Auditory monitoring during acoustic neuroma removal

Relationship of a "Fundal Fluid Cap" and Vestibular Schwannoma Volume: Analysis of Preoperative Radiographic Findings and Outcomes

OBJECTIVE

To evaluate the relationship between radiographic fundal fluid cap in the lateral internal auditory canal, preoperative clinical characteristics, and postoperative outcomes in patients with vestibular schwannoma who underwent microsurgical excision.

STUDY DESIGN

Retrospective chart review.

SETTING

Academic tertiary referral center.

PATIENTS

Thirty-six consecutive patients (mean age 49.4 yr [range 29-74]) who underwent microsurgical vestibular schwannoma excision.

INTERVENTIONS

Microsurgical excision.

MAIN OUTCOME MEASURES

Linear fundal fluid size and tumor size calculated using volumetric analysis were measured on preoperative magnetic resonance imaging, and correlated to hearing status and postoperative facial nerve function.

RESULTS

Mean fundal fluid size was 2.18 mm (range 0-7.32). Mean tumor volume was 5.58 cm (range, 0.210-40.3 cm). Short- and long-term postoperative House-Brackmann scores were 2.4 and 1.4, respectively. Fundal fluid size was associated with tumor volume (rs = 0.488, p = 0.003) but not preoperative hearing status (p = 0.333). The presence of fundal fluid and larger tumor volumes were statistically associated with poorer short-term and long-term postoperative facial nerve function (p < 0.05).

CONCLUSIONS

Radiographic fundal fluid size is correlated to tumor volume.

Accidental subcutaneous remifentanil infusion as a cause of delayed awakening after craniotomy

We report a case of accidental subcutaneous infusion of remifentanil as a cause of delayed awakening after a craniotomy.

Association between surgical steps and intraoperative auditory brainstem response and electrocochleography waveforms during hearing preservation vestibular schwannoma surgery

Intraoperative monitoring of the auditory pathway by means of either electrocochleography or auditory brainstem response audiometry is valuable during hearing preservation vestibular schwannoma (VS) surgery. A more than 75% intraoperative reduction of the amplitude of these evoked auditory potentials was thought to be related with clear hearing compromise of hearing. We identified 22 patients who satisfied this intraoperative criterion in a cohort of 86 consecutive patients who had attempted hearing preservation VS surgery. The surgical step that temporally coincided with the above event was considered to be the most critical step for hearing monitoring during this kind of surgery. Most frequently, drilling of the internal auditory canal and direct tumor resection were associated with the aforementioned changes, but also drilling of the cortical temporal bone at the very beginning of surgery or the opening of the dura could be implicated. This profound intraoperative amplitude decrease was associated with a profound postoperative hearing impairment in 84% of the cases.

Intraoperative auditory brainstem responses in patients with cerebellopontine angle meningiomas involving the inner auditory canal: analysis of the predictive value of the responses

Object. Meningiomas of the cerebellopontine angle (CPA) can either arise from or secondarily grow into the inner auditory canal (IAC). This location may have a great impact on hearing function following surgery to remove these lesions. The aim of this retrospective study was to investigate the reliability and predictive importance of auditory brainstem responses (ABRs) for the determination of postoperative auditory function in patients with CPA meningiomas in comparison with results obtained in patients who undergo surgery for vestibular schwannomas.

Methods. In a consecutive series of 1800 meningiomas surgically treated between 1978 and 2002, 421 lesions were located in the CPA. In 38 patients with CPA meningiomas involving the IAC, the findings of intraoperative ABR monitoring and the hearing status of each patient before and after surgery were retrospectively analyzed.

On analysis, ABR monitoring demonstrated stable findings in 24 patients throughout tumor resection and fluctuating signals in 10 patients. Among the 24 patients with stable ABRs, postoperative hearing function improved in three patients, remained the same in 15, and worsened in six patients, including one patient who displayed postoperative deafness. There was even one patient recovering from preoperative deafness. Among the 10 patients with unstable ABRs, intermittent decreases in amplitude and deformations of variable duration in the ABR wave were noted. The risk of deafness was considerably higher in patients with prolonged phases of intermittent ABR deterioration.

Conclusions. The presence and absence of ABRs during surgery for CPA meningiomas reliably predicted the presence and absence of postoperative auditory function. Intermittent deterioration of ABRs may result in postoperative deafness, depending on the duration of these events during surgery. Improvements in hearing are only seen when the ABRs are stable for amplitudes and latencies throughout surgery.

Vestibular function after acoustic neuroma removal with preservation of one branch of the vestibular nerve

BACKGROUND

Vestibular compensation after acoustic neuroma surgery is affected by many parameters. Apart from surgical approach, age of the patient, and comorbidity, the use of rehabilitative vestibular training and the degree of preoperative vestibular compensation play their respective roles.

OBJECTIVE

To examine whether and how surgical preservation of one branch of the vestibular nerve affects the compensation process in patients after acoustic neuroma removal.

