure in groups A and B. 68% of studies showed maximal activation cluster concordant with the presumed epileptic focus, 28% showed non-maximal activation at presumed focus.

SIGNIFICANCE

Focal epileptic activity is associated with bilateral functional activations despite lack of intact CC, and is associated with stronger contralateral activation in patients after anterior callosotomy compared to controls. These findings disprove our initial hypothesis, and combined with white matter structural imaging, may indicate that the CC is not a sole route of propagation of epileptic activity, which might spread via anterior commissure. Our study demonstrates the utility of EEG-fMRI in assessing epileptic networks and potentially aiding in tailoring surgical treatments in DRE patients with callosal anomalies, and in callosal surgeries.

A Pericallosal Lipoma Case with Abnormal Vasculature Mimicking Arteriovenous Malformation

Pericallosal lipomas (PCLs) are rare tumors of the central nervous system. They may be associated with some parenchymal and vascular anomalies of brain. Magnetic resonance imaging is the modality of choice to assess the extent of the PCLs and possible concomitant malformations such as callosal agenesis/disgenesis. Computerized tomography angiography may be indicated to evaluate the vasculature of the lesion. We report here a case of PCL with rare features including asymptomatic callosal agenesis, bilateral choroid plexus lipomas and abnormal vasculature.

The neuroimaging findings of monocarboxylate transporter 1 deficiency

Monocarboxylate transporter 1 (MCT1) deficiency was first described in 2014 by Hasselt et al. as a novel genetic cause of recurrent ketoacidosis. Patients present in the first year of life with acute episodes of ketoacidosis triggered by fasting or infections. Patients with homozygous mutations are known to have a more severe phenotype with mild to moderate developmental delay and an increased prevalence of epilepsy. There is only one recent report of the neuroimaging findings of this disorder as reported by Al-Khawaga et al. (Front Pediatr. 7:299, 2019). We report the neuroimaging abnormalities in two siblings with similar clinical presentation of recurrent ketoacidosis, seizures, and developmental delay. Whole exome sequencing in the younger sibling confirmed a known pathogenic homozygous mutation in MCT1, also known as SLC16A1 gene. Brain MRI showed a similar very distinctive pattern of signal abnormality at the gray-white matter junction, basal ganglia, and thalami in both patients. Both siblings had agenesis of the corpus callosum. Knowledge of this pattern of brain involvement might contribute to an earlier diagnosis and timely management of this rare and under recognized disorder.

Septo-optic Dysplasia : Assessment of Associated Findings with Special Attention to the Olfactory Sulci and Tracts

PURPOSE

Septo-optic dysplasia is a congenital disorder consisting of optic nerve hypoplasia and absent septum pellucidum. While associated anomalies have been described, olfactory sulcus and bulb-tract hypoplasia have been scantily reported and was the focus of this study.

METHODS

The picture archival and communications system and radiology information system (PACS-RIS) was searched over 15 years for patients with suspected septo-optic dysplasia (n = 41) and cerebral magnetic resonance imaging (MRI). Included patients had coronal (≤3 mm), axial (≤4 mm), and sagittal (≤4 mm) imaging reviewed by two staff neuroradiologists by consensus. Both olfactory sulcus and bulb-tract hypoplasia were ascribed a grade of 0 (normal) to 3 (complete hypoplasia). Other associated congenital anomalies were recorded, if present. Incidence of anomalies were compared to age-matched and gender-matched control patients.

RESULTS

Out of 41 septo-optic dysplasia patients 33 were included (mean age = 120.7 months), with 8 excluded due to isolated septum pellucidum absence (n = 5), isolated bilateral optic hypoplasia (n = 2), or inadequate imaging (n = 1). An olfactory sulcus was hypoplastic on one or both sides in 14/33 (42.4%). Olfactory bulb hypoplasia was noted in one or both tracts in 15/33 (45.4%). A significant correlation was found between degree of olfactory sulcal and bulb-tract hypoplasia (ρ = 0.528, p = 0.0009). Other anomalies were: anterior falx dysplasia (n = 16, 48.5%), incomplete hippocampal inversion (n = 14, 42.4%), polymicrogyria (n = 11, 33.3%), callosal complete or partial agenesis (n = 10, 30.3%), schizencephaly (n = 8, 24.2%), ectopic posterior pituitary (n = 6, 18.2%), and nodular heterotopia (n = 4, 12.1%). Of the age-matched control patients 10/33 (30.3%) had at least mild anterior falx hypoplasia, and 1 control patient was noted to have unilateral incomplete hippocampal inversion (IHI); none of the age-matched control patients had olfactory sulcus or bulb-tract hypoplasia.

