The Craniovertebral Junction in Rheumatoid Arthritis: State of the Art.

Rheumatoid arthritis (RA) is a chronic inflammatory disorder, characterized by polyarticular inflammation causing progressive joint damage and disability. The mechanisms underlying its pathogenesis involve activation of innate and adaptive immunity, microvascular endothelial cell activation, and inflammatory infiltration of lymphocytes and monocytes into the synovium. Spinal involvement in RA is not typical; when it occurs, the main radiological features are (1) atlantoaxial subluxation (AAS), which is the most typical form of cervical spine involvement; (2) cranial settling-also known as basilar impression, atlantoaxial impaction or superior migration of the odontoid-which is the most severe form of associated spinal instability; and (3) subaxial subluxation. A combination of these alterations may occur. Synovitis is characterized by infiltration of innate and adaptive immune cells; joint destruction is a consequence of activation of synovial fibroblasts, which acquire aggressive, inflammatory, invasive features, associated with increased chondrocyte catabolism and synovial osteoclastogenesis.Neck pain is the most frequent symptom of spinal involvement in RA; it occurs in 40-80% of patients and is mostly localized at the craniocervical junction. Other symptoms-caused by compression of neural structures such as the greater occipital nerve (at C2), the nucleus of the spinal trigeminal tract and the greater auricular nerve-are occipital neuralgia, facial pain and ear pain, respectively. Irritation of the lesser occipital nerve (at C1) can cause pain in the suboccipital region. Sometimes patients may complain of a sensation of their head falling down with flexion, weakness, reduced endurance, loss of ability, gait alterations, paraesthesias or other symptoms due to cord and medullary compression, and upper or lower motor neuron signs, or both. Surgical management of RA remains a challenging field.

Ossification of the Posterior Longitudinal Ligament: Analysis of the Role of Craniovertebral and Spinal Instability.

BACKGROUND: This paper reviews an experience of surgically treating ossification of the posterior longitudinal ligament (OPLL) with fixation of the involved spinal segments alone, without resorting to any bony or soft tissue decompression or attempts at direct resection of the OPLL. While in the early part of the experience, stabilization of only the involved subaxial cervical spinal segments was done, in the later part of the experience, atlantoaxial fixation was included in the multisegmental spinal fixation construct. This treatment is based on the understanding that spinal instability that includes atlantoaxial instability forms the nodal point of the pathogenesis and development of OPLL, and maturation of the presenting clinical symptoms. MATERIALS AND METHODS: Twenty-nine patients were treated in this series. There were 28 males and one female, and their ages ranged from 28 to 75 years (average 57 years). All patients presented with symptoms of neck pain, and progressive and disabling myelopathy-related quadriparesis. In the early part of the series (from 2012 to 2014), 14 patients underwent multilevel subaxial cervical spinal fixation by a transarticular technique of facetal fixation. After November 2014, atlantoaxial lateral mass fixation was included in the fixation construct in the subsequent 15 patients. Clinical assessments were done using a visual analogue scale (VAS), the Japanese Orthopaedic Association (JOA) scale and Goel's clinical grading scale. RESULTS: All patients' clinical symptoms improved in the immediate postoperative period, and the improvement was sustained and progressive in 28 patients. CONCLUSION: Atlantoaxial and subaxial spinal instability seems to be the nodal pathogenetic factor in OPLL. Only stabilization of spinal segments that includes the atlantoaxial joint can provide a safe, simple and rational form of treatment.

Gorham-Stout Disease of the Skull Base With Hearing Loss: Dramatic Recovery and Antiangiogenic Therapy.

Gorham-Stout disease (GSD) is a rare disorder of unknown etiology. We present a 6-year-old male with GSD involving the skull base who presented with recurrent cerebrospinal fluid (CSF) rhinorrhea, severe hearing loss, and facial palsy secondary to cerebellar herniation into the internal auditory canal. After 2 months of treatment with pegylated interferon (IFN) α-2b (50 µg/week), his hearing recovered dramatically. Two years later, new bone formation appeared radiologically and IFN was switched to sirolimus. One year after the switch, CSF rhinorrhea disappeared. Antiangiogenic therapy might inhibit proliferation of vascular endothelial cells in osteolytic lesions and lead to new bone formation.

Tension pneumocephalus as a result of endonasal surgery: an uncommon intracranial complication.

