Intersurgeon Variability in the Selection of Anterior and Posterior Commissures and Its Potential Effects on Target Localization

Abstract

Background: This study reports the intersurgeon variability in manual selection of the anterior and posterior commissures (AC and PC). The study also investigates the effect of this variability on the localization of targets like the subthalamic nucleus, ventralis intermedius nucleus and globus pallidus internus. The additional effect of variation in the selection of the mid-plane on target localization is also evaluated. Methods: 43 neurosurgeons (38 attendings, 5 residents/ fellows) were asked to select the AC and the PC points (as routinely used for stereotactic neurosurgical planning) on two MRI scans. The corresponding mid-commissural points (MCPs) and target coordinates were calculated. Results: The collected data show that the MCP is more reliable than either the AC or the PC points. These data also show that, even for experienced neurosurgeons, variations in selecting the AC and the PC point result in substantial variations at the target points: 1.15 ± 0.89 mm, 1.45 ± 1.25 mm, 1.21 ± 0.83 for the subthalamic nucleus, ventralis intermedius nucleus, and globus pallidus internus, respectively, for the first MRI volumeand 1.08 ± 1.37 mm, 1.35 ± 1.71 mm, 1.12 ± 1.17 mm for the same structures for the second volume. These variations are larger when residents/fellows are included in the data set. Conclusions: The data collected in this study highlight the difficulty in establishing a common reference system that can be used to communicate target location across sites. It indicates the need for the development and evaluation of alternative normalization methods that would permit specifying targets directly in image coordinates or the development of improved imaging techniques that would permit direct targeting.

Automated Optimization of Subcortical Cerebral MR Imaging−Atlas Coregistration for Improved Postoperative Electrode Localization in Deep Brain Stimulation

“…3 Yet, optimal precise target localization remains controversial. Assessment of localizations on postoperative structural MR imaging data in their specific anatomic context requires spatial normalization to transform individual anatomic variability [4][5][6] by geometric alignment of corresponding structures across patients (patient-to-patient) or to a standard (patient-to-atlas). Commonly, the position of the electrode is indirectly reported in coordinates along the 3 axes relative to the midcommissural point (MCP) between the anterior commissure (AC) and posterior commissure (PC) 1,[6][7][8][9][10][11] and is normalized by the individual distance from the AC to the PC in relation to a standard atlas ACPC distance.…”

“…16,17 For instance, the AC can vary in diameter from 3 to 8 mm, 18 and the inter-rater ambiguity in manual selection leads to considerable variations in assessment of the target STN and GPi. 6 These inconsistencies erroneously scale distances along all 3 axes by misjudging the ACPC distance, on which this normalization is based.…”

Validation of a Fully Automatic Method for the Routine Selection of the Anterior and Posterior Commissures in Magnetic Resonance Images

“…As shown in Pallavaram et al [2] , there is substantial intersurgeon variability in the manual selection of the AC and PC points, which complicates the creation of atlases. Indeed, errors in the localization of the AC and PC points in the atlases produce prediction errors independent of the registration accuracy.…”

“…Therefore, any discussion of target localization is limited by the variability of AC and PC selection. In a 2008 study [2] , we used data from 43 neurosurgeons to quantify errors that occur in selecting the DBS targets because of inaccuracies in the manual selection of AC and PC points. The findings suggested the need for automated and robust methods for the localization of these points of reference.…”

Microelectrode Recording Duration and Spatial Density Constraints for Automatic Targeting of the Subthalamic Nucleus

“…However, targeting the STN based on preoperative images alone may be suboptimal for at least two key reasons. Firstly, the STN target cannot always be well identified on the preoperative image [10,11,12]. Secondly, the clinical application accuracy of the various stereotactic systems is 0.1–5.0 mm [13,14,15,16,17,18], an error which approaches the dimension of the STN itself.…”