Transsylvian Resection of an Insular Low-Grade Glioma Medial to the Porto Alegre Line: Surgical Strategy for Preservation of the Lenticulostriate Arteries. Surgical Video.

Abstract

Introduction: Maximal safe resection remains the primary goal in the surgical management of insular gliomas. However, tumors extending medial to the Porto Alegre Line (PAL) are at increased risk of involving the lenticulostriate arteries (LSAs), making aggressive medial resection potentially devastating. In these cases, preservation of the lenticulostriate arteries rather than subcortical stimulation of the internal capsule represents the critical determinant of the medial limit of resection. We present the surgical strategy for transsylvian resection of an insular low-grade glioma extending beyond the Porto Alegre Line.

Case Report: A 42-year-old woman presented with medically refractory focal epilepsy. Magnetic resonance imaging demonstrated a right insular lesion that was hypointense on T1-weighted imaging, hyperintense on T2-weighted and FLAIR sequences, without gadolinium enhancement. Perfusion MRI demonstrated low relative cerebral blood volume, while MR spectroscopy revealed an elevated choline peak, findings consistent with a diffuse low-grade glioma.Preoperative imaging demonstrated that the medial portion of the tumor extended beyond the Porto Alegre Line, indicating probable intimate relationship with the lenticulostriate arteries. Based on this anatomical finding, a planned subtotal resection was adopted to minimize the risk of permanent motor deficits.

A microsurgical transsylvian approach was performed with wide splitting of the sylvian fissure, allowing exposure of the insular cortex and M2 branches of the middle cerebral artery. Progressive subpial tumor resection was carried out from lateral to medial. Following intraoperative identification of the first lateral lenticulostriate artery, this vessel was deliberately defined as the medial limit of resection, and the tumor surrounding the lenticulostriate complex was intentionally preserved. In this surgical strategy, the anatomical location of the lenticulostriate arteries, rather than subcortical stimulation of the internal capsule, was considered the principal determinant of the safe medial resection boundary.

Histopathological examination confirmed a diffuse low-grade glioma.

Results: The patient experienced no new postoperative neurological deficits. At follow-up, she remained seizure-free, with complete resolution of her medically refractory epilepsy.

Conclusion: The Porto Alegre Line is a practical and reliable preoperative anatomical landmark for predicting medial extension of insular gliomas and their relationship with the lenticulostriate arteries. In tumors extending medial to this line, planned preservation of the lenticulostriate artery complex should take precedence over pursuit of gross-total resection, as these perforating vessels - not the internal capsule identified by subcortical stimulation - constitute the true functional limit of safe medial resection. This strategy maximizes neurological preservation while maintaining the oncological principles of maximal safe resection.