Tag: Subcortical stimulation

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Continuous subcortical motor evoked potential stimulation using the tip of an ultrasonic aspirator for the resection of motor eloquent lesions

Continuous subcortical motor evoked potential stimulation

J Neurosurg 123:301–306, 2015

Resection of a motor eloquent lesion has become safer because of intraoperative neurophysiological monitoring (IOM). Stimulation of subcortical motor evoked potentials (scMEPs) is increasingly used to optimize patient safety. So far, scMEP stimulation has been performed intermittently during resection of eloquently located lesions. Authors of the present study assessed the possibility of using a resection instrument for continuous stimulation of scMEPs.

Methods An ultrasonic surgical aspirator was attached to an IOM stimulator and was used as a monopolar subcortical stimulation probe. The effect of the aspirator’s use at different ultrasound power levels (0%, 25%, 50%, 75%, and 100%) on stimulation intensity was examined in a saline bath. Afterward monopolar stimulation with the surgical aspirator was used during the resection of subcortical lesions in the vicinity of the corticospinal tract in 14 patients in comparison with scMEP stimulation via a standard stimulation electrode. During resection, the stimulation current at which an MEP response was still measurable with subcortical stimulation using the surgical aspirator was compared with the corresponding stimulation current needed using a standard monopolar subcortical stimulation probe at the same location.

Results The use of ultrasound at different energy levels did result in a slight but irrelevant increase in stimulation energy via the tip of the surgical aspirator in the saline bath. Stimulation of scMEPs using the surgical aspirator or monopolar probe was successful and almost identical in all patients. One patient developed a new permanent neurological deficit. Transient new postoperative paresis was observed in 28% (4 of 14) of cases. Gross-total resection was achieved in 64% (9 of 14) cases and subtotal resection (> 80% of tumor mass) in 35% (5 of 14).

Conclusions Continuous motor mapping using subcortical stimulation via a surgical aspirator, in comparison with the sequential use of a standard monopolar stimulation probe, is a feasible and safe method without any disadvantages. Compared with the standard probe, the aspirator offers continuous information on the distance to the corticospinal tract.

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Association of dorsal inferior frontooccipital fasciculus fibers in the deep parietal lobe with both reading and writing processes: a brain mapping study

Relation of dorsal IFOF to both reading and writing processes

J Neurosurg 121:142–148, 2014

Alexia and agraphia are disorders common to the left inferior parietal lobule, including the angular and supramarginal gyri. However, it is still unclear how these cortical regions interact with other cortical sites and what the most important white matter tracts are in relation to reading and writing processes.

Here, the authors present the case of a patient who underwent an awake craniotomy for a left inferior parietal lobule glioma using direct cortical and subcortical electrostimulation. The use of subcortical stimulation allowed identification of the specific white matter tracts associated with reading and writing. These tracts were found as portions of the dorsal inferior frontooccipital fasciculus (IFOF) fibers in the deep parietal lobe that are responsible for connecting the frontal lobe to the superior parietal lobule.

These findings are consistent with previous diffusion tensor imaging tractography and functional MRI studies, which suggest that the IFOF may play a role in the reading and writing processes. This is the first report of transient alexia and agraphia elicited through intraoperative direct subcortical electrostimulation, and the findings support the crucial role of the IFOF in reading and writing.

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Clinical Application of Motor Pathway Mapping Using Diffusion Tensor Imaging Tractography and Intraoperative Direct Subcortical Stimulation in Cerebral Glioma Surgery

Neurosurgery 71:1170–1184, 2012

Glioma surgery in eloquent areas remains a challenge because of the risk of postoperative motor deficits.

OBJECTIVE: To prospectively evaluate the efficiency of using a combination of diffusion tensor imaging (DTI) tractography functional neuronavigation and direct subcortical stimulation (DsCS) to yield a maximally safe resection of cerebral glioma in eloquent areas.

METHODS: A prospective cohort study was conducted in 58 subjects with an initial diagnosis of primary cerebral glioma within or adjacent to the pyramidal tract (PT). The white matter beneath the resection cavity was stimulated along the PT, which was visualized with DTI tractography. The intercept between the PT border and DsCS site was measured. The sensitivity and specificity of DTI tractography for PT mapping were evaluated. The efficiency of the combined use of both techniques on motor function preservation was assessed.

RESULTS: Postoperative analysis showed gross total resection in 40 patients (69.0%). Seventeen patients (29.3%) experienced postoperative worsening; 1-month motor deficit was observed in 6 subjects (10.3%). DsCS verified a high concordance rate with DTI tractography for PT mapping. The sensitivity and specificity of DTI were 92.6% and 93.2%, respectively. The intercepts between positive DsCS sites and imaged PTs were 2.0 to 14.7 mm (5.262.2 mm). The 6-month Karnofsky Performance Scale scores in 50 postoperative subjects were significantly increased compared with their preoperative scores.

CONCLUSION: DTI tractography is effective but not completely reliable in delineating the descending motor pathways. Integration of DTI and DsCS favors patient-specific surgery for cerebral glioma in eloquent areas.

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