Intersurgeon variability in the selection of anterior and posterior commissures and its potential effects on target...

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.

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.

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.

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.