Management of 1000 vestibular schwannomas (acoustic neuromas): the facial nerve--preservation and restitution of function

Microneurosurgery and radiosurgery--an attractive combination

Microneurosurgery and radiosurgery have made tremendous progress in terms of increasing efficacy and reducing treatment related mobility. Both techniques have clear indications; however, there is still competition between the two modalities in a variety of diseases. In all instances, this rivalry should be replaced by the concept of using both methods as complementary. Skull base tumours, metastases as well as certain AVMs are good candidates for this approach.

Results of outpatient gamma knife radiosurgery for primary therapy of acoustic neuromas

Stereotactic radiosurgery (SRS) has been recognized as a non-invasive alternative to surgery for the treatment of acoustic neuromas. Purpose of the current study was to define the impact of outpatient gamma knife radiosurgery (GKS) for patients with unilateral sporadic acoustic neuromas treated within ten years. Follow-up images were analyzed using tumor volume measurements. 219 patients with sporadic acoustic neuromas were treated by GKS as primary therapy. Patients with NF-2 tumors were excluded. Patients were eligible for GKS up to a size limit of 12.5 cm3. The median follow up time was 6 years after radiosurgery. The local tumor control rate was high (97%). Cranial nerve morbidities were comparably low. 10% of the patients developed hearing loss after radiosurgery and one patient experienced a transient facial neuropathy (0.5%). Transient trigeminal neuropathy developed in 12 patients (5%) and was found to be dependent on the tumor size before treatment. Outpatient gamma knife radiosurgery is a safe and effective treatment method for selected patients with sporadic vestibular schwannomas.

One-stage Removal of Residual Intracanalicular Acoustic Neuroma and Hemihypoglossal-intratemporal Facial Nerve Anastomosis: Technical Note

OBJECTIVE AND IMPORTANCE

Incomplete removal of residual intracanalicular tumor and injury to the facial nerve are the main problems associated with surgery of large acoustic neuromas via the retromastoid suboccipital approach. In patients with residual or recurrent intracanalicular neuromas, the translabyrinthine approach is the preferred surgical route, allowing complete tumor removal; it may eventually also be used for exposure of the intratemporal portion of the facial nerve for a hemihypoglossal-facial nerve anastomosis when a postoperative facial palsy exists This one-stage procedure has not been described previously.

CLINICAL PRESENTATION

Three patients with postoperative facial palsy and residual intracanalicular tumor after surgical removal of a large acoustic neuroma via the retromastoid suboccipital approach underwent reoperation via the translabyrinthine approach and one-stage removal of the residual tumor and hemihypoglossal-facial nerve anastomosis. All three patients had a complete facial palsy of House-Brackmann Grade VI and a residual tumor of 8 to 12 mm.

TECHNIQUE

A classic translabyrinthine approach was used to open the internal auditory canal and remove the residual intracanalicular tumor. The facial nerve was exposed in its mastoid and tympanic parts, mobilized, and transected; then, the long nerve stump was transposed into the neck and used for an end-to-side anastomosis into the hypoglossal nerve. The operation resulted in variable improvement of the facial muscle function up to Grade III (one patient) and Grade IV (two patients).

CONCLUSION

Reoperation via the translabyrinthine approach is indicated for removal of residual intracanalicular acoustic neuroma and realization of a hypoglossal-facial nerve anastomosis in a single procedure. It is suggested that this type of anastomosis may also be used during the initial operation for acoustic neuroma removal when the facial nerve is inadvertently sectioned.

Clinical and histopathologic features of recurrent vestibular schwannoma (acoustic neuroma) after stereotactic radiosurgery

OBJECTIVE

Stereotactic radiosurgery for vestibular schwannoma entails uncertain long-term risk of tumor recurrence and delayed cranial neuropathies. In addition, the underlying histopathologic changes to the tumor bed are not fully characterized. We seek to understand the clinical and histologic features of recurrent vestibular schwannoma after stereotactic radiation therapy.

STUDY DESIGN

Retrospective review.

SETTING

Tertiary referral center.

PATIENTS

Four patients who underwent microsurgical resection of vestibular schwannoma after primary stereotactic radiation therapy.

INTERVENTION

Patients were treated primarily with gamma knife radiosurgery or fractionated stereotactic radiotherapy followed by salvage microsurgery. Retrosigmoid craniotomy was used in all cases.

MAIN OUTCOME MEASURES

Histopathologic review. Preoperative and postoperative facial nerve function was assessed with the House-Brackmann scale.

RESULTS

We observed highly inconsistent radiation changes in the cerebellopontine angle and internal auditory canal. Fibrosis outside and within the tumor bed varied markedly, complicating microsurgical dissection. Light microscopy confirmed the presence of viable tumor in all cases. Histopathologic features were typical of vestibular schwannoma, and there was no significant scarring that could be attributed to radiation effect.

CONCLUSIONS

The variable fibrosis in the cerebellopontine angle and lack of radiation changes seen histopathologically in irradiated vestibular schwannoma suggest that a uniform treatment effect was not achieved in these cases. Although all four patients with preoperative cranial neuropathies were found intraoperatively to have fibrosis in the cerebellopontine angle, excellent preservation of facial nerve anatomy and function was possible with salvage microsurgical resection. Additional analyses are needed to clarify the histopathologic and molecular characteristics associated with vestibular schwannoma growth after stereotactic radiation.

[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.

[High jugular bulb and its relationship with acoustic neurinoma surgery]

The jugular bulb is formed by the junction of the sigmoid sinus, inferior petrous sinus and the jugular vein. It is housed in the jugular fossa of the petrous pyramid. Variations in its size, location and relationship to the internal acoustic canal (IAC) have been reported. When the jugular bulb is located medial and less than 2 mm from the posterior wall of the internal acoustic canal, it is named as high jugular bulb. If the surgeon is not aware of this variation, damage to this structure can result in profuse haemorrhage and air embolism. This anatomical change also makes difficult the access to the intracanalicular portion of acoustic neurinomas when these tumours are excised by a retrosigmoid approach. We present the case of a patient with an acoustic schwannoma in whom a preoperative axial cranial CT revealed a high jugular bulb. To control this venous structure, we opened the IAC in a longitudinal manner achieving a total excision of the lesion preserving the function of the facial nerve. We conclude that preoperative radiological investigations in acoustic schwannomas surgery should include cranial MR and TC, to rule out the presence of a high jugular bulb. Cranial axial CT including bony windows and slices of 1.5 mm thick, should be carried out to exclude a high jugular bulb.

Delayed facial palsy after resection of vestibular schwannoma

OBJECT

In this study the authors investigate delayed facial palsy (DFP), which is an underreported phenomenon after surgery for vestibular schwannoma (VS). The authors identified 15 (4.8%) patients from a consecutive series of 314 who underwent surgery for VS between 1988 and 2000, and in whom DFP developed. Delayed facial palsy was defined as a deterioration of facial nerve function from House-Brackmann Grades 1 or 2 more than 3 days postoperatively.

