Predictive value of Blink reflex and facial corticobulbar motor evoked potential in cerebellopontine angle tumor surgery.

OBJECTIVE: The current study examined the efficacy of the facial corticobulbar motor evoked potentials (FCoMEPs) and blink reflex (BR) on predicting postoperative facial nerve function during cerebellopontine angle (CPA) tumor surgery. METHODS: Data from 110 patients who underwent CPA tumor resection with intraoperative FCoMEPs and BR monitoring were retrospectively reviewed. The association between the amplitude reduction ratios of FCoMEPs and BR at the end of surgery and postoperative facial nerve function was determined. Subsequently, the optimal threshold of FCoMEPs and BR for predicting postoperative facial nerve dysfunction were determined by receiver operating characteristic curve analysis. RESULTS: Valid BR was record in 103 of 110 patients, whereas only 43 patients successfully recorded FCoMEP in orbicularis oculi muscle. A reduction over 50.3% in FCoMEP (O. oris) amplitude was identified as a predictor of postoperative facial nerve dysfunction (sensitivity, 77.1%; specificity, 83.6%). BR was another independent predictor of postoperative facial nerve deficit with excellent predictive performance, especially eyelid closure function. Its optimal cut-off value for predicting long-term postoperative eyelid closure dysfunction was was 51.0% (sensitivity, 94.4%; specificity, 94.4%). CONCLUSIONS: BR can compensate for the deficiencies of the FCoMEPs. The combination of BR and FCoMEPs can be used in CPA tumor surgery. SIGNIFICANCE: The study first proposed an optimal cut-off value of BR amplitude deterioration (50.0%) for predicting postoperative eyelid closure deficits in patients undergoing CPA tumor surgery.

Intraoperative transcranial facial motor evoked potential monitoring in surgery of cerebellopontine angle tumors predicts early and late postoperative facial nerve function.

OBJECTIVE: We propose a novel method that predicts facial nerve function (FNF) calculated from the drop and recovery of facial motor evoked potential (FMEP) amplitude ratio during the surgery of cerebellopontine angle tumors. METHODS: We enrolled 73 patients with cerebellopontine angle tumor, and used a biphasic, constant current, and suprathreshold stimulation (BCS) protocol to record FMEP of the orbicularis oris. We measured the intraoperative minimum-to-baseline amplitude ratio (MBR), the final-to-baseline amplitude ratio (FBR), and the recovery value (RV). RV was measured by subtracting MBR from FBR. Using those values, we evaluated FNF both at early postoperative (EP) and late postoperative (LP) periods. RESULTS: We successfully obtained 62 FMEP readings. Facial palsies occurred in 22 patients during the EP period, and 14 patients recovered during the LP period. Both MBR and FBR showed a significant correlation with FNF in the EP period. RV showed a good predictive power of FNF recovery during the LP period for the first time. CONCLUSIONS: RV is a new and useful predictor of FNF recovery. MBR can be an intraoperative predictor of FNF in the EP period. SIGNIFICANCE: FNF outcome in the early and late postoperative periods can be predicted by FMEP.

Management of Neonatal Facial Paralysis due to Cerebellopontine Angle Arachnoid Cyst: A Case Report.

Arachnoid cysts are benign, cerebrospinal fluid-filled collections that can be located in the brain or spinal cord. Arachnoid cysts form approximately 1% of all intracranial lesions. They are accepted as arachnoid developmental anomaly and arise from membrane splitting or duplication. Generally, lesion growth causes symptoms because of mass effect or obstruction. Arachnoid cyst growing mechanisms are a largely controversial issue. We report the case of a neonatal female patient who presented with congenital facial paralysis. Magnetic resonance imaging showed a right cerebellopontine angle arachnoid cyst causing severe mass effect on the brain stem. Cyst fenestration and cystocisternal shunt was performed through retrosigmoid suboccipital craniotomy.

Continuous and Dynamic Facial Nerve Mapping During Surgery of Cerebellopontine Angle Tumors: Clinical Pilot Series.

