Late course of preserved hearing and tinnitus after acoustic neurilemoma surgery

Role of the neurotologist in posterior fossa meningioma surgery

Posterior fossa meningiomas that impinge on structures of the temporal bone or clivus may be difficult to access for optimal resection that maximizes tumor control and minimizes short- and long-term morbidities. To address this challenge, the contemporary neurosurgery-neurotology team works collaboratively by managing patients jointly at every stage of care: preoperative evaluation, intraoperative intervention, and postoperative treatment. The neurotologist is important at all stages of posterior fossa meningioma surgery. First, detailed preoperative evaluation of auditory, facial, vestibular, and lower cranial nerve integrity enables assessment of new neurologic deficit risk, prognosis of functional recovery, and pros and cons of candidate surgical approaches. Second, intraoperative partitioning of surgical steps by provider and adopting an overlapping tumor resection philosophy creates an efficient and confident surgical team built on trust. Third, postoperative closure of cerebrospinal fluid leak and treatment of facial weakness, audiovestibular dysfunction, and voicing and swallowing impairments organized by the neurotologist reduces the impact of negative outcomes. The role of the neurotologist in posterior fossa meningioma surgery is to deliver nuanced evaluative metrics, facilitate shared decision making, perform precise bone and soft tissue microsurgery, and mitigate perioperative morbidities.

Intracanalicular Vestibular Schwannoma: A Systematic Review and Meta-analysis of Therapeutics Outcomes

OBJECTIVE

To perform a systematic review and meta-analysis summarizing the current evidence on the management of intracanalicular vestibular schwannoma.

DATA SOURCES

Embase (1947-), Medline (1946-), Cochrane library (1947-), Scopus (2010-), and CINAHL (1961-) were searched from 1969 to October 5, 2019 (50 years).

STUDY SELECTION

A search strategy was performed to identify patients with vestibular schwannoma confined to the internal auditory canal without extension to the cerebellopontine angle. Studies with patients aged less than 18, Neurofibromatosis type 2, revision cases, and non-English language were excluded.

DATA EXTRACTION

A standardized collection sheet was used for the extracted data and a quality assessment was performed using the Newcastle-Ottawa Scale with the comparability criterion omitted.

DATA SYNTHESIS

Seventy-one studies were included with 24 on observation, 14 on radiotherapy, and 34 on surgery. The primary outcome was serviceable hearing preservation. Secondary outcomes were preservation of facial nerve function, growth, involution, and dizziness. Sub-analysis on the type of surgery and type of radiotherapy were performed. Excel 2016 with MIX 2.0 Pro add-on package was used to analyze the data and create forest plots. Data were presented in proportion with a 95% confidence interval.

CONCLUSIONS

Serviceable hearing was observed in 31% of patients after observation, 56% after radiotherapy, and 51% after surgical treatment with mean follow-up time of 4.04 years, 4.92 years, and 2.23 years, respectively. Facial nerve function was found to be best preserved in both observation and radiotherapy groups. Vestibular schwannoma growth occurred in 33% of patients under observation. Involution occurred in 2% of patients under observation and in 38% after radiotherapy.

Predicting hearing outcomes before primary radiosurgery for vestibular schwannomas

OBJECTIVE

Optimizing outcomes in the management of patients with vestibular schwannomas (VSs) requires consideration of the patient's goals. Earlier recognition of VS by imaging has led to an evolution in management. Stereotactic radiosurgery (SRS) has emerged as a frequently used strategy designed to reduce management risks, obtain long-term tumor control, and preserve current neurological function. The authors analyzed features that impact hearing preservation rates in patients with serviceable hearing prior to SRS.

METHODS

The study included 307 patients who had serviceable hearing (Gardner-Robertson hearing scale [GR] grade 1 or 2, speech discrimination score ≥ 50%, pure tone average ≤ 50 dB) at the time of SRS. The authors evaluated parameters that included age, tumor volume, hearing status, disequilibrium, tinnitus, Koos class, sex, and tumor margin dose. The Pittsburgh Hearing Prediction Score (PHPS) was evaluated as a method to predict long-term hearing outcomes in these cases.

RESULTS

At a median of 7.6 years after SRS (range 1-23 years), tumor control was achieved in 95% of patients. The overall serviceable hearing preservation rate was 77.8% at 3 years, 68.8% at 5 years, and 51.8% at 10 years. The PHPS assigns a total of 5 points based on patient age (1 point if < 45 years, 2 points if 45-59 years, and 3 points if ≥ 60 years), tumor volume (0 points if < 1.2 cm3, 1 point if ≥ 1.2 cm3), and GR grade (0 points if grade 1 hearing, 1 point if grade 2 hearing) The serviceable hearing preservation rate was 92.3% at 10 years in patients whose score total was 1. In contrast, none of the patients whose PHPS was 5 maintained serviceable hearing at 10 years (p < 0.001).

CONCLUSIONS

SRS resulted in a high rate of long-term tumor control and cranial nerve preservation. The PHPS helped to predict long-term hearing preservation rates in patients who underwent SRS when they still had serviceable hearing. The best long-term hearing preservation rates were found in younger patients with smaller tumor volumes.

Postoperative Tinnitus after Vestibular Schwannoma Surgery: A Neglected Entity

Background

This prospective study analyzes the factors responsible for pre and postoperative persistent tinnitus following vestibular schwannoma (VS) surgery and discusses the possible etiopathogenetic mechanisms.

Materials and Methods

Sixty-seven consecutive patients with unilateral VS operated via the retrosigmoid-suboccipital approach were included in the study. The Cochlear nerve, often unidentifiable from the tumor capsule, was resected during the surgery. Tinnitus Handicap Inventory (THI) score assessed the severity of pre and postoperative tinnitus.

Result

Twenty-eight (41%) patients had preoperative tinnitus. Out of those 28 patients, 24(85%) had significantly improvement in postoperative THI score. In 15 of the 24 patients, tinnitus subsided completely. In 3 of the 28 (10%) patients, THI scores were unaltered, and in 1 of the 28 (3.5%) patients, THI scores worsened. In 39 (58.2%) patients without preoperative tinnitus, 4 (10%) developed a new-onset postoperative tinnitus. Patients with severe sensory neural hearing loss (SNHL) had significantly higher incidence of postoperative persistent tinnitus (PPT) (P = 0.00) compared to those with mild-to-moderate SNHL. Patients with profound SNHL, however, had a much lower incidence of PPT (P = 0.007; odds ratio = 0. 0.077; 95% CI: 0.009-0.637). Large (P = 0.07) and giant schwannomas (P = 0.03) VS had an increased risk of PPT. Patients with PPT further analyzed with brain stem auditory evoked response (BAER) showed normal contralateral waveform.

Conclusion

Assessment of tinnitus is mandatory during the management of VS as there are high chances (nearly 46%) of PPT. Preoperative tinnitus, linked to the degree of SNHL (higher incidence in severe SNHL compared to mild-to-moderate/profound SNHL), is dependent on an intact cochlear nerve functioning. However, PPT is dependent on other mechanisms (brain stem/ipsilateral cochlear nuclei compression, and cortical reorganization) as it persists despite cochlear nerve resection.

Congress of Neurological Surgeons Systematic Review and Evidence-Based Guidelines on Hearing Preservation Outcomes in Patients With Sporadic Vestibular Schwannomas

Question 1

What is the overall probability of maintaining serviceable hearing following stereotactic radiosurgery utilizing modern dose planning, at 2, 5, and 10 yr following treatment?

Recommendation

Level 3: Individuals who meet these criteria and are considering stereotactic radiosurgery should be counseled that there is moderately high probability (>50%-75%) of hearing preservation at 2 yr, moderately high probability (>50%-75%) of hearing preservation at 5 yr, and moderately low probability (>25%-50%) of hearing preservation at 10 yr.

Question 2

Among patients with AAO-HNS (American Academy of Otolaryngology-Head and Neck Surgery hearing classification) class A or GR (Gardner-Robertson hearing classification) grade I hearing at baseline, what is the overall probability of maintaining serviceable hearing following stereotactic radiosurgery, utilizing modern dose planning, at 2, 5, and 10 yr following treatment?

Recommendation

Level 3: Individuals who meet these criteria and are considering stereotactic radiosurgery should be counseled that there is a high probability (>75%-100%) of hearing preservation at 2 yr, moderately high probability (>50%-75%) of hearing preservation at 5 yr, and moderately low probability (>25%-50%) of hearing preservation at 10 yr.

Question 3

What patient- and tumor-related factors influence progression to nonserviceable hearing following stereotactic radiosurgery using ≤13 Gy to the tumor margin?

