The arcuate fasciculus: Combining structure and function into surgical considerations

BACKGROUND

Two Centuries from today, Karl Friedrich Burdach attributed the nomenclature "arcuate fasciculus" to a white matter (WM) pathway connecting the frontal to the temporal cortices by arching around the Sylvian fissure. Although this label remained essentially unvaried, the concepts related to it and the characterization of the structural properties of this bundle evolved along with the methodological progress of the past years. Concurrently, the functional relevance of the arcuate fasciculus (AF) classically restricted to the linguistic domain has extended to further cognitive abilities. These features make it a relevant structure to consider in a large variety of neurosurgical procedures.

OBJECTIVE

Herein, we build on our previous review uncovering the connectivity provided by the Superior Longitudinal System, including the AF, and provide a handy representation of the structural organization of the AF by considering the frequency of defined reports in the literature. By adopting the same approach, we implement an account of which functions are mediated by this WM bundle. We highlight how this information can be transferred to the neurosurgical field by presenting four surgical cases of glioma resection requiring the evaluation of the relationship between the AF and the nearby structures, and the safest approaches to adopt.

CONCLUSIONS

Our cumulative overview reports the most common wiring patterns and functional implications to be expected when approaching the study of the AF, while still considering seldom descriptions as an account of interindividual variability. Given its extension and the variety of cortical territories it reaches, the AF is a pivotal structure for different cognitive functions, and thorough understanding of its structural wiring and the functions it mediates is necessary for preserving the patient's cognitive abilities during glioma resection.

Photosensitivity Reaction From Operating Room Lights After Oral Administration of 5-Aminolevulinic Acid for Fluorescence-Guided Resection of a Malignant Glioma

Orally administered 5-aminolevulinic acid (5-ALA), which was approved in the United States in 2017, is preferentially metabolized by malignant glioma cells into protoporphyrin IX and enhances tumor visualization when using a blue light filter on an operating microscope. Photosensitivity after 5-ALA administration is a known side effect, but a photosensitivity reaction from operating room lights has not yet been documented. We report the case of a 56-year-old man with a history of previous resection of a grade II astrocytoma who presented with imaging concerning for tumor recurrence and possible malignant transformation. Repeat surgical resection utilized 5-ALA. Soon after the surgery, he developed reddening of his skin, particularly over the right side of his head and neck, with blistering and peeling in a distribution that was particularly exposed to operating room lights during surgery. No other areas of his skin experienced the same redness, blistering, or peeling. Topical lotions were applied and the skin changes resolved spontaneously over weeks. Significant photosensitivity after administration of oral 5-ALA is a rare complication, but neurosurgeons who perform fluorescence-guided tumor resection should remain cognizant of its potential association with exposure to intense light, including in the operating room. Phototoxicity typically is self-limited, but awareness is important to minimize its occurrence.

Combined use of minimal access craniotomy, intraoperative magnetic resonance imaging, and awake functional mapping for the resection of gliomas in 61 patients

OBJECTIVECurrent management of gliomas involves a multidisciplinary approach, including a combination of maximal safe resection, radiotherapy, and chemotherapy. The use of intraoperative MRI (iMRI) helps to maximize extent of resection (EOR), and use of awake functional mapping supports preservation of eloquent areas of the brain. This study reports on the combined use of these surgical adjuncts.METHODSThe authors performed a retrospective review of patients with gliomas who underwent minimal access craniotomy in their iMRI suite (IMRIS) with awake functional mapping between 2010 and 2017. Patient demographics, tumor characteristics, intraoperative and postoperative adverse events, and treatment details were obtained. Volumetric analysis of preoperative tumor volume as well as intraoperative and postoperative residual volumes was performed.RESULTSA total of 61 patients requiring 62 tumor resections met the inclusion criteria. Of the tumors resected, 45.9% were WHO grade I or II and 54.1% were WHO grade III or IV. Intraoperative neurophysiological monitoring modalities included speech alone in 23 cases (37.1%), motor alone in 24 (38.7%), and both speech and motor in 15 (24.2%). Intraoperative MRI demonstrated residual tumor in 48 cases (77.4%), 41 (85.4%) of whom underwent further resection. Median EOR on iMRI and postoperative MRI was 86.0% and 98.5%, respectively, with a mean difference of 10% and a median difference of 10.5% (p < 0.001). Seventeen of 62 cases achieved an increased EOR > 15% related to use of iMRI. Seventeen (60.7%) of 28 low-grade gliomas and 10 (30.3%) of 33 high-grade gliomas achieved complete resection. Significant intraoperative events included at least temporary new or worsened speech alteration in 7 of 38 cases who underwent speech mapping (18.4%), new or worsened weakness in 7 of 39 cases who underwent motor mapping (18.0%), numbness in 2 cases (3.2%), agitation in 2 (3.2%), and seizures in 2 (3.2%). Among the patients with new intraoperative deficits, 2 had residual speech difficulty, and 2 had weakness postoperatively, which improved to baseline strength by 6 months.CONCLUSIONSIn this retrospective case series, the combined use of iMRI and awake functional mapping was demonstrated to be safe and feasible. This combined approach allows one to achieve the dual goals of maximal tumor removal and minimal functional consequences in patients undergoing glioma resection.

Younger age at surgery and lesser seizure frequency as prognostic factors for favorable seizure-related outcome after glioma resection in adults

The identification of variables predictive of good seizure control following surgical tumor resection in adult glioma patients with tumor-related epilepsy would greatly benefit treatment decisions. Therefore, we analyzed the clinical data of adult patients with tumor-related epilepsy who underwent tumor resection at our institute between November 2011 and August 2013. Patients were divided into seizure-free (Engel Ia) and unfavorable outcome groups (Engel Ib-IV), and potential prognostic factors were analyzed. Of 90 patients, 61 (68%) had a favorable outcome at an average of 3 years after surgery. Our analyses indicated that younger age at surgery (P=0.048) and rare seizure frequency (P=0.006) were associated with significantly more favorable postoperative seizure-related outcomes. In conclusion, younger age at surgery and lesser seizure frequency were independent predictors of favorable epileptic seizure control after glioma resection in adults. Thus, early surgical resection is necessary for achieving favorable seizure outcome.

Wide-field spectrally resolved quantitative fluorescence imaging system: toward neurosurgical guidance in glioma resection

In high-grade glioma surgery, tumor resection is often guided by intraoperative fluorescence imaging. 5-aminolevulinic acid-induced protoporphyrin IX (PpIX) provides fluorescent contrast between normal brain tissue and glioma tissue, thus achieving improved tumor delineation and prolonged patient survival compared with conventional white-light-guided resection. However, commercially available fluorescence imaging systems rely solely on visual assessment of fluorescence patterns by the surgeon, which makes the resection more subjective than necessary. We developed a wide-field spectrally resolved fluorescence imaging system utilizing a Generation II scientific CMOS camera and an improved computational model for the precise reconstruction of the PpIX concentration map. In our model, the tissue's optical properties and illumination geometry, which distort the fluorescent emission spectra, are considered. We demonstrate that the CMOS-based system can detect low PpIX concentration at short camera exposure times, while providing high-pixel resolution wide-field images. We show that total variation regularization improves the contrast-to-noise ratio of the reconstructed quantitative concentration map by approximately twofold. Quantitative comparison between the estimated PpIX concentration and tumor histopathology was also investigated to further evaluate the system.