Frameless Stereotactic Neuronavigation for Space Occupying Lesions

Prior to the widespread advent of frameless stereotaxy, intracranial tumour surgery relied upon a 3-D conceptualisation of anatomy from pre-operative imaging. External anatomical landmarks such as the coronal suture and auricle helped guide the placement of a craniotomy. Bone flaps were often planned with a margin for error, particularly when locating non-lobar tumours. The choice of an appropriate trajectory for a burr hole biopsy was frequently suboptimal with negative biopsies and significant associated morbidity. For less accessible lesions a frame-based stereotactic craniotomy was performed. This entailed placement of a stereotactic frame, acquisition of pre-operative images and calculation of tri-planar coordinates. Such procedures, although cumbersome and to some extent restrictive in the access they provide, remain part of the armamentarium for small deep targets. However, the evolution of sophisticated, accurate frameless stereotaxy has significantly changed the surgical approach to the majority of patients with space occupying lesions. Application of stereotactic technology can also be used to locate other lesions such as cavernomas and abscesses. Neuronavigation is also used to facilitate rigid endoscopic procedures. This paper aims to outline the principles of neuronavigation for neuro-oncology.