Authors :
Virginia Berry, BS – College of Medicine, University of Tennessee Health Science Center, Memphis, TN, USA
Negar Noorizadeh, Ph.D. – University of Tennessee Health Science Center and Le Bonheur Neuroscience Institute, Le Bonheur Children's Hospital, Memphis, TN, USA
Victoria Tryba, BS – Le Bonheur Neuroscience Institute, Le Bonheur Children's Hospital, Memphis, TN, USA
James Wheless, BScPharm, MD, FAAP, FACP, FAAN, FAES, FCNS – University of Tennessee Health Science Center and Le Bonheur Children's Hospital
Presenting Author: Shalini Narayana, PhD – University of Tennessee Health Science Center and Le Bonheur Neuroscience Institute, Le Bonheur Children's Hospital, Memphis, TN, USA
Rationale:
Tuberous Sclerosis Complex (TSC) is characterized by hamartomas in multiple organs, with those in the brain referred to as tubers. These tubers are common cause of epilepsy, and their resection has been associated with seizure freedom [Moshel et al., 2010, Epilepsia. 51(7):1242-51]. Tubers can demonstrate epileptogenicity while simultaneously preserving certain normal functions [2]. Therefore, while planning a tuber resection, its proximity to eloquent cortex underscores the crucial need for comprehensive clinical evaluation and functional mapping. In this study, we utilized advanced anatomical and functional mapping techniques to investigate whether tubers located around the central sulcus demonstrated preserved motor function.
Methods:
In this retrospective study approved by our institutional regulatory board, we identified 20 TSC patients (age 12.4 ± 9.2 y, range 1.7 – 30.5 y, 85% children, 11 female) who had complete neuroimaging and Transcranial magnet stimulation (TMS) motor mapping studies. The cortical locations where TMS elicited motor evoked potentials in the contralateral abductor pollicis brevis (hand) and tibialis anterior (leg) muscles were marked on the patient’s T1 weighted MRI. Each patient’s diffusion MRI were used for fiber tracking (DSI Studio; https://dsi-studio.labsolver.org). The corticospinal tract (CST) identified by automated fiber tracking served as the seeding region, and the TMS-identified motor cortex was used as the region of interest. Tubers around the primary motor cortex were identified using T2-flair MRI images and overlayed with the tracts to identify CST fibers traveling through/near the tubers. The fractional anisotropy (FA) was extracted to assess CST integrity with its threshold set at 0.3.
Results:
TMS successfully identified hand motor cortex in all 20 subjects, while the leg motor cortex was localized in 16 subjects. Among the 20 subjects analyzed, all had tubers located within or near their motor cortices. The white matter fibers of the CST originating in each patient’s motor cortex as identified by TMS were noted to pass through or near these tubers in all 20 subjects (See Figure 1 for an example). The FA value on average was 0.4 (±0.06) for CST from hand motor cortex, and 0.45 (± 0.09) for CST from leg motor cortex, and was above the 0.3 threshold in 19 patients. Conclusions:
In this largest study of TMS motor mapping combined with tractography in TSC patients to date, we demonstrate both structural and functional integrity of white matter tracts within tubers in the motor cortex. These findings highlight the importance of combined use of tractography and TMS in planning epilepsy surgery in patients with TSC. The results underscore their application in refining surgical margins not only for tuber resections but also for other neurosurgical interventions. Our results provide further evidence that while tuber resection can provide seizure freedom, both the location and functionality of the tuber must be carefully considered.
Funding:
UTHSC Medical Student Research Fellowship (MSRF) summer research program