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Table of Contents    
Year : 2021  |  Volume : 69  |  Issue : 6  |  Page : 1560-1564

Trans-Sylvian Resection of Giant Left Insular Glioma: Operative Technique and Nuances

Department of Neurosurgery, All India Institute of Medical Sciences, New Delhi, India

Date of Submission13-Dec-2021
Date of Decision13-Dec-2021
Date of Acceptance13-Dec-2021
Date of Web Publication23-Dec-2021

Correspondence Address:
Sarat P Chandra
Department of Neurosurgery, All India Institute of Medical Sciences (AIIMS), New Delhi – 110 029
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0028-3886.333450

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 » Abstract 

Background: Insular glioma was considered a nonsurgical entity due to resection-associated morbidities. The advancement in neurosurgical techniques and adjuncts used in the last two decades made the resection of insular gliomas simpler for neurosurgeons with the maximum extent of resection and acceptable morbidity rates. The complex anatomy of this region remains a challenge for neurosurgeons and requires expertise. The key factors to achieve complete resection in the insular region are the thorough knowledge of surgical anatomy and meticulous microsurgical techniques. Intraoperative adjuncts such as image guidance along with cortical and subcortical mapping assist in excellent outcomes.
Objective: In this study, we describe the operative technique and application of trans-Sylvian approach to do the compartmental dissection done by the senior author, along with challenges faced, with the hope to highlight the efficacy of the approach to achieve maximal resection of this entity without compromising patient's safety.
Materials and Methods: A 32-year-old right-handed gentleman presented with episodes of excessive salivation, tingling sensation on the right side of the body along with nausea that lasted for 15–20 s for the last 8 months and one episode of speech arrest without any loss of consciousness and motor or sensory deficit. CEMRI of the brain was suggestive of left insular glioma. The patient underwent left pterional craniotomy, and gross total resection of the tumor was done using compartmental dissection.
Results: At follow-up after 1 month, the patient is seizure-free without any speech difficulty and motor or sensory deficit.
Conclusion: Compartmental dissection of insular glioma is a safe and efficacious technique to achieve gross total resection of the tumor in this complex region without morbidity.

Keywords: Bubbling, charring, compartmental resection, image guidance/neuronavigation, insular glioma, neuromonitoring, subcortical mapping
Key Message: Compartmental dissection of insular glioma is a safe technique to achieve gross total removal of the tumor, with minimal morbidity and excellent resection. This technique demands precise knowledge of the microsurgical anatomy of this complex region coupled with the surgeon's experience and learning curve.

How to cite this article:
Agrawal R, Arumulla S, Manjunath N, Meena R, Doddamani R, Singh PK, Chandra SP. Trans-Sylvian Resection of Giant Left Insular Glioma: Operative Technique and Nuances. Neurol India 2021;69:1560-4

How to cite this URL:
Agrawal R, Arumulla S, Manjunath N, Meena R, Doddamani R, Singh PK, Chandra SP. Trans-Sylvian Resection of Giant Left Insular Glioma: Operative Technique and Nuances. Neurol India [serial online] 2021 [cited 2022 Jan 19];69:1560-4. Available from:

Insula in Latin connotes island, and J. C. Reil, a German neurologist, aptly coined the term “island of Reil” for this region. It is often referred to as the fifth lobe of the brain which lies deep to the lateral sulcus (Sylvian fissure), surrounded by eloquent white matter tracts and basal ganglia structures. Insula is divided into anterior and posterior parts, with the anterior portion housing three short gyri separated by a prominent sulcus from two long gyri in the posterior part [Figure 1].[1],[2]
Figure 1: Illustration of the human insular cortex: asg, anterior short insular gyrus; msg, middle short insular gyrus; psg, posterior short insular gyrus; alg, anterior long insular gyrus; plg, posterior long insular gyrus; tg, transverse insular gyrus; cis, central insular sulcus; aps, anterior periinsular sulcus; sps, superior periinsular sulcus; ips, inferior periinsular sulcus; li, limen insulae; T2, middle temporal gyrus; mog, medial orbital gyrus; F2, middle frontal gyrus; pcg, precentral gyrus; pg, postcentral gyrus; f2, inferior frontal sulcus; pcs, precentral sulcus; cs, central sulcus of Rolando; ps, postcentral sulcus

