Divergence between functional magnetic resonance imaging and clinical indicators of language dominance in preoperative language mapping

Bilateral and asymmetrical localization of language function identified by the superselective infusion of propofol in an epilepsy patient with a mild malformation of cortical development: illustrative case

BACKGROUND

Atypical localization of language function can result in unexpected postsurgical deficits after cortical resection, but it is difficult to predict the risk in the presurgical evaluation. The authors experienced a rare case of the bilateral and independent existence of different components of language function identified by segmented evaluation of anatomical anterior and posterior language areas using the superselective infusion of propofol.

OBSERVATIONS

A 32-year-old right-handed female presented with drug-resistant epilepsy. Comprehensive epilepsy evaluation suggested that the epileptic foci involved the whole left frontal lobe but provided less evidence of structural abnormality. To estimate the extent of functional deterioration likely to be caused by an extended left frontal lobectomy, the authors evaluated segmented cortical function in the ipsi- and contralateral hemispheres by the superselective infusion of propofol into the branches of the intracranial artery. The results revealed bilateral and asymmetrical localization of language function because the patient presented with different components of aphasia in each hemisphere. Based on the authors' assessment of her functional tolerance, an extended left frontal lobectomy was performed and resulted in neurological deficits within the anticipated range.

LESSONS

An accurate understanding of the correlations between vascular and functional anatomy and the highly specific evaluation of language function provides more advanced presurgical assessment, allowing more tailored planning of cortical resection.

Surgical treatment of temporal lobe epilepsy: comparative results of selective amygdalohippocampectomy versus anterior temporal lobectomy from a referral center in Brazil

BACKGROUND

Temporal lobe epilepsy (TLE) is a high prevalence neurological disorder. Surgery has emerged as a promising treatment.

OBJECTIVE

The objective of this work is to compare the surgical results of anterior temporal lobectomy (ATL) versus selective amygdalohippocampectomy (SAH) in a cohort of 132 patients.

METHODS

We performed a retrospective study of 146 patients operated for TLE from 2008 to 2019. Initially, 13 patients were excluded from the study due to insufficient medical record data or follow-up loss. One patient was excluded from the analysis of the results due to death in the first postoperative week. We used the ILAE scale to classify seizure control after surgery. In patients with left hippocampal sclerosis, SAH was performed and in right temporal lobe epilepsy, ATL was the approach of choice.

RESULTS

The mean follow-up time after surgery was 57.2 months (12-137). In our data analysis, we found that the group of patients undergoing ATL had a higher prevalence of being completely seizure-free (ILAE I) (57.1% versus 31%) and a higher rate of satisfactory seizure control (88.6% versus 69.3%) p = 0,006, when compared with patients undergoing SAH.

CONCLUSION

The literature is still controversial about seizure control concerning the technique used due to the lack of a robust methodology. Our data analysis identified the superiority of ATL over SAH in seizure outcomes. ATL may be the best option for adequately controlling seizures with minimal additional morbidity in countries with a cost limitation for extended propaedeutics.

Concordance of Lateralization Index for Brain Asymmetry Applied to Identify a Reliable Language Task

How can we determine which language task is relevant for examining functional hemispheric asymmetry? A problem in measuring brain asymmetry using functional magnetic resonance imaging lies in the uncertain reliability of the computed index regarding the “true” asymmetry degree. Strictly speaking, the results from the Wada test or direct cortical stimulation cannot be an exact “ground truth”, specifically for the degree of asymmetry. Therefore, we developed a method to evaluate task performance using reproducibility independent of the phenomenon of functional lateralization. Kendall’s coefficient of concordance (W) was used as the statistical measure. The underlying idea was that although various algorithms to compute the lateralization index show considerably different index values for the same data, a superior language task would reproduce similar individual ranking sequences across the algorithms; the high reproducibility of rankings across various index types would indicate a reliable task to investigate functional asymmetry regardless of index computation algorithms. Consequently, we found specificity for brain locations; a verb-generation task demonstrated the highest concordance across index types along with sufficiently high index values in the inferior frontal gyrus, whereas a narration–listening task demonstrated the highest concordance in the posterior temporo-parietal junction area.

Roles of fMRI and Wada tests in the presurgical evaluation of language functions in temporal lobe epilepsy

Surgical treatment of pharmacoresistant temporal lobe epilepsy (TLE) carries risks for language function that can significantly affect the quality of life. Predicting the risks of decline in language functions before surgery is, consequently, just as important as predicting the chances of becoming seizure-free. The intracarotid amobarbital test, generally known as the Wada test (WT), has been traditionally used to determine language lateralization and to estimate their potential decline after surgery. However, the test is invasive and it does not localize the language functions. Therefore, other noninvasive methods have been proposed, of which functional magnetic resonance (fMRI) has the greatest potential. Functional MRI allows localization of language areas. It has good concordance with the WT for language lateralization, and it is of predictive value for postsurgical naming outcomes. Consequently, fMRI has progressively replaced WT for presurgical language evaluation. The objective of this manuscript is to review the most relevant aspects of language functions in TLE and the current role of fMRI and WT in the presurgical evaluation of language. First, we will provide context by revising the language network distribution and the effects of TLE on them. Then, we will assess the functional outcomes following various forms of TLE surgery and measures to reduce postoperative language decline. Finally, we will discuss the current indications for WT and fMRI and the potential usefulness of the resting-state fMRI technique.