Recommendation

Level 3: Individuals who meet these criteria and are considering stereotactic radiosurgery should be counseled regarding the probability of successful hearing preservation based on the following prognostic data: the most consistent prognostic features associated with maintenance of serviceable hearing are good preoperative word recognition and/or pure tone thresholds with variable cut-points reported, smaller tumor size, marginal tumor dose ≤12 Gy, and cochlear dose ≤4 Gy. Age and sex are not strong predictors of hearing preservation outcome.

Question 4

What is the overall probability of maintaining serviceable hearing following microsurgical resection of small to medium-sized sporadic vestibular schwannomas early after surgery, at 2, 5, and 10 yr following treatment?

Recommendation

Level 3: Individuals who meet these criteria and are considering microsurgical resection should be counseled that there is a moderately low probability (>25%-50%) of hearing preservation immediately following surgery, moderately low probability (>25%-50%) of hearing preservation at 2 yr, moderately low probability (>25%-50%) of hearing preservation at 5 yr, and moderately low probability (>25%-50%) of hearing preservation at 10 yr.

Question 5

Among patients with AAO-HNS class A or GR grade I hearing at baseline, what is the overall probability of maintaining serviceable hearing following microsurgical resection of small to medium-sized sporadic vestibular schwannomas early after surgery, at 2, 5, and 10 yr following treatment?

Recommendation

Level 3: Individuals who meet these criteria and are considering microsurgical resection should be counseled that there is a moderately high probability (>50%-75%) of hearing preservation immediately following surgery, moderately high probability (>50%-75%) of hearing preservation at 2 yr, moderately high probability (>50%-75%) of hearing preservation at 5 yr, and moderately low probability (>25%-50%) of hearing preservation at 10 yr.

Question 6

What patient- and tumor-related factors influence progression to nonserviceable hearing following microsurgical resection of small to medium-sized sporadic vestibular schwannomas?

Recommendation

Level 3: Individuals who meet these criteria and are considering microsurgical resection should be counseled regarding the probability of successful hearing preservation based on the following prognostic data: the most consistent prognostic features associated with maintenance of serviceable hearing are good preoperative word recognition and/or pure tone thresholds with variable cut-points reported, smaller tumor size commonly less than 1 cm, and presence of a distal internal auditory canal cerebrospinal fluid fundal cap. Age and sex are not strong predictors of hearing preservation outcome.

Question 7

What is the overall probability of maintaining serviceable hearing with conservative observation of vestibular schwannomas at 2, 5, and 10 yr following diagnosis?

Recommendation

Level 3: Individuals who meet these criteria and are considering observation should be counseled that there is a high probability (>75%-100%) of hearing preservation at 2 yr, moderately high probability (>50%-75%) of hearing preservation at 5 yr, and moderately low probability (>25%-50%) of hearing preservation at 10 yr.

Question 8

Among patients with AAO-HNS class A or GR grade I hearing at baseline, what is the overall probability of maintaining serviceable hearing with conservative observation at 2 and 5 yr following diagnosis?

Recommendation

Level 3: Individuals who meet these criteria and are considering stereotactic radiosurgery should be counseled that there is a high probability (>75%-100%) of hearing preservation at 2 yr, and moderately high probability (>50%-75%) of hearing preservation at 5 yr. Insufficient data were available to determine the probability of hearing preservation at 10 yr for this population subset.

Question 9

What patient and tumor-related factors influence progression to nonserviceable hearing during conservative observation?

Recommendation

Level 3: Individuals who meet these criteria and are considering observation should be counseled regarding probability of successful hearing preservation based on the following prognostic data: the most consistent prognostic features associated with maintenance of serviceable hearing are good preoperative word recognition and/or pure tone thresholds with variable cut-points reported, as well as nongrowth of the tumor. Tumor size at the time of diagnosis, age, and sex do not predict future development of nonserviceable hearing during observation.  The full guideline can be found at: https://www.cns.org/guidelines/guidelines-manage-ment-patients-vestibular-schwannoma/chapter_3.

Hearing Preservation Surgery in Vestibular Schwannoma: The Hidden Truth

To compare the results of hearing preservation surgeries using different approaches — the enlarged middle cranial fossa approach and the retrosigmoid approach — and different classification systems, stressing the importance of preserving “normal hearing,” we performed a retrospective case review in a tertiary care medical center. The charts of 107 patients with vestibular schwannoma who underwent tumor resection were reviewed. Hearing preservation was reported according to 2 different classification systems: the modified Sanna classification and the classification of the American Academy of Otolaryngology—Head and Neck Surgery. The facial nerve results were graded according to the House-Brackmann scale. The hearing preservation rates differed markedly depending on the classification used. We conclude that hearing preservation in acoustic neuroma is a more difficult proposition than most surgeons appreciate, especially in terms of serviceable hearing.

Topographic Changes in Petrous Bone Anatomy in the Presence of a Vestibular Schwannoma and Implications for the Retrosigmoid Transmeatal Approach

BACKGROUND:

The maneuver of transmeatal drilling carries the risk of injuring inner ear structures, which may cause immediate or delayed hearing loss.

OBJECTIVE:

To describe the changes in petrous bone anatomy caused by the tumor and to analyze both the incidence and the risk pattern for violation of the endolymphatic system in a surgical series.

METHODS:

One hundred patients operated on for vestibular schwannoma were included in this prospective study. Thin-slice computed tomography was performed before and after surgery. We assessed topographic measurements on both the pathological and healthy sides. Postoperatively, we evaluated anatomic and functional values.

RESULTS:

The diameter of the internal auditory canal was significantly larger (P &lt; .001) in the petrous bones of the affected sides than in the contralateral healthy sides. An average of 5.6 ± 1.8 mm of the internal auditory canal was drilled, and the distance from the medial border of the sigmoid sinus to the drilling line (tangential to the drilled surface of the posterior lip of the internal auditory canal) was 9.8 ± 2.9 mm. A postoperative violation of the vestibular aqueduct (VA) was detected in 41 cases; the VA was intact in 55 cases; and the VA could not be clearly defined in 4 cases. The incidence of VA injury increased with increasing tumor size. In the patient group with good preoperative and postoperative hearing function, a VA injury occurred in 26% of cases, whereas the incidence increased to 67% in preoperatively deaf patients.

CONCLUSION:

Vestibular schwannomas cause significant distortion of the petrous bone anatomy. Detailed preoperative knowledge of the topography is necessary for the preservation of function.

Long-term hearing outcome after retrosigmoid removal of vestibular schwannoma

Although many investigators have reported the hearing function in the immediate postoperative period in patients with vestibular schwannoma (VS), little is known about the long-term outcomes of the postoperative hearing. The aim of this study was to analyze the long-term hearing outcomes at a mean follow-up of 5 years in patients with unilateral VS treated via the retrosigmoid approach. Twenty-four patients with immediate postoperative serviceable hearing who underwent repeated audiogram or phone interview were included in this study. During the mean follow-up period (68.8 ± 30.2 months, range 14–123 months), serviceable hearing was preserved in 20 out of the 24 patients (83%). Pure tone average (PTA) was reevaluated within 6 months in seven patients. In the two patients whose PTA deteriorated ≥ 5 dB in 6 months after surgery, their PTA worsened ≥ 15 dB compared to the immediate postoperative PTA. In the remaining five patients whose PTA deteriorated < 5 dB in 6 months after surgery, PTA was maintained within a 15-dB deterioration at the final follow-up (p = 0.04, Fisher's exact test). According to Kaplan–Meier survival plots, the 5-year or 7-year preservation rate of serviceable hearing was 86.2% or 71.8%, respectively. Further study will be needed to clarify the mechanism underlying the long-term decline of serviceable hearing; however, the deterioration of PTA in the early postoperative period may help to predict the long-term outcomes of hearing.

Durability of hearing preservation after microsurgical treatment of vestibular schwannoma using the middle cranial fossa approach

Object

The middle cranial fossa (MCF) approach is a microsurgical technique described as a primary option in the treatment of small, intracanalicular schwannomas involving the eighth cranial nerve. Excellent rates of complete tumor resection, hearing preservation, preservation of facial nerve function, and low complication rates have been reproduced using this technique. However, the durability of hearing preservation attained using the various treatment options has not been adequately assessed. The purpose of this study was to evaluate the durability of long-term hearing preservation in patients with vestibular schwannoma (VS) treated via the MCF approach. The authors hypothesize that hearing preservation in these patients will prove to be durable years after treatment in a high percentage of cases.

Methods

Retrospective medical chart review was performed in 103 consecutive patients undergoing resection of VS via a modified MCF approach between 1999 and 2008. Patients in whom surgical goals were gross-total resection and hearing preservation were included. Preoperative and postoperative hearing assessment was performed using standard audiometric testing, and classified according to American Academy of Otolaryngology–Head and Neck Surgery (AAO-HNS) guidelines as a primary outcome measure. Outcomes and neurological complications initially, and at 1, 3, and 5 years following operation were analyzed.