METHODS

All patients underwent intraoperative neurophysiological monitoring of facial nerve function. The average latency of DFP was 10.9 days (range 4-30 days). In six patients (40%) minor deterioration (< or = two House-Brackmann grades) had occurred at a mean of 10.2 days postsurgery, whereas in nine patients (60%) moderate deterioration (> or = three House-Brackmann grades) had occurred at a mean of 11.8 days postoperatively. Five (33%) of 15 patients recovered to Grade 1 of 2 function within 6 weeks of DFP onset. Of the 15 patients with DFP, 14 had completed 1 year of follow up at the time of this study. Twelve (80%) of these 15 patients recovered to Grade 1 or 2 function within 3 months, and 13 (93%) of 14 patients recovered within 1 year. In all cases, stimulation of the seventh cranial nerve on completion of tumor resection revealed the nerve to be intact, both anatomically and functionally, to proximal and distal stimulation at 0.1 mA. A smaller tumor diameter correlated with greater recovery of facial nerve function. There was no correlation between the latency or severity of or recovery from DFP, and the patient's age or sex, the surgical approach, frequency of neurotonic seventh nerve discharges, anatomical relationship of the facial nerve to the tumor, patient's history of tobacco use, or cardiovascular disease.

CONCLUSIONS

It appears that DFP is an uncommon consequence of surgery for VS. Although excellent recovery of facial nerve function to its original postoperative status nearly always occurs after DFP, the magnitude and time course of the disorder were not predictors for subsequent recovery of facial nerve function.

Is hearing preservation useful in vestibular schwannoma surgery?

The goal of our study was to examine the usefulness of preserved hearing after unilateral vestibular schwannoma removal. The patients were assessed by clinical evaluation, preoperative and postoperative audiometric evaluation, operative findings, and postoperative functional results. Hearing was preserved in 47 of 119 patients. The postoperative hearing was better than 30 dB in 10 patients. During the follow-up, the hearing decreased 5 dB on average, and almost all of the decrement occurred during the first 6 months. Subjectively, the preserved hearing assisted in understanding of speech in 62% of the patients. Tinnitus did not interfere with understanding of speech. The age of the patients was the most significant factor associated with preserved hearing. Sixty-six percent of the patients with hearing preservation rated their preserved hearing as valuable. Neither tinnitus nor speech distortion reduced the appreciation for hearing preservation. We conclude that efforts to preserve hearing are worthwhile.

Predictive factors of long-term facial nerve function after vestibular schwannoma surgery

OBJECTIVE

To assess predictive factors of long-term facial nerve function in a series of patients undergoing vestibular schwannoma surgery and to evaluate the reproducibility of the relevant parameters.

STUDY DESIGN

Prospective.

SETTING

Three tertiary referral neurotology units in two separate countries.

PATIENTS

A total of 67 patients, with normal preoperative facial function and an anatomically intact facial nerve postoperatively, undergoing vestibular schwannoma surgery during a sequential 18-month period.

INTERVENTIONS

Recording of intraoperative stimulus amplitudes (minimum intensity medial to the tumor after excision) and postoperative facial nerve function up to 2 years after surgery.

MAIN OUTCOME MEASURES

Long-term facial nerve function related to tumor size, early postoperative facial nerve function, and intraoperative electrophysiologic intensities.

RESULTS

Multivariate logistic regression model identified tumor size and the minimum intensity required to provoke a stimulus threshold event medial to the tumor after excision as independent predictors of a favorable initial outcome. Immediate facial nerve function was the only independent predictor of long-term normal function. The sensitivity of this predictor was 95% (95% confidence interval [CI], 89-100%); specificity, 83% (95% CI, 62-100%); positive predictive accuracy, 96% (95% CI, 91-100%); and negative predictive accuracy, 77% (95% CI, 54-100%).

CONCLUSION

The combination of electrophysiologic intensities and tumor size are reproducible and better predictors of initial facial nerve function than any individual parameter, but long-term facial nerve function is more likely to have a better outcome if the nerve is left intact and a per-operative graft repair is not performed. The study suggests that although the best available predictor of overall long-term facial nerve outcome is the level of early postoperative function, this factor is not useful in surgical rehabilitation decision making.

Neural conservation in skull base surgery

Surgical treatment of lesions of the skull base carries significant risk to the functioning of the cerebral hemispheres, the brain stem and the cranial nerves. This risk is due both, to problems associated with maintaining an adequate blood flow while exposing and removing the tumor and to direct or indirect trauma to the brain, perineural tissues and cranial nerves. These risks may be reduced if information about possible implications of surgical maneuvers on the cerebral blood flow and on the function of the patients central nervous system and cranial nerves is available and can be monitored during surgery of the skull base. The use of electromyographic neuromonitoring for the facial nerve and of BERA-monitoring for the auditory nerve have been described and are now standard methods to achieve these goals. In acoustic tumors in the last several years beside preservation of the function of the facial nerve hearing preservation especially in small tumors has been one of the primary goals in acoustic neuroma surgery. Computer assisted surgery and intraoperative imaging for lateral skull base surgery are still in their infancy but promise to allow further improvement of neural conservation.

Analysis of risk factors associated with radiosurgery for vestibular schwannoma

OBJECT

The aim of this study was to identify factors associated with delayed cranial neuropathy following radiosurgery for vestibular schwannoma (VS or acoustic neuroma) and to determine how such factors may be manipulated to minimize the incidence of radiosurgical complications while maintaining high rates of tumor control.

METHODS

From July 1988 to June 1998, 149 cases of VS were treated using linear accelerator radiosurgery at the University of Florida. In each of these cases, the patient's tumor and brainstem were contoured in 1-mm slices on the original radiosurgical targeting images. Resulting tumor and brainstem volumes were coupled with the original radiosurgery plans to generate dose-volume histograms. Various tumor dimensions were also measured to estimate the length of cranial nerve that would be irradiated. Patient follow-up data, including evidence of cranial neuropathy and radiographic tumor control, were obtained from a prospectively maintained, computerized database. The authors performed statistical analyses to compare the incidence of posttreatment cranial neuropathies or tumor growth between patient strata defined by risk factors of interest. One hundred thirty-nine of the 149 patients were included in the analysis of complications. The median duration of clinical follow up for this group was 36 months (range 18-94 months). The tumor control analysis included 133 patients. The median duration of radiological follow up in this group was 34 months (range 6-94 months). The overall 2-year actuarial incidences of facial and trigeminal neuropathies were 11.8% and 9.5%, respectively. In 41 patients treated before 1994, the incidences of facial and trigeminal neuropathies were both 29%, but in the 108 patients treated since January 1994, these rates declined to 5% and 2%, respectively. An evaluation of multiple risk factor models showed that maximum radiation dose to the brainstem, treatment era (pre-1994 compared with 1994 or later), and prior surgical resection were all simultaneously informative predictors of cranial neuropathy risk. The radiation dose prescribed to the tumor margin could be substituted for the maximum dose to the brainstem with a small loss in predictive strength. The pons-petrous tumor diameter was an additional statistically significant simultaneous predictor of trigeminal neuropathy risk, whereas the distance from the brainstem to the end of the tumor in the petrous bone was an additional marginally significant simultaneous predictor of facial neuropathy risk. The overall radiological tumor control rate was 93% (59% tumors regressed, 34% remained stable, and 7.5% enlarged), and the 5-year actuarial tumor control rate was 87% (95% confidence interval [CI] 76-98%). Analysis revealed that a radiation dose cutpoint of 10 Gy compared with more than 10 Gy prescribed to the tumor margin yielded the greatest relative difference in tumor growth risk (relative risk 2.4, 95% CI 0.6-9.3), although this difference was not statistically significant (p = 0.207).

