Stereotactic biopsies guided by an optical navigation system: technique and clinical experience.

Frame-based stereotactic biopsies are time-consuming procedures making necessary head fixation in a ring, explicit coordinate calculation and setting of the parameters. Frameless systems make many of these intermediate steps unnecessary, impose less mechanical restrictions regarding access to the lesions, and with slight modifications can be used to perform stereotactic biopsies. A special adaptation designed to fix the holder and the biopsy instrument is described. The neuronavigation optical tracking system of Radionics was used. CT scans were performed with 6 skin markers. Calibration was performed after head fixation in the Mayfield clamp. Mean calibration error was 2.19 +/- 0.81 mm. The light-emitting diode holder of the pointer was fixed into 2 Leila arms and moved under visual control based on CT images. The target point was selected, Leila arms fixed and a burr hole performed. The cannula was introduced to the target, being fitted with a depth stop in a length identical to that of the pointer on the screen. If necessary a second trajectory was easily selected. 49 patients underwent a frameless stereotactic biopsy. All targets except seven were superficial or in the white matter. In selected cases the biopsies were taken from deep-seated lesions. A histological diagnosis was obtained in 100 % of the cases. Four cases deteriorated postoperatively, two of these related to intratumoral bleeding. Navigation is a simple and effective method to perform biopsies of superficial and relatively large lesions. Frame-based procedures are restricted to brainstem tumors and lesions less than 1.5 cm in diameter.