Results

Initial hearing preservation rates were in keeping with the best previously published results. At initial postoperative audiometric follow-up, of the patients presenting with Class A hearing, 67% remained Class A, 17% were Class B, 1% were Class C, and 15% were Class D. Of patients presenting with Class B hearing, 24% were Class A, 53% remained Class B, 6% were Class C, and 18% were Class D. Of patients presenting with Class C hearing, 100% remained Class C.

To assess the durability of hearing preservation in our patients, the authors evaluated hearing function at regular intervals after the initial postoperative audiometric follow-up. Audiometric data were available for 56 patients at 5-year follow-up. Of the 20 patients with Class A hearing at initial postoperative follow-up with 5-year follow-up, 13 (65%) remained Class A, 6 (30%) were Class B, and 1 (5%) was Class C. Of the 12 patients with Class B hearing at initial postoperative follow-up with 5-year follow-up, 4 (33%) were Class A, 4 (33%) remained Class B, and 4 (33%) were Class C. Of the 3 patients with Class C hearing at initial postoperative follow-up with 5-year follow-up, all 3 (100%) remained Class C.

Conclusions

A majority of patients with preserved hearing following the MCF approach for treatment of VS experience durability of their preserved hearing at 5-year follow-up. The initial AAO-HNS classification was preserved in 13 (65%) of the 20 patients who had Class A hearing at 5 years, and in 8 (67%) of the 12 who had Class B hearing at 5 years. Overall, a decline in AAO-HNS classification was noted in 15% of patients with preserved Class A hearing, and in 33% of those with preserved Class B hearing. Facial nerve function was preserved in 91% of cases. Superior hearing preservation as well as good outcomes in facial nerve function and few serious complications can be accomplished using the MCF approach for resection of small VSs.

Auditory findings after stereotactic radiosurgery in acoustic neurinoma

Auditory function after gamma knife stereotactic radiosurgery (GK) was evaluated in 22 patients with newly diagnosed unilateral acoustic neurinoma who had had some measurable hearing preoperatively. No tumor growth was observed in any patients. The preservation rates for useful hearing (n = 13) and any measurable hearing (n = 22) were 62% and 86%, respectively, at 2 years after GK. Postoperative hearing dysfunction was attributed to progressive cochlear impairment in 13 patients and to progressive injury in the retrocochlear auditory pathway in 5 patients. Hearing tended to be well preserved when caloric response was unchanged postoperatively. Preservation of hearing was not associated with the initial tumor volume, decrease of tumor size, maximum tumor dose, or peripheral tumor dose.

Does hearing preservation surgery for acoustic neuromas affect tinnitus?

Questionnaires returned from 202 patients who had undergone acoustic neuroma resection were analyzed with special reference to the effect on tinnitus of surgery that attempted to preserve hearing versus surgery that did not. We also examined the relationship between postoperative hearing and tinnitus following surgery to preserve hearing (103 patients, HP group). The incidence of preoperative tinnitus in the HP group was 78.6%; postoperatively it increased to 89.3% (p = 0.0367). The remaining 99 patients (non-HP) underwent labyrinthectomy during tumor resection. In this group tinnitus occurred in 72.7% preoperatively and in 67.3% postoperatively (p = 0.4097). Our findings show that when tinnitus was absent preoperatively, 85% of the HP group developed it postoperatively compared to 31% of patients in the non-HP group. The outcome of surgery to preserve hearing had no bearing on the loudness or annoyance of postoperative tinnitus. Although postoperative tinnitus is tolerable to most patients, they must be informed prior to surgery about its possible occurrence or worsening, especially if the goal is to preserve hearing.

Mechanical stress-induced reactive gliosis in the auditory nerve and cochlear nucleus

OBJECT

Hearing levels following microsurgical treatment gradually deteriorate in a number of patients treated for vestibular schwannoma (VS), especially in the subacute postoperative stage. The cause of this late-onset deterioration of hearing is not completely understood. The aim of this study was to investigate the possibility that reactive gliosis is a contributory factor.

METHODS

Mechanical damage to nerve tissue is a feature of complex surgical procedures. To explore this aspect of VS treatment, the authors compressed rat auditory nerves with 2 different degrees of injury while monitoring the compound action potentials of the auditory nerve and the auditory brainstem responses. In this experimental model, the axons of the auditory nerve were quantitatively and highly selectively damaged in the cerebellopontine angle without permanent compromise of the blood supply to the cochlea. The temporal bones were processed for immunohistochemical analysis at 1 week and at 8 weeks after compression.

RESULTS

Reactive gliosis was induced not only in the auditory nerve but also in the cochlear nucleus following mechanical trauma in which the general shape of the auditory brainstem response was maintained. There was a substantial outgrowth of astrocytic processes from the transitional zone into the peripheral portion of the auditory nerve, leading to an invasion of dense gliotic tissue in the auditory nerve. The elongated astrocytic processes ran in parallel with the residual auditory neurons and entered much further into the cochlea. Confocal images disclosed fragments of neurons scattered in the gliotic tissue. In the cochlear nucleus, hypertrophic astrocytic processes were abundant around the soma of the neurons. The transverse diameter of the auditory nerve at and proximal to the compression site was considerably reduced, indicating atrophy, especially in rats in which the auditory nerve was profoundly compressed.

CONCLUSIONS

The authors found for the first time that mechanical stress to the auditory nerve causes substantial reactive gliosis in both the peripheral and central auditory pathways within 1-8 weeks. Progressive reactive gliosis following surgical stress may cause dysfunction in the auditory pathways and may be a primary cause of progressive hearing loss following microsurgical treatment for VS.

Effect of tumor removal on tinnitus in patients with vestibular schwannoma

OBJECT

Tinnitus is one of the most common symptoms in patients with vestibular schwannomas (VSs), but the effect of surgery on this symptom has not been fully evaluated. The aim of this study was to define the effect on tinnitus of tumor removal, cochlear nerve resection, and useful hearing preservation in patients with VSs.

METHODS

The authors retrospectively analyzed the status of tinnitus before and after surgery in 242 patients with unilateral VSs who underwent surgery via the retrosigmoid lateral suboccipital approach.

RESULTS

Of 242 patients, 171 (70.7%) complained of tinnitus before surgery; the symptom disappeared in 25.2%, improved in 33.3%, remained unchanged in 31.6%, and worsened in 9.9% of these cases after tumor removal. In the 171 patients with preoperative tinnitus, the cochlear nerve was resected in 85 (49.7%) and preserved in 86 (50.3%), but there was no significant difference in the incidence of postoperative tinnitus between these 2 groups (p = 0.293). In the 71 patients without preoperative tinnitus, the symptom developed postoperatively in 6 cases (8.5%). Among those without preoperative tinnitus, the cochlear nerve was resected in 45 cases (63.4%) and tinnitus appeared postoperatively in 3 (6.7%). The authors also analyzed the association between postoperative tinnitus and useful hearing preservation, but could not find any statistically significant association between the 2 factors (p = 0.153).

CONCLUSIONS

Tumor removal via the retrosigmoid lateral suboccipital approach may provide some chance for improvement of tinnitus in patients with VSs; however, neither cochlear nerve resection nor useful hearing preservation affects the postoperative development of tinnitus.

Hearing preservation in surgery for large vestibular schwannomas

OBJECT

Hearing preservation remains a challenging problem in vestibular schwannoma (VS) surgery. The ability to preserve hearing in patients with large tumors is subject to particular difficulty. In this study, the authors focus on hearing preservation in patients harboring large VSs.

METHODS

A total of 344 consecutive patients underwent surgical removal of VSs over the past 9 years. Of these 344 cases, 195 VSs were > 20 mm in maximum cisternal diameter. Of the 195 cases, hearing preservation surgery was attempted for 54 patients who had a Class A, B, C, or D preoperative hearing level; that is, a pure tone average <or= 60 dB and speech discrimination score >or= 50% according to the Sanna/Fukushima classification. The tumors were classified as moderately large (21-30 mm based on the largest extrameatal diameter), large (31-40 mm), and giant (>or= 41 mm) according to the international criteria. The authors categorized patients with Class A, B, C, D, or E hearing (pure tone average <or= 80 dB and speech discrimination score >or= 40%) as having preserved hearing postoperatively.

RESULTS

Forty-one tumors (75.9%) were totally removed and 13 (24.1%) had near-total removal. Of the 54 patients, 29 maintained their hearing postoperatively; the overall hearing preservation rate was 53.7%. Analysis based on the preoperative hearing level showed that hearing was preserved in 14 (77.8%) of 18 cases for Class A; in 8 (47.1%) of 17 cases for Class B; in 4 (57.1%) of 7 cases for Class C; and in 3 (25.0%) of 12 cases for Class D. In addition, according to the analysis based on the tumor size, 20 (52.6%) of 38 patients with moderately large tumors retained their hearing, as did 5 (50.0%) of 10 patients with large tumors and 4 (66.7%) of 6 patients with giant tumors. Complications included 2 cases of bacterial meningitis that were cured by intravenous injection of antibiotics, 3 cases of subcutaneous CSF leakage that resolved without any surgical repair, and 1 case of temporary abducent nerve palsy. There were no deaths in this series.

