Temporal mediobasal tumors: a proposal for classification according to surgical anatomy

Objective Development of a classification for temporal mediobasal tumors based on anatomical and neuroradiological aspects to help evaluate surgical accessibility and risk. Methods Preoperative magnetic resonance imaging, surgical approaches and outcomes of 235 patients with a temporal mediobasal tumor were analyzed retrospectively. Surgical landmarks were defined in accordance with operative anatomy. Previous classifications of these tumors were reviewed and a new classification system was developed. Results The new classification system recognises four types of temporal mediobasal tumor based on anatomical landmarks, location, and size. Type A comprises lesions confined to the uncus, hippocampus, parahippocampus, and/or amygdala. Type B comprises lesions in the area immediately lateral to the structures where type A tumors are located but sparing lateral gyri. Type C tumors are larger lesions, which occupy the area of type A and type B simultaneously. Type D tumors originate from the temporal mediobasal region and invade into the adjacent structures of the temporal stem, insular cortex, claustrum, putamen, or pallidum. The area occupied by a tumor in the axial plane was divided into anterior (a) and posterior (p) subregions. Progressive grading from A to D and from a to p was based on the view that larger and more posteriorly growing tumors were more difficult to remove. Lesions located in the anterior subregion (n=173) were easier to remove by the transsylvian route (39%) or after partial anterior lobectomy (32%). For the posterior lesions (n=62), a subtemporal approach was more appropriate (75%). Conclusions Based on a series of 235 temporal mediobasal tumors, a classification system was designed to aid in decision making about operability, surgical risk, and approach.