Tension pneumocephalus (TP) is a clinical entity characterized by continued build-up of air within the cranial cavity, leading to abnormal pressure exerted upon the brain and subsequent neurologic deterioration, due to development of a mass effect and potentially a herniation syndrome. Intracranial complications of endoscopic sinus surgery (ESS) and other endonasal procedures are fortunately very rare, occurring in less than 3% of cases. We report 4 cases of small bone defects (<3 mm) in the anterior cranial base accompanied by TP, caused by ESS and other endonasal procedures. The pathophysiology and management of this clinical entity is discussed with a pertinent literature. Four patients with small (<3 mm) skull base defects were identified. All patients presented with active cerebrospinal fluid leaks. CT scans showed intracranial tension pneumocephalus. Using image-guided endoscopic techniques, all defects were addressed with multi-layer repair. Closure was achieved in all patients on the first attempt, with an average follow-up of 36 months. Tension pneumocephalus is a rare event that can occur as a result of traumatic or iatrogenic violation of the dura and should be considered in all patients presenting with altered mental status after endoscopic sinus surgery or other surgical and diagnostic procedures that violate either the cranial or spinal dura. Because of the potential for rapid clinical deterioration and death, prompt brain imaging is warranted to rule out the diagnosis, and urgent neurosurgical consultation is indicated for definitive management.

[Scoliotic spine deformity in children and adolescents associated with the craniovertebral junction pathology].

This literature review is devoted to the clinical and pathogenic aspects of the relationship between Chiari type I malformation (CMT) and scoliosis. The view of the clinical presentation development in CMT associated with scoliosis is considered on the basis of both the CSF dynamics disturbances and vascular pathology of the craniovertebral junction. The role of the posterior atlanto-occipital membrane is evaluated. Case reports of the risk factors for scoliosis progression in patients with CMT are presented.

[The giant fungal body in the sphenoidal sinus and the destruction of the skull base].

The objective of the present study was to estimate the efficacy of the optical systems with the variable visual field angle applied for the endoscopic interventions on the paranasal sinuses. The authors report a clinical observation of the patient presenting with the giant fungal body in the sphenoidal sinus responsible for the partial destruction of the bone canal of the optic nerve and the internal carotid artery. The patient was treated by endoscopic shenoidotomy through the paraseptal approach with the use of a sinuscope with the variable visual field angle. It was shown that the use of optical devices with the variable visual field angle makes it possible to significantly reduce the duration of the surgical intervention, facilitates orientation in the difficult-of-access regions , and ensures adequate control during the removal of neoplasms at the basis of the skull.

Multiple cranial neuropathy as the initial presentation of metastatic prostate adenocarcinoma: case report and review of literature.

The skull base is an atypical metastatic site for prostate carcinoma. It is usually encountered late in the disease process in patients with known advanced disease. However, skull base involvement causing cranial nerve palsies may rarely be the presenting sign of prostate carcinoma. Such patients may present to a number of specialties including neurosurgery and can pose a diagnostic challenge in the absence of lower urinary tract symptoms. Here, we describe an unusual case of prostate adenocarcinoma presenting as a central skull base tumour with multiple cranial neuropathy.

Taxonomy of the Lateral Strain Patterns at the Sphenobasilar Synchondrosis for Osteopathic Cranial Manipulative Medicine.

Lateral strain is a type of nonphysiologic cranial dysfunction that occurs at the sphenobasilar synchondrosis. In this dysfunction, the sphenoid and occiput rotate in the same directions along 2 vertical axes. There is currently no consensus on the nomenclature for this cranial dysfunction. In this article, the authors provide a standard nomenclature for lateral strains using the historical writings of pioneers in osteopathic medicine, including William Gardner Sutherland, DO, Anne L. Wales, DO, and Harold Magoun, DO. The authors establish the following consensus: (1) Lateral strains are named for the side to which the basisphenoid shifts; (2) The more prominent greater wing of the sphenoid is on the same side to which the basisphenoid shifts; (3) In vault and fronto-occipital holds, the holds form a parallelogram shape, with the index fingers pointing to the same side as the more prominent greater wing; and (4) The hand that is on the side of the prominent greater wing will shift anteriorly while the hand on the opposite side will shift posteriorly.

Peak Sinus Pressures During Sneezing in Healthy Controls and Post-Skull Base Surgery Patients.