CONCLUSIONS

The results indicate that successful hearing preservation surgery in large VSs is possible with meticulous technique and attention to adhesions between the tumor and the cochlear nerves.

HEARING PRESERVATION AFTER INTRACANALICULAR VESTIBULAR SCHWANNOMA RADIOSURGERY

OBJECTIVE

Tumor control, facial function preservation, and hearing preservation are important criteria for successful management of intracanalicular vestibular schwannomas, whether observation, microsurgery, or radiosurgery is chosen. We collected data prospectively to assess hearing preservation after intracanalicular vestibular schwannoma radiosurgery.

METHODS

Between 1987 and 2003, 96 patients (65 men and 31 women) underwent gamma knife stereotactic radiosurgery (SRS) for intracanalicular tumors. The median patient age was 54 years (range, 22–80 years). Hearing was graded using the Gardner-Robertson (GR) and the American Academy of Otolaryngology–Head and Neck Surgery classifications. Dose planning was performed on intraoperative stereotactic images using multiple 4-mm isocenters. The median tumor volume was 0.112 mm3 (range, 0.05–0.447 mm3), and the median margin dose was 13 Gy (range, 10–18 Gy).

RESULTS

The mean and median audiologic follow-up periods were 42 months and 28 months (range, 12–144 months), respectively. Serviceable hearing was preserved in 31 of 40 (77.5%) patients with initial American Academy of Otolaryngology–Head and Neck Surgery Class A hearing. Serviceable hearing was preserved in 40 of 79 (64.5%) patients with GR Grade I or II pre-SRS hearing. Ninety-two patients had GR Grade I, II, or III hearing before SRS, and GR Grade I, II, or III hearing was maintained in 78 patients (85%). Hearing grades improved in 7 patients. Facial and trigeminal nerve function was preserved in all patients. The tumor control rate (freedom from additional intervention) was 99.0% (95 of 96) at a median follow-up of 28 months (range, 12–144 months). One patient underwent tumor resection 18 months after radiosurgery.

CONCLUSION

SRS is a minimally invasive first-line management option for patients with intracanalicular tumors and provides high rates of hearing preservation with minimal morbidity.

Vestibular schwannoma management: What is the 'best' option?

There is an abundance of medical literature describing the management options for vestibular schwannomas. However, the lack of high quality clinical trials means that, for any individual patient, the decision is often based on the clinician's personal biases. The management options that are available are conservative treatment, surgery, single-dose stereotactic radiosurgery and fractionated radiotherapy. In this review, we set out what the aims of managing a vestibular schwannoma should be and compare how these different treatment modalities perform. The particular objectives of tumour control, cranial nerve preservation, prevention of malignancy, quality of life and cost-effectiveness are discussed. It remains difficult to differentiate between these methods when more than one is suitable; the literature confirms that they are all safe and effective, but the decision must be the patient's, based on their individual priorities. This review should equip the clinician to provide an informed overview of the options.

Endolymphatic Duct Status During Middle Fossa Dissection of the Internal Auditory Canal: A Human Temporal Bone Radiographic Study

OBJECTIVE

Successful hearing preservation after acoustic neuroma resection is sometimes complicated by delayed hearing deterioration. The middle fossa approach appears to offer superior long-term hearing results when compared to the retrosigmoid surgical approach. The goal of this study is to investigate the hypothesis that internal auditory canal (IAC) drilling during middle fossa acoustic neuroma removal is associated with a lower incidence of endolymphatic duct (ELD) injury, a potential cause of delayed hearing loss (HL) known to accompany retrosigmoid hearing preservation dissection techniques.

STUDY DESIGN

A human temporal bone anatomic and radiographic study complemented with a literature review.

METHODS

Twenty human temporal bones were analyzed with high-resolution multislice computed tomography (HRMCT) and subjected to standard extended middle fossa IAC dissection with labyrinthine preservation and follow-up HRMCT for analyses of the ELD.

RESULTS

Zero of 20 (0%) temporal bones were found to have violation of the ELD with preservation of the labyrinthine structures and the endolymphatic sac. Reviews of human and animal studies indicate that injury to the ELD may create endolymphatic hydrops, a known cause of hearing deterioration.

CONCLUSION

The ELD is not vulnerable to injury during IAC dissection using the middle fossa approach. A previous radiographic study has shown that the ELD is violated in 24% of temporal bones during retrosigmoid dissection of the IAC. These findings support and may help explain other outcome studies that show that long-term hearing results are superior with the use of the middle fossa approach when compared to results following retrosigmoid dissection.

Radiosurgery for vestibular schwannomas

BACKGROUND

Radiosurgery has been established as an important alternative to microsurgery. We report our experience with radiosurgery for tumor control and the complications of unilateral vestibular schwannomas.

METHODS

We reviewed our early experience regarding clinical presentation, management and outcomes in 45 patients with acoustic schwannomas who underwent gamma knife stereotactic radiosurgery. The median follow-up period was 25 months (range, 6-48 months). Thirteen patients had undergone 1 or more previous resections before radiosurgery; 32 underwent radiosurgery as the first procedure. Median tumor volume was 4.5 mL (range, 0.5-30.0), and median radiotherapy dose was 11.5 Gy (range, 10.5-14.0 Gy).

RESULTS

Tumor control was achieved in 43 patients (95.6%). Loss of central contrast enhancement was a characteristic change and was noted in 29 patients (64.4%). Reduction in tumor size was shown in 15 patients (33.3%). Thirteen patients (28.9%) had good or serviceable hearing preoperatively, and in all of these, the preoperative status was retained immediately after radiosurgery. At follow-up, however, 10 patients (76.9%) had preserved hearing and 3 (23.1%) had reduced hearing on the treated side. Hearing in 1 patient that was not serviceable preoperatively later improved to a serviceable level. No patients had delayed facial palsy or lower cranial nerve dysfunction, but one had delayed trigeminal sensory loss.

CONCLUSION

Radiosurgery achieved a high tumor control rate and a relatively low post-radiosurgical complication rate for acoustic neuromas.

Neurostimulation as a New Treatment for Severe Tinnitus: A Pilot Study

BACKGROUND

Tinnitus is an uncomfortable symptom for the patient and an embarrassing one for the consulted physician. So far, there is no treatment that can be considered well established in terms of providing long-term reduction of tinnitus in excess of placebo effects. There is considerable evidence of pathophysiological similarity between tinnitus and chronic pain. Some forms of chronic pain can be treated by neurostimulation.

OBJECTIVE

This study was designed to investigate the feasibility of neurostimulation of the cochlear nerve in order to reduce tinnitus.

STUDY DESIGN

Pilot study.

SETTING

Tertiary referral center.

PATIENTS

Five patients with therapeutically refractory tinnitus were selected for this study.

INTERVENTION

Placing a stimulation lead around the cochlear nerve through the suboccipital approach and connecting the stimulation lead to a pulse generator.

MAIN OUTCOME MEASURES

The patients experienced 1) an absence of major or minor complications, such as death, meningitis, cranial nerve deficit, and vestibular problems; 2) tolerance of the procedure as considered by the patient; 3) relief of tinnitus in at least one patient.

RESULTS

Implantation of the neurostimulation system was accomplished in each patient without any difficulty. None of the patients considered the treatment unbearable. No major or minor complications occurred in this study. Subjective tinnitus reduction was accomplished in four patients.

CONCLUSION

Our preliminary data show that neurostimulation of the cochlear nerve is feasible, is bearable for the patient, and is a safe treatment modality without major complications. The effects on tinnitus are promising.

Endolymphatic Duct Violation During Retrosigmoid Dissection of the Internal Auditory Canal: A Human Temporal Bone Radiographic Study

OBJECTIVE/HYPOTHESIS

Successful hearing preservation after acoustic neuroma resection is sometimes complicated by delayed hearing deterioration. The goal of this study was to investigate the hypothesis that internal auditory canal (IAC) drilling during retrosigmoid acoustic neuroma removal may result in endolymphatic duct (ELD) injury, a potential cause of delayed hearing loss (HL) after hearing preservation surgery.

STUDY DESIGN

Temporal bone anatomic and radiographic study and literature review.

METHODS

Twenty-one human temporal bones were analyzed with high-resolution multislice computed tomography (HRMCT) and subjected to standard retrosigmoid IAC dissection with labyrinthine preservation and follow-up HRMCT for analyses of the ELD. A MEDLINE search was performed of studies documenting long-term hearing preservation outcomes after retrosigmoid dissection.