HomotopicLI: Rationale, characteristics, and implications of a new threshold-free lateralization index of functional magnetic resonance imaging

The reliable preoperative estimation of brain hemispheric asymmetry may be achieved through multiple lateralization indices using functional magnetic resonance imaging. Adding to our previously developed AveLI, we devised a novel threshold-free lateralization index, HomotopicLI, which computes a basic formula, (Left - Right) / (Left + Right), using voxel values of pairs located symmetrically in relation to the midsagittal line as the terms Left and Right, and averages them within the regions-of-interest. The study aimed to evaluate HomotopicLI before clinical applications. Data were collected from 56 healthy participants who performed four language tasks. We compared seven index types, including HomotopicLI, AveLI, and BaseLI; BaseLI was calculated using the sums of voxel values as the terms. Contrary to our expectations, HomotopicLI performed similarly to AveLI but better than BaseLI in detecting right dominance. A detailed analysis of unilaterally activated voxels of the homotopic pairs revealed that unilateral activation occurred more frequently on the right than on the left when HomotopicLI indicated right dominance. The voxel values during right unilateral activation were smaller than those in the left, causing right dominances in the homotopic pairs by HomotopicLI. These unique features provide an advantage in detecting residual, compensative functions spreading weakly in the non-dominant hemisphere.

Current and Future Challenges of Functional MRI and Diffusion Tractography in the Surgical Setting: From Eloquent Brain Mapping to Neural Plasticity

Decades ago, Spetzler (1986) and Sawaya (1998) provided a rough brain segmentation of the eloquent areas of the brain, aimed to help surgical decisions in cases of vascular malformations and tumors, respectively. Currently in clinical use, their criteria are in need of revision. Defining functions (eg, sensorimotor, language and visual) that should be preserved during surgery seems a straightforward task. In practice, locating the specific areas that could cause a permanent vs transient deficit is not an easy task. This is particularly true for the associative cortex and cognitive domains such as language. The old model, with Broca's and Wernicke's areas at the forefront, has been superseded by a dual-stream model of parallel language processing; named ventral and dorsal pathways. This complicated network of cortical hubs and subcortical white matter pathways needing preservation during surgery is a work in progress. Preserving not only cortical regions but most importantly preserving the connections, or white matter fiber bundles, of core regions in the brain is the new paradigm. For instance, the arcuate fascicululs and inferior fronto-occipital fasciculus are key components of the dorsal and ventral language pathways, respectively; and their damage result in permanent language deficits. Interestedly, the damage of the temporal portions of these bundles -where there is a crossroad with other multiple bundles-, appears to be more important (permanent) than the damage of the frontal portions - where plasticity and contralateral activation could help. Although intraoperative direct cortical and subcortical stimulation have contributed largely, advanced MR techniques such as functional MRI (fMRI) and diffusion tractography (DT), are at the epi-center of our current understanding. Nevertheless, these techniques posse important challenges: such as neurovascular uncoupling or venous bias on fMRI; and appropriate anatomical validation or accurate representation of crossing fibers on DT. These limitations should be well understood and taken into account in clinical practice. Unifying multidisciplinary research and clinical efforts is desirable, so these techniques could contribute more efficiently not only to locate eloquent areas but to improve outcomes and our understanding of neural plasticity. Finally, although there are constant anatomical and functional regions at the individual level, there is a known variability at the inter-individual level. This concept should strengthen the importance of a personalized approach when evaluating these regions on fMRI and DT. It should strengthen the importance of personalized treatments as well, aimed to meet tailored needs and expectations.

Divergence between functional magnetic resonance imaging and clinical indicators of language dominance in preoperative language mapping

Accurate determination of hemispheric language dominance prior to epilepsy surgery is critically important to minimize cognitive morbidity. Functional MRI (fMRI) is a noninvasive method that is highly concordant with other clinical indicators of language laterality, and is now commonly used to confirm language dominance. However, there is also a high frequency of divergence between fMRI findings and other clinical indices that complicate determination of dominance and surgical decision-making in individual patients. Despite this, divergent cases are rarely published or discussed. This article provides three illustrative examples to demonstrate common scenarios where fMRI may produce conflicting or otherwise difficult-to-interpret findings. We will also discuss potential reasons for divergence and propose a flow-chart to aid clinical decision making in such situations.