The Changing Paradigm for the Surgical Treatment of Large Vestibular Schwannomas

Large vestibular schwannoma treated using a cranial nerve sparing approach with planned subtotal microsurgical resection and stereotactic radiosurgery: meta-analysis and International Stereotactic Radiosurgery Society (ISRS) practice guidelines

INTRODUCTION

Stereotactic radiosurgery (SRS) has become a standard of care for small- to medium- size vestibular schwannomas (VS), while the majority of patients with large VS still require microsurgical resection due to potential consequences of long tract and cranial nerve compression, intracranial hypertension or hydrocephalus.

METHODS

We performed a systematic review and meta-analysis of the literature specific to planned subtotal resection for large VSs followed by SRS to the residual tumor to inform clinical practice guideline development. The Medline and Embase databases were used to apply the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) approach to search for manuscripts reporting outcomes for large VSs treated with this paradigm, with a search end date of June 1st 2023. Crude outcomes were pooled using weighted random effects.

RESULTS

12 series met inclusion criteria reporting on treatment outcomes for 677 patients. Overall tumor control was 89.9% (86.9-92.9%, p < 0.001), with tumor stability observed in 43.9% (19.9-68%, p < 0.001) and tumor reduction in 39.9% (57-74.2%, p = 0.02) post-SRS. Facial nerve functional preservation immediately after microsurgery was 88.0% (82.7-93.3%, p < 0.001), improving to 94.4% (91.4-97.4%, p < 0.001) at last follow-up. Cochlear functional preservation immediately after microsurgery was 58.8% (33.2-84.4%, p < 0.001), decreasing to 57.4% (33-81.8%, p < 0.001) at last follow-up.

CONCLUSIONS

A cranial nerve sparing approach with planned subtotal microsurgical resection and SRS to the residual tumor achieves high rates of tumor control with highly satisfactory outcome of facial and cochlear functional preservation. Clinical practice consensus recommendations on behalf of the International Stereotactic Radiosurgery Society (ISRS) are also presented.

Characterization of jugular bulb position on computed tomography (CT) with implications for excision of vestibular schwannomas

To describe the distribution of jugular bulb position and pneumatization of posterior lip of internal auditory meatus (IAM) in patients with vestibular schwannoma (VS). This retrospective study included 43 patients who had a thin slice (< 2 mm) CT temporal bone for preoperative planning of retrosigmoid approach for excision of VS between March 2011 and March 2021. On computed tomography (CT), high riding jugular bulb was defined by its relationship to IAM and correlated with type of jugular bulb according to Manjila et al. classification. The most common position of the jugular bulb was type 2a on the side of the tumor (26/43, 60.5%) and contralateral to the side of the tumor (28/43, 65.1%). High riding jugular bulb was noted in 9 (20.9%) patients. Seven among the 9 (77.9%) patients with high riding jugular bulb had Manjila et al. type 4 jugular bulb. Pneumatization of posterior lip of IAM was noted in 8 (18.6%) patients. Avoidance of drilling of the IAM in the subgroup of 23 patients who underwent total excision of the tumor was significantly associated with Manjila et al. type 4 jugular bulb (3/4, 75%, p = 0.04) and pneumatization of posterior lip (3/4, 75%, p = 0.04). Ideally all patients with VS should undergo petrous bone CT of < 2 mm slice thickness as it can help in qualifying the jugular bulb position and recognizing pneumatization of the IAM. The presence of Manjila et al. type 4 jugular bulb or pneumatization of the posterior lip in patients with VS should alert the surgeon to anticipate and prevent complications related to drilling the posterior lip of the IAM.

