Multimodal Assessment Reveals Late-Onset Hemispheric Shift of Language in a Child with Meningocerebral Dysplasia^[*]

The ultimate goal of epilepsy surgery is to achieve long-term seizure freedom without giving rise to postsurgical functional deficits. For this purpose, the meticulous presurgical delineation of the epileptogenic zone is coupled with rigorous efforts to identify and preserve adjacent eloquent cortical areas. This involves the demarcation of normal as well as aberrant cortical networks implicated in the key domains of language and motor functions. The understanding of their organization plays a crucial role in presurgical counseling as well as in postsurgical rehabilitation.

Although the vast majority of healthy individuals are left hemisphere dominant for language, atypical representation may be encountered as a result of early acquired left hemispheric lesions.[1] Atypical, that is, right-sided or bilateral, language representation is overall more frequent in patients with focal epilepsy than in healthy individuals.[2] The process of maintaining functions by activating an innate reorganization of connectivity reportedly relies on several parameters, including the localization of brain injury and the extent of interictal epileptic activity.[3] However, the specific ability of the right hemisphere to sustain the acquisition or recovery of language following extensive damage to the left hemisphere has been largely related to the age at brain injury.[4] Perinatal insults are linked to superior language functions compared with those occurring later in life, suggesting a steep decline of plasticity beyond the first years of life.

The cerebral organization, and reorganization, of language in epilepsy has originally been studied with invasive procedures such as electrical stimulation mapping (ESM) and the Wada test, which have gradually given over to noninvasive neuroimaging techniques nowadays, such as functional magnetic resonance imaging (fMRI),[5] functional transcranial Doppler sonography (fTCD),[6] magnetoencephalography (MEG),[7] near-infrared spectroscopy (NIRS),[8] and diffusion-weighted imaging (DWI) tractography.[9] ESM still remains the gold standard for identifying critical language areas, deriving from the observation of language disruption induced by direct cortical stimulation. However, the inherent limitations of incomplete cortical coverage provided by depth and/or subdural recordings,[10] the occasional failure to identify language in children,[11] the risk of electrically induced seizures, and the general hazards of invasive EEG recordings have fuelled the development of several alternative approaches. The reliability of language fMRI has been recently addressed in a meta-analysis including 504 patients with epilepsy who also underwent the Wada test.[5] The Wada test and fMRI agreed in 94% for typical language lateralization and in only 51% for atypical language lateralization, thus supporting the conclusion that patients with atypical language dominance still require the Wada test. While the Wada test is yet an option for patients with severe developmental delay, fTCD, MEG, NIRS, and DWI tractography include passive verbal auditory tasks, thus offering several noninvasive approaches for this patient group.

In this issue of Neuropediatrics, Lorenzen et al[12] present a highly illustrative example of challenging language delineation in the context of pediatric epilepsy surgery. Late hemispheric language reorganization in this case apparently commenced at the age of 8 years, triggered by progressive frontal lobe tissue destruction due to meningocerebral angiodysplasia. The hemispheric shift of language functions, resulting in mixed language dominance, was suggested by the clinical observation of gradual language improvement over the course of several years following the insult. Late reorganization, albeit with remaining language functions in the affected hemisphere, was corroborated by the findings of consecutive fMRI, Wada, and ESM investigations. This uncovered a unique pattern of language reorganization, as compared with both homotopic, interhemispheric reorganization, occurring in young children after stroke, and intrahemispheric, perilesional reorganization, occurring in adults. The implementation of both noninvasive and invasive methods resulted in an optimal delineation of the language network in this patient and facilitated the preservation of language functions further to the accomplishment of postsurgical seizure freedom. This case showcases the strengths and shortcomings of three language delineation methods, commonly applied in presurgical evaluation, and underlines the necessity of a comprehensive multimodal assessment for the detection of atypical patterns and the prevention of postsurgical neurological deficit.

^* This article is an editorial on “Multimodal assessment reveals late-onset hemispheric shift of language in a child with meningocerebral dysplasia” by Lorenzen et al (Neuropediatrics 2016;47(6):341–345).

• References

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