Monopolar tDCS might affect brainstem reflexes: A computational and neurophysiological study.

OBJECTIVE: To assess whether monopolar multi-electrode transcranial direct current stimulation (tDCS) montages might selectively affect deep brain structures through computational predictions and neurophysiological assessment. METHODS: Electric field distribution in deep brain structures (i.e., thalamus and midbrain) were estimated through computational models simulating tDCS with two monopolar and two monopolar multi-electrode montages. Monopolar multi-electrode tDCS was then applied to healthy subject, and effects on pontine and medullary circuitries was evaluated studying changes in blink reflex (BR) and masseter inhibitory reflex (MIR). RESULTS: Computational results suggest that tDCS with monopolar multi-electrode montages might induce electric field intensities in deep brain structure comparable to those in grey matter, while neurophysiological results disclosed that BR and MIR were selectively modulated by tDCS only when cathode was placed over the right deltoid. CONCLUSIONS: Multi-electrode tDCS (anodes over motor cortices, cathode over right deltoid) could induce significant electric fields in the thalamus and midbrain, and selectively affect brainstem neural circuits. SIGNIFICANCE: Multi-electrode tDCS (anodes over motor cortices, cathode over right deltoid) might be further explored to affect brainstem activity, also in the context of non-invasive deep brain stimulation.

2D versus 3D Endoscopy: Head-to-Head Comparison in a Simulated Model of Endoscopic Endonasal Dural Suturing.

Objective Endonasal dural suturing (EDS) has been reported to decrease the incidence of cerebrospinal fluid fistula. This technique requires handling of single-shaft instrumentation in the narrow endonasal corridor. It has been proposed that three-dimensional (3D) endoscopes were associated with improved depth perception. In this study, we sought to perform a comparison of two-dimensional (2D) versus 3D endoscopy by assessing surgical proficiency in a simulated model of EDS. Materials and Methods Twenty-six participants subdivided into groups based on previous endoscopic experience were asked to pass barbed sutures through preset targets with either 2D (Storz Hopkins II) or 3D (Storz TIPCAM) endoscopes on 3D-printed simulation model. Surgical precision and procedural time were measured. All participants completed a Likert scale questionnaire. Results Novice, intermediate, and expert groups took 11.0, 8.7, and 5.7 minutes with 2D endoscopy and 10.9, 9.0, and 7.6 minutes with 3D endoscopy, respectively. The average deviation for novice, intermediate, and expert groups (mm) was 5.5, 4.4, and 4.3 with 2D and 6.6, 4.6, and 3.0 with 3D, respectively. No significant difference in procedural time or accuracy was found in 2D versus 3D endoscopy. 2D endoscopic visualization was preferred by the majority of expert/intermediate participants, while 3D endoscopic visualization by the novice group. Conclusion In this pilot study, there was no statistical difference in procedural time or accuracy when utilizing 2D versus 3D endoscopes. While it is possible that widespread familiarity with 2D endoscopic equipment has biased this study, preliminary analysis suggests that 3D endoscopy offers no definitive advantage over 2D endoscopy in this simulated model of EDS.

Primary Dural Repair via an Endoscopic Endonasal Corridor: Preliminary Development of a 3D-Printed Model for Training.

Objectives Endonasal suturing is an investigational method for dural repair that has been reported to decrease the incidence of cerebrospinal fluid fistula. This method requires handling of single-shaft instrumentation in the narrow endonasal corridor. In this study, we designed a low-cost, surgical model using three-dimensional (3D) printing technology to simulate dural repair through the endonasal corridor and subsequently assess the utility of the model for surgical training. Methods Using an Ultimaker 2+ printer, a 3D-printed replica of the cranial base and nasal cavity was fitted with tissue allograft to recapitulate the dural layer. Residents, fellows, and attending surgeons were asked to place two sutures using a 0-degree endoscope and single-shaft needle driver. Task completion time was recorded. Participants were asked to fill out a Likert scale questionnaire after the experiment. Results Twenty-six participants were separated into groups based on their prior endoscope experience: novice, intermediate, and expert. Twenty-one (95.5%) residents and fellows rated the model as "excellent" or "good" in enhancing their technical skills with endoscopic instrumentation. Three of four (75%) of attendings felt that the model was "excellent" or "good" in usefulness for training in dural suturing. Novice participants required an average of 11 minutes for task completion, as compared with 8.7 minutes for intermediates and 5.7 minutes for experts. Conclusion The proposed model appears to be highly effective in enhancing the endoscopic skills and recapitulating the task of dural repair. Such a low-cost model may be especially important in enhancing endoscopic facility in countries/regions with limited access to cadaveric specimens.

Risk of Infection Associated with Transmucosal Placement of Instrumentation in Clean-Contaminated Field: Systematic Analysis.

Instability of the craniovertebral junction (CVJ) following odontoidectomy is relatively common. Traditionally, separate stage posterior atlantoaxial ± occipitocervical fusion is used for treatment. A transmucosal approach using a clean-contaminated route is associated with hypothetical risks of infectious complications. There is a paucity of information in the literature assessing the risk of surgical site infection (SSI) using the transmucosal approach for hardware placement. The authors conducted a literature search through PubMed identifying patients with pathology requiring transmucosal (i.e., transnasal or transoral) CVJ fixation. Studies that described 1) cases requiring a transmucosal approach and 2) associated infectious complications were included. Rates of SSIs, device removal, unplanned reoperation, and hardware failures were analyzed. Descriptive statistics and odds ratios (ORs) were used to compare complications. Nine studies with a total of 431 patients were identified. There were 4 (0.93%) superficial SSIs and 4 (0.93%) deep SSIs. In total, 1.86% of patients experienced SSI. There were 18 (4.18%) cases of unplanned reoperation, 4 (0.93%) related to SSI. Five (1.16%) patients required removal of their anterior fixation device, 4 (0.93%) related to SSI. ORs comparing our results with Medvedev et al's retrospective National Surgical Quality Improvement Program study assessing the risk associated with posterior cervical fixation showed no statistical difference between postoperative infection rates (OR = 0.72, P = 0.36). An extensive review of the literature found no evidence to suggest placement of spinal hardware via transmucosal corridor is associated with an increased risk of SSI.