Atypical propositional language organization in prenatal and early-acquired temporal lobe lesions

Impact of development and recent-onset epilepsy on language dominance

OBJECTIVE

Reorganization of the language network from typically left-lateralized frontotemporal regions to bilaterally distributed or right-lateralized networks occurs in anywhere from 25%-30% of patients with focal epilepsy. In patients who have been recently diagnosed with epilepsy, an important question remains as to whether it is the presence of seizures or the underlying epilepsy etiology that leads to atypical language representations. This question becomes even more interesting in pediatric samples, where the typical developmental processes of the language network may confer more variability and plasticity in the language network. We assessed a carefully selected cohort of children with recent-onset epilepsy to examine whether it is the effects of seizures or their underlying cause that leads to atypical language lateralization.

METHODS

We used functional magnetic resonance imaging (fMRI) to compare language laterality in children with recently diagnosed focal unaware epilepsy and age-matched controls. Age at epilepsy onset (age 4 to 6 years vs age 7 to 12 years) was also examined to determine if age at onset influenced laterality.

RESULTS

The majority of recent-onset patients and controls exhibited left-lateralized language. There was a significant interaction such that the relationship between epilepsy duration and laterality differed by age at onset. In children with onset after age 6, a longer duration of epilepsy was associated with less left-lateralized language dominance. In contrast, in children with onset between 4 and 6 years of age, a longer duration of epilepsy was not associated with less left language dominance.

SIGNIFICANCE

Our results demonstrate that although language remained largely left-lateralized in children recently diagnosed with epilepsy, the impact of seizure duration depended on age at onset, indicating that the timing of developmental and disease factors are important in determining language dominance.

Temporal Artery and Temporal Region Supplied by the Middle Cerebral Artery: An Anatomical Study

ABSTRACT

This study was conducted to describe in detail the branching patterns of cortical branches from the middle cerebral artery supplying the feeding of the temporal region, to define the arterial structure of temporal artery (TA) and to determine the effect of this arterial supply to the temporal region. The arteries of brains (n = 22; 44 hemispheres) were prepared for dissection after filling them with colored latex. TA was defined, and its classification was described, specifying its relationship with other cortical branches. A new classification was defined related to TA terminology. TA was found in 95% of cadavers, and it originated as an early branch in 75% and from the inferior trunk in 24% of cadavers. TA was classified as Type 0: No TA, Type I: single branch providing two cortical branches, Type II: single branch providing three or more cortical branches and Type III: double TA. Type I-TA (45%) was the most common, and Type II-TA arterial diameter was significantly larger than that of other types. All cadavers showed the cortical branches of temporal region from middle cerebral artery, anterior TA , middle TA, posterior TA and temporooccipital artery, except temporopolar artery (81%). Temporopolar artery, anterior TA, and middle TA primarily originated from TA, an early branch, but posterior TA and temporooccipital artery primarily originated from the inferior trunk. Detailed knowledge about cortical branches together with TA and also this region's blood supply would enable increased prediction of complications, especially in cases with these region-related pathologies, and would make interventions safer.

Lesion characteristics driving right-hemispheric language reorganization in congenital left-hemispheric brain damage

Pre- or perinatally acquired ("congenital") left-hemispheric brain lesions can be compensated for by reorganizing language into homotopic brain regions in the right hemisphere. Language comprehension may be hemispherically dissociated from language production. We investigated the lesion characteristics driving inter-hemispheric reorganization of language comprehension and language production in 19 patients (7-32years; eight females) with congenital left-hemispheric brain lesions (periventricular lesions [n=11] and middle cerebral artery infarctions [n=8]) by fMRI. 16/17 patients demonstrated reorganized language production, while 7/19 patients had reorganized language comprehension. Lesions to the insular cortex and the temporo-parietal junction (predominantly supramarginal gyrus) were significantly more common in patients in whom both, language production and comprehension were reorganized. These areas belong to the dorsal stream of the language network, participating in the auditory-motor integration of language. Our data suggest that the integrity of this stream might be crucial for a normal left-lateralized language development.

Predictors of language skills in the long term after pediatric epilepsy surgery

OBJECTIVE

The objective of this study was to evaluate language skills in a heterogeneous cohort of patients who underwent or were considered for epilepsy surgery in childhood 4-11years earlier. The few existing studies that have evaluated cognitive function in the long term after surgery have examined intelligence and memory.

METHOD

Participants were 97 patients, of whom 61 underwent surgery. They completed standardized tests of picture naming, vocabulary, letter fluency, semantic fluency and intelligence at baseline and, on average, 7years later.

RESULTS

Among all patient groups, scores across language tasks were similar at baseline and follow-up. Language skills were largely independent of surgical status but were associated with seizure control. Seizure freedom and/or a longer proportion of life without seizures were associated with higher scores across all language tasks at follow-up. However, few patients showed meaningful improvements or deterioration at the individual level. Older age at epilepsy onset, higher IQ, and higher baseline scores were associated with higher follow-up scores on all language tasks. Localization and lateralization of epileptogenic foci and language lateralization were associated with higher scores on some language tasks at follow-up. Most of these variables were also predictive of change in scores over time on some of the language tasks.

