Abstracts

Rationale: The unique ability of TMS to non-invasively induce evoked responses and virtual lesions combined with the improved accuracy afforded by image guidance has spurred on its clinical applications. TMS generated motor and expressive language maps in adult patients are in good agreement with those generated by direct cortical stimulation (1,2). However, at the present time, the utility of presurgical motor and language mapping studies using TMS in children is in its infancy. We report here, successful functional mapping of both motor and language cortices in children.Methods: Ten children diagnosed with brain tumors (6 males, 10.7±5 years, range 2.5-17) underwent functional mapping with TMS using Navigated TMS system. The patient demographics and diagnoses are detailed in Table 1. The motor mapping included determination of motor threshold, extent of motor cortex, and corticomotor latency. Language areas were localized as patients performed an object-naming task at baseline and during TMS stimulation (5 Hz; electric field of 80 to 100 volts/meter at a depth of 20-25 mm) time-locked to stimulus presentation. TMS was applied to lateral temporal and frontal regions in both hemispheres. The observed errors were categorized using previously established criteria (1,2) as speech arrest, performance errors, or semantic errors.Results: All patients tolerated TMS and did not experience any adverse effects. TMS was successful in mapping the motor cortex in all 10 patients and localizing language areas in 7 patients. The youngest patient to undergo successful motor mapping was a 2.5 year old male (P3) and language mapping was a 5.3 year old female (P6). The motor cortex was found to be located along the precentral gyrus in all patients. The evoked response in the affected extremity was absent (P6) or delayed (see Figure 1, P3) indicating damage to the corticospinal tracts. In patient 9, motor cortices were found to be along the anterior and the medial margins of the lesion, (Figure 1, P9) and therefore the motor strip was left intact during surgery. In three patients (2, 5, and 8) the language areas were found to be along the margins of the lesions (Figure 1; P2 and P5). Total resection of the tumors was possible in patients 2 and 8 under the guidance of intraoperative MRI with no significant postoperative deficits. Surgery was deferred and patient 5 was referred for chemotherapy and radiation therapy. The language areas were found to be away from the lesion in patients 4, 6, 7 and 10 and complete resection of the tumor was possible in each patient.Conclusions: TMS is a safe and noninvasive means of localizing motor and language functions in the brain in children. Recent improvements in accuracy and ease of application of TMS are especially beneficial in pediatric neurosurgery and neurology. We believe that the critical information that TMS provides, coupled with its ease of use, will result in increasing pediatric applications in the near future. REFERENCES 1. Picht T et al. Neurosurgery. 2013;72:808-819. 2. Tarapore PE et al. J Neurosurg. 2012;117:354-362.