Comparing the accuracy of ultrasound-based measurements of the cervical vagus nerve.

Vagus nerve stimulation (VNS) has become a promising therapy especially for drug resistant epilepsy and other pathologies. Side effects or missing therapeutic success are observed due to cuff electrodes that are too narrow or too wide. Preoperative high-resolution ultrasound is used to evaluate the size of the cervical vagus nerve (CVN) to estimate the size of cuff electrodes for VNS. It remains unclear how precise ultrasound reflects the CVN dimensions, which has been the objective of this study. CVN cross-sections and diameters were investigated in 23 sides from 12 bodies, using ultrasound, histology, and CVN casting in situ as a reference. Morphometric data were obtained including fascicle count and nerve composition in histology. CVN yielded significant side-, age-, and BMI-related differences. CVN cross-sections were smaller in ultrasound when compared to casting and histology (1.5 ± 0.4 vs. 3.1 ± 0.9 vs. 2.3 ± 0.7 mm2). With the given setting in ultrasound, CVN cross-sections were consistently underestimated when compared to casting. Ultrasound-based cross-section measurements are related to a biased estimation of CVN size. A factor to correct for method related differences may help to adjust for accurate cuff electrode sizes for patient needs and to reduce undesired effects and potentially material consumption.

The Use of 5-Aminolevulinic Acid to Assist Gross Total Resection of Paediatric Posterior Fossa Tumours.

BACKGROUND: 5-aminolevulinic acid (5-ALA) use is well established in the resection of adult high-grade gliomas. There is growing interest in its usefulness in the paediatric population. The potential benefit of 5-ALA-guided resection motivated our unit to offer the established adult protocol as off-label use. OBJECTIVE: to determine if 5-ALA guided resection was routinely useful and offered increased gross total resection (GTR) results. METHODS: Nineteen patients harbouring a posterior fossa tumour suggestive of either an ependymoma or medulloblastoma (MB) underwent surgery between January 2018 and October 2019. The mean age was 5 years (range 2-12 years). A dose of 20 mg/kg of 5-ALA (Gliolan®) was given 4 h preoperatively. Intraoperatively, the tumours were viewed under violet-blue light and the presence of fluorescence was recorded. Fluorescence status was compared with histopathological classification and grade, Ki-67 index, GTR rate, and a subjective determination of "usefulness" was determined. RESULTS: The case series included ependymoma grade II (n = 6), ependymoma grade III (n = 4), and MB grade IV (n = 9). For the combined cohort, the strong fluorescence rate was 68% (n = 13), the heterogenous fluorescence rate was 26% (n = 5), and the completely negative fluorescence rate was 5% (n = 1). The strong fluorescence rate of 90% found in the combined ependymoma group compared to the 45% strong fluorescence rate in the MB group was statistically significant (p = 0.05). Within the MB group the Ki-67 index was found to be significantly higher in the strongly fluorescent group as opposed to the patchy or non-fluorescent group (77.5 vs. 40%, p = 0.016). Fluorescence was determined to be useful in 63% of all cases. There was no significant relationship between fluorescence and GTR. The relationship between perceived usefulness and resection was not statistically significant. No adverse drug reactions were recorded. CONCLUSION: This case series adds to the growing body of evidence demonstrating the safety of 5-ALA in the paediatric population. 5-ALA guided resection was found to be useful in the majority of cases but this did not correlate with GTR status. Ependymomas reliably fluoresce in 90% of cases, and 5-ALA-guided resection should be considered when a preoperative diagnosis of ependymoma is suspected.

Intra-Operative Detection of a Left-Sided Non-Recurrent Laryngeal Nerve during Vagus Nerve Stimulator Implantation.