STUDY DESIGN

Prospective study involving 29 patients with acoustic neuromas. In 15 patients operated on by the middle fossa or retrosigmoid approach, one branch of the vestibular nerve could be preserved intraoperatively, and the course of the compensation process was followed (Group 1). Fourteen other patients with acoustic neuroma, who were operated on via a translabyrinthine approach, served as a control group (Group 2).

MAIN OUTCOME MEASURE

The evaluation of vestibular compensation was accomplished clinically, by electronystagmography, and by dynamic posturography.

RESULTS

An accelerated vestibular compensation was found in all examinations for Group 1, and 3 months after surgery 47% of the patients in this group were back to work without substantial restrictions, compared with 29% of Group 2. At the end of 6 months, however, there was no more significant difference between the two groups.

CONCLUSION

The long-term results of vestibular compensation do not seem to be influenced by partial preservation of the vestibular nerve, whereas the compensation process seems to be accelerated when the nerve is partially preserved.

Intraoperative neuromonitoring

BACKGROUND

Intraoperative neuromonitoring (IONM) has been a valuable part of surgical procedures for over 25 years. Insight into the nervous system during surgery provides critical information to the surgeon allowing reversal or avoidance of neural insults.

REVIEW SUMMARY

Electrophysiological tests including electroencephalography, electromyography, and multiple types of evoked potentials (somatosensory, auditory, and motor) are monitored during surgeries that involve risk to the nervous system. Deterioration of signals suggests a surgical insult and is associated with an increased risk of postoperative deficit. Intraoperative identification of this risk allows corrective action. In addition, IONM teams make use of their armamentarium of tests to evaluate anatomy or function of the nervous system in response to specific questions posed by the surgical team.

CONCLUSIONS

Intraoperative recordings are now a routine part of many surgical procedures. Their correct application leads to improved surgical outcome.

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.

Distortion-product otoacoustic emission monitoring of cochlear blood flow

Distortion-product otoacoustic emissions (DPOAEs) have been shown to be ideally sensitive to interruptions of the cochlear blood flow. However, a 15- to 30-second latency typically occurs between cessation of circulation and measurable DPOAE level changes. DPOAEs can also be characterized by phase measures. The aim of the present study was to determine in 10 rabbits the effects on DPOAE phase of repetitively compressing the internal auditory artery. In contrast to the delays measured by DPOAE level, phase changes were detected 1 to 5 seconds after internal auditory artery compression. These data suggest that the essentially "real time" monitoring of cochlear function with DPOAE phase can be used to ensure hearing preservation during surgery involving the porus acousticus and skull base.

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.

Management of 1000 vestibular schwannomas (acoustic neuromas): hearing function in 1000 tumor resections

OBJECTIVE

The realistic chances of hearing preservation and the comparability of international results on hearing preservation in complete microsurgical vestibular schwannoma resections were the focus of this study in a large patient population treated by uniform principles.

METHODS

One thousand vestibular schwannomas were operated on at Nordstadt Neurosurgical Department, from 1978 to 1993, by the senior surgeon (MS). There were 1000 tumors in 962 patients, i.e., 880 patients with unilateral tumors and 82 patients operated on for bilateral tumors in neurofibromatosis-2 (120 cases). Preservation of the cochlear nerve was attempted whenever possible. The audiometric data were analyzed by the Nordstadt classification system and graded in steps of 30 dB by audiometry and in steps of 10 to 30% by speech discrimination; for comparability, the data were also evaluated by the criteria of Gardner, Shelton, and House, and they were assessed in relation to the Hannover tumor extension grading system.

RESULTS

Anatomic cochlear nerve preservation was achieved in 682 of 1000 cases (68%), as well as in some preoperatively deaf patients, a very few of whom regained some hearing. Of a total of 732 cases with some preoperative hearing, anatomic cochlear nerve preservation was achieved in 580 cases (79%) and functional cochlear nerve preservation in 289 (39.5%); analysis over time revealed an actual preservation rate of 47% in the most recent 200 cases. Specific factors, such as gender, tumor extension, preoperative hearing quality, and symptom duration, were investigated for their predictive value for hearing preservation. Male gender, small to medium tumor size (mainly extending within the cerebellopontine cistern; Classes T2 and T3), good to moderate hearing (up to 40-dB loss), and short duration of hypoacusis (< 1.5 yr) or of vestibular disturbances (< 0.7 yr) were advantageous factors, with chances of hearing preservation between 47 and 88%.

CONCLUSION

Functional cochlear nerve preservation in complete microsurgical resection should belong to the contemporary standard of treatment goals.

Preserved Hearing Following Vestibular Schwannoma Surgery

Audiologic test results were reviewed for 30 patients whose hearing was preserved following eighth nerve tumor surgery. Speech reception thresholds, 4,000-Hz thresholds, acoustic reflexes, and ABR wave I absolute latencies were generally unchanged or poorer following surgery; word recognition scores were essentially unchanged. By contrast, ABR waves III and V, and the I–III and I–V interpeak intervals, were generally improved postoperatively, including several patients who had clear waves following surgery despite absent preoperative responses. The improved ABR tracings likely indicate increased neural synchrony due to reduced pressure on the cochlear nerve following surgery, whereas the reduced hearing sensitivity probably reflects cochlear damage coincident to the surgery.

