New Classification for Insular Tumors and Surgical Results of 40 Patients

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Abstract
The insular lobe is anatomically deep seated and located close to vital structures (middle cerebral artery, internal capsule, and corresponding opercula). Most insular tumors are of low grade and encountered in younger patients. Radical surgical intervention in this area is challenging but is superior to other treatment modalities. Because of the central location of the insula, most large paralimbic tumors involve it, and they present as insular tumors on radiologic examination. The surgical technique required for removal differs according to the size and location of the tumor. Thus, a classification system to aid in the choice of technique would be helpful. In this retrospective study, 40 patients (24 female and 16 male with mean age of 27 years) with insular tumors (62.5% were of low grade, 37.5% were of high grade) operated on between November 1996 and January 2001 were evaluated. Preoperative localization was classified according to our tentative new system based on preoperative magnetic resonance imaging (MRI): 15 of the tumors were restricted to the insula and corresponding opercula, and the others involved more mesocortical and/or allocortical areas. All the patients were operated on microsurgically by the transsylvian route. Comparing the preoperative and postoperative MRI studies, the patients were classified into three groups based on gross total (almost total) resection, nearly total resection (80%–100%), and partial resection (50%–80%) according to the reduction of tumor diameter as measured by neuroradiologists. Resection was gross total in 60% of cases, nearly total in 30%, and partial in 10%. Residual tumors were located near the internal capsule or beyond the posterior parahippocampal area. There was no perioperative mortality, and major complications were permanent hemiparesis in 2 patients and dysphasia in 1. During the follow-up period (mean of 24 months), 6 patients died as the result of uncontrollable tumor progression (4 cases of glioblastoma multiforme, 1 metastasis, and 1 grade 3 astrocytoma), and we still have 1 glioblastoma multiforme, 1 grade 3 oligoastrocytoma, 1 grade 2 oligoastrocytoma, and 1 grade 2 astrocytoma patients with tumor progression. To achieve more radical resection, the insular tumors originating from any parts of the paralimbic or limbic structures need a practical classification system based on the degree of extension obtained by means of preoperative MRI.