Frameless neuronavigation using the ISG-system in practice: from craniotomy to delineation of lesion

The overall performance of a "pointer" neuronavigation system (the ISG ALLEGRO Viewing Wand) in everyday surgical use was evaluated by investigating the practical utility of the technical set-up for one particular surgical task. The basis of the analysis was the numerical evaluation of four areas of fundamental importance for most brain surgery: site and size of craniotomy, localisation of lesion, the trajectory through the brain, and the delineation of the lesion. In a protocol of 65 patients we based our examination on a subjective 4-point rating scale ranging from 0 (= no help) to 3 (= very helpful) for each of the four above categories. We investigated the potential influence of three factors: the lesions histology (4 groups), its size (3 categories) and the depth from the cortical surface (3 levels). Our experience is that the histology of the lesions has significant influence on the relative usefulness of neuronavigation for craniotomy (P < 0.017) and for delineation of the lesion (P < 0.003). We found neuronavigation most helpful for removing gliomas. Second, this system was found to be very helpful in locating small, hitherto hard-to-find, lesions (P < 0.01). Lesion's depth had no effect on the ratings (P > 0.2). Overall, the use of this system led to more precise skin incisions, better site and size of craniotomies tailored to the pathology, the trajectory through the brain, and to more precise delineation of the lesion.