Left sided non-recurrent laryngeal nerves (NRLN) are very rarely observed during surgery in the head and neck region. Arising directly from the cervical aspect of the vagus nerve, the NRLN lies in a vulnerable position distant from its normal location. NRLNs are normally associated with embryological branchial arch aberrations and subsequent vascular anomalies. The anomalous course of the NRLN makes it more susceptible to injury during surgery in the neck region. Knowledge of this anatomical variant will reduce the potential for injury and resultant vocal cord paralysis. During microsurgical dissection of the carotid sheath for the implantation of a vagus nerve stimulator in a 19-year-old female patient with refractory epilepsy, a moderate-sized branch of the main vagus nerve trunk was identified postero-medially within the carotid sheath. Intra-operative stimulation of this nerve resulted in a compound muscle evoked potential from the left vocal cord. Thus, this branch was confirmed to be a left-sided NRLN. The patient had no associated vascular anomalies. This is first reported case of a left-sided NRLN found during VNS insertion. Awareness of the possibility of an NRLN is imperative to prevent iatrogenic injury. A medial location of the vagus nerve within the carotid sheath should alert the surgeon to the possible presence of an NRLN. The absence of fourth branchial arch remnant anomalies is not a guarantee as to the absence of a left-sided NRLN. The addition of intra-operative nerve monitoring for vagus nerve stimulator (VNS) implantation procedures should be strongly considered to help avoid iatrogenic injury.

5-Aminolevulinic Acid-Guided Surgery for Recurrent Supratentorial Pediatric Neoplasms.

BACKGROUND: The use of 5-aminolevulinic acid (5-ALA) in pediatric neuro-oncology is considered off-label, and little data are available on its use in tumor recurrence surgery. Here we present our experience with 5-ALA fluorescence-guided surgery for recurrent supratentorial tumors in the pediatric population. METHODS: Eleven pediatric patients presenting with recurrence of a supratentorial high-grade malignancy (5 glioblastoma [GBM], 6 non-GBM) underwent 5-ALA-assisted surgery. Biopsy specimens were obtained from pathological and normal-appearing areas of the tumor margin. RESULTS: From the margin of the tumor displaying solid fluorescence, a total of 36 samples were obtained. All of these histological samples were found to harbor tumor cells. From areas of vague enhancement, a total of 49 histological samples were taken, of which 38 samples (77%) harbored tumor cells. There was no significant difference in the percentage of biopsy-positive vague fluorescent areas between the GBM cases (80%) and non-GBM cases (75%). A total of 59 biopsy specimens were taken from the tumor margin that appeared completely negative for fluorescence. On analysis, 24 (40.7%) of these specimens demonstrated tumor cells. There was no significant difference in the number of false-negative biopsies between the GBM group (40%) and the non-GBM group (41%). CONCLUSIONS: The positive predictive value of solid fluorescence is high in recurrent disease but is substantially lower in areas of vague fluorescence. The rate of false-negative fluorescence is high. 5-ALA should be considered as an adjuvant in revision surgery with the aforementioned caveats in mind.

Duplicated Vagus Nerve in Adolescence: Case Report and Review of Literature.

BACKGROUND: Vagus nerve stimulation (VNS) has become an increasingly popular procedure for the treatment of epilepsy and depression. Significant complications or side effects associated with VNS surgery may result from either the inadvertent direct injury to the vagus nerve as part of the surgical approach, placement of the electrode, or the concomitant stimulation of vagal efferent fibers. To mitigate these effects, the recognition of anatomic variants that may place the nerve at increased risk is necessary. CASE DESCRIPTION: During microsurgical dissection of the carotid sheath for the implantation of a vagus nerve stimulator in a 17-year-old male patient with refractory epilepsy, additional nonidentified nerve tissue was found running parallel to the vagus nerve. These fibers were two thirds of the thickness of the vagus nerve and ran medial to it, from the most superior to the most inferior aspect of the carotid sheath dissection, found at a distance of at least 4 cm in a craniocaudal direction. This duplicated nerve did not appear to branch from the vagal trunk nor exit the sheath but rather paralleled the course of the vagus nerve. The parallel course and the proximity of the unidentified nerve make this structure likely to be a duplicated vagus nerve. CONCLUSIONS: This is the first reported case of cervical vagus nerve duplication presented in the literature. Surgeons performing VNS implantations should be cognizant of this potential anomaly in order to avoid inadvertent injury to the nerve.