Subtotal resection of vestibular schwannoma with subsequent Gamma Knife irradiation - tumor growth control, facial and cochlear nerve outcome - preliminary results

<b>Introduction:</b> The choice of treatment of vestibular schwannoma (VS) depends on several factors, including the tumor size, the patient's age and overall health, and the presence and severity of symptoms.<b>Aim:</b> The aim of the study was to assess the effectiveness of intentional subtotal resection (STR) of tumor followed by Gamma Knife surgery (GKS) in patients with larger VS (Koos 3 and 4).<b>Materials and methods:</b> The retrospective analysis was performed on 18 patients. Data of VS volumes measured in MRI, the facial nerve function assessed in the House-Brackmann scoring system (HB), and the results of audiological examination expressed on the Gardner-Robertson scale (GR) were collected preoperatively, postoperatively, and post-GKS.<b>Results:</b> Preoperatively, the main symptom was hearing loss observed in 13 out of 18 patients. The facial nerve function was assessed as HB 1 in 16, whereas HB 2 in 2 patients. The mean volume of the tumor in the initial MRI amounted to 16.81 cm³ . Postoperatively, the facial nerve was assessed as HB 1 or 2 in 16, whereas HB 3 in 2 patients. Serviceable hearing was presented by only 4 persons. The Mean diameter of the tumor after subtotal surgery amounted to 3.16 cm³ , 1.83 cm³ after GKS, and 1.58 cm³ at the last follow-up. The facial nerve function and hearing level remained the same as before GKS in all patients.<b>Conclusions:</b> STR followed by GKS can be a safe and effective method of treatment of large VS concerning the functional outcome of the facial nerve and the tumor volume growth control.

Single-Center Experience in Microsurgical Resection of Acoustic Neurinomas and the Benefit of Microscope-Based Augmented Reality

Background and Objectives: Microsurgical resection with intraoperative neuromonitoring is the gold standard for acoustic neurinomas (ANs) which are classified as T3 or T4 tumors according to the Hannover Classification. Microscope-based augmented reality (AR) can be beneficial in cerebellopontine angle and lateral skull base surgery, since these are small areas packed with anatomical structures and the use of this technology enables automatic 3D building of a model without the need for a surgeon to mentally perform this task of transferring 2D images seen on the microscope into imaginary 3D images, which then reduces the possibility of error and provides better orientation in the operative field. Materials and Methods: All patients who underwent surgery for resection of ANs in our department were included in this study. Clinical outcomes in terms of postoperative neurological deficits and complications were evaluated, as well as neuroradiological outcomes for tumor remnants and recurrence. Results: A total of 43 consecutive patients (25 female, median age 60.5 ± 16 years) who underwent resection of ANs via retrosigmoid osteoclastic craniotomy with the use of intraoperative neuromonitoring (22 right-sided, 14 giant tumors, 10 cystic, 7 with hydrocephalus) by a single surgeon were included in this study, with a median follow up of 41.2 ± 32.2 months. A total of 18 patients underwent subtotal resection, 1 patient partial resection and 24 patients gross total resection. A total of 27 patients underwent resection in sitting position and the rest in semi-sitting position. Out of 37 patients who had no facial nerve deficit prior to surgery, 19 patients were intact following surgery, 7 patients had House Brackmann (HB) Grade II paresis, 3 patients HB III, 7 patients HB IV and 1 patient HB V. Wound healing deficit with cerebrospinal fluid (CSF) leak occurred in 8 patients (18.6%). Operative time was 317.3 ± 99 min. One patient which had recurrence and one further patient with partial resection underwent radiotherapy following surgery. A total of 16 patients (37.2%) underwent resection using fiducial-based navigation and microscope-based AR, all in sitting position. Segmented objects of interest in AR were the sigmoid and transverse sinus, tumor outline, cranial nerves (CN) VII, VIII and V, petrous vein, cochlea and semicircular canals and brain stem. Operative time and clinical outcome did not differ between the AR and the non-AR group. However, use of AR improved orientation in the operative field for craniotomy planning and microsurgical resection by identification of important neurovascular structures. Conclusions: The single-center experience of resection of ANs showed a high rate of gross total (GTR) and subtotal resection (STR) with low recurrence. Use of AR improves intraoperative orientation and facilitates craniotomy planning and AN resection through early improved identification of important anatomical relations to structures of the inner auditory canal, venous sinuses, petrous vein, brain stem and the course of cranial nerves.

