Preservation of hearing in tumors of the internal auditory canal and cerebellopontine angle

Surgery of the lateral skull base: a 50-year endeavour

Disregarding the widely used division of skull base into anterior and lateral, since the skull base should be conceived as a single anatomic structure, it was to our convenience to group all those approaches that run from the antero-lateral, pure lateral and postero-lateral side of the skull base as “Surgery of the lateral skull base”. “50 years of endeavour” points to the great effort which has been made over the last decades, when more and more difficult surgeries were performed by reducing morbidity. The principle of lateral skull base surgery, “remove skull base bone to approach the base itself and the adjacent sites of the endo-esocranium”, was then combined with function preservation and with tailoring surgery to the pathology. The concept that histology dictates the extent of resection, balancing the intrinsic morbidity of each approach was the object of the first section of the present report. The main surgical approaches were described in the second section and were conceived not as a step-by-step description of technique, but as the highlighthening of the surgical principles. The third section was centered on open issues related to the tumor and its treatment. The topic of vestibular schwannoma was investigated with the current debate on observation, hearing preservation surgery, hearing rehabilitation, radiotherapy and the recent efforts to detect biological markers able to predict tumor growth. Jugular foramen paragangliomas were treated in the frame of radical or partial surgery, radiotherapy, partial “tailored” surgery and observation. Surgery on meningioma was debated from the point of view of the neurosurgeon and of the otologist. Endolymphatic sac tumors and malignant tumors of the external auditory canal were also treated, as well as chordomas, chondrosarcomas and petrous bone cholesteatomas. Finally, the fourth section focused on free-choice topics which were assigned to aknowledged experts. The aim of this work was attempting to report the state of the art of the lateral skull base surgery after 50 years of hard work and, above all, to raise questions on those issues which still need an answer, as to allow progress in knowledge through sharing of various experiences. At the end of the reading, if more doubts remain rather than certainties, the aim of this work will probably be achieved.

Acoustic Neuroma in a Private Neurotology Practice: Trends in Demographics and Practice Patterns

OBJECTIVES/HYPOTHESIS

To determine whether changes in demographics and management of patients with acoustic neuromas occurred between the years 1990 and 2005.

STUDY DESIGN

Retrospective chart review.

METHODS

Charts of all 614 patients with a diagnosis of acoustic neuroma, excluding neurofibromatosis-2, from 1990 through 2005 were reviewed. Age at diagnosis, tumor size, hearing, and initial therapy (observation, stereotactic radiation, or surgical excision) were obtained. Patients were grouped by time period (1990-1994, 1995-2000, 2001-2005).

RESULTS

Mean age at diagnosis increased slightly from the middle period (53.4 yr) to the most recent (56.9 yr) (P < or = .025). The proportion of patients 65 years or older increased from 21% to 29% to 32%, respectively, but the change was not significant. Average tumor size decreased from 1.7 cm initially to 1.4 cm most recently (P < or = .039). There were no significant changes in hearing. Although surgical excision remains our most common treatment (58.5% in 2001-2005), it is becoming less frequent (>80% in earlier periods) (P < or = .001). Observation with serial imaging was recommended in 37.3% in 2001 to 2005 as compared with 18.3% and 11.6% in the previous two time periods (P < or = .001). These changes in initial treatment choices occurred for all age groups and primarily for small tumors. Use of radiation has increased only slightly, to 4.2% in the recent period.

CONCLUSION

: Patients with acoustic neuroma are presenting with increased age and smaller tumors compared with 16 years ago. However, these changes cannot totally account for the large change in treatment trends. Technology and demographics are influential in these changes, but other difficult to measure forces, such as patient influence and patient use of the Internet, are also factors.