RESULTS

Five of 21 (24%) bones were found to have violation of the ELD despite preservation of labyrinthine structures and the endolymphatic sac. These results correlate with the mean incidence of long-term hearing decline (26.6%). Reviews of human and animal studies indicate that injury to the ELD may create endolymphatic hydrops.

CONCLUSIONS

The ELD is vulnerable to injury during IAC dissection even if labyrinthine structures at the lateral aspect of the IAC are preserved. These findings may be helpful in explaining and potentially preventing some cases of long-term hearing deterioration that may be a result of endolymphatic hydrops after ELD injury during acoustic tumor removal. Careful preoperative review of imaging studies using HRMCT may prove useful before retrosigmoid dissection.

[Cerebellopontine angle surgery. Part 2: Specific remarks]

OBJECTIVES

Cerebellopontine angle tumors are uncommon lesions that can potentially be cured by microsurgical removal. The primary objective of the surgical treatment differs between vestibular schwannoma and meningioma. This feature may be influenced by the site of tumor origin and displacement of neurovascular structures as well as by their different tumor biology.

METHODS

A review of the current literature was conducted.

RESULTS AND CONCLUSIONS

Relevant cranial nerves and vascular involvement as well as anatomical location with respect to the cerebellopontine angle are discussed for vestibular schwannoma and meningioma. The main factors influencing the surgical outcome are outlined with special reference to facial and cochlear nerve function and cerebrospinal fluid leakage. The retrosigmoid approach offers a comparable success rate for hearing conservation and probably a superior outcome in terms of facial nerve function when compared with the middle fossa approach. The intrameatal limitations of the retrosigmoid approach can be excluded by the intraoperative assistance of an endoscope. The advantages of endoscope-assisted surgery may include improved visualization of relevant structures, more complete tumor removal, and a lowered risk of cerebrospinal fluid leakage.

Hearing preservation in acoustic neuroma surgery: importance of adhesion between the cochlear nerve and the tumor

OBJECT

To evaluate the possible prognostic factors for hearing preservation, the authors retrospectively reviewed the results of 30 consecutive acoustic neuroma operations in which hearing preservation was attempted, in a total series of 63 acoustic neuromas.

METHODS

Intracanalicular tumors or those that extended less than 3 mm outside the porus acusticus (10 cases) were resected via the middle fossa approach. The retrosigmoid approach was used for tumors exceeding the limits for the middle fossa approach (20 cases). Overall, hearing was preserved (pure tone average < or = 50 dB and speech discrimination score > or = 50%) in 21 patients (70%). There were 11 patients with severe adhesion between the cochlear nerve and tumor capsule, and 19 without. Hearing was preserved postoperatively in only two (18.2%) of 11 patients with severe adhesion, whereas all 19 without severe adhesion had hearing preservation.

CONCLUSIONS

The presence or absence of severe adhesion in the interface between the cochlear nerve and the tumor might be the most significant prognostic factor for hearing preservation postsurgery.

Hearing restoration after resection of an intracanalicular vestibular schwannoma: a role for emergency surgery? Case report and review of the literature

Patients with vestibular schwannomas (VSs) most commonly present with sensorineural hearing loss, which is often insidious or gradual. Up to 26% of patients may present with sudden hearing loss, however, which poses an important surgical challenge. Sudden hearing loss has been attributed to spasm or occlusion of the labyrinthine artery resulting from tumor compression, and it is usually treated with corticosteroids. Hearing preservation surgery is not usually attempted in patients who have poor or nonserviceable hearing preoperatively. The authors describe a 68-year-old man with complete deafness of the left ear since childhood, who developed sudden, profound sensorineural hearing loss in the right ear. Magnetic resonance imaging revealed a small right-sided intracanalicular tumor. Treatment with high-dose corticosteroids produced only minimal improvement in hearing. Subsequent emergency decompression and resection of a VS resulted in rapid improvement and restoration of hearing, with facial nerve preservation. Although most neurotologic lesions in patients with hearing in only one ear are managed nonsurgically, resection of small tumors in the setting of sudden hearing loss should be considered in selected cases. This finding indicates that a therapeutic window may exist during which sudden hearing loss caused by intracanalicular tumors is reversible.

Prevention of cerebrospinal fluid leakage and delayed loss of preserved hearing after vestibular schwannoma removal: reconstruction of the internal auditory canal in the suboccipital transmeatal approach--technical note

The suboccipital transmeatal approach uses packing of a muscle or fat graft into the internal auditory canal (IAC) to prevent postoperative cerebrospinal fluid (CSF) leakage. However, preserved hearing after removal of vestibular schwannomas may decline over time because of the progressive constriction of cochlear vascular supply due to scarring of the IAC. We propose a surgical technique for IAC reconstruction, which separates the preserved cochlear nerve and vasculature from the graft, and regains the CSF space in the IAC. Prior to the drilling of the posterior wall of the IAC, the dura mater of the petrous bone forming the posterior wall of the IAC is harvested for IAC reconstruction. After completion of tumor removal, a "roof" of the IAC is reconstructed using the dura mater, and a muscle or fat graft soaked with fibrin glue is placed on the "roof" of the IAC. The IAC was reconstructed using this technique in 26 consecutive patients with vestibular schwannomas who underwent tumor removal via the suboccipital transmeatal approach. Postoperative magnetic resonance imaging confirmed the regained CSF space in the IAC. No delayed hearing loss occurred in four patients with preserved hearing. No CSF leakage occurred after surgery. This new technique of IAC reconstruction may prevent delayed hearing loss as well as postoperative CSF leakage after removal of vestibular schwannomas via the suboccipital transmeatal approach.

The long-term outcome of hearing preservation following vestibular schwannoma surgery

OBJECTIVE

The aim of this study is to describe the long-term outcome of preserved hearing after vestibular schwannoma surgery.

METHODS

Subjects are 20 unilateral vestibular schwannoma patients whose class A hearing of the AAO-HNS classification was preserved successfully after tumor removal. Hearing preservation surgery was attempted via the middle cranial fossa (MCF) or the extended MCF approach. The follow-up periods ranged from 2 to 16 years. The outcome measures included the pure tone average (PTA) and speech discrimination score (SDS).

RESULTS

PTA was maintained in less than 30 dB in 11 out of 20 patients within 2 years follow-up, six out of 13 patients within 4 years follow-up, and two out of five patients within 6 years follow-up, respectively. SDS was maintained in more than 70% in 17 out of 20 patients within 2 years follow-up, ten out of 13 patients within 4 years follow-up, and three out of five patients within 6 years follow-up, respectively.

CONCLUSIONS

The preserved hearing maintained about more than 40% of the patients with the class A hearing in every 2 years follow-up. From this result, we can conclude that the hearing preservation surgery could be one of the best treatments for vestibular schwannoma patients with class A hearing. However, further study will be needed to clarify the mechanism of the deterioration in hearing after hearing preservation surgery.

Selection of surgical approaches for small acoustic neurinomas

BACKGROUND

The purpose of this study was to evaluate the results of surgery for small acoustic neurinomas at our institute via the middle cranial fossa and retrosigmoid approaches, and to determine the indications for each approach.

METHODS

Fifty-three patients with unilateral tumors less than 2 cm in diameter were studied. Surgery was performed via the middle cranial fossa approach in 36 tumors and via the retrosigmoid approach in 17 tumors.

RESULTS

The hearing preservation rate was 68% (36/53) in all patients, 93% (14/15) in patients with intracanalicular tumors, 79% (15/19) in patients with tumors less than 1 cm in diameter, and 43% (7/19) in patients with tumors between 1 and 2 cm in diameter. The facial nerve function was excellent or good in 80% (42/53), 74% (11/15), 84% (16/19), and 78% (15/19), respectively. Among the 19 patients with tumors between 1 and 2 cm in diameter, the frequencies of hearing preservation and of excellent or good facial nerve function (47% and 87%, respectively) in the 15 patients approached via the retrosigmoid approach were higher than those (0% and 50%, respectively) in the four patients approached via the middle cranial fossa approach.

CONCLUSIONS

We conclude that tumors smaller than 2 cm should be removed because preservation of hearing as well as facial nerve function may be possible in almost all of these patients. Tumors larger than 1 cm should be surgically treated through the retrosigmoid approach.

Fractionated stereotactic radiosurgery and preservation of hearing in patients with vestibular schwannoma: a preliminary report

OBJECTIVE

Microsurgery and stereotactic radiosurgery (SRS) for vestibular schwannomas are associated with a relatively high incidence of sensorineural hearing loss. A prospective trial of fractionated SRS was undertaken in an attempt to preserve hearing and minimize incidental cranial nerve injury.