OBJECTIVES/HYPOTHESIS: Patients are frequently advised to sneeze with an open mouth and avoid nose-blowing following an endoscopic endonasal approache (EEA) to the skull base, despite a lack of quantitative evidence. This study applies computational fluid dynamics (CFD) to quantify sinus pressures along the skull base during sneezing. STUDY DESIGN: Case-control series. METHODS: Computed tomography or magnetic resonance imaging scans of four post-EEA patients and four healthy controls were collected and analyzed utilizing CFD techniques. A pressure drop of 6,000 Pa was applied to the nasopharynx based on values in the literature to simulate expiratory nasal airflow during sneezing. Peak pressures along the skull base in frontal, ethmoid, and sphenoid sinuses were collected. RESULTS: Significant increases in skull base peak pressure was observed during sneezing, with significant individual variations from 2,185 to 5,685 Pa. Interestingly, healthy controls had significantly higher pressures compared to post-EEA patients (5179.37 ± 198.42 Pa vs. patients 3,347.82 ± 1,472.20 Pa, P < .05), which could be related to higher anterior nasal resistance in unoperated healthy controls (0.44 ± 0.22 vs. 0.31 ± 0.16 Pa/mL/sec for patients, P = .38). The sinus pressure buildup may be due to airway resistance functioning as a valve preventing air from being released quickly. Supporting this theory, there was a strong correlation (r = 0.82) between peak skull base pressure and the ratio of anterior resistance to total resistance. Within-subject variation in pressures between different skull base regions was much lower (average = ~5%). CONCLUSIONS: This study provided the first quantitative analysis of air pressure along the skull base during sneezing in post-EEA patients through CFD, suggesting that pressure buildup may depend on individual anatomy. LEVEL OF EVIDENCE: 3b Laryngoscope, 130:2138-2143, 2020.

A Case of Autosomal Dominant Osteopetrosis Type 2 with a CLCN7 Gene Mutation

Osteopetrosis is a rare genetic disease characterized by increased bone density and bone fractures due to defective osteoclast function. Autosomal dominant osteopetrosis type 2 (ADO-2), Albers-Schonberg disease, is characterized by the sclerosis of bones, predominantly involving the spine, pelvis and the base of the skull. Here, we report a typical case of osteopetrosis in a 17.7-year-old male who carries a heterozygous c.746C>T mutation in exon 9 in the chloride voltage-gated channel 7 (CLCN7) gene. The patient's spine showed multiple sclerotic changes including sandwich vertebra. His father had the same mutation but his skeletal radiographs were normal. This is the first reported case of ADO-2, confirmed by genetic testing in a Korean patient.

Sutural strain in orthopedic headgear therapy: a finite element analysis.

INTRODUCTION: The goal of this study was to analyze the strains induced in the sutures of the midface and the cranial base by headgear therapy involving orthopedic forces. Does the mechanical signal induced in the sutures sufficiently account for a growth-influencing effect? METHODS: A finite element model of the viscerocranium and the neurocranium was used. It consisted of 53,555 tetrahedral elements and 97,550 nodes. The strain induced in the sutures of the cranial base and the midface when applying orthopedic headgear forces of 5 and 10 N was computed and recorded with an interactive measurement tool. RESULTS: The magnitude and the distribution of the measured strains depended on the level and the direction of the acting force. Overall, the strain values measured at the sutures of the midface and the cranial base were moderate. The measured peak values at a load of 5 N per side were usually just below 20 microstrain irrespective of the force direction. A characteristic distribution of strain values appeared on the anatomical structures of the midface and the cranial base for each vector direction. The measurements based on the finite element method provided a good overview of the approximate magnitudes of sutural strains with orthopedic headgear therapy. The signal arriving in the sutures is apparently well below threshold, since the maximum measured strains in most sutures were about 100 fold lower than the minimal effective strain. A skeletal effect of the orthopedic headgear due to a mechanical effect on sutural growth cannot be confirmed from these results. CONCLUSIONS: The good clinical efficacy of headgear therapy with orthopedic forces is apparently based mainly on dentoalveolar effects, whereas the skeletal effect due to inhibition of sutural growth is somewhat questionable.

Association of Obstructive Sleep Apnea With Calvarial and Skull Base Thinning.

