Intraoperative image-directed dye marking of tumor margins

The incorporation of interactive image guidance during intracranial tumor s urgery offers the possibilities of reduced operative trauma, shorter operat ion time, greater precision, and an increased understanding of complex anat omy and pathology. A basic weakness with these systems though is that they cannot account for movement of target points due to brain shift by draining of CSF or removal of pathology during the operative procedure. We have dev eloped a stereotactic (frameless) guided injector probe for marking the tum or boundary with dye injection in conjunction with a neuronavigation system . The device consisted of a rigid blunt hollow probe (2 mm dia.) with 4 sma ll side holes at the tip. The catheter is mounted in a holder equipped with 3 LEDs supplying guidance information for the neuronavigation system. A sm all manual aliquoting pump delivers a measured amount of dye in each track. Isotonic methylene blue was injected in 6 to 8 tracks around the periphery of the tumor as determined by the contract ring in MR scans. The dye was i njected using image-directed guidance before resection of the tumor was sta rted (often with the dura intact). Tumor tissue could then be resected unti l the dye became visible at the tumor boundary. Identification of the dye i n the tissue was enhanced with the use of the operating microscope. The 3-d imensional position of the dye track could be determined at the end of tumo r resection and compared with its initial position giving a good estimate o f local brain shift. The method has proved especially helpful for the resec tion of large gliomas allowing for a more radical operative result.