Abstracts

Rationale: Anterior temporal lobectomy (ATL) is a common surgical procedure undertaken to treat medically refractory temporal lobe epilepsy (TLE). It often removes large amounts of cortical tissue, and yet few studies have attempted to quantify the impact of this major surgical operation on the remainder of the cortex. Here, we examine the effects of this surgery on cortical morphology measured in independent variables both near the resection and remotely.

Methods: We studied 101 patients with TLE (55 left, 46 right onset) who underwent ATL. For each patient we considered one pre-surgical MRI and one follow-up scan within one year after surgery. We used our newly developed method for the local computation of raw morphological variables (average cortical thickness, exposed surface area, and total surface area), as well as the independent measures K, I, and S, where K is a measure of white matter tension, I captures isometric scaling, and S contains the remaining information about the shape of the cortex. We did this whilst controlling for healthy ageing effects occurring during scans, and used the Matlab toolbox SurfStat for random field theory clustering to assess the changes across the cortex caused by the resective surgery.

Results: We found strong effects of the surgery to the remaining cortex in all morphological variables. Ipsilaterally, as expected, we saw changes in all variables but thickness to the ventrolateral prefrontal cortex. We also observed ipsilateral effects in the pre and post central gyri in S, I, and the surface areas for both onset sides, and in right TLE, this region also saw changes in thickness and K. In left TLE, we saw an increase in K in the frontal pole in both hemispheres. In right TLE, all measures but thickness also had differences in the ipsilateral superior occipital gyrus, and on the contralateral hemisphere we saw an increase in thickness in the superior parietal lobule, superior occipital gyrus, occipital pole, temporal pole, and middle frontal gyrus.

Conclusions: In a large cohort of patients with TLE we captured changes in cortical morphology due to surgical resection, isolated from ageing effects. We found that regions near the resected area were affected, but we also saw more widespread effects, even contralaterally. This is evidence for a general restructuration of cortical regions structurally or functionally connected to the resected tissue. Our use of independent morphological measures was able to capture changes not visible in the raw morphological measures alone.

Funding: K.L. was supported by the Engineering and Physical Sciences Research Council, Centre for Doctoral Training in Cloud Computing for Big Data (EP/L015358/1). Y.W. was supported by Wellcome Trust (208940/Z/17/Z) and UKRI Future Leaders Fellowship (MR/V026569/1).