Stereotactic surgery

Main Principle:

Stereotactic surgery aims at introducing cannula or electrodes with high precision into the deeply located small brain structures along a straight path. The required target point is determined by consulting CT / MR images of the patient and is achieved by means of a mechanically precise apparatus.

Mechanical components of the Stereotactic System:

In the Department of Neurosurgery in Homburg the Riechert-Mundinger stereotactic system is used for these operations. The system consists of the following main components:

1. Basic Ring: This is rigidly fixed (under anesthesia) on the patient's skull. It provides a fixed reference system in all three directions of the room (Fig.1).

2. Localization disks: These are attached to the ring and used to calculate the coordinates of the destination from CT / MR images. The stereotactic frame in CT with laser must be aligned exactly parallel to the gantry (Fig.2).

Fig.1

Fig.2

3. Phantom or target point simulator: The target point simulator is a mechanical device that mimics "in the dry" the operation on the patient. It consists of a ring that corresponds to the patient base ring and a pointer which can be moved along the x, y and z axis and its tip exactly marks the target within the brain. With this device, the access and the arrival at the target point can be controlled (Figure 3).

Fig.3

Fig.4

4. Aiming Arm: This allows a precise guiding of the probe to the target point. The insertion handle in the Riechert-Mundinger system uses a polar coordinate system with 4 angles, to reach any point in the brain (Figure 4).

Software:
The target point calculation is performed by a technically sophisticated special computer. This allows us to carry out the planning of the target point in advance by consulting magnetic resonance images. Hereby the path of the probe is selected in order to minimize the risk of injury of important anatomical structures or vessels. On operation day, the images of these MRI-based planning are overlaid with current CT images, which were performed under stereotactic conditions, and the destination in the brain where the electrode tip or biopsy needle will be placed, is calculated exactly by 1mm.