Microsurgery versus radiosurgery in the treatment of small acoustic neurinomas

Microsurgical preservation of the facial nerve during removal of acoustic neurinomas can hardly be compared with microsurgery of the eighth cranial nerve. Many more anatomical and pathogenetic factors are involved that need careful consideration. In small neurinomas, of grades I and II, total extirpation of the tumour with preservation of both the facial nerve and segments of the vestibulocochlear nerve not directly involved by the tumour has become a safe and practical technique. In small acoustic neurinomas immediate facial nerve function could be preserved in 88% and "useful hearing" could be preserved in 78%. A number of different types of tumour-cranial nerve relationships could be established in small acoustic neurinomas, showing also the effects of adjusted surgical techniques on the preservation of hearing. Optimal selective separation of cranial nerves from the tumour is only possible through open surgical intervention, while radiosurgery requires the irradiation of the entire tumour/nerve complex.

Preservation of hearing in surgery for acoustic neuromas

Preservation of hearing was attempted in 161 cases of histologically confirmed acoustic neuroma removed by the senior author between January 1, 1970, and September 30, 1991. There were 136 patients with unilateral tumors; 22 patients had bilateral tumors (neurofibromatosis 2) and underwent a total of 25 procedures. Hearing was initially preserved in 35% of patients with unilateral tumors and in 44% of those with bilateral tumors. Results are reported in terms of pre- and postoperative pure tone average and speech discrimination scores. Surgical access to the tumor was obtained via middle cranial fossa and suboccipital approaches. The latter has been used more often over the past 5 years because of a lower associated incidence of transient facial paresis. Persistent postoperative headaches have been the most common complication following the suboccipital approach. The results of preoperative brain-stem auditory evoked response (BAER) studies were useful in predicting the outcome of hearing preservation attempts. Patients with intact BAER waveform morphology and normal or delayed latencies had a higher probability of hearing preservation in comparison to those with abnormal preoperative BAER morphology.

An algorithm for the management of acoustic neuromas regarding age, hearing, tumor size, and symptoms

An algorithm has evolved for the management of patients with acoustic neuroma. Decisions as to surgery vs. observation, surgical approach, and whether hearing preservation should be attempted depend on age, patient symptoms, size of the tumor, residual hearing, and degree of facial nerve involvement at the time of surgery. Conservative management is used for patients over 65 years of age. This consists of observation or subtotal resection through a translabyrinthine approach, depending on the absence or presence of brainstem signs or symptoms. In patients under 65 years of age, hearing preservation is attempted through the retrosigmoid approach in tumors 1.5 cm or less if pure-tone average is less than 30 dB and the discrimination score is greater than 70%. The translabyrinthine approach is our preferred approach for tumors of any size when hearing is not serviceable. A near-total excision is performed when the facial nerve cannot be separated from the tumor. The rationale for this algorithm in the management of 130 cases of acoustic neuroma over the past 17 years is presented.

Current results of the retrosigmoid approach to acoustic neurinoma

Since 1984 when cranial nerve monitoring became routinely performed at the Mayo Clinic, 255 patients have undergone 256 procedures using the retrosigmoid approach for the removal of acoustic neurinomas. Of these, 221 patients had some hearing before surgery and 52 maintained hearing following surgery. The anatomical continuity of the facial nerve was preserved in 237 of these 256 procedures. It was possible to perform a primary end-to-end anastomosis in seven of the remaining 19 patients, and one patient had a cable graft inserted. Thus, 95.7% of these patients were believed to have potential for spontaneous facial nerve function. Of the 11 patients in whom this was not possible, seven underwent early spinal accessory facial anastomosis, in two hypoglossal-facial anastomosis was performed, and two had no facial nerve procedures and have paralysis of the facial nerve. There were two deaths from a pulmonary embolus in the early postoperative period, both 4 days following otherwise uneventful surgery. The most common postoperative complication was cerebrospinal fluid leakage, which has not resulted in significant permanent morbidity although early repair for this problem is now routinely recommended. Other complications were quite rare and have generally not resulted in any major change in patient lifestyle or activity level. This review reconfirms that the retrosigmoid surgical treatment of acoustic tumors continues to be an acceptable treatment option.