METHODS

Thirty-three patients with vestibular schwannomas were treated with 2100 cGy in three fractions during a 24-hour period using conventional frame-based linear accelerator radiosurgery. The median tumor diameter was 20 mm (range, 7-42 mm). Baseline and follow-up evaluations included audiometry and contrast-enhanced magnetic resonance imaging. End points were tumor progression, preservation of serviceable hearing, and treatment-related complications.

RESULTS

Thirty-one patients (32 tumors) were assessable for tumor progression and treatment-related complications and 21 patients for preservation of serviceable hearing, with a median follow-up interval of 2 years (range, 0.5-4.0 yr). Tumor regression or stabilization was documented in 30 patients (97%) and tumor progression in 1 (3%). The patient with tumor progression remains asymptomatic and has not required surgical intervention. Five patients (16%) developed trigeminal nerve injury at a median of 6 months (range, 4-12 mo) after SRS; two of these patients had preexisting trigeminal neuropathy. One patient (3%) developed facial nerve injury (House-Brackmann Class 3) 7 months after SRS. Preservation of useful hearing (Gardner-Robertson Class 1-2) was 77% at 2 years. All patients with pretreatment Gardner-Robertson Class 1 to 2 hearing maintained serviceable (Class 1-3) hearing as of their last follow-up examination.

CONCLUSION

Three-fraction SRS with a conventional stereotactic frame is feasible and well tolerated in the treatment of acoustic neuroma. This study demonstrates a high rate of hearing preservation and few treatment-related complications among a relatively high-risk patient cohort (tumors >15 mm or neurofibromatosis Type 2). Longer follow-up will be required to assess the durability of tumor control.

The prognostic value of intraoperative BAEP patterns in acoustic neurinoma surgery

Based on a consecutive series of 70 hearing patients with unilateral acoustic neurinomas and intraoperative monitoring of brain-stem auditory evoked potentials (BAEP), 4 dynamic BAEP patterns could be characterized. These patterns correspond with early and late postoperative hearing outcome. All patients with stable wave V (pattern 1) showed definite hearing preservation, all patients with irreversible abrupt loss of BAEP (pattern 2) lost their hearing, despite early hearing preservation in two cases. All patients with irreversible progressive loss of either wave I or wave V (pattern 3) eventually suffered from definite postoperative hearing loss, despite early hearing preservation in two cases. Those cases with intraoperative reversible loss of BAEP (pattern 4) showed variable short and long term hearing outcome. In 34% hearing was preserved, 44% suffered from postoperative hearing loss, the remaining 22% showed postoperative hearing fluctuation, either as a delayed hearing loss or as reversible hearing loss. Postoperative hearing fluctuation indicates anatomical and functional preservation of the cochlear nerve during surgery and is suggestive of a pathophysiological mechanism initiated during the surgical procedure and continuing thereafter. Patients at risk for delayed hearing loss can be identified during surgery by a characteristic BAEP pattern and may benefit from vasoactive treatment.

Dose reduction improves hearing preservation rates after intracanalicular acoustic tumor radiosurgery

OBJECTIVE

To assess the potential for long-term serviceable hearing preservation in intracanalicular acoustic tumor patients who underwent stereotactic radiosurgery.

METHODS

Between August 1987 and December 1997, 29 patients with intracanalicular acoustic tumors underwent stereotactic radiosurgery at our center using the Leksell gamma knife (Elekta Instruments, Inc., Atlanta, GA). Fifteen assessable patients had serviceable preradiosurgery hearing (pure tone average, < or = 50 dB; speech discrimination score, > or = 50%). We retrospectively analyzed our hearing results and compared hearing preservation in patients who received a minimal tumor dose of 14 Gy or less versus those who received more than 14 Gy to the tumor margin.

RESULTS

No perioperative patient morbidity or mortality was observed. Serviceable hearing was preserved in 11 (73%) of 15 assessable patients (actuarial rate, 65%). Long-term follow-up demonstrated serviceable hearing preservation in 10 (100%) of 10 patients who received marginal tumor doses of 14 Gy or less but in only one of five patients who received more than 14 Gy. Preradiosurgery Gardner-Robertson class was preserved in 49%, and testable hearing was present in 68% of patients who had any testable hearing at presentation. Five patients demonstrated improvement in hearing (three had serviceable and two had nonserviceable hearing before radiosurgery). No patient developed a facial or trigeminal neuropathy. Seven of 13 patients with preoperative tinnitus continued to experience tinnitus in follow-up. Episodic vertigo continued in 3 of the 11 patients who presented with vertigo.

CONCLUSION

Gamma knife radiosurgery (using conformal dose planning, small-beam geometry, and < or = 14 Gy to the margin) prevents tumor growth and achieves excellent hearing preservation rates.

Audiological assessment before and after fractionated stereotactic irradiation for vestibular schwannoma

PURPOSE

To find the audiological outcome after LINAC-based fractionated stereotactic irradiation (STI).

MATERIALS AND METHODS

Twenty-four patients with vestibular schwannoma treated by fractionated STI between 1991 and 1997 had measurable hearing before STI and were followed audiologically for more than 6 months. The pure tone average (PTA) was measured by averaging the air-conduction threshold for five main frequencies (250-4000 Hz) before and periodically after STI in the 24 patients. Several possible prognostic factors for hearing preservation (defined as a PTA change at the last follow-up of less than 10 dB) were investigated. The median follow-up time was 22 months, ranging from 5 to 69 months. The irradiation schedule was 36 Gy in 20 fractions in 5 weeks to 44 Gy in 22 fractions in 6 weeks followed by 4 Gy/1 fraction boost.

RESULTS

The pure tone average before STI was distributed from 7 to 73 dB. Fifty percent of patients showed a change in PTA of less than 10 dB, 79.2% of patients showed a change in PTA of less than 20 dB and 20.8% of patients showed a change in PTA of more than 21 dB at the last follow-up. Only one patient (4%) became deaf. Cases with a sudden loss of hearing were more likely to experience hearing preservation than those with gradual loss of hearing (P<0.05). The mean age was younger in patients whose hearing was preserved (P<0.05). Poor pretreatment PTA appeared to linearly correspond to the changes in PTA (regression coefficient 0.78). The size of the tumor was not related to the change in PTA. No relationship was observed between the maximum or peripheral dose and the PTA change. The real benefit of stereotactic boost after small-field fractionated irradiation was not certain.

CONCLUSION

Fractionated STI produced a hearing preservation rate compatible with meticulously collimated multi-spots single fraction irradiation. Further follow-up is required to confirm the long-term benefits of fractionation.

Vestibular schwannoma management in the next century: a radiosurgical perspective

PURPOSE

To discuss how the evolution of vestibular schwannoma radiosurgery, changes in health care delivery, and patient accessibility to medical information will affect the management of vestibular schwannomas in the future.

CONCEPT

In comparison with microsurgical resection of vestibular schwannomas, radiosurgery has a lower morbidity rate, a similar risk of requiring further surgery, and higher patient satisfaction. As this information becomes more widely available to patients and third-party payors, radiosurgery may replace surgical resection as the preferred management strategy for patients with small to medium sized vestibular schwannomas in the United States.

RATIONALE

It is estimated that 2500 patients are diagnosed with vestibular schwannomas each year in the United States. Assuming that 80% undergo surgery, 2000 operations are performed annually for newly diagnosed vestibular schwannomas. Data available since 1987 regarding the number of cases for which gamma knife radiosurgery was performed were used to predict the number of patients who will undergo vestibular schwannoma radiosurgery in the future. If the current trend continues, an equal number of patients will undergo surgical resection and radiosurgery to treat their vestibular schwannomas (approximately 1000/yr) sometime between 2005 and 2010. Moreover, it is predicted that by 2020, two-thirds of the patients who are newly diagnosed with vestibular schwannomas will undergo radiosurgery, with surgical resection being reserved for patients with large tumors associated with symptomatic brain stem compression.

DISCUSSION

Early data regarding vestibular schwannoma radiosurgery predicted an exponential growth curve. Although it is premature to assume that the current trend will continue, it is likely that an ever increasing percentage of patients will undergo radiosurgery as accessibility to this alternative increases, and more data are published regarding long-term tumor growth control rates. If the mathematical model proves to be accurate, then stereotactic radiosurgery will replace surgical resection as the preferred management strategy for the majority of patients with vestibular schwannomas.

Neurotopographic considerations in the microsurgical treatment of small acoustic neurinomas

OBJECT

The authors studied the relationships between tumor size, location, and topographic position relative to the intact facial nerve bundles in acoustic neurinomas to determine the influence of these factors on hearing preservation postoperatively. Consistent topographic relationships were found.

