Intraoperative Continuous Neuromonitoring for Vestibular Schwannoma Surgery: Real-Time, Quantitative, and Functional Evaluation

Pediatric vestibular schwannoma without evidence of neurofibromatosis: consecutive 18 microsurgical experiences

PURPOSE

Sporadic vestibular schwannoma (VS) is rare in children in contrast to adults, and detailed investigations of case series of these patients using a single fixed protocol are scarce. This study presents our surgical experience of pediatric VSs without clinical evidence of neurofibromatosis type 2 (NF2) at the initial diagnosis.

METHODS

Among 1385 consecutive sporadic VS surgeries, 18 pediatric patients (1.3%; 11-18 years old) were retrospectively investigated.

RESULTS

The most common initial symptom was hearing disturbance (72.2%), and 6 patients (33.3%) experienced a delayed diagnosis (over 2 years after initial symptom onset). Preoperative image characteristics of these tumors included a solid tumor, hypervascularity, and significant extension into the internal acoustic meatus, when compared with adults. Preoperative embolization was successfully accomplished for 2 recent hypervascular tumors. The tumor resection rate was 95-100% under sufficient intraoperative neuromonitoring, and no additional surgery was required during the follow-up period (average: 57.9 months). No patients experienced permanent facial nerve palsy, and serviceable hearing function was preserved in 6 of 11 patients. Signs of NF2, such as bilateral VSs, were not identified in any patients during the follow-up.

CONCLUSION

Safe and sufficient tumor resection was achieved under detailed neuromonitoring in pediatric patients with sporadic VS, although this tends to be difficult owing to hypervascularity, a small cranium, and significant meatal extension. Preoperative embolization may help safe resection of hypervascular tumors. Subsequent development of NF2 has not been observed up to the most recent follow-up, but careful observation is essential for these younger patients.

Facial Nerve Function After Microsurgical Resection in Vestibular Schwannoma Under Neurophysiological Monitoring

Background

The use of intraoperative neurophysiological monitoring, including direct nerve stimulation (especially the facial nerve), acoustic evoked potentials (AEP) and somatosensory evoked potentials (SSEP), is a helpful tool in the microsurgery of vestibular schwannoma to prevent nerve injury. Patient characteristics and intraoperative and postoperative variables might also influence the postoperative facial nerve function. The study was performed to investigate these variables and the intraoperative neurophysiological monitoring values.

Methods

Seventy-nine patients with vestibular schwannoma were included consecutively into this study. Intraoperative neurophysiological monitoring, including SSEP, AEP, and direct nerve stimulation for facial and trigeminal nerve electromyography, was performed utilizing digital data storage in all cases. The intensity (in volts) of the direct stimulation and the latency (in ms) for the orbicularis oculi and the orbicularis oris muscle and the amplitude (in mV) was measured. Univariate and multivariate statistical analyses concerning the different parameters was performed directly after the operation and in the subsequent follow-ups 3 and 6 months after the operation.

Results

The mean intensity was 0.79 V (SD.29). The latency and amplitude for the oris muscle was 5.2 ms (SD 2.07) and 0.68 mV (SD.57), respectively. The mean latency for the occuli muscle was 5.58 ms (SD 2.2) and the amplitude was 0.58 mV (SD 1.04). The univariate and multivariate statistical analyses showed significance concerning the postoperative facial nerve function and the amplitude of the direct stimulation of the facial nerve in the orbicularis oris muscle (p = 0.03), so repeated direct nerve stimulation might show FN function deterioration. The mean diameter of the tumors was 24 mm (range 10–57 mm). Cross total resection and near total was achieved in 76 patients (96%) and subtotal in three patients (4%). The preoperative House–Brakeman score (HBS) 1 was constant in 65 (82%) cases. The mortality in our series was 0%; the overall morbidity was 10%. The HBS was not influenced concerning the extent of resection. The mean follow-up was 28 months (range 6 to 60 months). The limitations of the study might be a low number of patients and the retrospective character of the study.

Conclusion

Intraoperative neurophysiological monitoring is crucial in vestibular schwannoma surgery. Repeated direct nerve stimulation and a detected decreased amplitude might show facial nerve function deterioration.

Application of Subperineural Resection Technique in Vestibular Schwannomas: Surgical Efficacy and Outcomes in 124 patients

Objective

We aimed to explore the application and prospects of the subperineural resection technique for tumor separation and removal under the perineurium during surgery for vestibular schwannomas (VSs).

Methods

This study retrospectively analyzed 124 patients with VSs who underwent surgery via a retrosigmoid approach from July 2015 to October 2020 in the Department of Neurosurgery, Tangdu Hospital, Air Force Military Medical University. The data will be discussed with regard to the following aspects: clinical features, surgical strategies, tumor resection extent, facial-acoustic function preservation, and postoperative complications.

Results

Gross total resection (GTR) of the tumor was achieved in 104 patients, with a GTR rate of 83.9%, and subtotal resection (STR) of the tumor was achieved in 20 patients. There was no significant difference in facial and acoustic nerve functional preservation between GTR and STR, as well as in tumor resection between solid and cystic tumors. The retention rate reached 97.6% in terms of complete anatomical facial nerve preservation. Facial nerve function was assessed using the House-Brackmann (HB) grading score. Consequently, HB grades of I-II, III-IV, and V-VI were determined for 96 (77.4%), 25 (20.2%), and 3 (2.4%) cases, respectively, 1 week postoperatively and accounted for 110 cases (88.7%), 13 cases (10.5%), and 1 case (0.8%), respectively, at 6 months. Fifteen of 35 (42.9%) patients with serviceable hearing before the operation still had serviceable hearing at 6 months postoperatively. There were 5 cases of cerebellar or brainstem bleeding after the operation, and one patient died. Multivariate logistic regression analysis showed that older age (≥60 years, p = 0.011), large tumor (>3 cm, p = 0.004), and cystic tumor (p = 0.046) were independent risk factors associated with the extent of adhesion between the tumor and the brainstem and facial-acoustic nerve.

Conclusion

We successfully applied the subperineural resection technique to a large series of patients with VSs and achieved satisfactory results. Accurate identification of the perineurium and subperineural resection of the tumor can effectively reduce the disturbance of the facial-acoustic nerve during the operation and provide an intuitive basis for judging the tumor boundary. The subperineural resection technique may be conducive to improving the rate of total tumor resection and facial-acoustic nerve functional preservation in the surgical treatment of VSs.