Neurophysiologic monitoring in posterior fossa surgery. II. BAEP-waves I and V and preservation of hearing

Of 135 cases operated upon for posterior fossa lesions 103 showed preoperative hearing. In 34 acoustic neurinomas 14 had postoperative initially preserved hearing, in 20 microvascular decompressions 19 had preserved postoperative hearing and in 49 other lesions 5 lost hearing. The relationship between preservation of hearing and the preservation or loss of brainstem auditory evoked potentials (BAEP) waves I and V in the three groups of namely: acoustic neurinomas, microvascular decompressions and other lesions are presented. It is noteworthy that only patients with preserved waves I or V are suitable candidates for intraoperative monitoring. The loss of wave V is usually associated with hearing loss (10 out of 13 cases). But hearing loss is also possible despite preservation of wave I (3 out of 60) or despite preservation of wave V (2 out of 68). The predictive value of the preservation of waves I and V is not an absolute one, but it strongly suggests preserved hearing postoperatively. The dilemma remains that once waves I or V are lost during surgery there is no certainty as to postoperative hearing. If wave V recovers after an initial loss, hearing is usually preserved but not in all cases. In wave I amplitude changes alone were more frequent than in wave V, where latency changes alone were more frequently observed. Particular surgical manoeuvres could be found to be often associated with a wave deterioration. Hearing preservation could never be achieved in patients who already preoperatively had no BAEP. It is concluded that BAEP monitoring is of great value in surgery for microvascular decompression and cerebello-pontine-angle (CPA) tumours with preserved hearing.

Acoustic neuroma surgery: results of translabyrinthine tumour removal in 300 patients. Discussion of choice of approach in relation to overall results and possibility of hearing preservation

The results from the Danish model of acoustic neuroma surgery are presented. In the period from 1976 to 1985, 300 patients with acoustic neuromas were operated upon using the translabyrinthine procedure. Only one small intrameatal tumour was encountered; 96 tumours were medium sized and 203 were larger than 25 mm. Of these 118 measured more than 40 mm. Mortality rate was 2%, CSF leaks occurred in 11%, and had to be closed surgically in 5%. Facial nerve function was postoperatively normal in 66%, slightly reduced in 17%, moderately reduced in 8% and abolished in 9%. Reconstruction, most often as a XII-VII anastomosis, was performed in only 6% of the patients. Cerebellar symptoms, which occurred in 45% preoperatively were present in only 7% after surgery. The preoperative hearing in both the tumour and non-tumour ear was analysed in 72 patients with tumours smaller than 2 cm. In the tumour ear, only four patients had a PTA of 0-20 dB and SDS of 81-100%; eight patients had a PTA of 0-40 dB and SDS of 61-100%; 14 had a PTA of 0-50 dB and SDS of 51-100%. This means that only a maximum of 5% of the patients, using the broadest criteria, could be candidates for hearing-conserving surgery. In all these patients the contralateral ear had hearing within normal limits (PTA 0-20 dB and SDS 95-100%). Since preservation of hearing would be achieved in only half of those subjected to suboccipital removal and since the hearing retained in patients with successful operations generally is poorer than the preoperative level, the number of patients obtaining serviceable hearing is so modest that preservation of hearing cannot be considered a valid argument in favour of suboccipital tumour removal. From a statistical point of view the risk of losing hearing in the opposite ear after tumour removal is negligible. The general morbidity after suboccipital surgery is higher than after translabyrinthine surgery, and hearing loss must be listed low among the other sequelae after tumour removal.

Criteria for preservation of vestibulocochlear nerve function during microsurgical removal of acoustic neurinomas

A careful examination of the shape, location and course of the 8th cranial nerve in medium-sized and large tumours exhibits three distinct variants. In all cases where cochlear function was preserved, the type III variant (12%) in the cranial nerve tumour relationship was observed. The author's experience clearly indicates that, if a tumour is resected in toto, anatomical nerve continuity cannot be preserved in the type I and II variants (48%, respect. 40%). However, in the type I and II variants the patients invariably had preoperative hearing loss. The important criteria which must be considered in order to preserve cochlear function when extirpating acoustic neurinomas are an anatomically intact nerve, the origin of the tumour and its direction of spread, further more the shape, location and course of the 8th nerve components, the quality of preoperative cochlear nerve function, the pattern of vascularization of the statoacoustic nerve and the inner ear, and lastly, but not least a possible infiltration of the vestibular and/or cochlear nerves by the tumour itself. Objective hearing function could be preserved in 62% of small neurinomas (grade II) and 10% of large tumours (grades III and IV).