Monitoring Cochlear Nerve Action Potential for Hearing Preservation in Medium/Large Vestibular Schwannoma Surgery: Tips and Pitfalls

The diagnosis of large vestibular schwannomas (VS) with retained useful hearing has become increasingly common. Preservation of facial nerve (FN) function has improved using intraoperative EMG monitoring, hearing preservation remains challenging, with the recent use of cochlear nerve action potential (CNAP) monitoring. This prospective longitudinal series of VS with useful hearing operated on using a retrosigmoid approach included 37 patients with a mean largest extrameatal VS. diameter of 25 ± 8.7 mm (81% of Koos stage 4). CNAP was detected in 51% of patients, while auditory brainstem responses (ABR) were present in 22%. Patients were divided into two groups based on the initial intraoperative CNAP status, whether it was present or absent. FN function was preserved (grade I-II) in 95% of cases at 6 months. Serviceable hearing (class A + B) was preserved in 16% of the cases, while 27% retained hearing with intelligibility (class A-C). Hearing with intelligibility (class A-C) was preserved in 42% of cases when CNAP could be monitored in the early stages of VS resection versus 11% when it was initially absent. Changes in both the approach to the cochlear nerve and VS resection are mandatory in preserving CNAP and improve the rate of hearing preservation.

Direct cochlear nerve stimulation monitoring through evoked muscle responses during retrosigmoid vestibular schwannoma resection surgery: technical note

OBJECTIVE

Cochlear nerve preservation during surgery for vestibular schwannoma (VS) may be challenging. Brainstem auditory evoked potentials and cochlear compound nerve action potentials have clearly shown their limitations in surgeries for large VSs. In this paper, the authors report their preliminary results after direct electrical intraoperative cochlear nerve stimulation and recording of the postauricular muscle response (PAMR) during resection of large VSs.

METHODS

The details for the electrode setup, stimulation, and recording parameters are provided. Data of patients for whom PAMR was recorded during surgery were prospectively collected and analyzed.

RESULTS

PAMRs were recorded in all patients at the ipsilateral vertex-earlobe scalp electrode, and in 90% of the patients they were also observed in the contralateral electrode. The optimal stimulation intensity was found to be 1 mA at 1 Hz, with a good cochlear response and an absent response from other nerves. At that intensity, the ipsilateral cochlear response had an initial peak at a mean (± SEM) latency of 11.6 ± 1.5 msec with an average amplitude of 14.4 ± 5.4 µV. One patient experienced a significant improvement in his audition, while that of the other patients remained stable.

CONCLUSIONS

PAMR monitoring may be useful in mapping the position and trajectory of the cochlear nerve to enable hearing preservation during surgery.

Salvage radiosurgery following subtotal resection of vestibular schwannomas: does timing influence tumor control?

OBJECTIVE

The goal of microsurgical resection of vestibular schwannoma (VS) is gross-total resection (GTR) to provide oncological cure. However, a popular strategy is to halt the resection if the surgical team feels the risk of cranial nerve injury is imminent, achieving a maximally safe subtotal resection (STR) instead. The tumor remnant can then be treated with stereotactic radiosurgery (SRS) once the patient has recovered from the immediate postoperative period, or it can be followed with serial imaging and treated with SRS in a delayed fashion if residual tumor growth is seen. In this study, the authors evaluated the efficacy of this multimodality approach, particularly the influence of timing and dose of SRS on radiological tumor control, need for salvage treatment, and cranial nerve function.

METHODS

VS patients treated with initial microsurgery and subsequent radiosurgery were retrospectively included from two tertiary treatment centers and dichotomized depending on whether SRS was given upfront (defined as before 12 months) or later. Radiological tumor control was defined as less than 20% tumor volume expansion and oncological tumor control as an absence of salvage treatment. Facial and cochlear nerve functions were assessed after surgery, at the time of SRS, and at last follow-up. Finally, a systematic literature review was conducted according to PRISMA guidelines.

