Abstracts

Rationale: There is considerable evidence for neuroplasticity and reorganization of cognitive functions after early brain injury, and particularly for the redistribution of language function to the right hemisphere following destructive lesions or surgery on the left hemisphere, especially in the first five years of life. Less is known about reorganization of nonverbal function following right hemisphere surgery and in later childhood or adolescence.Methods: Functional right hemispherectomy was performed in two patients, both 13-year-old males with medically refractory seizures originating from the right hemisphere. In Patient 1 (P1), seizures were caused by diffuse polymicrogyria of the right hemisphere (seizure onset at 6 years) , and in Patient 2 (P2) by perinatal right MCA and bilateral PCA strokes with bilateral subdural and subarachnoid hemorrhages (seizure onset at 5 years). Both patients were seizure-free following surgery (follow-up 2 years in P1 and 6 months in P2). Neuropsychological evaluations were conducted prior to surgery, at 6 months post-operation (P1 and P2) and at 30 months post-operation (P1). Reliable change indices (RCI) corrected for practice effects were also calculated (90% CI). For each patient, the most recent post-surgical neuropsychological data relative to pre-surgical function is reported as the primary outcome.Results: RCI analyses of repeated neuropsychological assessments indicated a pattern of improved nonverbal reasoning/memory, in contrast to a decline in verbal reasoning/memory. Specifically, both patients demonstrated significant decline on the Verbal Comprehension Index of the Wechsler Intelligence Scale for Children, Fourth Edition (WISC-IV); both improved on the Perceptual Reasoning Index of the WISC-IV, however only P1 had significant RCI corrected for practice. With regard to memory, both demonstrated improvement on the Faces subtest of the Children’s Memory Scale, again only P1 had significant RCI corrected for practice. Significant decline in word list learning and delayed free recall were seen in both P1 and P2 on the California Verbal Learning Test-Children’s Version. Neither patient reported qualitative change in memory function following surgery.Conclusions: These two right hemispherectomy cases provide evidence for neuroplasticity in adolescence. The changes in neuropsychological skills are consistent with the concepts of release of inhibition and crowding. Specifically, improved nonverbal functions indicate that left hemisphere systems may have undertaken functions that are frequently lateralized to the right (facial recognition); without the interference of the right hemisphere, left cerebral cortex may have been able to strengthen functional networks. The cost of this reorganization has been conceptualized by the theory of crowding and is evident in decline in verbal memory performance. Understanding the potential for functional reorganization, even into adolescent years, is important for clinical counseling in epilepsy surgery.