OBJECTIVE: To evaluate a new surgical tool combining suction and monopolar neurostimulation (stimulation sucker) for cerebellopontine angle (CPA) tumors. The usefulness for continuous (time) and dynamic (space) facial nerve mapping was studied. METHODS: Patients operated on with the stimulation sucker for a CPA tumor between April 2016 and May 2017 in a tertiary care center were identified. Clinical charts were retrospectively evaluated. The minimum follow-up time of patients was 12 months. RESULTS: The study population included 17 patients with tumor (6 women and 11 men). The age range was from 2 to 77 years (mean age, 45.7 years; standard error of the mean, 22.7 years). Most CPA tumors were large (Koos grade 4) vestibular schwannomas (n = 10); other pathologies included petrous meningioma (n = 1), metastasis (n = 1), medulloblastoma (n = 2), ependymoma (n = 2), and pilocytic astrocytoma (n = 1). One patient with trigeminal neuralgia served as the normal control subject. No complications because of the stimulation sucker were encountered. Clinical and radiologic outcomes compared favorably with institutional experience and literature. The stimulation sucker allowed for continuous (time) mapping of the facial nerve at the site of resection (space). This real-time feedback allowed early identification of the facial nerve. Handling and ergonomy were excellent and workflow improved. The shortcomings compared with a bayonet-shaped bipolar probe were decreased visibility of neurovascular structures and lower spatial discrimination. The new device did not simplify delicate at the brainstem and on the nerve. We think it should be considered as a complementary tool in the surgeon's armamentarium. CONCLUSIONS: Until now, nerve damage as assessed by neuromonitoring (e.g., facial nerve electromyography, motor evoked potential) served as surrogate for nerve function. This concept should be challenged. The studied stimulation sucker detected the facial nerve earlier than conventional techniques, preventing harm by surgical trauma. A larger, prospective study is warranted to better define its role in CPA surgery.

Bilateral cerebellopontine arachnoid cyst: A rare entity.

Bilateral cerebellopontine angle (CPA) arachnoid cysts (ACs) are very rare: only one case is reported in literature. Pathogenesis of those cysts is unknown; they are thought to be congenital. The presenting symptoms of CPA AC are frequently nonspecific or otological. The management of ACs of the CPA is controversial. We are reporting two cases of bilateral CPA AC with their pathophysiology and review of literature.

Superiority of tympanic ball electrodes over mastoid needle electrodes for intraoperative monitoring of hearing function.

OBJECT: Recording the auditory brainstem response (ABR) is a common method for monitoring the integrity of auditory pathways during surgery in the cerebellopontine angle. Electrocochleography (ECochG) is an alternative means of intraoperative neuromonitoring. In the present study the authors compared the practicability and prognostic significance of these two methods by performing simultaneous recordings in the operating room. METHODS: Between 2006 and 2011, 125 patients (mean age 55 years) underwent surgery in the cerebellopontine angle. Seventy-one percent of the patients presented with a hearing deficit, and 37% had useful hearing but with slight functional impairment. Auditory brainstem response was recorded with a subdermal needle electrode at the mastoid. For ECochG recording, a noninvasive ball electrode was attached to the tympanic membrane. Amplitudes obtained from both ECochG and ABR audiometry were compared and correlated to pre- and postoperative hearing deficits. RESULTS: Simultaneous intraoperative monitoring via ABR and ECochG was possible in 114 cases (91%). Postoperatively, 42% of patients showed some degree of new hearing deficit, whereas 4% had improvement. The mean amplitudes in ECochG monitoring were significantly higher (0.18 ± 0.04 µV) than the ABR potentials (0.08 ± 0.006 µV; p < 0.05). All waves recorded at the mastoid needle electrode could be recognized in the potentials of the tympanic ball electrode. Hearing outcome correlated more reliably with the relative amplitude changes in Waves III and V in ECochG (III: p = 0.0008, V: p = 0.0015) than in ABR monitoring (III: p = 0.2075, V: p = 0.0398). CONCLUSIONS: Intraoperative monitoring of the auditory system by recording with noninvasive tympanic ball electrodes is more practicable than with subcutaneous needle electrodes at the tragus. Since there is also a reliable correlation between ECochG and clinical outcome, the method can replace common ABR recording during surgery in the cerebellopontine angle.

Facial nerve monitoring during cerebellopontine angle and skull base tumor surgery: a systematic review from description to current success on function prediction.

BACKGROUND: Intraoperative neuromonitoring has been established as one of the methods by which modern neurosurgery can improve surgical results while reducing morbidity. Despite routine use of intraoperative facial nerve (FN) monitoring, FN injury still is a complication of major concern due to severe negative impact on patient's quality of life. METHODS: Through searches of PubMed, we provided a systematic review of the current literature up to February, 2011, emphasizing all respects of FN monitoring for cerebellopontine angle and skull base tumor surgery from description to current success on function prediction of standard and emerging monitoring techniques. RESULTS: Currently, standard monitoring techniques comprise direct electrical stimulation (DES), free-running electromyography (EMG), and facial motor evoked potential (FMEP). We included 62 studies on function prediction by investigating DES (43 studies), free-running EMG (13 studies), and FMEP (6 studies) criteria. DES mostly evaluated postoperative function by using absolute amplitude, stimulation threshold, and proximal-to-distal amplitude ratio, whereas free-running EMG used the train-time criterion. The prognostic significance of FMEP was assessed with the final-to-baseline amplitude ratio, as well as the event-to-baseline amplitude ratio and waveform complexity. CONCLUSIONS: Although there is a general agreement on the satisfactory functional prediction of different electrophysiological criteria, the lack of standardization in electrode montage and stimulation parameters precludes a definite conclusion regarding the best method. Moreover, studies emphasizing comparison between criteria or even multimodal monitoring and its impact on FN anatomical and functional preservation are still lacking in the literature.