RESULTS

A total of 110 VS patients underwent SRS following microsurgical resection, with a mean preradiosurgical tumor volume of 2.2 cm3 (SD 2.5 cm3) and mean post-SRS follow-up time of 5.8 years (SD 4.1 years). The overall radiological tumor control and oncological tumor control were 77.3% and 90.9%, respectively. Thirty-five patients (31.8%) received upfront SRS, while 75 patients (68.2%) were observed for a minimum of 12 months prior to SRS. The timing of SRS did not influence the radiological tumor control (p = 0.869), the oncological tumor control (p = 0.560), or facial nerve (p = 0.413) or cochlear nerve (p = 0.954) function. An escalated marginal dose (> 12 Gy) was associated with greater tumor shrinkage (p = 0.020) and superior radiological tumor control (p = 0.020), but it did not influence the risk of salvage treatment (p = 0.904) or facial (p = 0.351) or cochlear (p = 0.601) nerve deterioration.

CONCLUSIONS

Delayed SRS after close observation of residuals following STR is a safe alternative to upfront SRS regarding tumor control and cranial nerve preservation in selected patients.

Large and small vestibular schwannomas: same, yet different tumors

BACKGROUND

Vestibular schwannomas (VS) present at variable size with heterogeneous symptomatology. Modern treatment paradigms for large VS include gross total resection, subtotal resection (STR) in combination with observation, and/or radiation to achieve optimal function preservation, whereas treatment is felt to be both easier and safer for small VS. The objective is to better characterize the presentation and surgical outcomes of large and small VS.

METHODS

We collected data of patients who had surgically treated VS with a posterior fossa diameter of 4.0 cm or larger (large tumor group, LTG) and smaller than 1.0 cm in cisternal diameter (small tumor group, STG). Statistical significance was defined as p < 0.05.

RESULTS

LTG included 48 patients (average tumor size: 44.9 mm) and STG 38 (7.9 mm). Patients in STG presented more frequently with tinnitus and sudden hearing loss. Patients in LTG underwent more STR than STG (50.0% vs. 2.6%, p < 0.0001). LTG had more complications (31.3% vs. 13.2%, p = 0.049). Postoperative facial nerve function in STG was significantly better than LTG. STG had better hearing preoperatively (p < 0.0001) and postoperatively than LTG (p = 0.0002). Postoperative headache was more common in STG (13.2% vs. 2.1%, p = 0.045). The rate of recurrence/progression needing treatment was not statistically different between the groups (12.5% in LTG vs. 7.9% in STG, p = 0.49). Those patients who required periprocedural cerebrospinal fluid diversion had higher risk of infection (20.8% vs 4.8%, p = 0.022).

CONCLUSION

Large and small VS present differently. LTG showed more unsatisfactory outcomes in facial nerve function and postoperative hearing despite maximal efforts undertaken toward function-preservation strategy; however, similar tumor control was achieved.

Long-term outcome of Simpson IV meningioma resection: Would it improve with adjuvant SRS?

OBJECTIVE

Subtotal meningioma resection (STR) is often performed to minimize surgical morbidity. Nevertheless, only a few studies have reported on patient outcome after STR. We studied the long-term outcome of SIV (Simpson grade IV) resection and identified predictive factors of overall survival (OS), progression-free survival (PFS) and time to progression (TTP).

METHODS

A retrospective analysis was performed on 68 patients who underwent SIV resection of meningioma (grade I) from 2004 to 2010. Data were collected from clinical, surgical and pathology records and radiological imaging. Long-term outcomes were evaluated at least 10 years after surgery.

RESULTS

Permanent morbidity was 11.8%, 30-day mortality 2.9% and progression rate 50.0% for a median follow-up duration of 126.6 months. Median TTP was 86.2 months. Adjuvant SRS was the only significant factor associated with longer PFS (p = 0.0052) and TTP (p = 0.0079). Higher age (p = 0.0022), KPS (p = 0.0182), postoperative ECOG score (p = 0.0182) were reliable predictors of shortened OS and aSRS (p = 0.0445) was reliable predictor of longer OS.

CONCLUSION

STR in intracranial meningioma is still viable and often the only treatment option available in high-risk patients or high-risk tumors. Although surgical morbidity and mortality are high, the OS rate was 85.3% at 5 years and 79.4% at 10 years. Because of the considerable progression rate and rather a long term OS the adjuvant SRS should be considered following SIV resection.