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Insula is fed by M2 and M3 segments of the middle cerebral artery (MCA) through its perforating vessels, and venous drainage takes place via the deep middle cerebral veins. Short perforators can be safely coagulated and cut during subpial resection, but long perforating branches travel posteriorly and superiorly on the insula and supply the corona radiata and hence must be preserved to avoid ischemic injury resulting in hemiparesis. The lateral lenticulostriate (LLA) perforators (1–15) arise from the M1-MCA segment. Early identification of the LLA is the key landmark, which marks the medial most limit of insular resection. Transgression beyond the LLAs would lead to direct insult to the basal nuclei and the internal capsule, whereas injury to these perforators would lead to the ischemic insult to the internal capsule and dense hemiplegia[1],[2],[3],[4],[5] [Figure 2].
Figure 2: Representing the arterial supply of insular lesion along with the relationship with LLA- lateral lenticulostriate artery

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Insular gliomas are challenging because of their complex anatomy, functional significance, and intimate relationship with the internal carotid artery (ICA), MCA, and LLA. The Berger–Sanai classification system [Figure 3] was therefore introduced, dividing the insular cortex into quadrants (four zones) based on the Sylvian fissure and foramen of Monro planes.[4],[5],[6] Zone 1 (anterosuperior) constitutes the most common site of insular gliomas (35%), whereas zone 2 (posterosuperior), zone 3 (inferoposterior), and zone 4 (inferoanterior) tumors represented 6% of cases each, while multiple zones were involved in the remaining patients.[3],[4],[6],[7]
Figure 3: Representation showing the division of the insular cortex into quadrants (four zones) based on the Sylvian fissure and foramen of Monro

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 » Objective Top

This article is aimed at describing the operative technique step by step by using a trans-Sylvian corridor and performing compartmental dissection and highlighting the operative nuances involved in low-grade gliomas by using intraoperative neuromonitoring and image guidance.

Case study

A 32-year-old right-handed gentleman doctor by profession presented to us with the symptoms for the last 8 months in the form of episodes of excessive salivation and tingling sensation on the right side of the body along with nausea. The frequency of these episodes was 2–3 times/day and lasted for 15–20 s. He also developed one episode of speech arrest without any loss of consciousness or abnormal body movement. There were no associated comorbidities. He was started on appropriate antiepileptic medication. On examination, there were no significant deficits. Magnetic resonance imaging (MRI) of the brain revealed left insular lesion with heterogenous contrast enhancement along with predominant nonenhancing areas and patchy restriction on diffusion-weighted imaging (DWI) with moderate perilesional edema [Figure 4]. The patient was planned for tumor removal following appropriate consent.
Figure 4: Preoperative MRI Brain- (a) Post-contrast axial section showing left insular lesion with heterogeneous contrast enhancement. (b) On diffusion-weighted imaging, the lesion does not show restriction predominantly

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Surgical technique

The surgery was planned under general anesthesia using pterional craniotomy and the trans-Sylvian approach. The tumor removal was accomplished using sequential compartmental decompression in a systematic way based on the Berger–Sinai zones. The following special equipment were utilized in our technique:

  1. Variable impedance bipolar forceps, and Sutter Medizintechnik and Vesalius bipolar systems
  2. Neuronavigation system (Medtronic Stealth Station S7, USA) [Figure 5]
  3. Neuromonitoring system (Medtronic NIM-ECLIPSE System) [Figure 6]
  4. Cortical and subcortical stimulators; Monopolar and Suction type [Figure 6]
Figure 5: (a) Neuromonitoring system (b) subcortical mapping probe (suction type)

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Figure 6: (a) Neuronavigation/image guidance system. (b) Intraoperative assessment of the margin of tumor resection in our case

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The technique of compartmental dissection using the trans-Sylvian approach is divided into the following steps:

  1. Wide opening of Sylvian fissure
  2. Compartmental dissection of insular gliomas

    1. Antero and posterior superior, inferior anterior and posterior compartments, and finally the medial compartment

  3. Differentiation between tumor and normal brain tissue is of paramount importance. Bipolar cauterization of tumor tissue produces a bubbling effect owing to the high water content, whereas the normal brain tissue chars apart from punctate hemorrhages during suction aspiration.
  4. Resection margins can be further delineated using intraoperative image guidance along with neuromonitoring systems involving cortical and subcortical monitoring [Figure 6].
  5. Protocol of neuromonitoring: The stimulation intensity is initiated at 10–15 mA. We usually perform the surgery at high stimulation (up to 20 mA) settings. The amount of stimulation strength roughly corresponds to the distance from the eloquent white matter tracts, that is, 10-mA current corresponds to approximately 10-mm distance.