CONCLUSIONS

Five points must be noted. 1) Radiosurgery is a safe, effective treatment for small VSs. 2) Reduction in the radiation dose has played the most important role in reducing the complications associated with VS radiosurgery. 3) The dose to the brainstem is a more informative predictor of postradiosurgical cranial neuropathy than the length of the nerve that is irradiated. 4) Prior resection increases the risk of late cranial neuropathies after radiosurgery. 5) A prescription dose of 12.5 Gy to the tumor margin resulted in the best combination of maximum tumor control and minimum complications in this series.

Elevation of internal auditory canal pressure by vestibular schwannomas

OBJECTIVE

The exact mechanism of hearing loss, the most common presenting symptom in patients with vestibular schwannomas, remains unclear. To test whether increased pressure in the internal auditory canal from tumor growth is responsible for this clinical finding, the intracanalicular pressure in patients harboring these tumors was measured.

STUDY DESIGN

Prospective study.

SETTING

Tertiary referral hospital.

PATIENTS

Fifteen consecutive patients undergoing a retrosigmoid approach for resection of vestibular schwannomas were included in the study.

INTERVENTION

The intracanalicular pressure in every patient was measured by introducing a pressure microsensor into the internal auditory canal. The pressure readings, which were performed before tumor resection, were then correlated with tumor size and respective preoperative hearing status.

RESULTS

Placement of the pressure monitor into the internal auditory canal revealed a biphasic waveform in every patient. Whereas the mean intracanalicular pressure was 20 mm Hg, there was significant variability among patients (range, 1-45 mm Hg). The intracanalicular pressure directly correlated with the amount of tumor in the internal auditory canal (r > 0.63, p < 0.012) but not with the total tumor size (r </= 0.40, p > 0.075). Furthermore, eight patients with class A preoperative hearing (American Academy of Otolaryngology-Head and Neck Surgery classification) had lower intracanalicular pressures than did five patients with class B hearing (16 +/- 5 vs. 28 +/- 4). Although this observation suggested an inverse correlation between the intracanalicular pressure and hearing function, the difference between the two groups was not statistically significant (p = 0.14).

CONCLUSION

Pressure on the cochlear nerve as a result of tumor growth in the internal auditory canal may be responsible for hearing loss in patients with vestibular schwannomas. Modification of surgical techniques to address the elevated intracanalicular pressure may be beneficial in improving hearing preservation in these patients.

Stereotactic radiosurgery and fractionated stereotactic radiotherapy for the treatment of acoustic schwannomas: comparative observations of 125 patients treated at one institution

BACKGROUND

Stereotactic radiosurgery (SRS) and, more recently, fractionated stereotactic radiotherapy (SRT) have been recognized as noninvasive alternatives to surgery for the treatment of acoustic schwannomas. We review our experience of acoustic tumor treatments at one institution using a gamma knife for SRS and the first commercial world installation of a dedicated linac for SRT.

METHODS

Patients were treated with SRS on the gamma knife or SRT on the linac from October 1994 through August 2000. Gamma knife technique involved a fixed-frame multiple shot/high conformality single treatment, whereas linac technique involved daily conventional fraction treatments involving a relocatable frame, fewer isocenters, and high conformality established by noncoplanar arc beam shaping and differential beam weighting.

RESULTS

Sixty-nine patients were treated on the gamma knife, and 56 patients were treated on the linac, with 1 NF-2 patient common to both units. Three patients were lost to follow-up, and in the remaining 122 patients, mean follow-up was 119 +/- 67 weeks for SRS patients and 115 +/- 96 weeks for SRT patients. Tumor control rates were high (> or =97%) for sporadic tumors in both groups but lower for NF-2 tumors in the SRT group. Cranial nerve morbidities were comparably low in both groups, with the exception of functional hearing preservation, which was 2.5-fold higher in patients who received conventional fraction SRT.

CONCLUSION

SRS and SRT represent comparable noninvasive treatments for acoustic schwannomas in both sporadic and NF-2 patient groups. At 1-year follow-up, a significantly higher rate of serviceable hearing preservation was achieved in SRT sporadic tumor patients and may therefore be preferable to alternatives including surgery, SRS, or possibly observation in patients with serviceable hearing.

Intra-operative electromyographic monitoring of the lower cranial motor nerves (LCN IX-XII) in skull base surgery

The functional preservation of lower (motor) cranial nerves (LCN) is endangered during skull base surgery. Intra-operative EMG monitoring of the LCN IX-XII was investigated in 78 patients undergoing 80 operations on various skull base tumors with regard to technical feasibility and clinical efficacy. Ongoing 'spontaneous muscle activity' (SMA) and 'compound muscle action potentials' (CMAP) following supramaximal bipolar stimulation were intra-operatively recorded applying needle electrodes into the soft palate (CN IX: n=76), the vocal cord (CN X: n=72), the trapezius muscle (CN XI: n=18), and the tongue (CN XII: n=71). From 24/22/8 cases with LCN IX/X/XII deficits (despite monitoring) only 5/6/4 remained unchanged (3-6 months postoperative). An irreversible plegia of the LCN IX/X/XII occurred in three (1/1/1) patients. In 7/6/1 patients postoperative (3-6 months) LCN IX/X/XII function was better than preoperatively. In all patients accessory nerve function remained unchanged. 'Pathological' SMA of the LCN IX/X/XII occurred in 12/16/8 cases, but in only 6/5/3 cases corresponded to postoperative LCN deficits. Corresponding 'pathological' SMA patterns were found in 18/17/5 out of 24/22/8 cases with postoperative LCN IX/X/XII dysfunction. Reproducible CMAP of LCN IX/X/XI/XII could be recorded in 59/56/11/32 patients. Approximate 'normal' values were calculated and compared to (very few) data so far given in the literature. Electromyographic monitoring proved to be a safe tool for the intra-operative identification and localization of the LCN contributing to their anatomical and functional preservation. The predictive value of standard neurophysiological parameters for functional outcome, however, is limited.

Long-term results of the first 500 cases of acoustic neuroma surgery

OBJECTIVE

This retrospective study focuses on 2 outcome results after surgical intervention for acoustic neuroma: (1) facial nerve status, and (2) hearing preservation.

STUDY DESIGN

A total of 484 patients with an acoustic neuroma.

