Surgical resection of intrinsic insular tumors: complication avoidance

The contribution of the insula to motor aspects of speech production: a review and a hypothesis

Based on clinical and functional imaging data, the left anterior insula has been assumed to support prearticulatory functions of speech motor control such as the "programming" of vocal tract gestures. In order to further elucidate this model, a recent functional magnetic resonance imaging (fMRI) study of our group (Riecker, Ackermann, Wildgruber, Dogil, & Grodd, 200) investigated both overt (aloud) and covert (silent) production of highly overlearned word strings ("automatic speech"), based on the suggestion that "inner speech" might provide a "window" into preparatory motor activities (Jeannerod, 1994). As a control condition, subjects were asked to reproduce a nonlyrical tune. In contrast to hemodynamic responses within motor cortex and cerebellum, activation of the intrasylvian cortex turned out to be bound to overt task performance. Rather than prearticulatory processes, these findings suggest the left insula to contribute to the actual coordination of the up to 100 muscles engaged in articulation and phonation. Conceivably, the association of speech production with intrasylvian cortex might have evolved within the framework of phylogenetically older connections between the insula and limbic structures, on the one hand, and nonspeech functions of the upper midline musculature such as swallowing, on the other. Whereas (overt) speech tasks predominantly elicit activation within left anterior insula, reproduction of a nonlyrical tune yielded an opposite response pattern. Conceivably, the opposite distributional pattern of speaking and singing at the level of intrasylvian cortex reflects operation of the two hemispheres across different time domains ("double filtering by frequency theory": left hemisphere=segmental information, right hemisphere=intonation contours of verbal utterances and musical melodies; ). In line with this suggestion, a further study of our group (Ackermann et al., 2001) provided first evidence that differential hemispheric filtering might be bound to insular cortex.

Microsurgical anatomy of the insula and the sylvian fissure

Object. The purpose of this study was to define the topographic anatomy, arterial supply, and venous drainage of the insula and sylvian fissure.

Methods. The neural, arterial, and venous anatomy of the insula and sylvian fissure were examined in 43 cerebral hemispheres.

Conclusions. The majority of gyri and sulci of the frontoparietal and temporal opercula had a constant relationship to the insular gyri and sulci and provided landmarks for approaching different parts of the insula. The most lateral lenticulostriate artery, an important landmark in insular surgery, arose 14.6 mm from the apex of the insula and penetrated the anterior perforated substance 15.3 mm medial to the limen insulae. The superior trunk of the middle cerebral artery (MCA) and its branches supplied the anterior, middle, and posterior short gyri; the anterior limiting sulcus; the short sulci; and the insular apex. The inferior trunk supplied the posterior long gyrus, inferior limiting sulcus, and limen area in most hemispheres. Both of these trunks frequently contributed to the supply of the central insular sulcus and the anterior long gyrus. The areas of insular supply of the superior and inferior trunks did not overlap. The most constant insular area of supply by the cortical MCA branches was from the prefrontal and precentral arteries that supplied the anterior and middle short gyri, respectively. The largest insular perforating arteries usually arose from the central and angular arteries and most commonly entered the posterior half of the central insular sulcus and posterior long gyrus. Insular veins drained predominantly to the deep middle cerebral vein, although frequent connections to the superficial venous system were found. Of all the insular veins, the precentral insular vein was the one that most commonly connected to the superficial sylvian vein.

Surgical anatomy of the insula

The insula is the only cortical part of the brain which is not visible on the surface of the hemisphere. This is due to the fact that it is totally covered by the fronto-parietal and temporal opercula. The insula has a triangular shape, and is separated from the opercula by the anterior, superior, and inferior periinsular sulci. The limen insulae is the antero-inferiorly located insular cortical surface which conjoins the inferior insular point, the anterior perforated surface, and the temporo-mesial surface. The insula is morphologically divided into two parts by the central insular sulcus. The anterior part of the insula bears 3 gyri: the anterior, middle, and posterior short insular gyri, separated by the anterior and precentral insular sulcus. The posterior part of the insula contains the anterior and posterior long insular gyri, separated by the postcentral insular sulcus. The vascular supply of the insula is mainly provided by the M2 segment of the middle cerebral artery, which constitutes a substantial obstacle to any open or stereotactic procedure aiming at the insular region. Histologically, the insula is a part of the paralimbic cortex, as it bears in its antero-inferior part an allo and mesocortical area. The insula is functionally involved in cardiac rhythm and arterial blood pressure control, as well as in viscero-motor control and in viscero-sensitive functions. There is considerable evidence for the involvement of the insula as a somesthetic area, including a major role in the processing of nociceptive inputs. Its possible role in some epilepsies may explain some failures of temporal lobe resection. Surgery of the insular lobe is a technical challenge, whose risks can be minimized by the use of intra-operative direct cerebral stimulation.

