Congenital perisylvian syndrome: MRI and glucose PET correlations

Developmental Dynamic Dysphasia: Are Bilateral Brain Abnormalities a Signature of Inefficient Neural Plasticity?

The acquisition and evolution of speech production, discourse and communication can be negatively impacted by brain malformations. We describe, for the first time, a case of developmental dynamic dysphasia (DDD) in a right-handed adolescent boy (subject D) with cortical malformations involving language-eloquent regions (inferior frontal gyrus) in both the left and the right hemispheres. Language evaluation revealed a markedly reduced verbal output affecting phonemic and semantic fluency, phrase and sentence generation and verbal communication in everyday life. Auditory comprehension, repetition, naming, reading and spelling were relatively preserved, but executive function was impaired. Multimodal neuroimaging showed a malformed cerebral cortex with atypical configuration and placement of white matter tracts bilaterally and abnormal callosal fibers. Dichotic listening showed right hemisphere dominance for language, and functional magnetic resonance imaging (fMRI) additionally revealed dissociated hemispheric language representation with right frontal activation for phonology and bilateral dominance for semantic processing. Moreover, subject D also had congenital mirror movements (CMM), defined as involuntary movements of one side of the body that mirror intentional movements of the other side. Transcranial magnetic stimulation and fMRI during voluntary unimanual (left and right) hand movements showed bilateral motor cortex recruitment and tractography revealed a lack of decussation of bilateral corticospinal tracts. Genetic testing aimed to detect mutations that disrupt the development of commissural tracts correlating with CMM (e.g., Germline DCC mutations) was negative. Overall, our findings suggest that DDD in subject D resulted from the underdevelopment of the left inferior frontal gyrus with limited capacity for plastic reorganization by its homologous counterpart in the right hemisphere. Corpus callosum anomalies probably contributed to hinder interhemispheric connectivity necessary to compensate language and communication deficits after left frontal involvement.

Bilateral agenesis of arcuate fasciculus demonstrated by fiber tractography in congenital bilateral perisylvian syndrome

Congenital bilateral perisylvian syndrome (CBPS) is a type of cortical developmental abnormality associated with distinctive clinical and imaging features. Clinical spectrum of this syndrome is quite heterogeneous, with different degrees of neurological impairment in affected individuals. High-definition magnetic resonance imaging (MRI) has a great importance in revealing the presence of CBPS, but is limited in elucidating the heterogeneous clinical spectrum. The arcuate fasciculus (AF) is a prominent language tract in the perisylvian region interconnecting Broca and Wernicke areas, and has a high probability of being affected developmentally in CBPS. Herein, we report a case of CBPS with investigation of AF using diffusion tensor imaging (DTI) and fiber tractography in relation to clinical findings. We postulated that proven absence of AF on DTI and fiber tractography would correlate with a severe phenotype of CBPS.

Arcuate fasciculus and speech in congenital bilateral perisylvian syndrome

Standard magnetic resonance imaging can diagnose congenital bilateral perisylvian polymicrogyria, but is limited in explaining the heterogeneous clinical spectrum of the related congenital bilateral perisylvian syndrome, characterized by pseudobulbar dysfunction, developmental delay, and epilepsy. We analyzed arcuate fasciculi using diffusion tensor imaging, a major language tract in the perisylvian region interconnecting the Broca and Wernicke areas, and at high risk of becoming developmentally affected in this condition. Six patients with congenital bilateral perisylvian syndrome underwent diffusion tensor imaging and were evaluated. The arcuate fasciculus was manually isolated, using tractography. The tract was identified in three patients who had developed speech, and whose values for various diffusion parameters were similar to those in age-matched controls (patients/controls means: fractional anisotropy, 0.50/0.52; apparent diffusion coefficient, 0.0022/0.0022 mm(2)/second; P = ns for both). However, in three patients with severe impairment and no speech development, the arcuate fasciculus could not be identified by fiber-tracking. In this small series, the absence of arcuate fasciculi on diffusion tensor imaging correlated with a more severe phenotype, which cannot be appreciated via structural magnetic resonance imaging alone.

Congenital perisylvian dysfunction - is it a spectrum?

AIM

This study examines the overlap between children with bulbar cerebral palsy (Worster-Drought syndrome [WDS]) and perisylvian polymicrogyria.

METHOD

A total of 121 children (81 males, 40 females; mean age 5y 5mo, SD 3y 6mo; age range 1mo-15y 4mo) were studied using retrospective clinical data and magnetic resonance imaging. In all, 70 children had WDS with normal perisylvian imaging, 31 had congenital bilateral perisylvian polymicrogyria (CBPP), and 20 had congenital unilateral perisylvian polymicrogyria (CUPP).

RESULTS

All groups shared aetiological markers (male sex, congenital contractures, low familial incidence, excess antenatal events). There was a common phenotype of pseudobulbar palsy with mild limb pyramidal signs in all children with WDS, 90% of those with CBPP, and one-third of those with CUPP, often also associated with learning disability*, epilepsy, and behavioural difficulties. A further 15% of children with CUPP acquired this phenotype through an epileptic encephalopathy. Pseudobulbar palsy rather than polymicrogyria was more predictive of additional impairments other than epilepsy.

INTERPRETATION

We propose that congenital perisylvian dysfunction is a spectrum encompassing the WDS phenotype and perisylvian polymicrogyria imaging abnormalities. As with other prenatal brain abnormalities, there is not necessarily concordance between imaging and clinical findings, although the phenotype is often more severe to manifest imaging abnormality. Clinical phenotype is the best indicator of prognosis. Epileptic encephalopathy can cause an acquired form of perisylvian dysfunction where there is.