Surgical assessment of the insula. Part 1: surgical anatomy and morphometric analysis of the transsylvian and transcortical approaches to the insula

Abstract

obJective Transcortical and transsylvian corridors have been previously described as the main surgical approaches to the insula, but there is insufficient evidence to support one approach versus the other. The authors performed a cadaveric comparative study regarding insular exposure, surgical window and freedom, between the transcortical and transsylvian approaches (with and without cutting superficial sylvian bridging veins). Surgical anatomy and skull surface reference points to the different insular regions are also described. methods Sixteen cadaveric specimens were embalmed with a customized formula to enhance neurosurgical simulation. Two different blocks were defined in the study: first, transsylvian without (TS) and with the superficial sylvian bridging veins cut (TSVC) and transcortical (TC) approaches to the insula were simulated in all (16) specimens. Insular surface exposure, surgical window and surgical freedom were calculated for each procedure and related to the BergerSanai insular glioma classification (Zones I-IV) in 10 specimens. Second, the venous drainage pattern and anatomical landmarks considered critical for surgical planning were studied in all specimens. results In the insular Zone I (anterior-superior), the TC approach provided the best insular exposure compared with both TS and TSVC. The surgical window obtained with the TC approach was also larger than that obtained with the TS. The TC approach provided 137% more surgical freedom than the TS approach. Only the TC corridor provided complete insular exposure. In Zone II (posterior-superior), results depended on the degree of opercular resection. Without resection of the precentral gyrus in the operculum, insula exposure, surgical windows and surgical freedom were equivalent. If the opercular cortex was resected, the insula exposure and surgical freedom obtained through the TC approach was greater to that of the other groups. In Zone III (posterior-inferior), the TC approach provided better surgical exposure than the TS, yet similar to the TSVC. The TC approach provided the best insular exposure, surgical window, and surgical freedom if components of Heschl's gyrus were resected. In Zone IV (anterior-inferior), the TC corridor provided better exposure than both the TS and the TSVC. The surgical window was equivalent. Surgical freedom provided by the TC was greater than the TS approach. This zone was completely exposed only with the TC approach. A dominant anterior venous drainage was found in 87% of the specimens. In this group, 50% of the specimens had good alternative venous drainage. The sylvian fissure corresponded to the superior segment of the squamosal suture in 14 of 16 specimens. The foramen of Monro was 1.9 cm anterior and 4.42 cm superior to the external acoustic meatus. The M 2 branch over the central sulcus of the insula became the precentral M 4 (rolandic) artery in all specimens. coNclusioNs Overall, the TC approach to the insula provided better insula exposure and surgical freedom compared with the TS and the TSVC. Corti...

Awake craniotomy versus craniotomy under general anesthesia for the surgical treatment of insular glioma: choices and outcomes

“…Use of the transcortical approach for the resection of this type of tumor is another technique that is not performed in our hospital, even though it may provide greater exposure of the insula and therefore might facilitate a greater EOR [29]. However, in our experience, this technique is not in widespread use, plus it should be critically evaluated as it involves the use of an approach through healthy brain tissue.…”

The transsylvian approach for resection of insular gliomas: technical nuances of splitting the Sylvian fissure

“…This approach may be particularly useful for posterior insular lesions (zones 2 and 3) where the transsylvian approach is severely limited by the narrow Sylvian cistern [32]. An important consideration for the transcortical approach in cases of posterior-based insular lesions is that the surgical profile is highly dependent on brain mapping, thus difficulty to predict preoperatively.…”

“…Our group has shown that tumor location within the insula correlates with extent of resection [25] and recent cadaveric studies showed that for tumors in the anterior insula (zones 1 and 4), the transsylvian approach can provide sufficient exposure [32]. The sacrifice of Sylvian bridging veins may be required to achieve the desired exposure, however this can be dangerous in up to 30 % of patients where there is poor collateral outflow through the vein of Labbé or superior sagittal sinus [32,33]. It is also recognized that the transsylvian approach may in some cases require significant retraction, particularly for exposure of large insular tumors.…”

Neuronavigated Fiber Dissection with Pial Preservation: Laboratory Model to Simulate Opercular Approaches to Insular Tumors

“…An elastic maintains the tracker in a rigid position. 00: 13 The Axiem probe of the navigation system allows to trace the insular profile (corresponding to the anterior, superior and inferior insular sulcus) on the cortical surface. 00: 23…”

“…First, it allows to remain subpially to the vessels running on the insular surface, thus minimizing the risk of injury to M2/M3 arteries and veins. Second, the exposure has been shown to be much wider after operculum removal, rather than through the transylvian approach 13 , thus reducing opercular retraction.…”