 » Video link Top

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Video timeline with audio transcript

0:00–0:45: This video demonstrates the technique of performing compartmental dissection of a giant left insular glioma by using the trans-Sylvian approach.

A 32-year-old right-handed gentleman, a practicing physician by profession, presented to our institution with episodes of excessive salivation, nausea, and tingling on the right half of the body for a duration of 8 months. These episodes lasted for 15–20 s occurring 2–3 times a day.

He suffered one episode of speech arrest associated with a loss of awareness of his surroundings.

Examination revealed no sensory-motor deficits. He was started on appropriate antiepileptic drugs.

00:44–00:55: Insular gliomas are divided into four zones as per the Berger–Sinai classification system by the Sylvian fissure and the foramen of Monroe lines.

00:55–1.18: Contrast MRI of the brain revealed predominantly nonenhancing left insular space-occupying lesion with heterogenous patchy enhancement. On T2 weighted imaging, the lesion was hyperintense and involved all four zones, representing giant insular glioma.

1.18–1.28: Under general anesthesia, the patient's head was fixed with a Mayfield clamp with a 30-degree rotation in the supine position. Pterional craniotomy was performed and the dura was opened in a semicircular fashion.

1.29–01:36: The Sylvian fissure was widely opened in a standard fashion to expose the insular region.

2.19–2.45: Biopsy of the insular lesion is performed. Using bipolar and suction as dynamic retractors sequential compartmental resection as per the Berger–Sinai zones is commenced beginning with the anterior compartment. It can be seen that no retractors are used and only dynamic retraction with the help of bipolar and suction is being utilized.

2:56–3:09: The tumor is coagulated and sucked out using high bipolar coagulation settings along with a standard suction. It is important to note that the tumor tissue bubbles on coagulation owing to its high-water content.

03:30–03:39: The resection is performed by creating windows between the M3-MCA branches and posterior compartmental resection is continued

03:55–04:12: The use of image guidance serves as an important guide during surgery and prevents the surgeon from inadvertently going beyond the limits of the tumor. Thus, it should be used whenever in doubt, even though its accuracy is compromised by the brain shift.

04:13–04:34: Coagulation of the tumor followed by suction decompression is a very useful technique, especially for gliomas. The use of intraoperative cortical and subcortical mapping by using the suction monitoring probe acts as a valuable tool leading to optimal resection and at the same time preventing major motor deficits.

04:34–04:39: The resection is continued posterosuperiorly and then superiorly.

04:50–04:59: It is important to remember that the bubbling tissue represents the tumor tissue, which gives confidence to the surgeon for further resection.

5:00–5:32: The medial limit of the tumor should be meticulously perceived as it is bounded by the internal capsule and the basal ganglia. The lateral lenticulostriate arteries arising from the M1-MCA segment course anteriorly toward the basal ganglia. These perforators are vital and form an important landmark for limiting further medial resection. The cut nutmeg appearance suggests the beginning of the caudate nucleus. These landmarks should always be looked for during the medial resection.

05:34–05:43: The normal white matter chars on coagulation and is identified by the petechial hemorrhages that develop on suctioning.

5:52–06:12: Postoperative recovery was uneventful and the patient remained symptom-free. Histopathology revealed anaplastic oligodendroglioma. MRI performed at 1-month follow-up revealed near-total resection of the tumor. The patient was advised chemoradiotherapy in view of high-grade glioma.


This patient was operated in two sittings as it was a giant insular glioma. Following the second surgery, the patient's recovery was uneventful without any speech difficulty and motor or sensory deficits in the postop period as well as at follow-up after 1 month. A follow-up MRI of the brain showed a good resection of the tumor [Figure 7]. Histopathology confirmed the diagnosis of anaplastic oligodendroglioma (WHO grade 3). Therefore, the patient was advised to undergo chemoradiotherapy.
Figure 7: Follow-up MRI of the brain showing gross total excision of the tumor