Transtemporal planned partial resection of bilateral acoustic neurinomas

In an attempt to overcome the complete auditory deprivation of young patients with bilateral acoustic nerve schwannomas (Morbus v. Recklinghausen) a planned partial resection of the tumour was carried out in 11 hearing ears. The cerebello-pontine angle was exposed by the enlarged middle fossa approach (Wigand et al., HNO 1985). A strip of tumour was left in contiguity to the facial and cochlear nerves. Hearing was initially preserved in all cases. Four of them, however, developed total deafness after 3-39 months. Recurrent tumour growth was checked by CT scans. During the observation time one resting tumour became invisible, five remained unchanged. Two grew larger. Three cases dropped out of the follow-up. With regard to the high value of preserved auditory function during the first decades of life the planned partial resection may be considered preferable for cases of bilateral acoustic neuromas.

Is preservation of hearing in acoustic neuroma worthwhile?

In a series of 300 translabyrinthine removals of acoustic neuromas, comprising almost all tumours operated on in Denmark during a period of 10 years, the preoperative hearing in the tumour ear and in the contralateral ear was analysed in 72 patients with tumours smaller than 2 cm in extrameatal diameter. These patients constitute likely candidates for a hearing preserving operation via the suboccipital approach. In the tumour ear in 4 patients there was a pure-tone average (PTA) of 0-20 dB and a discrimination score (DS) of 81-100%. Applying this criterion to the whole series, 1% of the patients would be candidates for a hearing preserving procedure. Changing the criterion to a PTA of 0-40 dB and a DS of 61-100%, the number of candidates would increase to 8 patients (3%), and with a PTA of 0-50 dB and a DS of 51-100% 14 candidates (5%) would have been found. In all of these patients, contralateral hearing was normal (SRT 0-20 dB, DS 95-100%). Since preservation of hearing would be achieved in only half of those subjected to suboccipital removal and since the hearing retained in patients with successful operations is generally poorer than the preoperative level, the number of patients obtaining serviceable hearing is so modest that preservation of hearing cannot be considered an argument in favour of suboccipital tumour removal. It should be borne in mind that contralateral hearing is normal in these patients and that, according to most reports, the mortality rate is higher and paralysis of the facial nerve more frequent with the suboccipital approach than with the translabyrinthine procedure.

Preservation of hearing in surgical removal of acoustic neuromas of the internal auditory canal and cerebellar pontine angle

The surgical results in 69 patients with unilateral tumors of the cerebellopontine angle or internal auditory canal in whom total tumor removal was accomplished, and in whom an attempt was made to preserve hearing, are presented. The success rate of preservation of hearing and facial nerve function was correlated with the size of the tumor. Useful hearing, as defined by speech reception threshold no poorer than 70 dB and a discrimination score of at least 15%, was preserved in 73% of cases in which the tumor extension to the posterior fossa was no greater than 0.5 cm. In contrast, useful hearing was preserved in 22% of cases in which posterior fossa extension was greater than 2.5 cm. No significant correlation was found between preoperative evoked responses and success in preservation of hearing. The techniques and value of intraoperative monitoring of electrocochleogram (ECoG) and brain stem evoked responses are discussed. A theory of pathogenesis of intraoperative hearing loss, based on correlation of changes in evoked responses and simultaneous surgical events, is presented.