Use of supramaximal stimulation to predict facial nerve outcomes following vestibular schwannoma microsurgery: results from a decade of experience.

OBJECT: The goal of vestibular schwannoma surgery is tumor removal and preservation of neural function. Intraoperative facial nerve (FN) monitoring has emerged as the standard of care, but its role in predicting long-term facial function remains a matter of debate. The present report seeks to describe and critically assess the value of applying current at supramaximal levels in an effort to identify patients destined for permanent facial paralysis. METHODS: Over more than a decade, the protocol for stimulating and assessing the FN during vestibular schwannoma surgery at the authors' institution has consisted of applying pulsed constant-current stimulation at supramaximal levels proximally and distally following tumor resection to generate an amplitude ratio, which subtracted from 100% yields the degree to which the functional integrity of the FN "dropped off" intraoperatively. These data were prospectively collected and additional variables that might impact postoperative FN function were retrospectively reviewed from the medical record. Only patients with anatomically intact FNs and > 12 months of follow-up data were analyzed. RESULTS: There were 267 patients available for review. The average posterior fossa tumor diameter was 24 mm and the rate of long-term good (House-Brackmann Grade I-II) FN function was 84%. Univariate logistic regression analysis revealed that prior treatment, neurofibromatosis Type 2 status, tumor size, cerebellopontine angle extension, subjectively thinned FN at the time of operation, minimal stimulation threshold, percent dropoff by supramaximal stimulation (SMS), and postoperative FN function all correlated statistically (p < 0.05) with long-term FN function. When evaluating patients with significant FN weakness at the time of hospital discharge, only the percent dropoff by SMS remained a significant predictor of long-term FN function. However, the positive predictive value of SMS for long-term weakness is low, at 46%. CONCLUSIONS: In a large cohort of patients, the authors found that interrogating intraoperative FN function with SMS is safe and technically simple. It is useful for predicting which patients will ultimately have good facial function, but is very limited in identifying patients destined for long-term facial weakness. This test may prove helpful in the future in tailoring less than gross-total tumor removal to limit postoperative facial weakness.

Diplopia due to skew deviation following neurotologic procedures.

OBJECTIVE: To describe and characterize diplopia resulting from skew deviation after cerebellopontine angle (CPA) surgery and labyrinthectomy. PATIENTS AND INTERVENTIONS: Retrospective case series of 4 patients who developed vertical diplopia from skew deviation after resection of tumors in the CPA or labyrinthectomy MAIN OUTCOME MEASURE: Complete neuro-opthalmologic examination including opticokinetic testing, confrontational visual field assessment, color plate, pupillary reflex, slit lamp examination, and head tilt test. RESULTS: Four patients with residual hearing preoperatively developed skew deviation immediately after surgical intervention, including translabyrinthine (n = 1) and retrosigmoid (n = 2) approaches to the CPA and labyrinthectomy (n = 1). Neuro-ophthalmologic examination demonstrated intact extraocular movements, and 2- to 14-mm prism diopter hypertropia on both primary gaze and head tilt testing. In all cases, skew deviation resolved spontaneously with normalization of the neuro-ophthalmologic examination within 10 weeks. CONCLUSION: Patients undergoing CPA surgery or labyrinthectomy can develop postoperative diplopia due to skew deviation as a consequence of acute vestibular deafferentation. Patients with significant hearing preoperatively, a probable marker for residual vestibular function, may be especially at risk for developing skew deviation postoperatively.

Giant syringobulbia associated with cerebellopontine angle arachnoid cyst and hydrocephalus.

