Computed tomography and histologic limits in glial neoplasms: tumor types and selection for volumetric resection.

Selective and accurate resection of any computed tomography (CT) or magnetic resonance imaging (MRI) defined intracranial volume is possible by employing imaging-based computer-assisted volumetric stereotactic methods. Although the target volume can be any intracranial lesion, volumetric resection techniques were most frequently applied to the most commonly referred intraaxial lesions: glial neoplasms located in eloquent brain regions. Requirements for understanding of glial neoplasms as target volumes prompted investigations of the three-dimensional spatial configuration of these lesions, their histologic margins, and the accuracy with which these margins could be detected on CT and MRI. Stereotactic serial biopsy studies have shown that glial neoplasms frequently comprise two elements: tumor tissue and isolated tumor cells which infiltrate brain parenchyma. The tumor tissue component of high grade gliomas is most accurately defined by the volume which exhibits contrast enhancement. However, tumor tissue in low grade (nonpilocytic) gliomas is usually indistinguishable from infiltrated parenchyma on CT and MRI; both are hypodense on CT and do not usually exhibit contrast enhancement. Stereotactic serial biopsy is the only reliable method by which CT hypodense tumor tissue can be differentiated from infiltrated parenchyma in low grade (nonpilocytic) astrocytomas, oligodendrogliomas, and mixed gliomas. Stereotactic volumetric resection of infiltrated parenchyma defined by CT/MRI is advisable only in nonessential brain regions. In eloquent brain areas, stereotactic resection is appropriate for the glial tumor tissue component of high grade glial neoplasms, pilocytic astrocytomas, and low grade CT hypodense gliomas in which a stereotactic serial biopsy procedure has confirmed tumor tissue only.