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Background:  Chiari malformations, usually congenital, can rarely be associated with arteriovenous (AV) fistulas. We present the first case involving a type IV dural AV fistula with a Chiari type I malformation., Methods:  Retrospective chart review was performed to obtain pertinent details regarding history and examination, pathologic findings, and treatment course., Results:  A 63-year-old woman with a 2-year history of migraines presented with 5 months of occipital, right-sided headaches and neck pain exacerbated by Valsalva maneuvers. Computed tomography (CT) and magnetic resonance imaging (MRI) of the head showed a possible right occipital AV malformation, bilateral cerebellar subdural hygromas, and tonsillar crowding at the foramen magnum indicating an acquired Chiari type I malformation. Angiography demonstrated a Cognardtype IV right posterior occipital dural AV fistula supplied by bilateral middle meningeal and posterior meningeal arteries., Conclusion:  After treatment of the dural AV fistula, hygroma evacuation, and decompression of the acquired Chiari malformation, the patient's Valsalva-induced headaches abated., Competing Interests: None declared., (Thieme. All rights reserved.)

Introduction  The application of cranial tissue sealants to assist with postoperative closure is widespread, but data are lacking regarding its utility in endoscopic endonasal surgery (EEA). A prospective study was conducted to assess the effect of sealant usage on postoperative cerebrospinal fluid (CSF) leak rate following standard reconstruction. Methods  A prospective trial of sealant usage after endoscopic endonasal skull base surgery was performed from May 2016 to June 2019 at a tertiary referral cranial base center. This study enrolled 300 consecutive adult and pediatric patients with skull base pathology who underwent EES in which an intraoperative CSF leak occurred. Patients were sequentially stratified into equally sized groups who did or did not receive sealant as part of their reconstruction. Results  Three hundred consecutive adult and pediatric patients were enrolled in the study and had a confirmed intraoperative CSF leak. The intervention cohort with sealant (first 150 patients) had 21 postoperative CSF leaks (14% rate) compared with 9 postoperative CSF leaks (6% rate) in the control group without sealant ( p  = 0.02). On multivariate analysis, sealant usage was associated with a higher rate of postoperative CSF leak (odds ratio [OR] = 2.7; p  = 0.025). Male gender (OR = 2.4; p  = 0.04) and high-flow intraoperative CSF leak (OR = 3.1; p  = 0.038) were also found to be associated with postoperative CSF leak. Conclusion  Among all patients undergoing EES with an intraoperative CSF leak, the addition of sealant to standard closure techniques did not reduce the rate of postoperative CSF leaks., Competing Interests: Conflict of Interest None declared., (Thieme. All rights reserved.)

Objective  Previous work categorized skull base chordoma (SBC) into three genetic risk groups based on 1p36 and homozygous 9p21(p16) deletions, accounting for a wide variability in prognosis (A = low-risk, B = intermediate-risk, C = high-risk). However, it remains unclear how these groups could guide management. Study Design  By integrating surgical outcome and adjuvant radiation (AdjXRT) information with genetic data on 152 tumors, we sought to develop an evidence-based management algorithm for SBC. Results  Gross total resections (GTRs) were associated with improved progression free survival (PFS) in all genetic groups. For Group C tumors, GTR and AdjXRT independently contributed to PFS (multivariate Cox proportional hazard ratio [HR] = 0.14, p  = 0.002, and HR = 0.40, p  = 0.047, respectively). For Group B tumors, AdjXRT improved outcomes only when GTR was not feasible (log-rank p  = 0.008), but not following GTR (log-rank p  = 0.54). However, 24 of 25 Group A tumors underwent GTR, and AdjXRT for these did not confer any benefit (log-Rank p  = 0.285). The high GTR rates in Group A could be explained by smaller tumor sizes (mean = 0.98cc/4.08cc/4.92cc for Group A/B/C, respectively, p  = 0.031) and lack of invasiveness. Group A tumors were also more frequently diagnosed in young people ( p  = 0.002) as asymptomatic lesions ( p  = 0.001), suggesting that they could be precursors to tumors in higher risk groups. Conclusion  Genotypic grouping by 1p36 and homozygous 9p21(p16) deletions can predict prognosis in SBC and guide management. GTR remains the cornerstone of SBC treatment and can be sufficient without AdjXRT in low and intermediate risk tumors. Low-risk tumors are associated with a less invasive phenotype, which makes them more amenable to GTR., Competing Interests: Conflict of Interest None declared., (Thieme. All rights reserved.)

Ventral masses of the craniocervical junction threaten the medulla and upper spinal cord leading to lower cranial nerve dysfunction and myelopathy. Traditional transoral and newer endonasal approaches can access ventral pathology in this region, though both remain challenging due to the competing goals of achieving sufficient decompression, yet mitigating risk to nearby critical neurovascular structures. Transoral approaches have traditionally been avoided for degenerative pseudotumor which generally slowly regresses following posterior fixation. Here, we present two cases of patients with significant retroodontoid degenerative pseudotumor and pannus causing dysphagia and myelopathy. The first patient was found with a large broad pannus requiring a wide decompression extending from lower clivus to inferior aspect of the C1 arch and odontoid process. The second patient had a more focal mass effect due to pannus and synovial cyst at the level of the inferior half of C1 and midodontoid. Both patients underwent an endoscopic endonasal transodontoid approach for immediate decompression followed by a posterior C1-C2 fusion. In these surgical videos, we highlight anatomic considerations in this critical area, demonstrate nuances of technique, and outline strategies to avoid complications and maximize exposure. The link to the video can be found at: https://youtu.be/19I-GQYGIr4 ., Competing Interests: Conflict of Interest Dr. Gardner reports other from SPIWay, LLC, outside the submitted work; Dr. Snyderman reports other from SPIWay, LLC, outside the submitted work.

Introduction  Facial weakness can result from surgical manipulation of the facial nerve. Intraoperative neuromonitoring reduces functional impairment but no clear guidelines exist regarding interpretation of intraoperative electrophysiological results. Most studies describe subjects with facial nerves encumbered by tumors or those with various grades of facial nerve weakness. We sought to obtain the neurophysiological parameters and stimulation threshold following intraoperative facial nerve triggered electromyography (t-EMG) stimulation during microvascular decompression for trigeminal neuralgia to characterize the response of normal facial nerves via t-EMG. Methods  Facial nerve t-EMG stimulation was performed in seven patients undergoing microvascular decompression for trigeminal neuralgia. Using constant current stimulation, single stimulation pulses of 0.025 to 0.2 mA intensity were applied to the proximal facial nerve. Compound muscle action potentials, duration to onset, and termination of t-EMG responses were recorded for the orbicularis oculi and mentalis muscles. Patients were evaluated for facial weakness following the surgical procedure. Results  Quantifiable t-EMG responses were generated in response to all tested stimulation currents of 0.025, 0.05, 0.1, and 0.2 mA in both muscles, indicating effective nerve conduction. No patients developed facial weakness postoperatively. Conclusions  The presence of t-EMG amplitudes in response to 0.025 mA suggests that facial nerve conduction can take place at lower stimulation intensities than previously reported in patients with tumor burden. Proximal facial nerve stimulation that yields responses with thresholds less than 0.05 mA may be a preferred reference baseline for surgical procedures within the cerebellopontine angle to prevent iatrogenic injury., Competing Interests: Competing Interests Statement The authors have no personal or institutional interest with regards to the authorship and/or publication of this manuscript., (© Thieme Medical Publishers.)