[Computer tomography-guided stereotaxic biopsy of intracranial lesions. Simple technic for the calculation of coordinates; method for the reduction of operative risk in the critical areas of the brain].

The authors describe an original technique to calculate the coordinates for CT-guided stereotactic biopsies of brain lesions. On the basis of simple trigonometric formulas it is possible to get an accuracy of +/- 1 mm. By means of the standard software of a high precision CT and with a CT-compatible stereotactic apparatus the x, y, and z coordinates are obtained in a quick and reliable way. A further development of the trigonometric approach to the stereotactic calculations is the "double target technique". It allows to preset the path of the biopsy-device through a selected point, to reach the final target: in this way a valuable reduction of the surgical risk is afforded especially in critical areas of the brain (brain stem, pineal region etc.).