Predictors of long-term tumor control after stereotactic radiosurgery for Koos grade 4 vestibular schwannomas

PURPOSE

To evaluate the predictors of long-term tumor control following stereotactic radiosurgery (SRS) for Koos grade 4 vestibular schwannomas (VSs).

METHODS

Overall, 203 sporadic VS patients with compression of the brainstem were treated with SRS. The median tumor volume was 6.7 cm³ (range, 2.0-28.9 cm³) and the median marginal dose was 12 Gy (range, 9-13.5 Gy).

RESULTS

The median follow-up period was 152 months (range, 12-277 months). Tumor control (TC) rates at 3, 5, and 10 years were 89%, 85%, and 82%, respectively. Operation-free survival (OFS) rates at 3, 5, and 10 years were 92%, 85%, and 83%, respectively. Middle cerebellar peduncle (MCP) compression on pre-SRS magnetic resonance imaging scans was significant for both TC (p < 0.001, hazard ratio 1.332) and OFS (p < 0.001, hazard ratio 1.306). The 3-, 5-, and 10-year OFS rates were 98%, 94%, and 92% in the low-risk group (MCP compression < 9.8 mm and > 48 years old), and 58%, 25%, and 17% in high-risk group (MCP compression ≥ 9.8 mm and ≤ 48 years old), respectively. Ten patients (4.9%) developed delayed cyst-related complications. Eleven patients (5.4%) developed newly developed or worsened trigeminal neuralgia. No patient developed persistent facial palsy as an adverse radiation effect. A ventricular peritoneal shunt was required in six patients (3%) who developed hydrocephalus after SRS.

CONCLUSION

SRS is an acceptable treatment option in selected patients with Koos grade 4 VSs. Risk group classification based on patient age and MCP compression is useful in decision-making of Koos grade 4 VSs.

Subtotal Resection Followed by Adjuvant Radiosurgery for Large Vestibular Schwannomas: Outcomes with Regard to the Timing and Regimen of Irradiation

OBJECTIVE

To evaluate the results of combined management of large vestibular schwannomas (VS) with initial subtotal resection (STR) followed by adjuvant stereotactic radiosurgery (SRS), with a particular emphasis on the timing and regimen of irradiation.

METHODS

Seventeen patients underwent STR of a VS followed by SRS, whereas five others were observed after STR. Early SRS (<6 months after surgery) and late SRS (>6 months after surgery) were done in 8 and 9 patients, respectively. Single- and multisession SRS treatments were administered in 10 and 7 patients, respectively. The mean follow-up durations after surgery and SRS were 40 and 28 months, respectively.

RESULTS

The rates of radiological and oncological tumor control after SRS were 82% and 100%, respectively. The tumor volume at the last follow-up and its relative changes after SRS did not differ significantly on the basis of the irradiation timing (early versus late) or on the basis of the irradiation regimen (single-session versus multisession). In no patient who was observed after STR of a VS was tumor regrowth noted during a mean follow-up period of 49 months. At 12 months after surgery, motor function of the ipsilateral facial nerve corresponded to House-Brackmann grades I, II, III, and IV in 16 patients (73%), 3 patients (14%), 1 patient (5%), and 2 patients (9%), respectively. Facial nerve function at the last follow-up did not differ significantly on the basis of the irradiation timing (early versus late) or on the basis of the irradiation regimen (single-session versus multisession).

CONCLUSION

The combination of initial STR followed by adjuvant SRS is an effective treatment strategy for patients with a large VS. Although the optimal timing and regimen of postoperative irradiation of the residual lesion should be defined further, our preliminary data suggest that either early or late SRS after surgery may provide good tumor control and optimal functional results.