Importance: Spontaneous cerebrospinal fluid leaks (sCSF-L) of the temporal bone are associated with obesity, calvarial thinning, and obstructive sleep apnea (OSA), and the incidence has doubled in the past decade. It is currently unknown if OSA is independently associated with skull thinning. Objective: To determine if patients with OSA have thinner skulls than patients without OSA. Design, Setting, and Participants: A retrospective cohort study of patients who underwent a level 1 polysomnogram (PSG) and also had high-resolution computed tomographic (CT) imaging of the head from January 2010 to March 2017 at Indiana University was carried out. Patients with moderate to severe OSA (apnea-hypopnea index [AHI]≥25/h) and without OSA (AHI<5/h) were matched for age and body mass index (BMI, calculated as weight in kilograms divided by height in meters squared). Interventions: Measurement of calvarial thickness, extracranial zygoma thickness, skull base height and tegmen dehiscence (>4 mm) when blinded to OSA status. Main Outcomes and Measures: Primary outcomes were calvarial, skull base, and zygoma thickness differences between patients with OSA vs those without OSA. Results: A total of 22 933 patients had a PSG and 1012 also had head CT imaging. Of the 1012 patients with both PSG and CT, the mean (SD) age was 50.8 (16.2) years and 624 (61.7%) were women. Those patients with moderate to severe OSA (56) and without OSA (58) were matched for mean (SD) age (50.3 [6.5] vs 49.8 [6.1] years]) and BMI (37.4 [8.1] vs 38.6 [6.8]). Patients with OSA had thinner mean (SD) calvaria (2.73 [0.67] vs 2.47 [0.52] mm; difference, -0.26 mm; 95% CI, -0.49 to -0.04; Cohen d, 0.44) and thinner skull bases (5.03 [1.40] vs 4.32 [1.28] mm; difference, -0.71; 95% CI, -1.23 to -0.19; Cohen d, 0.53). The mean (SD) extracranial zygoma thickness was the same (4.92 [0.87] vs 4.84 [0.84] mm; difference, -0.07 mm; 95% CI, -0.39 to 0.24). The tegmen mastoideum was dehiscent in nearly twice as many patients with OSA as those without (37% vs 20%; difference, 17%; 95% CI, 0.4-32). Conclusions and Relevance: Obstructive sleep apnea was independently associated with intracranial bone (calvaria and skull base) thinning and not with extracranial (zygoma) thinning. These findings support a possible role of OSA in the pathophysiologic development of sCSF-L.

Complications and donor site morbidity of 3-layer reconstruction with iliotibial tract of the anterior skull base: Retrospective analysis of 186 patients.

BACKGROUND: Anterior skull base reconstruction after resection of sinonasal cancers may be challenging when pedicled flaps are unavailable. The purpose of the present study was to analyze the complication rate and donor site morbidity of 3-layer reconstruction with the iliotibial tract (ITT). METHODS: We retrospectively reviewed all anterior skull base reconstructions with ITT performed from 2007 to 2015. Donor site morbidity was investigated by a dedicated questionnaire. Factors impacting on cerebrospinal fluid (CSF) leak were assessed using the Fisher's exact test. RESULTS: One hundred eighty-six patients were included. The overall complication rate was 9.7%. A CSF leak occurred in 11 patients (5.8%). Twenty patients (10.8%) and 130 patients (69.9%) underwent previous or adjuvant radiotherapy, respectively. Neither radio(chemo)therapy nor age impacted the risk of CSF leak. Six patients (3.2%) experienced complications at the donor site. The questionnaire demonstrated minimal functional and aesthetic morbidity. CONCLUSION: Three-layer reconstruction with the ITT is a safe procedure with acceptable complication rate and donor site morbidity.

Analysis of sutural strain in maxillary protraction therapy.

OBJECTIVE: The goal of the study was to examine the strain in the sutures of the midface and the cranial base with maxillary protraction therapy and to clarify whether such stretching suggests a skeletal effect of the apparatus employed for that purpose. MATERIALS AND METHODS: Using a finite elements model, a maxillary protraction therapy was simulated with various force levels and vectors, and the strains appearing at the sutures (in microstrain) were measured at the midface and the cranial base. The simulation model we employed consisted of 53,555 individual elements; the simulated forces were 2 x 3 N and 2 x 5 N, while the vectors of the applied forces were in the anterior and anterior caudal direction. RESULTS: The maximum measured strains were on average below 10 microstrain, while higher values were measured only at the nasal bone and at the cranial base at the oval and spinous foramina with anterior directed force vectors (26.4 microstrain). With an anterior-caudal force vector, the measured values were usually lower. DISCUSSION: The measured strains were on average about hundredfold lower than the Frost thresholds (2000 microstrain). It does not seem probable that the strains occurring upon maxillary protraction therapy suffice to stimulate any additional bone growth. CONCLUSION: The good clinical efficacy of maxillary protraction therapy is apparently based, for the most part, on dental effects, while its skeletal effects still remain doubtful.

