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

Development of a classification for temporal mediobasal tumors based on anatomical and neuroradiological aspects to help evaluate surgical accessibility and risk.

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.

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%).

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.