Fractionated Radiosurgical Treatment of Intracerebral Schwannoma: A Case Report and Literature Review

Intracranial schwannomas (ICS) unrelated to the cranial nerves are extremely rare; around 70 cases have been reported worldwide. The available literature consists of case reports and small series that present variable characteristics distinguishing these lesions. Brain parenchyma schwannomas are typically benign tumors with currently unknown origins. Diagnosis of intraparenchymal schwannoma is almost never made preoperatively. The management of these tumors usually consists of gross total resection, chemotherapy, and radiotherapy in cases of recurrence. The authors present a case of fractionated Gamma Knife radiosurgical treatment of intracerebral schwannoma following partial microsurgical resection.

Management von Patienten mit Vestibularisschwannomen Typ IV

Hintergrund Vestibularisschwannome (VS) sind benigne Tumoren, die anhand der Hannover-Klassifikation bzw. der Koos-Klassifizierung eingeteilt werden. Trotz der umfangreichen Literatur sind die Klinik und die Behandlungskonzepte speziell bei großen VS selten beschrieben.

Material und Methoden Zwischen 2003 und 2018 wurden 61 Patienten mit VS Typ IV durch die Arbeitsgruppe Schädelbasischirurgie am Klinikum Dortmund behandelt. Die radiologischen und klinischen Daten wurden retrospektiv ausgewertet. Zudem erfolgte eine Subgruppenanalyse zwischen Patienten mit und ohne Kompression des IV. Ventrikels.

Ergebnisse Neben einer Hörminderung bei 55 Patienten (90 %) hatten die meisten Patienten multiple Symptome wie eine Trigeminusaffektion bei 16 (26 %), eine Fazialisparese bei 7 (12 %), eine Ataxie bei 27 (45 %) und Symptome eines Hirndruckanstiegs durch einen Hydrozephalus bei 4 Patienten (7 %). Bei Patienten mit einem VS Typ IVb wurde signifikant häufiger eine Ataxie, eine tonsilläre Herniation bzw. ein Hydrozephalus festgestellt. Eine komplette Resektion wurde in 48 Patienten (78 %) erreicht und eine weitestgehende Tumorentfernung in 12 Patienten (20 %). In der Langzeituntersuchung zeigten 90 % einen günstigen Outcome bezüglich des Nervus facialis (House-und-Brackman-Grad I–III). 6 Patienten (10 %) benötigten einen dauerhaften ventrikulo-peritonealen Shunt. Mehr als 90 % der Patienten erzielten einen Karnofsky-Index > 70 %.

Diskussion VS Typ IV sind häufig assoziiert mit Hydrozephalus, Ataxie, multiplen Hirnnervenausfällen und gelegentlich Zeichen eines intrakraniellen Druckanstiegs. Die primäre mikrochirurgische Resektion ist weiterhin eine entscheidende Therapieoption.

Facial nerve function and hearing after microsurgical removal of sporadic vestibular schwannomas in a population-based cohort

BACKGROUND

Vestibular schwannoma (VS) is a benign tumor originating from the vestibulocochlear nerve. The optimal treatment strategy is debated, since surgery may result in iatrogenic facial nerve injury. We report the results of VS surgery in a population-based unselected cohort in a center with access to Cyber Knife (CK) radiosurgery.

METHODS

We reviewed 117 consecutive operations and found 95 patients who had their primary operation due to vestibular schwannoma between 2001 and 2017. Facial nerve function was evaluated with the House-Brackmann (HB) scale and hearing with the EU classification.

RESULTS

The population consisted of 37 males and 58 females with a median age of 54 years (range 19-79). One year after surgery 67% of patients had a good outcome (HB 1-2). The rate of good outcome was 90% if no facial nerve damage was observed during intraoperative monitoring, the size of the tumor was under 30 mm and no hydrocephalus was present. During the study period, the treatment strategy changed from total to near-total resection after the introduction of CK radiosurgery, which could be used as a second-line treatment in case of residual tumor regrowth. This resulted in an improvement of outcomes (0% HB 5-6) despite the larger tumor sizes (25 ± 14 mm vs. 31 ± 9 mm, p < 0.05). Hearing preservation rates did not increase.

CONCLUSIONS

Near-total resection and subsequent CK radiosurgery in case of residual tumor regrowth during follow-up seems to provide a good outcome of facial nerve function even in large VSs.