Transcortical 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: Surgical treatment of dominant insular gliomas requires balancing maximal safe resection with preservation of language and motor function. Tumors extending medial to the Porto Alegre Line (PAL) have close anatomical relationships with the lenticulostriate arteries (LSAs), which represent the principal limitation to medial tumor removal due to the risk of ischemic injury to the internal capsule. In dominant hemisphere lesions, awake cortical and subcortical mapping allows preservation of essential language networks, while the medial limit of resection is ultimately determined by the anatomical location of the lenticulostriate arteries rather than subcortical stimulation alone. This surgical video demonstrates our transcortical strategy for resection of a dominant insular low-grade glioma. Case Report: A 24-year-old woman presented with medically refractory focal epilepsy. Magnetic resonance imaging demonstrated a left insular tumor hypointense on T1-weighted imaging and hyperintense on T2-weighted and FLAIR sequences, without gadolinium enhancement, associated with low perfusion and increased choline peak on magnetic resonance spectroscopy, consistent with diffuse low-grade glioma. Preoperative imaging showed extension medial to the Porto Alegre Line, suggesting intimate involvement with the lenticulostriate artery territory. The procedure was performed under awake craniotomy with continuous cortical and subcortical language mapping. After identification of functional areas in the dominant frontal operculum, a corticotomy was performed through the left inferior frontal gyrus, providing a direct transcortical corridor to the insular lesion. Tumor removal proceeded using a subpial technique from lateral to medial. Posterior resection was limited when subcortical stimulation produced reproducible paraphasic errors, corresponding anatomically to the superior longitudinal fasciculus (SLF), which defined the functional posterior boundary of resection. During medial dissection, the superiorly located lateral lenticulostriate artery was identified at the deepest portion of the surgical field, above the inferior fronto-occipital fasciculus (IFOF). This vessel was considered the definitive medial limit of resection, and the tumor component surrounding the lenticulostriate artery complex was intentionally preserved to prevent ischemic injury to the internal capsule. Near-total tumor removal was achieved while maintaining preservation of the critical vascular structures. Histopathological examination confirmed a WHO grade 2 diffuse glioma. Results: The patient experienced no permanent postoperative language or motor deficits and became seizure-free after surgery. Conclusion: In dominant insular gliomas extending medial to the Porto Alegre Line, awake transcortical surgery provides safe access for maximal functional resection. Subcortical language mapping allows identification of functional posterior limits through the superior longitudinal fasciculus, whereas the medial boundary should be determined by direct microsurgical identification of the lenticulostriate arteries. The Porto Alegre Line represents a valuable preoperative anatomical landmark for predicting vascular involvement and guiding planned subtotal resection, maximizing neurological preservation while maintaining the principles of maximal safe glioma surgery.