Sarcoidosis of the nervous system.

Although sarcoidosis is rarely confined to the nervous system, any neurological features that do occur frequently happen early in the course of the disease. The most common neurological presentation is with cranial neuropathies, but seizures, chronic meningitis and the effects of mass lesions are also frequent. The diagnostic process should first confirm nervous system involvement and then provide supportive evidence for the underlying disease; in the absence of any positive tissue biopsy, the most useful diagnostic tests are gadolinium enhanced MRI of the brain and CSF analysis, although both are non-specific. The mainstay of treatment is corticosteroids, but these often have to be combined with other immunosuppressants such as methotrexate, hydroxychloroquine or cyclophosphamide. There is increasing evidence that infliximab is a safe treatment with good steroid sparing capacity.

Management of Penetrating Skull Base Injury: A Single Institutional Experience and Review of the Literature.

BACKGROUND: Penetrating skull base injury (PSBI) is uncommon among head injuries, presenting unique diagnostic and therapeutic challenges. Although many cases of PSBIs have been reported, comprehensive understanding of its initial diagnosis, management, and outcome is still unavailable. MATERIALS AND METHODS: A retrospective review was performed for patients treated in neurosurgical department of Changzheng Hospital for PSBIs. Presurgical three-dimensional (3D) Slicer-assisted reconstructions were conducted for each patient. Then we reviewed previous literature about all the published cases of PSBIs worldwide and discussed their common features. RESULTS: A total of 5 patients suffering PSBIs were identified. Penetrating points as well as the surrounding neurovascular structures were clearly visualized, assisting in the presurgical planning of optimal surgical approach and avoiding unexpected vascular injury. Four patients underwent craniotomy with foreign bodies removed successfully and 1 patient received conservative treatment. All of them presented good outcomes after proper management. CONCLUSION: Careful physical examination and radiological evaluation are essential before operation, and angiography is recommended for those with suspected vascular injuries. 3D modeling with 3D Slicer is practicable and reliable, facilitating the diagnosis and presurgical planning. Treatment decision should be made upon the comprehensive evaluation of patient's clinicoradiological features and characteristics of foreign bodies.

Delayed pneumocephalus following shunting for hydrocephalus.

Delayed pneumocephalus is a rare but well-reported complication of cerebrospinal fluid diversion procedures. In most cases the air enters the intracranial cavity via a skull base defect. We report a case of hydrocephalus secondary to aqueduct stenosis. The patient developed pneumocephalus 2 months after successful placement of a ventriculoperitoneal shunt. We describe an attempt at endoscopic diagnosis and repair of the fistula. This was unsuccessful, presumably because the defect was too small to localize even with the use of intrathecal fluorescein. We subsequently performed a conventional craniotomy and anterior fossa repair with placement of an antisiphon device. We suggest that in certain cases, when patients present with long-standing hydrocephalus, it may be advisable to insert either a high-pressure valve or antisiphon device as a primary measure.

Rinosinusitis micótica alérgica con destrucción de base de cráneo / Allergic fungal rhinosinusitis with skull base destruction

La sinusitis micótica alérgica es una enfermedad inflamatoria de la mucosa rinosinusal producida por hongos que pueden aislarse de la cavidad de nasal de individuos sanos. Se produce indirectamente por los hongos que actúan como antígeno y desencadenan una reacción inmunológica mediada por IgE que origina pólipos y una secreción mucosa espesa con detritus e hifas denominada mucina. Su presentación clínica más frecuente es una sinusitis crónica unilateral o bilateral con pólipos. Con menos frecuencia, las sustancias originadas por la desgranulación de los eosinófilos producen remodelación o destrucción ósea y la sinusitis puede simular una neoplasia. Se describe el caso clínico de un paciente que padeció una sinusitis micótica alérgica con destrucción ósea masiva de la base del cráneo y que tuvo extensión intracraneal extradural e intraorbitaria de la enfermedad. Fue tratado con éxito mediante cirugía y corticoides. (AU)