Hearing preservation in vestibular schwannoma surgery: what factors influence outcome?

The goals in the management of patients with vestibular schwannomas have changed drastically over the past few decades, with preservation of useful hearing representing the newest challenge. The true incidence of preserved useful hearing, however, has become clouded by a lack of uniformity in reporting results. The authors have analyzed 56 consecutive cases, in which directed attempts were made to preserve hearing on the involved side, to understand what factors play a major role in postoperative hearing preservation. Of the 56 cases reviewed, there were 46 patients who had "good" preoperative hearing (pure tone average < 50 dB; speech discrimination score > 50%). We found that, in this group of patients, if the tumor was less than 2 cm in diameter from pons to petrous, there was a 52% (16 of 31 patients) chance of preserving good hearing and if the tumor was 1 cm or less, the chances increased to 83%. Factors such as preoperative hearing status, tumor size and location, tumor consistency, and preoperative and intraoperative brainstem auditory evoked potentials are discussed in detail as they relate to postoperative outcome.

Microsurgical anatomy around the foramen of Luschka in relation to intraoperative recording of auditory evoked potentials from the cochlear nuclei

Three cadaveric heads were dissected to investigate the microsurgical anatomy around the foramen of Luschka. It was found possible to place a recording electrode in proximity to the cochlear nuclei by inserting it in the lateral recess of the fourth ventricle through the foramen of Luschka. In operations of the cerebellopontine angle using the retromastoid approach, access to the foramen of Luschka and the lateral recess is obtained by retracting the biventral lobule of the cerebellum in a caudal-rostral direction under a caudal-rostral/medial field of vision. The craniectomy might need to be enlarged a few millimeters in the caudal direction. A wick electrode can be inserted in the lateral recess beneath the choroid plexus in a rostromedial direction and to a depth of approximately 3 to 5 mm from the foramen of Luschka without excessive retraction of the cerebellum. The optimum position for the recording electrode is in the triangle formed by the axis of the cochlear nerve and the glossopharyngeal nerve and by the lip of the foramen of Luschka. The caudal retromastoid approach is more suitable than the translabyrinthine technique for recording from the cochlear nuclei as well as for implantation of stimulating electrodes into the cochlear nuclei for use as hearing prostheses.

Hearing preservation in acoustic tumour surgery

900 acoustic neurinomas were removed by the suboccipital approach at Nordstadt Neurosurgical Department from 1978 to 1992 by the same surgeon (M. S.). While 247 patients were deaf on the involved side before surgery, there were 653 patients ears with some preoperative hearing. Preservation of the cochlear nerve was always attempted, and the overall-rate of hearing preservation was 38% (249 of 653), regardless of pre- and postoperative quality of hearing or of tumour sizes. In small tumour sizes below 3 cm of diameter preservation rate was 51%, in large tumours above 3 cm of diameter it was 22%. A classification system of hearing quality was made up considering pure tone audiometric hearing losses (PTA HL) at 1 to 3 kHz, and individual maximum speech discrimination scores. The usefulness of the preserved hearing is further evaluated considering the quality of hearing in the contralateral ear, and by application of other classification schemes. Presentation of the surgical strategies and their refinements by personal experience provide the base for discussion questioning whether and how further progress may still be anticipated.

Preservation of hearing in operations on acoustic tumors: an alternative to recording brain stem auditory evoked potentials

The monitoring of auditory function by recording brain stem auditory evoked potentials in patients undergoing removal of acoustic tumors is hampered by the small amplitude of the brain stem auditory evoked potentials. Because several thousands of responses must be added, it takes several minutes to obtain an interpretable record. Recordings done directly from the exposed eighth nerve have much higher amplitudes, and, therefore, interpretable responses can be obtained after only a few responses have been added. However, it is difficult to place the recording electrode in an optimal position and the electrode may interfere with the removal of the tumor. In this report, we show that evoked potentials from the cochlear nucleus, which can be recorded by placing an electrode in the lateral recess of the fourth ventricle, have a large amplitude, and that the electrode placed in this way does not interfere with the removal of the tumor. This way of monitoring, therefore, yields interpretable responses within 15 to 20 seconds, or less, and makes it possible to detect injuries to the entire intracranial portion of the eighth nerve, just as brain stem auditory evoked potentials do, but 20 to 50 times faster.

Evaluation of patients with acoustic neuroma with dynamic posturography

The purpose of the present work was to consider the use of posture tests in patients who had known acoustic tumors. The results suggest that it might be possible to determine whether the tumor is on the inferior or superior branch of the vestibular nerve. This would have clinical significance for planning a surgical approach to the tumor.

Intracranial schwannoma as atypical facial pain. Case report

Facial pain is a common complaint that leads those who have it to seek professional help. Often times, the general dentist is the first clinician that a patient consults because of a presumed odontogenic origin of the pain. Occasionally a small number of these patients will be found to have an intracranial tumor. The case reported here is one such patient who was diagnosed and treated for a seventh nerve schwannoma.