The role of stereotactic biopsy in radiosurgery.

Radiosurgery offers a very powerful, minimally invasive therapeutic tool in the modern treatment of intracranial lesions. A direct contact with the lesion, as always takes place, e.g. in a stereotactic biopsy or microsurgical operation, is no longer an absolute prerequisite. Treatment planning is done using modern imaging techniques like computer assisted tomography (CT) or magnetic resonance imaging (MRI). Both provide high resolution and contrast images. The lesions can be displayed with high accuracy. The specificity of these techniques is adequate enough to provide neuropathological data which are a prerequisite for treatment? In 1991 we published a retrospective study in which the diagnosis based on CT was compared with the histological diagnosis following stereotactic biopsy on a series of 181 patients with intracranial processes. We could show clearly that CT alone does not offer a reliable basis for therapy planning. Overall CT-scan was inaccurate in 22% of the cases. Now in an additional series of 195 patients with intracranial processes, we have compared the MRI diagnosis with the neuropathological diagnosis. MRI results and the neuropathological diagnosis based on microsurgical operation were compared and evaluated according to the following criteria: 1. Absolute agreement between MRI and histological diagnosis. 2. No agreement between MRI and histological diagnosis. 3. Conditional agreement: the MRI result offered several differential diagnoses one of which was accurate.