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Pearls and pitfalls

  • Thorough anatomical knowledge of the insular region is very important for the operating surgeon to avoid damage to critical vessels to achieve lesser/no neurological deficit.
  • A wide opening of Sylvian fissure is a key step to achieve gross total resection without damaging the eloquent cortices in the vicinity.
  • Compartmental decompression of the insular glioma as demonstrated during the surgery provides a systematic approach for tumor removal.
  • Limit of resection may be best appreciated intraoperatively while using bipolar coagulation. The tumor bubbles during the coagulation owing to its high-water content, whereas the normal white matter chars; moreover, punctate hemorrhages become visible upon suction aspiration.
  • The lateral lenticulostriates form the medial-most resection limit during the surgery for insular gliomas. Identification of these perforators is vital in preventing catastrophic complications due to infarcts in the internal capsule, either due to direct mechanical or thermal injury during coagulation.
  • Neuronavigation is an important adjunct in the assessment of the tumor margin during the surgery, although the accuracy is lost following gross brain shift. However, it still provides a fair idea regarding the residual lesion and the white matter tracts depending upon the surgeon's experience.
  • Functional mapping can be done easily by subcortical motor mapping for the identification of white matter tracts during resection.

 » Discussion Top

Recent cadaveric studies showed that for tumors in the anterior insula (zones 1 and 4), the transsylvian approach provides sufficient exposure.[1],[2],[3],[4],[5],[6],[7],[8],[9],[10] Resection of these tumors is feasible, relatively safe, and with a significant impact on patient outcomes.[2]

The resection of insular gliomas has been refined in recent times with a better understanding of the microsurgical anatomy and use of intraoperative adjuncts such as image guidance and neuromonitoring. The surgeon's experience along with a definite learning curve remains key to successful surgical results and outcomes.[7],[8],[9],[10]

 » Conclusion Top

Compartmental resection of insular gliomas by using meticulous microsurgical dissection along with the use of intraoperative adjuncts such as neuronavigation and neurophysiological monitoring makes this surgery safe and efficacious with minimum morbidity.

Declaration of patient consent

Full and detailed consent from the patient/guardian has been taken. The patient's identity has been adequately anonymized

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

 » References Top

Uddin LQ, Nomi JS, Hébert-Seropian B, Ghaziri J, Boucher O. Structure and function of the human insula. J Clin Neurophysiol 2017;34:300-6.  Back to cited text no. 1
Rey-Dios R, Cohen-Gadol AA. Technical nuances for surgery of insular gliomas: Lessons learned. Neurosurg Focus 2013;34:E6.  Back to cited text no. 2
Benet A, Hervey-Jumper SL, Sánchez JJ, Lawton MT, Berger MS. Surgical assessment of the insula. Part 1: Surgical anatomy and morphometric analysis of the transsylvian and transcortical approaches to the insula. J Neurosurg 2016;124:469-81.  Back to cited text no. 3
Hervey-Jumper SL, Li J, Osorio JA, Lau D, Molinaro AM, Benet A, et al. Surgical assessment of the insula. Part 2: Validation of the Berger-Sanai zone classification system for predicting extent of glioma resection. J Neurosurg 2016;24:482-8.  Back to cited text no. 4
Yaşargil MG, von Ammon K, Cavazos E, Doczi T, Reeves JD, Roth P. Tumours of the limbic and paralimbic systems. Acta Neurochir (Wien) 1992;118:40-52.  Back to cited text no. 5
Hervey-Jumper SL, Berger MS. Insular glioma surgery: An evolution of thought and practice: JNSPG 75th anniversary invited review article. J Neurosurg 2019;130:9-16.  Back to cited text no. 6
Meena R, Doddamani RS, Chipde H, Agrawal D, Mahajan S, Chandra PS. Management dilemma in a rare case of bilateral temporo-insular glioma. Neurol India 2021;69:470-4.  Back to cited text no. 7
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Martinez-Perez R, Hardesty DA, Li R, Carrau RL, Prevedello DM. Sylvian and insular exposure in the extended minipterional approach: Landmarks, benefits, and quantitative analysis using a cadaveric study. World Neurosurg 2020;138:e859-66.  Back to cited text no. 8
Safaee MM, Englot DJ, Han SJ, Lawton MT, Berger MS. The transsylvian approach for resection of insular gliomas: Technical nuances of splitting the Sylvian fissure. J Neurooncol 2016;130:283-7.  Back to cited text no. 9
Panigrahi M, Doshi S, K Chandrasekhar YB, Vooturi S. Avoiding Complications in surgical resection of insular gliomas-Single surgeon experience. Neurol India 2021;69:904-9.  Back to cited text no. 10
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  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7]


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