METHODS

Four hundred fifty-two patients with acoustic neurinoma treated via a retrosigmoid approach were analyzed with respect to hearing preservation and facial nerve function. One hundred fifteen tumors were identified as small and were categorized as Grades I and II. Patients with Grade I tumors, that is, purely intracanalicular lesions, all had good hearing preoperatively, defined by a less than 50-dB pure tone average and 50% speech discrimination score. All 14 Grade I tumors were removed, resulting in preservation of the patient's hearing by these criteria. There were no particular topographic anatomical relationships associated with these tumors that affected hearing preservation. Grade II tumors, defined as those protruding into the cerebellopontine angle without contacting the brainstem, were found in 101 patients and were divided by size into two grades: IIA (< 1 cm) and IIB (1-1.8 cm). In 90 patients with Grade IIA tumors, 72 (89%) of 81 who had preserved hearing preoperatively maintained it postoperatively, and in the 11 patients with Grade IIB tumors, six of whom had good hearing preoperatively, four (67%) had preserved hearing postoperatively. Six morphological types were identified based on their neurotopographic relationships to the elements of the vestibulocochlear nerve.

CONCLUSIONS

Hearing preservation postsurgery by tumor type was as follows: 1A, 92%; 1B, 88%; 1C, 100%; 2A, 83%; 2B, 92%; and 3, 57%. Combined, this represents a hearing preservation rate of 87% after surgical treatment of Grade II acoustic neurinomas. Full nerve function was maintained in 88% of patients with anatomically preserved facial nerves in both Grade I and II tumors. The remaining 12% of patients retained partial function of the facial nerve. Two patients in the series lost anatomical integrity of the nerve due to surgery.

Current concepts in the clinical management of patients with tinnitus

The current management in tinnitus of sensorineural origin is reviewed. Epidemiological data demonstrates that 90% of patients with hearing loss experience some tinnitus. Approximately 1% of the population suffer from a chronic tinnitus that causes severe distress and requires some type of management intervention. Present non-surgical therapies include masking techniques, psychological counseling, and biofeedback. There are also a number of drugs that have been applied, the most common being antidepressants. These have had the most success in managing patients with tinnitus, although it is currently felt that antidepressants treat underlying psychological problems rather than directly affect the tinnitus. The other large class of drugs include benzodiazopans, in addition to a new synthetic analog of a natural prostaglandin E1, misoprostol. Despite the many drugs now available, none has been approved by the United States Food and Drug Administration for the treatment of tinnitus. Many surgical therapies have been advocated but are directed towards the treatment of concurrent vertigo or for tumors of the cerebellopontine angle, with tinnitus sometimes being relieved by the operation. Specific surgical procedures such as cochlear resection and microvascular decompressions lack clear-cut efficacy. Despite author bias and a myriad of treatment modalities at present, there is still no specific therapy that definitively relieves tinnitus clinically.

Acoustic neurinomas. Diagnosis and treatment

We present our experience with 83 patients with acoustic neurinomas (January 1988 to November 1996); 81 patients underwent surgery and 2 patients with intracanalicular neurinomas received conservative therapy due to their advanced age (1 case) and patient's option (1 case). The surgical approach was retrosigmoid/transmeatal and the goal was total removal in one procedure with preservation of facial and cochlear nerves. Radical removal of lesion was attempted in 79 cases and it was possible in 77 patients. Subtotal tumor resection was planned in 2 cases. Facial nerve function (grades I to III, House and Brackman) was preserved in 90% and hearing in 58% of those with preoperative hearing. Three patients died due to postoperative complications. Early diagnosis of acoustic neurinomas is the most important factor in the prognosis and is one of the most important conquest of neurophysiology and modern neuroimaging. The management of these patients still present many controversial points. This article presents the diagnostic procedures used for acoustic neurinomas, the advantages and disadvantages of the different surgical approaches and the alternative management of these lesions.

Acoustic neuromas: results of current surgical management

OBJECTIVE

In this article, we review the surgical outcomes of 179 patients with acoustic neuromas.

METHODS

Most of the tumors (84%) were operated on using a retrosigmoid, transmeatal approach. A transpetrosal, retrosigmoid approach was used in 10% of the patients, most of whom had large tumors. The translabyrinthine (4%) and transmastoid, transpetrosal, partial labyrinthectomy approaches (2%) were used selectively. The operative approaches are discussed. Tumors were categorized according to their cerebellopontine angle dimensions as small (< 2 cm), medium (2.0-3.9 cm), and large (> or = 4 cm).

RESULTS

House-Brackmann evaluation of postoperative facial nerve function revealed excellent results (Grade I or II) in 96% of small tumors, 74% of medium tumors, and 38% of large tumors. A fair postoperative function (Grade III or IV) was achieved in 4% of small tumors, 26% of medium tumors, and 58% of large tumors. Functional hearing preservation, defined as Gardner-Robertson Class I or II, was achieved in 48% of small tumors and 25% of medium tumors. Hearing was not preserved in any of the three patients with large tumors in whom hearing preservation was attempted. Treatment complications consisted mainly of cerebrospinal fluid leakage (15% of the patients). The majority of the patients who experienced cerebrospinal fluid leakage were treated successfully with lumbar spinal drainage; only four patients (2% of the total group) required subsequent surgery for correction of cerebrospinal fluid leakage. There were two deaths (1%) in this series. One death occurred as the result of myocardial infarction and the other as the result of severe obstructive lung disease. One patient sustained disability because of cerebellar and brain stem injury. Complete tumor resection was accomplished in 99% of the patients, and there was no evidence of recurrence in this group. Only 1 of the 179 patients underwent incomplete tumor resection; he required subsequent surgery for symptomatic tumor regrowth. Our patient follow-up had a mean duration of 70 months and a median of 65 months (range, 3-171 mo).

CONCLUSION

Our results are similar to those of other large microsurgical series of acoustic neuromas. Unless a patient has major medical problems, microsurgery by an experienced team of surgeons is preferred over radiosurgery.

Hearing preservation in the removal of intracanalicular acoustic neuromas via the retrosigmoid approach

In a series of 514 consecutive operations for complete excision of acoustic neuromas, 94 procedures were performed via a retrosigmoid approach to preserve the patient's hearing. Twenty-six of these procedures (5.1%) were performed in cases of intracanalicular tumor and 68 (13.2%) were for larger lesions in which most of the tumor was located medial to the porus acusticus within the cerebellopontine angle. Preservation of useful hearing was achieved in 13 (50%) of 26 patients with intracanalicular tumors and in 20 (29%) of 68 with larger tumors. A trend toward higher success rates in intracanalicular tumors appears to be present, although the difference is not statistically significant (p = 0.09). Normal or near normal facial function (House and Brackmann Grades I and II) was present postoperatively in 25 (96%) of 26 patients. Indications for treatment of intracanalicular acoustic neuromas are considered and treatment alternatives are reviewed. Results from other series reporting removal of intracanalicular acoustic neuromas are considered with respect to hearing conservation and postoperative facial nerve function. Surgical excision of intracanalicular acoustic neuromas in otherwise healthy patients appears to be warranted if preservation of useful binaural hearing is considered a worthwhile objective and if perioperative morbidity can be maintained at an acceptably low level. The retrosigmoid approach is familiar to all neurosurgeons and offers a comparable success rate for hearing conservation and probably a superior outcome in terms of facial nerve function when compared with the middle fossa approach.

Influence of blood supply, thermal and mechanical traumata on hearing function in an animal model

Even with modern neurosurgical techniques preservation of functional hearing in acoustic neurinoma surgery is still impossible in a large number of cases. Due to the necessity of averaging the brainstem auditory evoked potentials (BAEP) this monitoring is not a real time measurement. Therefore the surgeon cannot be sure which manipulation during the tumour dissection has caused the loss of the BAEPs. The direct monitoring of the cochlear nerve (CNAP) may warn the surgeon earlier. But it is not able to explain, which manipulation has caused the worsening of the potentials. A loss of the waves after coagulation of a vessel next to the cochlear nerve may be the result of the heat or of the disturbance of the blood supply. Potentially harmful to cochlear nerve function may be the interruption of inner ear blood supply, thermal or mechanical traumata. Experimental studies are rare to nonexistent. We therefore tested selectively each trauma for its influence on the BAEPs in an animal model. In New Zealand rabbits a lateral craniectomy of the posterior fossa was performed. Care was taken not to retract the cerebellum or to open the inner ear system, because both factors might disturb the BAEPs. Each step of the operation was followed by BAEP recording. After reaching the internal auditory canal, the cerebellopontine angle of 6 animals was exposed to heated water with definitive increasing temperature. The BAEPs did not react significantly until 71 degrees C was reached and protein coagulation started. In the second group, the internal auditory artery of 6 rabbits was compressed with a microdissector for 3 minutes. Subsequently the BAEPs disappeared in all animals. In the last group a constant pressure of 10 g was applied to 6 cochlear nerves for 1 minute consistently causing the loss of the BAEPs. The results are statistically significant (p = 0.03). We therefore concluded that the blood supply of the inner ear is of the upmost importance for cochlear nerve function. Mechanical manipulation should be minimized whereas thermal traumatization of the nerve is only critical when the nerve itself is coagulated.

