Involved but not essential: cognitive activity in periventricular nodules and neuropsychological outcomes following...

Periventricular nodular heterotopia (PVNH) is a malformation of cortical development with high rates of epilepsy. The extent to which nodules participate in normal cerebral functions in addition to pathological processes is unclear. The authors assessed the functional utility (i.e., cognitive impacts) of surgically ablated epileptogenic PVNH tissue via comprehensive neuropsychological testing.

The sample included 32 patients with PVNH who underwent presurgical neuropsychological evaluation and a subsample of 16 patients who underwent MR-guided laser interstitial thermal therapy (MRgLITT) of nodules, with postsurgical neuropsychological testing. In 11 patients in whom intracranial recordings were performed, reading and naming tasks were tested to determine if there was task-related activation within the nodules. Postoperative changes were assessed at the domain level and across individual tests by using reliable change indices, with consideration of spatial distribution and hemisphere of surgery as potential modifiers of postoperative change.

Task-related activation during reading or naming was seen in 53% of electrodes localized within nodules that were later ablated; however, no related postsurgical language impacts were observed. No significant declines occurred following MRgLITT in any domain level z-scores. For single tests, the authors found substantial evidence in favor of the null hypothesis in 18/21 tests. Significant decline was seen only in spatial learning. A substantial association with laterality was identified in the perceptual reasoning index.

The functionality of PVNH tissue was evaluated by direct recordings and changes in cognitive assessments following MRgLITT ablation of epileptogenic nodules. Despite language-related activity seen in these nodules, no pattern of change was observed within any cognitive domain. The only significant decline observed was in spatial learning, whereas perceptual reasoning improved for individuals with surgery in the nondominant hemisphere. These results offer strong evidence against the role of epileptogenic PVNH in cognitive functions. This work speaks to the need for caution in assigning causality to activations seen in functional imaging without evidence from lesional methods.