The aim in reporting this case was to discuss the pathophysiology and treatment issues in an infant with a giant syringobulbia associated with a right cerebellopontine angle (CPA) arachnoid cyst causing noncommunicating hydrocephalus. This 7-month-old infant presented to the hospital with a history of delayed milestones and an abnormal increase in head circumference. Magnetic resonance images and CT scans of the brain showed a large CSF cavity involving the entire brainstem and a right CPA arachnoid cyst causing obstruction of the fourth ventricle and dilation of the lateral and third ventricles. Cerebrospinal fluid diversion was performed by direct communication from the syringobulbia cavity to the left lateral ventricle and from the left lateral ventricle through another ventricular catheter; external ventricular drainage was performed temporarily for 5 days. Communication between the syrinx and arachnoid cyst was confirmed. Clinically, there was a reduction in head circumference, and serial MR imaging of the brain showed a decrease in the size of the syrinx cavity and the ventricle along with opening of the normal CSF pathways. The postoperative course was uneventful, and no further intervention was necessary. On follow-up of the child at 3 years, his developmental milestones were normal. Surgical intervention for this condition is mandatory. The appropriate type of surgery should be performed on the basis of the pathophysiology of the developing syringobulbia.

Cerebellopontine angle arachnoid cyst containing ectopic choroid plexus--case report.

We present a rare and interesting case of a cerebellopontine angle cyst containing ectopic choroid plexus tissue in a 26 year-old female. Surgical resection was performed, and histological examination confirmed the presence of choroid plexus in the cyst wall. This is the first reported case of ectopic choroid plexus at the cerebellopontine angle in an adult. We present the case and review the literature.

Subacute onset of deafness and vertigo in a patient with leptomeningeal metastasis from ovarian cancer.

Ovarian carcinoma is a common gynecological malignancy. Distant metastases usually involve the liver and lung while neurological complications are rare. We describe the case of a 63-year-old woman diagnosed from an ovarian carcinoma with peritoneal seed, which was treated surgically and with chemotherapy. After 4 years she was admitted to our Department for the development of subacute right deafness, vertigo and imbalance. MRI revealed the presence of leptomeningeal carcinomatosis and an expansive formation in the right pontocerebellar angle, suggesting involvement of the right VIII cranial nerve. Examination of the cerebrospinal fluid disclosed the presence of neoplastic cells. Subsequently the patient rapidly deteriorated and eventually died. Involvement of VIII cranial nerve as the presentation of leptomeningeal carcinomatosis in ovarian carcinoma is rare. In the literature at least two other cases presented with deafness, suggesting that leptomeningeal carcinomatosis should be considered in the differential diagnosis when deafness appears in a cancer patient.

Comparison of vestibular function between large cerebellopontine angle meningioma and schwannoma.

CONCLUSION: Abnormal caloric and vestibular evoked myogenic potential (VEMP) responses are frequently encountered with a large cerebellopontine angle (CPA) schwannoma, while normal caloric responses and abnormal VEMPs are noted with a large CPA meningioma. This difference may possibly exist because schwannoma causes vestibular deficits via parenchymal involvement, while vestibular deficits in the meningioma are mostly due to compression neuropathy. OBJECTIVES: This study aimed to compare the tumor characteristics in relation to vestibular function, i.e. caloric and VEMP responses, between large-sized (>2.5 cm) meningioma and schwannoma in the CPA. PATIENTS AND METHODS: Five patients with large CPA meningioma and nine patients with large CPA schwannoma were enrolled in this study. Each patient underwent a battery of tests including audiometry, caloric test, VEMP test, and MRI study. RESULTS: The meningioma group showed 20% caloric abnormality and 75% VEMP abnormality, while the schwannoma group revealed 100% caloric and 100% VEMP abnormalities. A significant difference existed in relation to caloric abnormality between the two groups, but not in relation to VEMP abnormality.

Growth rate of non-operated meningiomas.

INTRODUCTION: Meningiomas are dural-based brain tumors that are typically histologically benign. Some meningiomas grow slowly or seemingly not at all with planimetric measurement. Volumetric measurement may be more accurate because tumors may grow in different directions than the planimetric axes. METHODS: Twenty-one patients (with 22 tumors) had serial MRI brain scans available for review. We reviewed the charts and measured tumor dimensions on the MRI scans. Relative growth rates were calculated for volume and maximum initial diameter using published formulas. Patient demographics, tumor location, and special radiologic characteristics (calcification, T2 hypointensity, dural tail, mass effect, and midline shift) were compared to the volumetric growth rate. RESULTS: Patients included 17 females and 4 males; age at diagnosis 36 to 74 years (mean 61). Follow-up was 2.08 to 10.83 years (mean 3.64). Most tumors were located in the convexity (27.27 %), sphenoid wing (27.27 %), or cerebellopontine angle (13.04 %). Two meningiomas (9.09 %) demonstrated no growth. The mean relative volumetric growth rate was 5.82 %/year, and planimetric was 2.00 %/year (difference 3.82 %/year, p-value < 0.0001). Convexity location had near significant association with slower relative volumetric growth. There were no significant associations between other tumor locations, age, gender, or radiologic characteristics and volumetric growth. CONCLUSIONS: The mean volumetric growth rate was significantly greater than the planimetric growth rate, suggesting that volumetric measurement conveys more information and is superior in assessing tumor growth. This information could have clinical value in determining the frequency of follow-up imaging and the urgency of surgical intervention.

