- Division of Neurosurgery, University of Nebraska Medical Center, 982035 Nebraska Medical Center, Omaha, NE 68198-2035, USA
Arun Angelo Patil
Division of Neurosurgery, University of Nebraska Medical Center, 982035 Nebraska Medical Center, Omaha, NE 68198-2035, USA
DOI:10.4103/2152-7806.70957© 2010 Patil AA This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
How to cite this article: Patil AA. A modified stereotactic frame as an instrument holder for frameless stereotaxis: Technical note. Surg Neurol Int 11-Oct-2010;1:62
How to cite this URL: Patil AA. A modified stereotactic frame as an instrument holder for frameless stereotaxis: Technical note. Surg Neurol Int 11-Oct-2010;1:62. Available from: http://sni.wpengine.com/surgicalint_articles/a-modified-stereotactic-frame-as-an-instrument-holder-for-frameless-stereotaxis-technical-note/
Background:In order to improve the targeting capability and trajectory planning and provide a more secure probe-holding system, a simple method to use a stereotactic frame as an instrument holder for the frameless stereotactic system was devised.
Methods:A modified stereotactic frame and BrainLab vector vision neuronavigation sys¬tem were used together. The patient was placed in the stereotactic head-holder to which a reference array of the neuronavigation system was attached. The pointer of the frameless system was placed in the probe-holder of the frame. An offset in distances was kept between the radius of the arch of the frame and the tip of the pointer so that the pointer was always outside the head during navigation. The offset correction was made on the BrainLab monitor so that the center of the arc of the frame was at the tip of the probe line on the monitor. Then, using the frame’s coordinate adjuster system, the center of the arc was positioned on the target. This method was used to insert depth electrodes (seven procedures) and gain access to the temporal horn (three procedures).
Results:Post-operative scans showed that the accuracy was within 2.5 mm in all three planes for depth electrode placement, and easy access to the temporal horn was obtained in two other patients.
Conclusion:This is a simple method to use a stereotactic frame to improve coordinate and trajectory adjustments and provides a better method to stabilize the pointer and the probe-holder during frameless stereotactic procedures.
Keywords: Coordinates adjuster, frameless stereotaxis, instrument holder, stereotactic frame
Horsley first introduced frame-based stereotaxis into neurosurgery.[
The Frameless Stereotactic System
The BrainLab vector vision neuronavigation system (BrainLAB AG, Feldkirchen, Germany) was used in combination with a frame-based custom-designed stereotactic system for the procedure.
The stereotactic frame is a modified Patil system[
(Y = yoke; P = probe-holder; RA = reference array; PL = pivot-line; C = center of the arc; P = pivot; CC = c-clamp; CP = coordinate platform; H = head holder; BP = base plate). The lines converging from the yoke to the center of the arc represent the trajectories of the holes in the horizontal arm of the yoke
Over the past 2 years, this method was used in 10 procedures. Seven of these procedures were for placement of depth electrodes for seizure activity recording, six for the amygdalohippocampal complex and one for the supplementary motor cortex. Three procedures were for entry into the temporal horn through the middle temporal gyrus during seizure surgery.
Pre-operatively, MR and CT images were obtained using the standard protocol for the frameless system. Image fusion of both these modalities were performed and then loaded onto the computer used for navigation.
The procedure was performed under general anesthesia. The patient’s head was firmly fixed in the stereotactic head-holder with three head-pins. The reference array was attached to the head-holder by means of a c-clamp. To secure it in place tightly, sand paper was interposed between the clamp and the head-holder. Facial surface registration was performed using a z-touch laser pointer (BrainLAB AG). In addition, vertex and occipital area registration were performed using the pointer. The registration was recorded through the infrared camera. To improve the accuracy, both sides of the face were included in the registration. After good accuracy of the system was confirmed, the procedure was started. The cranial opening was made. The yoke was attached to the pivot and the pointer was inserted through the middle hole on the yoke [
These images on the navigation system’s monitor were obtained after the center of the arc was brought on the target using the X-Y-Z adjuster. The outer cross-mark represents the position of the pointer tip while the deeper cross-mark represents the position of the center of the arc of the stereotactic frame
There were no complications from the procedure. Post-operative scans showed the electrodes to be within 2.5 mm of the planned target in all three planes. During open craniotomy, there was very little obstruction of the view by the probe holder and the temporal horn was reached easily and accurately.
Although a frameless system has the distinct advantage of being able to quickly navigate the surgical site and provide information about the site of surgical action on CT and/or MR images, this capability can also become a disadvantage because the location of the pointer tip can quickly come off target as the surgeon’s eyes move away from the operative site to the monitor. In addition, when there is the need to place a probe at a very small target, a stabilizing device is necessary. There are different types of probe-stabilizing attachments available for use with a frameless system. One type of system has articulated arms[
In the author’s system, the pointer of the frameless system is securely held in place and its position is adjusted by rack and pinion movement on the frame. The probe-holder can therefore be moved discreetly in three planes, enabling the pointer to precisely aim at small targets with ease. In addition, because it is a center of the arc system, the trajectory can be changed in both the sagittal and the coronal planes without altering the aim of the pointer on the target. The yoke that holds the probe-holder is extremely thin, thereby minimizing the obstruction of the surgeon’s view. The reduction in weight also minimizes the potential sag that is inherent in a single-armed yoke design. To further reduce the weight the probe holding holes are within the yoke, with their trajectories centered around a point on the pivot line. This point, thus, forms the center of a virtual arc created by the positions of the holes. The system was designed with only one coordinate platform to improve freedom of movement of the yoke.
Conventional frames are difficult to use during open craniotomy procedures because they are bulky and cumbersome. The modified frame described in this paper solves this problem because the yoke of the frame (which is very thin) is the only hardware in the operative field. This is evident in Figure
The system has the following additional advantages: (1) pre-operative images can be obtained without the frame, (2) coordinates can be adjusted by simply identifying the target on the monitor and moving the center of the arc on it, without the need to measure or calculate the coordinates, (3) dynamic trajectory planning can be done by moving the arc and viewing the structures on CT and/or MR images plane by plane. The combination method does not preclude the use of a frameless system by itself. The pointer can, therefore, also be used free-handedly to navigate the operative site. The current technique is best suited for placement of electrodes or probe (to act as a guide during dissection toward a deep target or for biopsy purpose) into deep structures. Therefore, for other applications such as tumor resection, the free-handed technique will still be necessary. The author has used the current system in only 10 procedures over the last 2 years, because it was used mainly for placement of probes or electrodes into deep structures for which sub-millimeter accuracy was not as critical.
The current technique is basically frameless stereotaxis. Its accuracy therefore will be as good as the accuracy of the frameless system. This method has the disadvantage of introducing inaccuracies if the reference array moves or if surface registration is inadequate. The stability and the attachment of the reference array clamp to the head-holder can be improved by interposing sandpaper between them. The registration process can be improved by performing a z-touch laser beam registration on both sides of the face and pointer registration on both sides of the vertex and occipital areas. Accuracy can also be improved by including CT images in the registration and navigation process.
In summary, this is a simple technique to combine the advantages of frame-based and frameless stereotactic systems. Its main advantages include the ability to precisely aim the pointer at the target with ease, maintain the aim of the pointer on the target while planning the trajectory and the ability to firmly hold a probe in place. This method is suited for biopsy of deep lesions, placement of deep electrodes into brain and open craniotomy approach to deep structures.
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