RESULTS

Postoperative facial nerve outcomes were significantly different (P < 0.001) according to the size of the tumors. Tumor size had even more influence on the immediate postoperative results. In addition, statistical significance (P < 0.05) was demonstrated in comparing facial nerve outcomes with the surgeon's surgical experience. We also noted that as the patient's age increases, the likelihood for facial dysfunction may increase for all postoperative intervals. The overall success rate of retaining useful hearing was 27% (26 of 95). Class A hearing was retained in 66% (10 of 15) of cases operated on through middle fossa approach in the last 5 years.

CONCLUSION

This study demonstrates that tumor size and surgeon's experience are the most significant factors influencing the facial nerve status and hearing outcome after removal of acoustic neuroma.

Analysis of the results obtained in 120 patients with large acoustic neuromas surgically treated via the translabyrinthine-transtentorial approach

OBJECT

The authors review the results of a series of 120 acoustic neuromas that were surgically treated via the translabyrinthine-transtentorial approach between 1986 and 1999.

METHODS

The authors retrospectively evaluated a series of 120 acoustic neuromas with extrameatal diameters of 2 cm or greater, 99 (82.5%) of which had diameters longer than 3 cm. Complete tumor removal, as ascertained using computerized tomography or magnetic resonance imaging, was achieved in 110 patients (91.7%). The facial nerve was anatomically preserved in 97 patients (80.8%). The main postoperative complications were cerebrospinal fluid (CSF) leakage through the scalp wound (13.3%) requiring surgical revision in 2.5%, meningitis (9.2%), CSF rhinorrhea (6.7%) requiring surgical revision in 2.5%, and epileptic seizures (the only permanent complication) requiring medication (3.3%). There was no death directly related to the surgery. Long-term follow-up examination of the facial nerve revealed recovery of function to the level of House-Brackmann Grade I or II in 56.2% of the patients.

CONCLUSIONS

The results and complications presented in this series are comparable to those reported in the literature. The authors conclude that the combined translabyrinthine-transtentorial approach is a safe route for removing acoustic neuromas with a diameter of 2 cm or greater.

Conventionally fractionated stereotactic radiotherapy (FSRT) for acoustic neuromas

PURPOSE

Analysis of local tumor control and functional outcome following conventionally fractionated stereotactic radiotherapy (FSRT) for acoustic neuromas.

PATIENTS AND METHODS

From 11/1989 to 9/1999 51 patients with acoustic neuromas have been treated by FSRT. Mean total dose was 57.6 +/- 2.5 Gy. Forty-two patients have been followed for at least 12 months and were subject of an outcome analysis. Mean follow-up was 42 months. We analyzed local control, hearing preservation, and facial and trigeminal nerve functional preservation. We evaluated influences of tumor size, age, and association with neurofibromatosis Type 2 (NF2) on outcome and treatment related toxicity.

RESULTS

Actuarial 2- and 5-year tumor control rates were 100% and 97.7%, respectively. Actuarial useful hearing preservation rate was 85% at 2 and 5 years. New hearing loss was diagnosed in 4 NF2 patients. Pretreatment normal facial nerve function was preserved in all cases. Two cases of new or impaired trigeminal nerve dysesthesia required medication. No other cranial nerve deficit was observed. In Patients without NF2 tumor size or age had no influence on tumor control and cranial nerve toxicity. Diagnosis of NF2 was associated with higher risk of hearing impairment (p = 0.0002), the hearing preservation rate in this subgroup was 60%.

CONCLUSION

FSRT has been shown to be an effective means of local tumor control. Excellent hearing preservation rates and 5th and 7th nerve functional preservation rates were achieved. The results support the conclusion that FSRT can be recommended to patients with acoustic neuromas where special attention has to be taken to preserve useful hearing and normal cranial nerve function. For NF2 patients, FSRT may be the treatment of choice with superior functional outcome compared to treatment alternatives.

Continuous electromyography monitoring of motor cranial nerves during cerebellopontine angle surgery

OBJECT

Electromyography (EMG) monitoring is expected to reduce the incidence of motor cranial nerve deficits in cerebellopontine angle surgery. The aim of this study was to provide a detailed analysis of intraoperative EMG phenomena with respect to their surgical significance.

METHODS

Using a system that continuously records facial and lower cranial nerve EMG signals during the entire operative procedure, the authors examined 30 patients undergoing surgery on acoustic neuroma (24 patients) or meningioma (six patients). Free-running EMG signals were recorded from muscles targeted by the facial, trigeminal, and lower cranial nerves, and were analyzed off-line with respect to waveform characteristics, frequencies, and amplitudes. Intraoperative measurements were correlated with typical surgical maneuvers and postoperative outcomes. Characteristic EMG discharges were obtained: spikes and bursts were recorded immediately following the direct manipulation of a dissecting instrument near the cranial nerve, but also during periods when the nerve had not yet been exposed. Bursts could be precisely attributed to contact activity. Three distinct types of trains were identified: A, B, and C trains. Whereas B and C trains are irrelevant with respect to postoperative outcome, the A train--a sinusoidal, symmetrical sequence of high-frequency and low-amplitude signals--was observed in 19 patients and could be well correlated with additional postoperative facial nerve paresis (in 18 patients).

CONCLUSIONS

It could be demonstrated that the occurrence of A trains is a highly reliable predictor for postoperative facial palsy. Although some degree of functional worsening is to be expected postoperatively, there is a good chance of avoiding major deficits by warning the surgeon early. Continuous EMG monitoring is superior to electrical nerve stimulation or acoustic loudspeaker monitoring alone. The detailed analysis of EMG-waveform characteristics is able to provide more accurate warning criteria during surgery.

Can continuous intraoperative facial electromyography predict facial nerve function following cerebellopontine angle surgery?

Intraoperative cranial nerve monitoring has significantly improved the preservation of facial nerve function following surgery in the cerebellopontine angle (CPA). Facial electromyography (EMG) was performed in 60 patients during CPA surgery. Pairs of needle electrodes were placed subdermally in the orbicularis oris and orbicularis oculi muscles. The duration of facial EMG activity was noted. Facial EMG potentials occurring in response to mechanical or metabolic irritation of the corresponding nerve were made audible by a loudspeaker. Immediate (4-7 days after tumor excision) and late (6 months after surgery) facial nerve function was assessed on a modified House-Brackmann scale. Late facial nerve function was good (House-Brackmann 1-2) in 29 of 60 patients, fair (House-Brackmann 3-4) in 14, and poor (House-Brackmann 5-6) in 17. Postmanipulation facial EMG activity exceeding 5 minutes in 15 patients was associated with poor late function in five, fair function in six, and good function in four cases. Postmanipulation facial EMG activity of 2-5 minutes in 30 patients was associated with good late facial nerve function in 20, fair in eight, and poor in two. The loss of facial EMG activity observed in 10 patients was always followed by poor function. Facial nerve function was preserved postoperatively in all five patients in whom facial EMG activity lasted less than 2 minutes. Facial EMG is a sensitive method for identifying the facial nerve during surgery in the CPA. EMG bursts are a very reliable indicator of intraoperative facial nerve manipulation, but the duration of these bursts do not necessarily correlate with short- or long-term facial nerve function despite the fact that burst duration reflects the severity of mechanical aggression to the facial nerve.