Hyperventilation-induced nystagmus in peripheral vestibulopathy and cerebellopontine angle tumor.

OBJECTIVE: To determine the incidence and characteristics of hyperventilation-induced nystagmus (HIN) in cerebellopontine angle (CPA) tumors and unilateral peripheral vestibulopathy (UPV), and to elucidate differential contribution of hyperventilation to bring out vestibular asymmetry between acute and chronic phases of UPV. METHODS: We recorded horizontal HIN in 33 patients with CPA tumors and 145 with UPV. The UPV included patients of either acute (7 days or less from symptom onset, n = 47) or chronic (more than 7 days from symptom onset, n = 98) phases. RESULTS: The incidence of HIN was higher in the CPA tumor than in the UPV group (82 vs 34%, p < 0.01) and was also higher in the acute than in the chronic UPV group (60 vs 21%, p < 0.01). Furthermore, HIN was more commonly ipsilesional (i-HIN) in the CPA tumor than in the UPV group (52 vs 8%, p < 0.01) and more commonly ipsilesional in the acute than in the chronic UPV group (21 vs 1%, p < 0.01). The patients with i-HIN and acoustic neuroma had a tendency to harbor smaller tumors and to have less severe caloric asymmetry. CONCLUSIONS: The contribution of hyperventilation on vestibular nystagmus differs depending on the disease phase or underlying pathologies. Our study demonstrates that hyperventilation-induced nystagmus (HIN) beating to the side of reduced caloric response, hearing impairment, or abnormal auditory brainstem response responses may be a valuable sign for bedside detection of cerebellopontine angle (CPA) tumors. CPA tumor should be a prime suspicion in patients with acute vertigo and ipsilesional HIN, especially when the vertigo accompanies hearing impairments.

Meningioma in the posterior fossa without dural attachment.

A 14-year-old boy presented with a very rare meningioma in the posterior cranial fossa without dural attachment. Magnetic resonance imaging revealed a 3-cm, well-circumscribed, heterogeneously enhanced, round mass without dural tail sign in the right side of the posterior fossa. Right vertebral angiography revealed very faint tumor staining supplied by the right posterior inferior cerebellar artery. Total removal of the tumor was performed. Intraoperatively, the mass exhibited no attachment to the dura mater, cerebellar parenchyma, or choroid plexus, but was firmly attached to the arachnoid tissue near the foramen of Luschka. Histological and immunohistochemical studies established the diagnosis of meningothelial meningioma (World Health Organization grade I).

Unusual exophytic subependymoma in the bulbo-cerebellar angle. Case report.

Subependymoma was first described by Scheinker in 1945; it frequently occurs in the ventricles and rarely in the spinal canal representing 0.7% of all central nervous system tumours. Most of these intraventricular tumours are subclinical entities, remaining of small size and discovered at autopsy with 0.4%incidence. We report a case of subependymoma with a completely exophytic growth from the foramen of Luscka: only a similar one has been described in the literature but with a lesser cysternal involvement. Neuroradiological and anatomopathological features of subependymoma are discussed.

The role of endoscopic third ventriculostomy in the management of hydrocephalus associated with cerebellopontine angle tumours.

BACKGROUND: Progressive hydrocephalus secondary to cerebellopontine angle tumours has been traditionally managed with ventriculo-peritoneal shunting. Endoscopic third ventriculostomy provides an alternative treatment option and the success rate in this patient group has not previously been reported. METHODS: We report a retrospective series of 11 patients with cerebello-pontine angle tumours who presented with symptomatic hydrocephalus, or developed hydrocephalus following radiosurgery, who underwent endoscopic third ventriculostomy. RESULTS: Seven patients (63.6%) remain shunt free. There were no complications following endoscopy in any patient. Where the ventriculostomy failed there was no additional morbidity. CONCLUSIONS: Endoscopic third ventriculostomy is a low morbidity procedure, which avoids the inherent problems of shunts, particularly infection and should be considered for patients with hydrocephalus and cerebello-pontine angle tumours.