Allergic fungal sinusitis is an inflammatory disease of the rhinosinusal mucosa caused by fungi that can be isolated from the nasal cavity of healthy individuals. The pathology is produced indirectly by the fungus that acts as an antigen and triggers an IgE-mediated allergic reaction that causes polyps and a thick mucous discharge with detritus and hyphae called mucin. Its most common clinical presentation is unilateral or bilateral chronic sinusitis with polyps. Less commonly, substances originated by the degranulation of eosinophils cause bone remodeling or destruction, and sinusitis can simulate a neoplasia. We describe the clinical case of a patient who suffered from allergic fungal sinusitis with massive bone destruction of the skull base and who had intracranial, extradural and intraorbital extension of the disease. He was successfully treated with surgery and corticosteroids.Key words: allergic fungal sinusitis, intracranial extension, endoscopic surgery, transorbital transpalpebral approach. (AU)

[Biomechanics analysis of the impact of maxillofacial injury on skull base damage].

OBJECTIVE: To analyze the impact of maxillofacial injury on skull base. METHODS: A three-dimensional(3D)finite-element model of cranio-maxillofacial bone was established by CT scan data. A lead cylinder in base diameter of 3 cm was designed as an impactor. There regions(upper right maxilla, left infraorbital margin and left zygomatic body)subjected to an impact at the speed of 8.6 m/s(about 30 km/h)was simulated. Thirteen landmarks at the skull base were selected. The values of stress at the end of 0.5, 1.0, 1.5, 2.0 ms were obtained, and the results were analyzed. RESULTS: The dynamic process of the fracture of the jaw and the stress distribution and conduction of the skull base were successfully simulated in three parts of the face. When the impact was on the right maxillary bone region, the stress values of the three points(medial foramen rotundum, medial foramen rotundum, anterior clivus reached the peak at each time point, 26.2, 22.4, 21.5 MPa(t=0.5 ms)and 70.0, 55.0, 45.0 MPa(t=1.0 ms)and 38.0, 26.5, 39.5 MPa(t=1.5 ms)and 26.0, 19.0, 23.0 MPa(t=2.0 ms), respectively. When the impact was on the left margo infraorbitalis orbitaeta region, the stress values of the two points(medial left foramen rotundum, posterior clivus)reached the peak at each time point, 8.8, 16.0 MPa(t=0.5 ms)and 10.0, 18.0 MPa(t=1.0 ms)and 5.5, 6.0 MPa(t=1.5 ms)and 11.5, 12.5 MPa(t=2.0 ms), respectively. When the impact was on the body of left zygomatic bone, the stress values of posterior clivus were 45.0 MPa(t=0.5 ms), 40.0 MPa(t=1.0 ms), 12.0 MPa(t=1.5 ms), 42.5 MPa(t= 2.0 ms), respectively. CONCLUSIONS: According to the difference of stress distribution and conduction of maxillofacial and skull base bone, the speed and the path of force transfer to the skull base were different. Finite-element dynamic simulation can be used for the biomechanics research on maxillofacial trauma.

Intraoperative facial motor evoked potential monitoring with transcranial electrical stimulation during skull base surgery.

OBJECTIVE: To address the limitations of standard electromyography (EMG) facial nerve monitoring techniques by exploring the novel application of multi-pulse transcranial electrical stimulation (mpTES) to myogenic facial motor evoked potential (MEP) monitoring. METHODS: In 76 patients undergoing skull base surgery, mpTES was delivered through electrodes 1cm anterior to C1 and C2 (M1-M2), C3 and C4 (M3-M4) or C3 or C4 and Cz (M3/M4-Mz), with the anode contralateral to the operative side. Facial MEPs were monitored from the orbicularis oris muscle on the operative side. Distal facial nerve excitation was excluded by the absence of single pulse responses and by onset latency consistent with a central origin. RESULTS: M3/M4-Mz mpTES (n=50) reliably produced facial MEPs while M1-M2 (n=18) or M3-M4 (n=8) stimulation produced 6 technical failures. Facial MEPs could be successfully monitored in 21 of 22 patients whose proximal facial nerves were inaccessible to direct stimulation. Using 50, 35 and 0% of baseline amplitude criteria, significant facial deficits were predicted with a sensitivity/specificity of 1.00/0.88, 0.91/0.97 and 0.64/1.00, respectively. CONCLUSIONS: Facial MEPs can provide an ongoing surgeon-independent assessment of facial nerve function and predict facial nerve outcome with sufficiently useful accuracy. SIGNIFICANCE: This method substantially improves facial nerve monitoring during skull base surgery.