SIGNIFICANCE

Language skills largely remained similar at baseline and follow-up. Seizure freedom was associated with a modest advantage at the group level, and no significant change at the individual level, suggesting an abnormal neural substrate or epileptic activity prior to seizure control may hinder the long-term capacity for improvement, even in the absence of seizure activity.

Atypical language representation in children with intractable temporal lobe epilepsy

This study evaluated language organization in children with intractable epilepsy caused by temporal lobe focal cortical dysplasia (FCD) alone or dual pathology (temporal lobe FCD and hippocampal sclerosis, HS). We analyzed clinical, neurological, fMRI, neuropsychological, and histopathologic data in 46 pediatric patients with temporal lobe lesions who underwent excisional epilepsy surgery. The frequency of atypical language representation was similar in both groups, but children with dual pathology were more likely to be left-handed. Atypical receptive language cortex correlated with lower intellectual capacity, verbal abstract conceptualization, receptive language abilities, verbal working memory, and a history of status epilepticus but did not correlate with higher seizure frequency or early seizure onset. Histopathologic substrate had only a minor influence on neuropsychological status. Greater verbal comprehension deficits were noted in children with atypical receptive language representation, a risk factor for cognitive morbidity.

Role of the Wada test and functional magnetic resonance imaging in preoperative mapping of language and memory: two atypical cases

The Wada test is an invasive procedure used to determine cerebral memory and language dominance as well as risk of cognitive deficits following neurosurgery. However, the potential risks of Wada testing have led some to consider foregoing Wada testing in candidates for resective epilepsy surgery with right hemispheric seizure onset. We present two atypical cases in which the Wada test showed unexpected memory and language lateralization. These cases underscore the importance of functional magnetic resonance in which imaging and Wada examination in right-handed individuals even when the lesion would not suggest atypical language representation.

Language dominance in children with epilepsy: concordance of fMRI with intracarotid amytal testing and cortical stimulation

Accurate localization of language function is critical in children undergoing epilepsy surgery. Functional magnetic resonance imaging (fMRI) is a noninvasive mapping method that has begun to replace electrocortical stimulation mapping (ESM) and the intracarotid amytal test (IAT). We used both quantitative and qualitative methods to evaluate the concordance of fMRI with ESM and IAT in 20 children using a panel of language tasks. In no cases did fMRI assessment of language hemisphere dominance identify the opposite hemisphere from assessment by IAT or ESM. Concordance with IAT and ESM was higher using fMRI visual inspection than an fMRI laterality index, which failed to lateralize language in a number of the subjects. We have demonstrated that fMRI has good concordance with more traditional methods of language mapping. When fMRI demonstrates bilateral language activations, however, we continue to recommend confirmatory testing by either IAT or ESM prior to resection in classic language regions.

Asymmetry of planum temporale constrains interhemispheric language plasticity in children with focal epilepsy

Reorganization of eloquent cortex enables rescue of language functions in patients who sustain brain injury. Individuals with left-sided, early-onset focal epilepsy often show atypical (i.e. bilateral or right-sided) language dominance. Surprisingly, many patients fail to show such interhemispheric shift of language despite having major epileptogenic lesions in close proximity to eloquent cortex. Although a number of epilepsy-related factors may promote interhemispheric plasticity, it has remained unexplored if neuroanatomical asymmetries linked to human language dominance modify the likelihood of atypical lateralization. Here we examined the asymmetry of the planum temporale, one of the most striking asymmetries in the human brain, in relation to language lateralization in children with left-sided focal epilepsy. Language functional magnetic resonance imaging was performed in 51 children with focal epilepsy and left-sided lesions and 36 healthy control subjects. We examined the association of language laterality with a range of potential clinical predictors and the asymmetry of the length of the planum temporale. Using voxel-based methods, we sought to determine the effect of lesion location (in the affected left hemisphere) and grey matter density (in the unaffected right hemisphere) on language laterality. Atypical language lateralization was observed in 19 patients (38%) and in four controls (11%). Language laterality was increasingly right-sided in patients who showed atypical handedness, a left perisylvian ictal electroencephalographic focus, and a lesion in left anterior superior temporal or inferior frontal regions. Most striking was the relationship between rightward asymmetry of the planum temporale and atypical language (R = 0.70, P < 0.0001); patients with a longer planum temporale in the right (unaffected) hemisphere were more likely to have atypical language dominance. Voxel-based regression analysis confirmed that increased grey matter density in the right temporo-parietal junction was correlated with right hemisphere lateralization of language. The length of the planum temporale in the right hemisphere was the main predictor of language lateralization in the epilepsy group, accounting for 48% of variance, with handedness accounting for only a further 5%. There was no correlation between language lateralization and planum temporale asymmetry in the control group. We conclude that asymmetry of the planum temporale may be unrelated to language lateralization in healthy individuals, but the size of the right, contra-lesional planum temporale region may reflect a ‘reserve capacity’ for interhemispheric language reorganization in the presence of a seizure focus and lesions within left perisylvian regions.