Intrahemispheric reorganization of language in children with medically intractable epilepsy of the left hemisphere

TLDR

Interhemispheric reorganization of language has been documented in children with left‑hemisphere epilepsy, but this study is the first to systematically examine possible intrahemispheric reorganization following early insult. The study aimed to compare extraoperative stimulation mapping (ESM) findings across subjects and assess intrahemispheric language reorganization using a novel coregistration technique. Nine children with left‑hemisphere seizure foci underwent ESM for language localization, after which independent raters plotted 2‑D ESM sites into 3‑D standard space and compared them with a Broca’s‑area probability map. The coregistration yielded excellent inter‑rater agreement (mean 3.9 mm) and revealed language sites anterior and superior to canonical Broca’s area, indicating that early left‑hemisphere insult may cause anterior displacement of language within the frontal cortex.

Abstract

We investigated language representation in nine children (six male, three female; 5.6-17.7 years of age) who underwent surgical treatment of medically intractable epilepsy of the left hemisphere. Although interhemispheric reorganization has been previously documented in similar groups, this is the first study to systematically evaluate possible intrahemispheric effects of early insult. All cases had left hemisphere seizure foci and underwent extraoperative stimulation mapping (ESM) for language localization prior to receiving cortical resections. To compare ESM findings across subjects and to assess intrahemispheric reorganization, we developed a novel coregistration technique whereby independent raters plotted two-dimensional (2D) ESM findings in 3D standard space. Expressive language sites identified with ESM were compared with a structural probability map of pars opercularis, or Broca's area. The average difference between independent raters' estimates of 28 language sites was 3.9 mm (SD = 2.0), indicating excellent agreement; the coregistration procedure permitted assessment of 2D ESM findings in 3D standard space. We observed language sites in regions substantially anterior and superior to canonical Broca's area, possibly reflecting intrahemispheric reorganization. Findings suggest that left hemisphere insult in young children may result in anterior displacement of language within the frontal cortex.