Acoustic neuroma surgery as an interdisciplinary approach: a neurosurgical series of 508 patients

OBJECTIVES

To evaluate an interdisciplinary concept (neurosurgery/ear, nose, and throat (ENT)) of treating acoustic neuromas with extrameatal extension via the retromastoidal approach. To analyse whether monitoring both facial nerve EMG and BAEP improved the functional outcome in acoustic neuroma surgery.

METHODS

In a series of 508 patients consecutively operated on over a period of 7 years, functional outcome of the facial nerve was evaluated according to the House/Brackmann scale and hearing preservation was classified using the Gardner/Robertson system.

RESULTS

Facial monitoring (396 of 508 operations) and continuous BAEP recording (229 of 399 cases with preserved hearing preoperatively) were performed routinely. With intraoperative monitoring, the rate of excellent/good facial nerve function (House/Brackmann I-II) was 88.7%. Good functional hearing (Gardner/Robertson 1-3) was preserved in 39.8%.

CONCLUSION

Acoustic neuroma surgery via a retrosigmoidal approach is a safe and effective treatment for tumours with extrameatal extension. Functional results can be substantially improved by intraoperative monitoring. The interdisciplinary concept of surgery performed by ENT and neurosurgeons was particularly convincing as each pathoanatomical phase of the operation is performed by a surgeon best acquainted with the regional specialties.

Topography of the vestibulocochlear nerve

OBJECTIVE

The terms superior vestibular nerve and inferior vestibular nerve have been used in the field of neurosurgery to indicate anatomically the two respective vestibular components of the vestibulocochlear nerve. To reappraise the aptness of this terminology, fascicular patterns and the anatomic relationship of the vestibular and cochlear components were examined.

METHODS

Twenty vestibulocochlear nerve specimens were obtained from cadavers. The nerves were excised, with care taken to sustain their spatial relationships, then embedded in paraffin blocks and cross sectioned in 10-microm-thick slices. Serial cross sections were stained and examined with a light microscope.

RESULTS

The vestibular component was separated into two parts only at the lateral fundus of the internal auditory canal, lateral to the vestibular ganglion. In the internal auditory canal of all specimens, the vestibular component was represented by numerous fascicles. Around the porus acusticus, the fascicular pattern among the specimens was diverse: 13 of the 20 specimens were still polyfascicular, 4 specimens consisted of two large, distinct fascicles, and, in the remaining 3 specimens, a portion of the vestibular fascicles had fused with the cochlear component. Near the root entry zone, all vestibular fascicles fused and merged with the cochlear nerve to form a single trunk.

CONCLUSION

There was no evidence to support the anatomic correctness of specifying the superior and inferior vestibular nerves, except in the lateral fundus of the internal auditory canal.

Results of linear accelerator-based stereotactic radiosurgery for recurrent and newly diagnosed acoustic neuromas

Stereotactic radiosurgery (SRS) is used to treat acoustic neuromas, but additional information is needed to firmly establish its safety and efficacy. We review our experience over 7 years treating 29 consecutive patients with a modified linear accelerator (linac) SRS system. Between August 1989 and October 1995, 29 patients with a median age of 67 years (range 26 to 83) underwent linac SRS treatment. Twenty-five patients had unilateral acoustic neuromas, and four patients with neurofibromatosis type II had bilateral vestibular schwannoma. Eligibility criteria for SRS were recurrent tumors (n = 9), age >65 (n = 16), or patient preference (n = 6). Follow-up magnetic resonance imaging scans were performed on all patients. The most common presenting symptoms were hearing impairment (18 patients) and gait difficulties (17 patients). Ten patients were deaf in the affected ear prior to treatment. Doses to the periphery of the tumor ranged from 800 to 2,400 cGy (median 1, 600 cGy) prescribed to the 50% to 80% isodose line (median 80%). After a median radiographic follow-up of 49 months (range 4 to 110 months), 11 tumors were smaller, 17 were stable, and one had evidence of progression (at 41 months). The 5-year local disease control rate (Kaplan-Meier estimate) was 94%. Acute complications were minimal, with only two patients experiencing nausea and vomiting after the procedure. Long-term complications included new or progressive trigeminal and facial nerve deficits with estimated 5-year incidences of 15% and 32%, respectively. Subjective hearing reduction or loss occurred in 14 (74%) of the 19 patients who had useful hearing prior to treatment. Five patients died from unrelated causes. These results suggest that linac SRS provides excellent short-term tumor control rates. Since there was a high risk of cranial nerve neuropathy, we do not recommend using only computed tomography-based planning and high prescription doses. Int. J. Cancer (Radiat. Oncol. Invest.) 90, 145-151 (2000).

Hypoglossal-facial nerve anastomosis: assessment of clinical results and patient benefit for facial nerve palsy following acoustic neuroma excision

Despite advances in neuro-otological techniques permanent complete facial palsy may still occur in up to 10% of patients undergoing removal of cerebellopontine angle tumours. Hypoglossal-facial nerve anastomosis is the procedure of choice in our unit for facial reanimation in such patients and below we report the results of hypoglossal-facial nerve anastomosis performed on 29 patients. Assessment of patient benefit from hypoglossal-facial nerve anastomosis was obtained using a questionnaire based on the Glasgow Benefit Inventory. The results showed all patients to have an improvement in their House Brackmann grade following hypoglossal-facial anastomosis with 65% achieving grade III or better. Of the 20 patients who completed the questionnaire, 18 showed a positive benefit (median score 59.5, range 40-77). There was a significant correlation (P < 0.045) between the Glasgow benefit inventory score and House Brackmann grade. Outcome was not affected by the time interval between the acoustic neuroma surgery and performing the hypoglossal-facial nerve anastomosis, sex or length of follow-up. However the Glasgow benefit score was significantly influenced by age (P = 0.023) with younger patients showing more benefit independent of improvement in facial nerve function.

Gamma surgery for vestibular schwannoma

OBJECT

The goal of this study was to assess the results of gamma surgery (GS) for vestibular schwannoma (VS) in 200 cases treated over the last 10 years and to review the role of this neurosurgical procedure in the management of VS.

