Abstract
Objective: Mechanisms of motor plasticity are critical to maintain motor functions after cerebral damage. This study explores the mechanisms of motor reorganization occurring before and after surgery in four patients with drug-refractory epilepsy candidate to disconnective surgery.Methods: We studied four patients with early damage, who underwent tailored hemispheric surgery in adulthood, removing the cortical motor areas and disconnecting the corticospinal tract (CST) from the affected hemisphere. Motor functions were assessed clinically, with functional MRI (fMRI) tasks of arm and leg movement and Diffusion Tensor Imaging (DTI) before and after surgery with assessments of up to 3 years. Quantifications of fMRI motor activations and DTI fractional anisotropy (FA) color maps were performed to assess the lateralization of motor network. We hypothesized that lateralization of motor circuits assessed preoperatively with fMRI and DTI was useful to evaluate the motor outcome in these patients.Results: In two cases preoperative DTI-tractography did not reconstruct the CST, and FA-maps were strongly asymmetric. In the other two cases, the affected CST appeared reduced compared to the contralateral one, with modest asymmetry in the FA-maps. fMRI showed different degrees of lateralization of the motor network and the SMA of the intact hemisphere was mostly engaged in all cases. After surgery, patients with a strongly lateralized motor network showed a stable performance. By contrast, a patient with a more bilateral pattern showed worsening of the upper limb function. For all cases, fMRI activations shifted to the intact hemisphere. Structural alterations of motor circuits, observed with FA values, continued beyond 1 year after surgery.Conclusion: In our case series fMRI and DTI could track the longitudinal reorganization of motor functions. In these four patients the more the paretic limbs recruited the intact hemisphere in primary motor and associative areas, the greater the chances were of maintaining elementary motor functions after adult surgery. In particular, DTI-tractography and quantification of FA-maps were useful to assess the lateralization of motor network. In these cases reorganization of motor connectivity continued for long time periods after surgery.
Highlights
Functional imaging techniques such as functional MRI and Diffusion Tensor Imaging (DTI) can track the structural and functional changes occurring during recovery after brain damage or surgery
We studied with functional MRI (fMRI) and DTI the motor functions of four patients undergoing tailored hemispheric surgery for drugrefractory epilepsy
FMRI and DTI were useful non-invasive tools to investigate the mechanisms of motor plasticity in four patients candidate to disconnection surgery [20, 39, 40]
Summary
Functional imaging techniques such as functional MRI (fMRI) and Diffusion Tensor Imaging (DTI) can track the structural and functional changes occurring during recovery after brain damage or surgery. Disconnective surgery is used to treat drug-refractory hemispheric epilepsy caused by extensive congenital or acquired lesions, and provides seizure control in 60–90% of cases [1,2,3,4,5]. Patients often show residual function of their paretic limbs [6,7,8]. Motor functions remain unchanged in most cases (50–60%), while in a lower percentage of patients it may deteriorate or even improve [9,10,11]. Motor deterioration typically affects the upper limbs more than the lower limbs, while improvement can be more evident in children than in adults [12]
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