Transient Foix-Chavany-Marie syndrome after surgical resection of a right insulo-opercular low-grade glioma: case report

OBJECTIVE AND IMPORTANCE

We describe an atypical case of transient Foix-Chavany-Marie syndrome, or faciopharyngoglossomasticatory diplegia with automatic voluntary dissociation, occurring after surgical resection of a right insulo-opercular glioma.

CLINICAL PRESENTATION

A 26-year-old right-handed man experienced partial seizures that were poorly controlled by antiepileptic drugs during a 2-year period as a result of a right insulo-opercular low-grade glioma, leading to the proposal of surgical resection. In addition, 1 year before the operation, the patient experienced a severe brain injury that resulted in a coma. A computed tomographic scan revealed left opercular contusion. The patient recovered completely within 6 months.

INTERVENTION

Intraoperative corticosubcortical electrical functional mapping was performed along the resection, allowing the identification and preservation of the facial and upper limb motor structures. A subtotal removal of the glioma was achieved. The patient had postoperative anarthria, with loss of voluntary muscular functions of the face and tongue, and he had trouble chewing and swallowing. All of these symptoms resolved within 3 months.

CONCLUSION

These findings provide insight into the use of surgery to treat a right insulo-opercular tumor. First, surgeons must be particularly cautious in cases with a potential contralateral lesion (e.g., history of head injury), even if such a lesion is not visible on magnetic resonance imaging scans; preoperative metabolic imaging and electrophysiological investigations should be considered before an operative decision is made. Second, surgeons must perform intraoperative functional mapping to identify and to attempt to preserve the corticosubcortical facial motor structures. A procedure performed while the patient is awake should be discussed to detect the structures involved in chewing and swallowing in cases of suspected bilateral lesions. Third, the patient must be informed of this particular risk before surgery is performed.

Usefulness of intraoperative electrical subcortical mapping during surgery for low-grade gliomas located within eloquent brain regions: functional results in a consecutive series of 103 patients

OBJECT

Although a growing number of authors currently advocate surgery to treat low-grade gliomas, controversy still persists, especially because of the risk of inducing neurological sequelae when the tumor is located within eloquent brain areas. Many researchers performing preoperative neurofunctional imaging and intraoperative electrophysiological methods have recently reported on the usefulness of cortical functional mapping. Despite the frequent involvement of subcortical structures by these gliomas, very few investigators have specifically raised the subject of fiber tracking. The authors in this report describe the importance of mapping cortical and subcortical functional regions by using intraoperative real-time direct electrical stimulations during resection of low-grade gliomas.

METHODS

Between 1996 and 2001, 103 patients harboring a corticosubcortical low-grade glioma in an eloquent area, with no or only mild deficit, had undergone surgery during which intraoperative electrical mapping of functional cortical sites and subcortical pathways was performed throughout the procedure. Both eloquent cortical areas and corresponding white fibers were systematically detected and preserved, thus defining the resection boundaries. Despite an 80% rate of immediate postoperative neurological worsening, 94% of patients recovered their preoperative status within 3 months--10% even improved--and then returned to a normal socioprofessional life. Eighty percent of resections were classified as total or subtotal based on control magnetic resonance images.

CONCLUSIONS

The use of functional mapping of the white matter together with cortical mapping allowed the authors to optimize the benefit/risk ratio of surgery of low-grade glioma invading eloquent regions. Given that preoperative fiber tracking with the aid of neuroimaging is not yet validated, we used intraoperative real-time cortical and subcortical stimulations as a valuable adjunct to the other mapping methods.