METHODS

Follow-up reviews ranging from 1 to 10 years were available in 153 of these patients. Follow-up images in these cases were analyzed using computer software that we developed to obtain volume measurements for the tumors, and the clinical condition of the patients was assessed using questionnaires. Gamma surgery was the primary treatment modality in 96 cases and followed microsurgery in 57 cases. Tumors ranged in volume from 0.02 to 18.3 cm(3). In the group in which GS was the primary treatment, a decrease in volume was observed in 78 cases (81%), no change in 12 (12%), and an increase in volume in six cases (6%). The decrease was more than 75% in seven cases. In the group treated following microsurgery, a decrease in volume was observed in 37 cases (65%), no change in 14 (25%), and an increase in volume in six (11%). The decrease was more than 75% in eight cases. Five patients experienced trigeminal dysfunction; in three cases this was transient and in the other two it was persistent, although there has been improvement. Three patients had facial paresis (in one case this was transient, lasting 6 weeks; in one case there was 80% recovery at 18 months posttreatment; and in one case surgery was performed after the onset of facial paresis for presumed increase in tumor size). Over a 6-year period, hearing deteriorated in 60% of the patients. Three patients showed an improvement in hearing. No hearing deterioration was observed during the first 2 years of follow-up review.

CONCLUSIONS

Gamma surgery should be used to treat postoperative residual tumors as well as tumors in patients with medical conditions that preclude surgery. Microsurgery should be performed whenever a surgeon is confident of extirpating the tumor with a risk-benefit ratio superior to that presented in this study.

Quantitative parameters of intraoperative electromyography predict facial nerve outcomes for vestibular schwannoma surgery

OBJECTIVE

Facial nerve monitoring is an established method that is routinely used during cerebellopontine angle tumor surgery. The aim of this study was to determine quantitative electromyographic (EMG) parameters that were predictive of facial nerve outcomes.

METHODS

In 137 patients with intra-/extrameatal vestibular schwannomas, the most proximal (the exit from the brainstem) and distal (the fundus of the internal auditory canal) parts of the facial nerve were stimulated after total tumor removal. A quantitative analysis of absolute values and ratios (proximal/distal) of evoked EMG parameters (amplitude, latency, and duration) was performed, and parameters were correlated with postoperative (1 and 6 wk and 6 mo) facial nerve function (FNF).

RESULTS

Absolute values of EMG amplitudes were statistically correlated with FNF (P < 0.05). Amplitude ratios (proximal/distal) demonstrated an even greater predictive power. The risk of exhibiting facial palsy 6 months after surgery increased from 1.6% (amplitude ratio of >0.8) to 75% (ratio of <0.1). For EMG latencies, only the ratios revealed a significant correlation with FNF. The latency ratio-dependent risk of facial palsy after 6 months increased from 2.9% (ratio of <1.05) to 33% (ratio of >1.35). The durations of the muscle responses were not significantly correlated with clinical outcomes.

CONCLUSION

The predictive power of the amplitudes and latencies of electrically evoked muscle responses could be improved by calculating proximal/distal ratios. The proximal/distal amplitude ratio proved to be the most powerful parameter for intraoperative assessment of postoperative FNF.

Radiosurgery for bilateral neurinomas associated with neurofibromatosis type 2

OBJECTIVE

The clinical course of bilateral acoustic tumors associated with neurofibromatosis (NF2) is generally troublesome, and no definite treatment strategy has been established. Follow-up results of bilateral acoustic tumors after radiosurgery are reported herein.

METHODS

The current indications for radiosurgery are 1) a growing tumor less than 30 mm in mean diameter, 2) the ipsilateral ear has no serviceable hearing, and 3) there is risk of brain stem compression or brain stem dysfunction. Twenty cases of bilateral acoustic tumors were treated with the gamma knife, including 7 males and 13 females. The mean age was 38.2 years and the mean tumor size 24.4 mm. The tumors were treated with mean maximum and marginal doses of 26.8 Gy and 13.0 Gy, respectively. Among them, 12 patients had profound hearing loss in the ipsilateral (treated) ear, but the other 8 had serviceable hearing.

RESULTS

Tumors treated with radiosurgery showed central necrosis in 60% of the cases at 6 months and in 70% at 9 months after radiosurgery. Thereafter, the tumors often demonstrated slow regression. The rate of tumor shrinkage was 20% at 12 months, 35% at 24 months, and almost 60% at 36 months. At the last follow-up (mean 33.6 months), the tumors demonstrated shrinkage in 50% and tumor control in 100%. The contralateral tumors were stable in 12 (60%) and enlarged in 8 (40%). Preservation of serviceable hearing ipsilaterally was obtained in 33.3%. Deterioration of ipsilateral facial nerve function, either in the natural course or as a complication, occurred in 10%.

CONCLUSIONS

Because of good tumor control and tumor shrinkage as well as an acceptable complication rate, radiosurgery should be incorporated in the treatment strategy for bilateral acoustic tumors associated with NF2.

Microanatomical variations in the cerebellopontine angle associated with vestibular schwannomas (acoustic neuromas): a retrospective study of 1006 consecutive cases

OBJECT

Great advances in neuroimaging, intraoperative cranial nerve monitoring, and microsurgical technique have shifted the focus of acoustic neuroma surgery from prolonging life to preserving cranial nerve function in patients. An appreciation of the vascular and cranial nerve microanatomy and the intimate relationship between neurovascular structures and the tumor is essential to achieve optimum results. In this paper the authors analyze the microanatomical variations in location of the facial and cochlear nerves in the cerebellopontine angle (CPA) associated with acoustic neuromas and, additionally, describe the frequency of involvement of surrounding neural and vascular structures with acoustic tumors of varying size. The authors base these findings on their experience with 1006 consecutive patients who underwent surgery via a retrosigmoid or translabyrinthine approach.

METHODS

Between July 1969 and January 1998, the senior author (D.M.L.) performed surgery in 1022 patients for acoustic neuroma: 705 (69%) via the retrosigmoid (suboccipital); 301 (29%) via the translabyrinthine; and 16 (2%) via the middle fossa approach. Patients undergoing the middle fossa approach were excluded from the study. The remaining 1006 patients were subdivided into three groups based on tumor size: Group I tumors (609 patients [61%]) were smaller than 2.5 cm; Group II tumors (244 patients [24%]) were between 2.5 and 4 cm; and Group III tumors (153 patients [15%]) were larger than 4 cm. The senior author's operative notes were analyzed for each patient. Relevant cranial nerve and vascular "involvement" as well as anatomical location with respect to the tumor in the CPA were noted. "Involvement" was defined as adherence between neurovascular structure and tumor (or capsule), for which surgical dissection was required to free the structure. Seventh and eighth cranial nerve involvement was divided into anterior, posterior, and polar (around the upper or lower pole) locations. Anterior and posterior locations were further subdivided into upper, middle, or lower thirds of the tumor. The most common location of the seventh cranial nerve (facial) was the anterior middle third of the tumor for all groups, although a significant number were found on the anterior superior portion. The posterior location was exceedingly rare (< 1%). Interestingly, patients with smaller tumors (Group I) had an incidence (3.4%) of the seventh cranial nerve passing through the tumor itself, equal to that of patients with larger tumors. The most common location of the eighth cranial nerve complex was the anterior inferior portion of the tumor. Not surprisingly, larger tumors (Group III) had a higher incidence of involvement of fourth cranial nerve (41%), fifth cranial nerve (100%), ninth-11th cranial nerve complex (99%), and 12th cranial nerve (31%), as well as superior cerebellar artery (79%), anterior inferior cerebellar artery (AICA) trunk (91.5%), AICA branches (100%), posterior inferior cerebellar artery (PICA) trunk (59.5%), PICA branches (79%), and the vertebral artery (VA) (93.5%). A small number of patients in Group III also had AICA (3.3%), PICA (3.3%), or VA (1.3%) vessels within the tumor itself.

