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  • Accuracy Index of Minimally Invasive MRI-guided Stereotactic Laser Amygdalohippocampotomy

    Final Number:

    Mark Russell Witcher MD, PhD; Alaine Keebaugh; Robert E. Gross MD PhD; Jon Timothy Willie MD PhD

    Study Design:

    Subject Category:
    Functional Neurosurgery

    Meeting: 2016 ASSFN Biennial Meeting Late Breaking

    Introduction: MRI-guided Stereotactic Laser Amygdalohippocampotomy (SLAH) for mesial temporal lobe epilepsy may reduce collateral injury and cognitive morbidity normally associated with open temporal lobe surgery. Given the long trajectories and narrow anatomical corridors required for the safe and effective application of this therapy, however, accurate device placement and trajectory control is critical. Notably, the accuracies of various stereotactic methods reported in the literature may be for relatively shorter trajectories (e.g. biopsies, deep brain stimulation), necessitating a standardized assessment of accuracy relative to trajectory length. To assess the stereotactic accuracy of an MRI-compatible percutaneous skull-mounted miniframe (ClearPoint ScalpMount and SmartFrame, MRI Interventions, Irvine, CA) designed to accommodate minimally invasive access (twist drill craniostomy) while maintaining accuracy at both the target and entry point, we have defined the ‘accuracy index’, a proposed measure of 2D target accuracy relative to trajectory length.

    Methods: We utilized a miniframe to perform 41 procedures targeting the amygdalohippocampal complex for laser ablation in an interventional MRI suite. Trajectory planning and stereotactic navigation were completed at time of procedure and accuracy metrics were assessed postoperatively using the ClearPoint workstation.

    Results: The miniframe facilitated a stab incision and 3.2mm twist drill craniostomy (improving over a previous version that necessitated a larger incision and craniostomy) for SLAH. At mean trajectory length from bone outer table to target of 109.45 ± 8.29mm, the mean coronal 2D radial error was 0.98 ± 0.7 [Accuracy index = 0.0087]. The mean Euclidian distance between the initially planned and actual scalp entry point was 2.66 ± 1.4 mm.

    Conclusions: The miniframe accommodates minimally invasive MRI-guided stereotactic neurosurgical procedures while affording accuracy at both scalp entry and the intended intracranial target. Performing the entire procedure in the MRI suite provides immediate visualization of target anatomy and recognition of deflections or other sources of inaccuracy.

    Patient Care: By providing clinicians with an understanding of stereotactic methods necessary for accuracy in MRI-guided SLAH.

    Learning Objectives: By the conclusion of this session, participants should be able to: 1) Describe the importance of stereotactic accuracy relative to overall trajectory needs, 2) Understand the potential advantages of a percutaneous skull-mounted frame for MRI- guided procedures, and 3) Develop a sense of comparative accuracy to other frame-based and frameless stereotactic methods.


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