Validity of Presurgical Functional Localization. In: Stippich C, editor. Clinical Functional MRI. Berlin: Springer Berlin Heidelberg; 2007. pp. 167-87. [DOI: 10.1007/978-3-540-49976-3_7]

Longitudinal Disconnection Tractograms to Investigate the Functional Consequences of White Matter Damage: An Automated Pipeline

BACKGROUND AND PURPOSE

Neurosurgical resection is one of the few opportunities researchers have to image the human brain pre- and postfocal damage. A major challenge associated with brains undergoing surgical resection is that they often do not fit brain templates most image-processing methodologies are based on. Manual intervention is required to reconcile the pathology, requiring time investment and introducing reproducibility concerns, and extreme cases must be excluded.

METHODS

We propose an automatic longitudinal pipeline based on High Angular Resolution Diffusion Imaging acquisitions to facilitate a Pathway Lesion Symptom Mapping analysis relating focal white matter injury to functional deficits. This two-part approach includes (i) automatic segmentation of focal white matter injury from anisotropic power differences, and (ii) modeling disconnection using tractography on the single-subject level, which specifically identifies the disconnections associated with focal white matter damage.

RESULTS

The advantages of this approach stem from (1) objective and automatic lesion segmentation and tractogram generation, (2) objective and precise segmentation of affected tissue likely to be associated with damage to long-range white matter pathways (defined by anisotropic power), (3) good performance even in the cases of anatomical distortions by use of nonlinear tensor-based registration, which aligns images using an approach sensitive to white matter microstructure.

CONCLUSIONS

Mapping a system as variable and complex as the human brain requires sample sizes much larger than the current technology can support. This pipeline can be used to execute large-scale, sufficiently powered analyses by meeting the need for an automatic approach to objectively quantify white matter disconnection.

[Controversy in the management of WHO grade II gliomas in eloquent brain areas: recent literature review]

Recent studies have shown that diffuse grade II gliomas (GGII) located in eloquent brain areas represent over 80% of all GGII. The optimal management of these tumours is still controversial. It has long been considered that surgery is not an option for GGII within eloquent areas, due to the high risk of inducing postoperative sequelae in patients with normal neurological explorations. However, the safety of these surgeries has significantly improved in recent years due to the rapid development of techniques enabling a precise mapping of brain functions. Noninvasive functional neuroimaging techniques have been recently developed, enabling cortical mapping of the entire brain prior to surgical procedures. Such precise data provide a preoperative estimation of the location of eloquent areas in relation to the tumour, which is essential for surgical planning and preoperative assessment of morbidity for various surgical approaches. The intraoperative electrical stimulation (IES) mapping technique consists in the application of a bipolar electrode on the brain tissue, enabling an accurate location of brain functions. This provides unique assistance in GGII resection, as it generates a discrete and transient "virtual" lesion within the eloquent tissue. Tumour removal is then tailored according to functional boundaries in order to optimise the quality of resection and to minimise the risk of postoperative sequelae, preserving quality of life. For patients with a GGII in an eloquent area, the possibility of an early resection should be evaluated by a multidisciplinary neuro-oncology team specialising in the management of such tumours.

Brain mapping in neuro-oncology: what is the future?

Surgery is the first treatment in neuro-oncology. However, brain gliomas are frequently located within eloquent areas. Therefore, in order to maximize the extent of resection while preserving cerebral functions, owing to major interindividual anatomo–functional variability across patients, functional mapping is now mandatory. Preoperative functional neuroimaging allows a better understanding of the individual organization of brain networks, leading to optimized surgical indications and planning. Intrasurgical cortical and subcortical stimulation, often carried out in awake patients, enables assessment of the performance of online anatomo–functional correlations, with increased resection according to functional boundaries. Postoperative functional neuroimaging following recovery, regularly carried out after active rehabilitation, provides information regarding cerebral plasticity over time, possibly opening the door to another surgery(ies). In summary, brain mapping allows surgical removal in eloquent areas classically considered as ‘inoperable’, and also preservation or even improvement of quality of life, while increasing median survival. The future persepctive is now to move towards dynamic therapeutic strategy based on a multiple-stage surgical approach, combined with (neo)adjuvant chemotherapy and/or radiotherapy. In addition, cerebral mapping enables a better knowledge of brain processing, especially concerning connectivity and plasticity, creating a link between neuro-oncology and cognitive neurosciences, and opening the concept of ‘functional neuro-oncology’.