CONCLUSIONS

In this study, the authors show the great variation in anatomical location and involvement of neurovascular structures in the CPA. With this knowledge, they present certain technical lessons that may be useful in preserving nerve function during surgery and, in doing so, hope to provide neurosurgeons and neurootologists with valuable information that may help to achieve optimum outcomes in patients.

Comparison between observation policy and fractionated stereotactic radiotherapy (SRT) as an initial management for vestibular schwannoma

PURPOSE

To compare the use of an observation policy with that of stereotactic radiotherapy (SRT) for treatment of vestibular schwannoma.

METHODS AND MATERIALS

The study group consisted of 27 patients who underwent observation as an initial treatment (observation group) and 50 who received SRT (SRT group). The mean follow-up period was 35 months and 31 months, respectively. Stereotactic radiotherapy consisted of small-field fractionated radiotherapy (36-44 Gy in 20-22 fractions over 6 weeks) with or without a subsequent 4-Gy single irradiation boost.

RESULTS

Actuarial tumor control rate of the SRT group was significantly better than that of the observation group (p < 0.0001). The mean growth was 3.87 mm/year in the observation group and -0.75 mm/year in the SRT group (p < 0.0001). Eleven patients (41 %) in the observation group and 1 (2 %) in the SRT group received salvage therapy (p < 0.001). There was no difference in the actuarial Gardner and Robertson's class preservation curves for 5 years after the initial presentation.

CONCLUSION

Stereotactic radiotherapy using a fractionated schedule provides a better tumor control rate and a similar rate of deterioration for hearing levels compared to an observation policy. Initial SRT may be a reasonable alternative to a wait-and-see policy.

Report of 190 consecutive cases of large acoustic tumors (vestibular schwannoma) removed via the translabyrinthine approach

OBJECT

The choice of approach for surgical removal of large acoustic neuromas is still controversial. The authors reviewed the results in a series of patients who underwent removal of large tumors via the translabyrinthine approach.

METHODS

The authors conducted a database analysis of 190 patients (89 men and 101 women) with acoustic neuromas 3 cm or greater in size. The mean age of these patients was 46.1+/-15.6 years. One hundred seventy-eight patients underwent primary translabyrinthine surgical removal and 12 underwent surgery for residual tumor. Total tumor removal was accomplished in 183 cases (96.3%). The tumor was adherent to the facial nerve to some degree in 64% of the cases, but the facial nerve was preserved anatomically in 178 (93.7%) of the patients. Divided nerves were repaired by primary attachment or cable graft. Facial nerve function was assessed immediately after surgery, at the time of discharge, and at 3 to 4 weeks and 1 year after discharge. Excellent function (House-Brackmann facial nerve Grade I or II) was present in 55%, 33.9%, 38.8%, and 52.6% of the patients for each time interval, respectively, with acceptable function (Grades I-IV) in 81% at 1 year. Cerebrospinal fluid leakage that required surgical repair occurred in only 1.1% of the patients and meningitis in 3.7%. There were no deaths.

CONCLUSIONS

Use of the translabyrinthine approach for removal of large tumors resulted in good anatomical and functional preservation of the facial nerve, with minimum incidence of morbidity and no incidence of mortality. The authors continue to recommend use of this approach for acoustic tumors larger than 3 cm and for smaller tumors when hearing preservation is not an issue.

Report of 190 consecutive cases of large acoustic tumors (vestibular schwannoma) removed via the translabyrinthine approach

Object

The choice of approach for surgical removal of large acoustic neuromas is still controversial. The authors reviewed the results in a series of patients who underwent removal of large tumors via the translabyrinthine approach.

Methods

The authors conducted a database analysis of 190 patients (89 men and 101 women) with acoustic neuromas 3 cm or greater in size. The mean age of these patients was 46.1 ± 15.6 years. One hundred seventy-eight patients underwent primary translabyrinthine surgical removal and 12 underwent surgery for residual tumor. Total tumor removal was accomplished in 183 cases (96.3%). The tumor was adherent to the facial nerve to some degree in 64% of the cases, but the facial nerve was preserved anatomically in 178 (93.7%) of the patients. Divided nerves were repaired by primary attachment or cable graft. Facial nerve function was assessed immediately after surgery, at the time of discharge, and at 3 to 4 weeks and 1 year after discharge. Excellent function (House-Brackmann facial nerve Grade I or II) was present in 55%, 33.9%, 38.8%, and 52.6% of the patients for each time interval, respectively, with acceptable function (Grades I–IV) in 81% at 1 year. Cerebrospinal fluid leakage that required surgical repair occurred in only 1.1% of the patients and meningitis occurred in 3.7%. There were no deaths.

Conclusions

Use of the translabyrinthine approach for removal of large tumors resulted in good anatomical and functional preservation of the facial nerve, with minimum incidence of morbidity and no incidence of mortality. The authors continue to recommend use of this approach for acoustic tumors larger than 3 cm and for smaller tumors when hearing preservation is not an issue.

Late-onset facial nerve degeneration after vestibular schwannoma surgery: incidence, putative mechanisms, and prevention

Delayed facial nerve dysfunction after vestibular schwannoma surgery is a poorly understood phenomenon that has been reported to occur in 15 to 29% of patients undergoing microsurgery. It is a condition characterized by spontaneous deterioration of facial nerve function in a patient who has otherwise normal or near-normal facial function in the immediate postoperative period. This delayed paralysis is generally reported to occur in the first few days postsurgery, with the majority of patients eventually recovering their immediate postoperative facial function. However, infrequently, it can also occur more than 1 week after surgery (so-called late-onset facial nerve palsy).

The authors reviewed facial nerve outcome in 611 patients who underwent microsurgery between 1973 and 1994. The facial nerve was anatomically preserved in 596 patients (97.5%), and 90% of patients had House-Brackmann[6] Grade 1 or 2 function 1 year after surgery. Late-onset facial dysfunction was seen in 13 patients (2.1%). All of these had significant deterioration in facial nerve function between 1 and 4 weeks postoperatively, and all showed improvement by 1 year. In this study, the focus on these patients who developed late-onset facial palsy. The incidence, treatment strategies, and outcomes will be discussed with emphasis on possible pathophysiological mechanisms that contribute to this relatively rare condition.

Microanatomical variations in the cerebellopontine angle associated with vestibular schwannomas (acoustic neuromas)

Great advances in neuroimaging, intraoperative cranial nerve monitoring, and microsurgical technique have shifted the focus of acoustic neuroma surgery from prolonging life to preserving cranial nerve function in patients. An appreciation of the vascular and cranial nerve microanatomy and the intimate relationship between neurovascular structures and the tumor is essential to achieve optimum results. In this paper the authors analyze the microanatomical variations in location of the facial and cochlear nerves in the cerebellopontine angle (CPA) associated with acoustic neuromas and, additionally, describe the frequency of involvement of surrounding neural and vascular structures with acoustic tumors of varying size. The authors base their findings on their experience treating 1006 consecutive patients who underwent surgery via a retrosigmoid or translabyrinthine approach.