CONCLUSION

Olfactory sulcus and bulb-tract hypoplasia are fairly common in septo-optic dysplasia and can be discordant between sides. Of the other associated anomalies, anterior falx dysplasia seems to be the most common.

Proverb comprehension in individuals with agenesis of the corpus callosum

Comprehension of non-literal language involves multiple neural systems likely involving callosal connections. We describe proverb comprehension impairments in individuals with isolated agenesis of the corpus callosum (AgCC) and normal-range general intelligence. Experiment 1 compared Gorham Proverb Test (Gorham, 1956) performance in 19 adults with AgCC and 33 neurotypical control participants of similar age, sex, and intelligence. Experiment 2 used the Proverbs subtest of the Delis-Kaplan Executive Function System (D-KEFS, 2001) to compare 19 adults with AgCC and 17 control participants with similar age, sex, and intelligence. Gorham Proverbs performance was impaired in the AgCC group for both the free-response and multiple-choice tasks. On the D-KEFS proverbs test, the AgCC group performed significantly worse on the free-response task (and all derivative scores) despite normal levels of performance on the multiple-choice task. Covarying verbal intelligence did not alter these outcomes. However, covarying a measure of non-literal language comprehension considerably reduced group differences in proverb comprehension on the Gorham test, but had little effect on the D-KEFS group differences. The difference between groups seemed to be greatest when participants had to generate their own interpretation (free response), or in the multiple choice format when the test included many proverbs that were likely to be less familiar. Taken together, the results of this study clearly show that proverb comprehension is diminished in individuals with AgCC compared to their peers.

Learning and memory in individuals with agenesis of the corpus callosum

Damage to long white matter pathways in the cerebral cortex is known to affect memory capacity. However, the specific contribution of interhemispheric connectivity in memory functioning is only beginning to become understood. The present study examined verbal and visual memory processing in individuals with agenesis of the corpus callosum (AgCC) using the Wechsler Memory Scale-Third Edition (WMS-III; Wechsler, 1997b). Thirty participants with AgCC (FSIQ >78) were compared against 30 healthy age and IQ matched controls on auditory/verbal (Logical Memory, Verbal Paired Associates) and visual (Visual Reproduction, Faces) memory subtests. Performance was worse in AgCC than controls on immediate and delayed verbal recall for rote word pairs and on delayed recall of faces, as well as on percent recall for these tasks. Immediate recall for thematic information from stories was also worse in AgCC, but groups did not differ on memory for details from narratives or on recall for thematic information following a time delay. Groups also did not differ on memory for abstract figures or immediate recall of faces. On all subtests, individuals with AgCC had greater frequency of clinically significant impairments than predicted by the normal distribution. Results suggest less efficient overall verbal and visual learning and memory with relative weaknesses processing verbal pairs and delayed recall for faces. These findings suggest that the corpus callosum facilitates more efficient learning and recall for both verbal and visual information, that individuals with AgCC may benefit from receiving verbal information within semantic context, and that known deficits in facial processing in individuals with AgCC may contribute to their impairments in recall for faces.

Language lateralization in a patient with temporal lobe epilepsy and callosal agenesis

The corpus callosum has been proposed as a mechanism of interhemispheric inhibition that allows language dominance to develop [1]. Callosal agenesis or dysgenesis provides a test of this hypothesis, as patients lacking a normal corpus callosum should also lack normal language lateralization [2]. We report pre- and postoperative functional magnetic resonance imaging (fMRI) and neuropsychological testing in a patient with partial callosal agenesis who underwent a right temporal lobectomy for medically refractory seizures.

Clinical features and associated abnormalities in children and adolescents with corpus callosal anomalies

Callosal anomalies are frequently associated with other central nervous system (CNS) and/or somatic anomalies. We retrospectively analyzed the clinical features of corpus callosal agenesis/hypoplasia accompanying other CNS and/or somatic anomalies. We reviewed the imaging and clinical information of patients who underwent brain magnetic resonance imaging in our hospital, between 2005 and 2012. Callosal anomalies were isolated in 13 patients, accompanied by other CNS anomalies in 10 patients, associated with only non-CNS somatic anomalies in four patients, and with both CNS and non-CNS abnormalities in four patients. Out of 31 patients, four developed normally, without impairments in motor or cognitive functions. Five of nine patients with cerebral palsy were accompanied by other CNS and/or somatic anomalies, and showed worse Gross Motor Function Classification System scores, compared with the other four patients with isolated callosal anomaly. In addition, patients with other CNS anomalies also had a higher seizure risk.