Functional outcome after language mapping for insular World Health Organization Grade II gliomas in the dominant hemisphere: experience with 24 patients

OBJECT

Despite the report of recent experiences of insular surgery in the past decade, there has been no series specifically dedicated to studying functional outcome following resection of insular WHO Grade II gliomas involving the dominant hemisphere, in patients with no or only mild preoperative language deficit. In this article, the authors analyze the contribution of awake mapping for preservation of brain function, especially language, in a homogeneous series of 24 patients who underwent surgery for insular Grade II gliomas within the dominant insular lobe.

METHODS

Twenty-four patients underwent surgery for an insular Grade II glioma involving the dominant hemisphere (22 left, 2 right), revealed by seizures in all but 1 case. The preoperative neurological examination result was normal in 17 patients (71%), whereas 7 patients presented with language disorders detected using an accurate language assessment performed by a speech therapist. All surgeries were performed on awake patients utilizing intra-operative language mapping involving cortical and subcortical stimulation.

RESULTS

There were no intrasurgical complications or postsurgical sensorimotor deficits. Despite an immediate postoperative language worsening in 12 cases (50%), all patients recovered to a normal status within 3 months, and 6 cases even improved in comparison with their preoperative examination results. The 24 patients returned to normal social and professional lives. Moreover, the surgery had a favorable impact on epilepsy in all but 4 cases (83%). On control MR imaging, 62.5% of resections were total or subtotal. Three patients underwent a second or third awake surgery, with no additional deficit. All but 2 patients (92%) are alive after a mean follow-up of 3 years (range 3-133 months).

CONCLUSIONS

Although insular surgery was long believed to be too risky, the present results show that the rate of permanent deficit, especially dysphasia, following resection of Grade II gliomas involving the dominant insula has been dramatically reduced (none in this patient series), thanks to the systematic use of intraoperative awake mapping, even in cases of repeated operations. Furthermore, patient quality of life may be improved due to a decrease of epilepsy after surgery. Thus, the authors suggest systematically considering resection when an insular Grade II glioma is diagnosed after seizures in a patient with no or mild deficit, even a glioma invading the dominant hemisphere.

Intraoperative subcortical stimulation mapping of language pathways in a consecutive series of 115 patients with Grade II glioma in the left dominant hemisphere

OBJECT

Despite better knowledge of cortical language organization, its subcortical anatomofunctional connectivity remains poorly understood. The authors used intraoperative subcortical stimulation in awake patients undergoing operation for a glioma in the left dominant hemisphere to map the language pathways and to determine the contribution of such a method to surgical results.

METHODS

One hundred fifteen patients harboring a World Health Organization Grade II glioma within language areas underwent operation after induction of local anesthesia, using direct electrical stimulation to perform online cortical and subcortical language mapping throughout the resection.

RESULTS

After detection of cortical language sites, the authors identified 1 or several of the following subcortical language pathways in all patients: 1) arcuate fasciculus, eliciting phonemic paraphasia when stimulated; 2) inferior frontooccipital fasciculus, generating semantic paraphasia when stimulated; 3) subcallosal fasciculus, inducing transcortical motor aphasia during stimulation; 4) frontoparietal phonological loop, eliciting speech apraxia during stimulation; and 5) fibers coming from the ventral premotor cortex, inducing anarthria when stimulated. These structures were preserved, representing the limits of the resection. Despite a transient immediate postoperative worsening, all but 2 patients (98%) returned to baseline or better. On control MR imaging, 83% of resections were total or subtotal.

CONCLUSIONS

These results represent the largest experience with human subcortical language mapping ever reported. The use of intraoperative cortical and subcortical stimulation gives a unique opportunity to perform an accurate and reliable real-time anatomofunctional study of language connectivity. Such knowledge of the individual organization of language networks enables practitioners to optimize the benefit-to-risk ratio of surgery for Grade II glioma within the left dominant hemisphere.