The transcortical equatorial approach for gliomas of the mesial temporal lobe: techniques and functional outcomes

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Many surgical approaches have been described for lesions within the mesial temporal lobe (MTL), but there are limited reports on the transcortical approach for the resection of tumors within this region. Here, the authors describe the technical considerations and functional outcomes in patients undergoing transcortical resection of gliomas of the MTL.


Patients with a glioma (WHO grades I–IV) located within the MTL who had undergone the transcortical approach in the period between 1998 and 2016 were identified through the University of California, San Francisco (UCSF) tumor registry and were classified according to tumor location: preuncus, uncus, hippocampus/parahippocampus, and various combinations of the former groups. Patient and tumor characteristics and outcomes were determined from operative, radiology, pathology, and other clinical reports that were available through the UCSF electronic medical record.


Fifty patients with low- or high-grade glioma were identified. The mean patient age was 46.8 years, and the mean follow-up was 3 years. Seizures were the presenting symptom in 82% of cases. Schramm types A, C, and D represented 34%, 28%, and 38% of the tumors, and the majority of lesions were located at least in part within the hippocampus/parahippocampus. For preuncus and preuncus/uncus tumors, a transcortical approach through the temporal pole allowed for resection. For most tumors of the uncus and those extending into the hippocampus/parahippocampus, a corticectomy was performed within the middle and/or inferior temporal gyri to approach the lesion. To locate the safest corridor for the corticectomy, language mapping was performed in 96.9% of the left-sided tumor cases, and subcortical motor mapping was performed in 52% of all cases. The mean volumetric extent of resection of low- and high-grade tumors was 89.5% and 96.0%, respectively, and did not differ by tumor location or Schramm type. By 3 months’ follow-up, 12 patients (24%) had residual deficits, most of which were visual field deficits. Three patients with left-sided tumors (9.4% of dominant-cortex lesions) experienced word-finding difficulty at 3 months after resection, but 2 of these patients demonstrated complete resolution of symptoms by 1 year.


Mesial temporal lobe gliomas, including larger Schramm type C and D tumors, can be safely and aggressively resected via a transcortical equatorial approach when used in conjunction with cortical and subcortical mapping.

ABBREVIATIONS DWI = diffusion-weighted imaging; EOR = extent of resection; FLAIR = fluid-attenuated inversion recovery; MTL = mesial temporal lobe; UCSF = University of California, San Francisco.

Article Information

Correspondence Mitchel S. Berger: University of California, San Francisco, CA.

INCLUDE WHEN CITING Published online April 20, 2018; DOI: 10.3171/2017.10.JNS172055.

Disclosures The authors have no conflicts of interest to disclose.

© AANS, except where prohibited by US copyright law.



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    Illustration of tumor locations. Tumors were categorized as preuncus (blue), uncus (yellow), hippocampus/parahippocampus (magenta), and various combinations of the former groups. Medial (A) and inferior (B) views of the temporal lobe illustrate these descriptors. CN = cranial nerve. Copyright Mitchel Berger. Published with permission.

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    Surgical approaches for MTL gliomas. A–C: Depiction of various surgical approaches including the transcortical, subtemporal, transsylvian, anterior temporal, suboccipital, and posterior subtemporal approaches. D and E: Considerations for the transcortical approach. The center of the tumor equator is identified on preoperative imaging, and the shortest distance between the temporal cortical surface and the tumor equator is identified (blue lines). Alternative pathways, while potentially closer to the edge of the tumor, do not provide the shortest distance to the actual equatorial center. This corridor allows for access to all aspects of the tumor to allow for extensive resection. Mapping can be used for tumors located in language-dominant cortex to ensure that the entry point does not contain functional tissue. A larger Schramm type C lesion (D) and a smaller Schramm type A lesion (E) are depicted. TMC = tumor mass center. Copyright Mitchel Berger. Published with permission.

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    Resection of a Schramm type A WHO grade II diffuse astrocytoma within the uncus. Preoperative T1-weighted (A, axial) and FLAIR (B, axial; C, and coronal) MR images demonstrated a lesion isolated to the left uncus. Postoperative T1-weighted (D, axial) and FLAIR (E, axial; F, coronal) MR images showed extensive resection of the lesion.

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    Resection of a Schramm type D WHO grade II oligodendroglioma within the hippocampus/parahippocampus. Preoperative T1-weighted (A, axial) and T2-weighted (B, axial; C, coronal) MR images demonstrated a large lesion within the right MTL extending upward into deeper structures of the subcortical insula. Postoperative T1-weighted (D, axial) and FLAIR (E, axial; F, coronal) MR images revealed extensive resection of the lesion.





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