Early and late postoperative hearing preservation in patients with acoustic neuromas

OBJECTIVE

To examine the incidence of postoperative hearing preservation and the factors that influence early and late postoperative hearing in patients with acoustic neuromas.

METHODS

We reviewed the results of surgery and follow-up in 73 consecutive patients.

RESULTS

Of 73 patients, 51 demonstrated preoperative hearing levels equal to or better than Class 3, according to the classification system of Gardner and Robertson (8). After surgery, 21 (41.2%) of the 51 patients retained Class 1, 2, or 3 hearing. Hearing was more likely to be preserved after surgery if the tumor was small and if the preoperative hearing was good. The early postoperative hearing grade declined in 7 (33.3%) of the 21 patients, compared with the preoperative hearing level. The long-term follow-up of 17 patients in whom measurable hearing was retained after surgery indicated that 3 (17.6%) experienced delayed worsening of hearing, without evidence of tumor recurrence. The extent of hearing loss in patients with successful hearing preservation was not correlated with tumor size, preoperative hearing, patient age, or the shape of the cochlear nerve on the tumor surface. Hearing at long-term follow-up was significantly better in patients with excellent preoperative hearing.

CONCLUSION

Postoperative long-term preservation of hearing is more likely if surgery is performed while the tumor is still small and hearing is still excellent. Under these circumstances, it is more likely that the early and late hearing loss will be compensated.

The endolymphatic sac: microsurgical topographic anatomy

The endolymphatic sac is part of the membranous labyrinth; it plays an important role in the hearing mechanism. Injury to the endolymphatic sac may, over time, severely compromise hearing. The endolymphatic sac is located in a duplication of the dura of the posterior aspect of the petrous pyramid and is, therefore, in the surgical field of many neurosurgical operations performed on the posterolateral cranial base. The endolymphatic sac was exposed bilaterally in 10 anatomic specimens; the distance from the center of the sac to the posterior lip of the internal auditory meatus and to the XIth nerve in the jugular foramen was measured with a caliper. Also measured was the distance between the center of the sac and the closest point on the petrous ridge and the distance between that point and the petro-sigmoid intersection. The petro-sigmoid intersection was defined as the point at which the medial aspect of the sigmoid sinus intersects the lateral aspect of the petrous ridge. The dimensions of the sac were also recorded. On the average, the sac was found to be 15.7 mm posterosuperior (superolateral) to the XIth nerve in the jugular foramen (range, 11.0-18.5 mm) and 13.3 mm posterior (lateral) to the internal auditory meatus (range, 10.0-18.0 mm). The center of the sac was 24.1 mm (mean value) (range, 20.0-28.0 mm) in front of the petro-sigmoid intersection at a point 11.5 mm (mean value) (range, 8-17 mm) below the petrous ridge. The mean width and height of the sac were 3.83 (range, 2-6 mm) and 3.80 mm (range, 2.5-8 mm), respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Outcome analysis of acoustic neuroma management: a comparison of microsurgery and stereotactic radiosurgery

Currently, microsurgical resection of acoustic neuromas by an experienced, multidisciplinary team is thought to be the treatment of choice. During the past 20 years stereotactic radiosurgery has been used as an alternative to surgical removal. To compare the results of both microsurgery and stereotactic radiosurgery, we conducted a study of 87 patients with unilateral, previously unoperated acoustic neuromas with an average diameter less than 3 cm treated by the neurosurgical service during 1990 and 1991. Preoperative patient characteristics and average tumor size were similar between the treatment groups. State of the art microsurgical or radiosurgical techniques were used by experienced surgeons in both treatment groups. The treatment groups were compared based on cranial nerve preservation, tumor control, postoperative complications, patient symptomatology, length of hospital stay, total management charges, effect on employment status, and overall patient satisfaction. Stereotactic radiosurgery was more effective in preserving normal postoperative facial function (P < 0.05), and hearing preservation (P < 0.03) with less treatment associated morbidity (P < 0.01). Effect on preoperative symptoms were similar between the treatment groups. Postoperative functional outcomes and patients' satisfaction of their tumor management were greater after stereotactic radiosurgery when compared to the microsurgical group, although they did not reach statistical significance (P = 0.07 and P = 0.10, respectively). Patients returned to independent functioning sooner after stereotactic radiosurgery (P < 0.001). Hospital length of stay and total management charges were less in the radiosurgical group (P < 0.001). When compared to microsurgical removal, stereotactic radiosurgery proved to be an effective and less costly management strategy of unilateral acoustic neuromas less than 3 cm in diameter. For many acoustic neuroma patients, stereotactic radiosurgery should be offered as an alternative management strategy.

Stereotactic radiosurgery for acoustic nerve tumors in patients with useful preoperative hearing: results at 2-year follow-up examination

Twenty patients with acoustic nerve tumors (mean diameter < or = 30 mm) and useful preoperative hearing were examined 2 years after stereotactic radiosurgery to determine the effectiveness of the surgery in the control of tumor growth and the preservation of cranial nerve function. Results showed tumor volume stabilization (12 cases) or reduction (seven cases) was achieved in a total of 19 patients (95%). Useful hearing (defined as Gardner and Robertson Class I or II) preservation was obtained in 100% of cases immediately postoperatively, 50% at 6 months, and 45% at both 1 and 2 years. Two years after stereotactic radiosurgery, facial nerve function was preserved in 90% of patients and 75% continued to have normal trigeminal nerve function. All patients returned to and maintained their preoperative functional status within 3 to 5 days after radiosurgery. These findings indicate that stereotactic radiosurgery with multiple isocenters and narrow radiation beams is a safe and effective management strategy for progressive acoustic nerve tumors. Auditory, facial, and trigeminal nerve function can be preserved in most patients. Prevention of further growth and preservation of cranial nerve function appear to be satisfactory goals in the current management of patients with acoustic neuromas.

Preservation of hearing after surgery for acoustic schwannomas: correlation between cochlear nerve function and operative findings

The results of surgery in 66 patients with acoustic schwannoma in whom total tumor removal was accomplished are reviewed in terms of the relationships among tumor size, preoperative hearing level, operative findings (including the shape and location of the cochlear nerve at the tumor surface), and the extent of postoperative hearing preservation. Both tumor size and the preoperative hearing level were correlated with the shape of the cochlear nerve, which more frequently formed a solid bundle when the tumor was small or the preoperative hearing was excellent. Hearing was retained postoperatively only in cases in which the nerve formed a solid bundle and could be differentiated and separated from the tumor capsule without difficulty. These findings suggest that tumor size and preoperative hearing level, which have been reported to be the main prognostic factors of postoperative hearing preservation, may influence the results of surgery for acoustic schwannoma through the shape of the cochlear nerve.

Linear accelerator-based stereotactic radiosurgery for acoustic schwannomas

PURPOSE

Stereotactic radiosurgery (SRS) is currently being investigated for treatment of acoustic schwannomas in patients who are not good surgical candidates. The vast majority of the available data is based on gamma knife-treated patients. We present the largest series of patients treated with linear accelerator-based SRS.

METHODS AND MATERIALS

Thirty-two patients with acoustic schwannomas were treated with SRS between July 1988 and February 1993; follow-up ranged from 4-59 months. Age ranged from 34-88 years (mean, 62 years). The primary presenting symptom was hearing loss in 30 patients and dementia in two patients. Indications for SRS were age > 65 years (17 patients); recurrence after surgery (13 patients); and medical infirmity (two patients). Dose to the periphery of the lesion ranged from 10-22.5 Gy (mean, 15.5 Gy) specified at the 68-90% isodose line (mean, 80%). Collimator size ranged from 12-35 mm (mean, 23 mm), indicating that the sizes of the tumors were significantly larger than those reported in most gamma knife series.

RESULTS

Follow-up magnetic resonance imaging (MRI) and/or computed tomography (CT) scans revealed the following at 1 year: tumor regression, 12 patients (63%); and no change, seven patients (37%). At 2 years, 11 tumors (73%) were smaller and four tumors (27%) were unchanged. At 3 years, seven patients (78%) had experienced tumor regression and two (22%) had no change. No patient experienced tumor progression after SRS. Seven patients (22%) suffered one or more treatment complications: new onset of 5th and/or 7th cranial nerve deficit (six patients), ataxia (two patients), and/or hydrocephalus necessitating VP shunt (two patients).

CONCLUSION

Linear accelerator-based SRS provides excellent short-term local control and a relatively low incidence of complications for acoustic schwannomas. Our data compare favorably with results obtained with gamma knife-based SRS. Additional follow-up will be necessary to evaluate the long-term results of treatment.