Between July 1969 and January 1998, the senior author (D.M.L.) performed surgery in 1022 patients for acoustic neuroma: 705 (69%) via the retrosigmoid (suboccipital); 301 (29%) via translabyrinthine; and 16 (2%) via middle fossa approach. Patients undergoing the middle fossa approach were excluded from the study. Patients were subdivided into three groups based on tumor size: Group 1 tumors (609 patients [61%]) were smaller than 2.5 cm; Group 2 tumors (244 patients [24%]) were between 2.5 and 4 cm; and Group 3 tumors (153 patients [15%]) were larger than 4 cm. Operative notes were analyzed for each patient. Relevant cranial nerve and vascular “involvement” as well as anatomical location with respect to the tumor in the CPA were noted. “Involvement” was defined as intimate contact between neurovascular structure and tumor (or capsule), where surgical dissection was required to free the structure. Seventh and eighth cranial nerve involvement was divided into anterior, posterior, and polar (around the upper or lower pole) locations. Anterior and posterior locations were further subdivided into upper, middle, or lower thirds of the tumor.

The most common location of the seventh cranial nerve (facial) was the anterior middle third of the tumor for Groups 1, 2, and 3, although a significant number were found on the anterior superior portion. The posterior location was exceedingly rare (< 1%). Interestingly, patients with smaller tumors (Group 1) had an incidence (3.4%) of the seventh cranial nerve passing through the tumor itself equal to that of patients with larger tumors. The most common location of the seventh cranial nerve complex was the anterior inferior portion of the tumor. Not surprisingly, larger tumors (Group 3) had a higher incidence of involvement of sixth cranial nerve (41%), fifth cranial nerve (100%), ninth-11th cranial nerve complex (99%), 12th cranial nerve (31%), as well as superior cerebellar artery (79%), anterior inferior cerebellar artery (AICA) trunk (91.5%), AICA branches (100%), posterior inferior cerebellar artery (PICA) trunk (59.5%), PICA branches (79%), and the vertebral artery (93.5%). A small number of patients in Group 3 also had AICA (3.3%), PICA (3.3%), or vertebral artery (1.3%) vessels within the tumor itself.

In this study, the authors show the great variation in anatomical location and involvement of neurovascular structures in the CPA. With this knowledge, they present certain technical lessons that may be useful in preserving function during surgery and, in doing so, hope to provide neurosurgeons and neurootologists with valuable information that may help to achieve optimum cranial nerve outcomes in patients.

Decompression of the labyrinthine segment of the facial nerve in acoustic neuroma surgery: a consideration for minimizing postoperative delayed facial nerve dysfunction

Delayed facial nerve palsy, a condition characterized by spontaneous deterioration of facial nerve function in patients who had otherwise normal or near-normal facial function in the immediate postoperative period, has been reported in 15 to 29% of patients undergoing microsurgical resection of vestibular schwannomas. One putative mechanism for its occurrence suggests that edematous entrapment of the facial nerve in the meatal foramen (the narrowest segment of the internal auditory canal) may lead to nerve ischemia or necrosis and subsequent facial nerve dysfunction. To assess whether meatal decompression may help reduce the incidence of delayed facial nerve palsy during microsurgical resection of acoustic tumors, we compared 25 patients undergoing translabyrinthine removal of acoustic neuromas who received prophylactic decompression of the labyrinthine segment of the facial nerve (Group 1) with 40 patients who did not receive facial nerve decompression (Group 2). No patients in Group 1 had a delayed progressive facial paralysis with degeneration. In contrast, when Group 2 patients with larger, average-sized tumors were reviewed, eight patients (20%) developed delayed degeneration. These findings suggest that decompression of the labyrinthine segment may be of value in acoustic tumor surgery in reducing delayed facial nerve dysfunction. Further study is indicated in this important area.

Management of vestibular schwannomas (acoustic neuromas): auditory and facial nerve function after resection of 120 vestibular schwannomas in patients with neurofibromatosis 2

OBJECTIVE

Vestibular schwannomas (VSs) affect young patients with Neurofibromatosis 2 (NF-2) and cause very serious problems for hearing, facial expression, and brain stem function. Our objective was to determine a therapy concept for the right timing and indication of neurosurgical therapy.

METHODS

In 1000 consecutive VS resections, 120 tumors in 82 patients with NF-2 were surgically treated by the same surgeon (MS) at the Department of Neurosurgery at Nordstadt Hospital from 1978 to 1993. The mean age of the patients was 27.5 years. Sixty tumors were surgically treated in 41 male patients, and 60 tumors were surgically treated in 41 female patients. Bilateral tumor resection was performed in 38 patients (76 operations, after previous partial surgery in 15 cases elsewhere), and unilateral operations were performed in 44 patients, 5 of whom had undergone ipsi- or contralateral surgery that was performed elsewhere. The operative and clinical findings are evaluated and compared with the data of patients without NF-2.

RESULTS

In 105 cases, complete tumor resections were achieved. In 15 cases, deliberate subtotal resections were performed. These were for brain stem decompression in 4 cases and for hearing preservation in the last hearing ear in 11 cases, with successful preservation in 8 of the 11. Pre- and postoperative hearing rates were higher in male than in female patients (70% in male versus 65% in female patients before surgery and 40.5 versus 31%, respectively, after surgery). Hearing was preserved in 29 of 81 ears (36%). The rate of preservation was 24% in cases of large tumors and 57% in cases of small tumors (<30 mm). Twenty-one of 82 patients (26%) were bilaterally deaf before surgery. Twenty-five patients had uni- or bilateral hearing after surgery (i.e., 41 % of those with preoperative hearing or 30.5% of the whole group). Anatomic facial nerve preservation was achieved in 85%. The facial nerve was reconstructed intracranially at the cerebellopontine angle by sural grafting in 17 cases and by hypoglossal-facial reanimation in 5. Two deaths occurred 1 and 3 months postsurgically as a result of malignant tumor growth with brain stem dysfunction and respiratory problems. In summary, for patients with NF-2, the presentation ages are lower, tumor progression is faster, the chances of anatomic and functional nerve preservation are lower, the chances of good outcomes are best when surgery is performed early and when there is good preoperative hearing function, and the danger of sudden hearing loss is higher. The chances and danger often differ from side to side among individual patients.

CONCLUSION

The indication and the timing of tumor resections are in some respects different from normal VS handling and are dependent on the tumor extension and related necessity of brain stem decompression and on the auditory function. As an optimal goal, completeness of resection with functional cochlear nerve preservation is formulated, and as an acceptable compromise, subtotal microsurgical resection with functional cochlear nerve preservation in the last hearing ear is suggested.