Long-term hearing preservation after acoustic neuroma surgery

The past two decades have evidenced a remarkable improvement in the capacity of otologic surgeons to treat cerebellopontine angle tumors. Advances in instrumentation because of technologic changes, coupled with better surgical training, have contributed to a highly successful rate of tumor removal. The capability to extirpate the tumor now permits the otologic surgeon to attempt simultaneous preservation of the facial and cochlear nerve functions. Just as middle ear surgery improved to the point in the 1950s that reconstruction as well as disease eradication became possible, so can surgeons now consider preservation of function of the inner ear. It is now technically feasible--in some instances--to attempt to preserve hearing in tumors of the eighth nerve. Several studies have provided evidence that the cochlear nerve can be anatomically and functionally preserved when neuromas involve either the inferior or superior vestibular nerves. However, other studies assert that grossly intact nerves may contain microscopic islands of tumor cells intermingled with nerve fibers. If viable tumor cells were allowed to remain behind, one would expect them to grow; this would result in loss of hearing function and tumor recurrence, as evidenced by computed tomography (CT) or magnetic resonance imaging (MRI). This article will discuss the issues of cochlear nerve preservation and tumor excision, and review our experience over the past decade.

Prognostic factors for postsurgical hearing and facial nerve function in cases of cerebellopontine angle-tumours. The meaning of brain stem evoked response audiometry (BERA)

Presurgical and postsurgical brain stem evoked response audiometry (BERA) examinations were done in patients with tumours of the posterior cranial fossa. A correlation exists between the extent of presurgical BERA-alterations and postsurgical hearing-power and facial nerve function. Small tumours (less than 1 cm) correlate generally with small BERA-alterations and show a good prognosis. Conservation of hearing in cases of larger tumours can only be expected when BERA-alterations are small. Prognosis is generally bad in cases of big tumours (greater than 3 cm). BERA-alterations on the contralateral side point to an additional brain stem compression which can normalize after surgery.

Hearing preservation in acoustic neurinoma surgery

In a series of 120 patients with acoustic neurinoma, hearing preservation at removal of the tumour via the suboccipital approach was attempted in 30 ears. Hearing was preserved in 13 ears (43%), but in two, hearing was lost entirely in 3 to 4 years; thus the success rate was 36%. In 9 of the remaining 11 ears useful speech discrimination was present. Audiological tests showed increased retrocochlear loss after surgery. A surgical team should master the methods of both translabyrinthine and suboccipital surgery in order to choose the best approach for each patient.

Use of intraoperative auditory evoked potentials to preserve hearing in unilateral acoustic neuroma removal

Twenty-two patients with unilateral acoustic neuromas and preoperative speech discrimination scores of 35% or more had intraoperative monitoring of the electrocochleogram (ECoG) using a transtympanic electrode, and of the brain-stem auditory evoked potentials (BAEP's) using scalp electrodes. Rapid feedback was provided about the status of the cochlear microphonics from the hair cells of the inner ear (CM of the ECoG), the compound action potential of the auditory nerve (N-1 of the ECoG or Wave I of the BAEP's) and the potentials from the lower brain stem (Wave V of the BAEP's). All patients had total removal of the tumor. In 21, the cochlear nerve was anatomically preserved, and 20 had good postoperative facial nerve function. Correlation of tumor size with postoperative hearing was as follows: discrimination scores of more than 35% in three of four patients with 1-cm tumors, two of eight with 1.5-cm tumors, two of six with 2- to 2.5-cm tumors, and one of four with tumors of 3 cm or more. Two other patients with 1.5-cm tumors had discrimination scores of less than 35%, and one patient with a 2-cm tumor had only sound perception. In two patients, the discrimination scores improved. At the end of the operation, all patients with hearing had a detectable N-1, and, when recorded, CM. All but one patient with no hearing had lost N-1, and CM was absent or reduced. Unless Wave V was unchanged, it was a poor predictor of postoperative hearing, and its absence did not preclude preservation of good hearing. The electrophysiological changes during each stage of the operation were analyzed and correlated with events during surgery. Areas in which there was an increased risk of loss of the potentials were determined. In some patients monitoring was unnecessary, because either there were no significant changes or the changes were abrupt and no recovery occurred. However, in other patients, monitoring alerted the surgeon to a possible problem and the method of dissection was altered. Possible mechanisms of hearing loss were suggested from the changes in the recordings.

[Results of 110 microsurgical acoustic neuroma operations]

We report our experiences in 110 cases of microsurgical removal of acoustic neurinomas. The historic development, the chances of preservation of the facial nerve and hearing function and the mortality risks are described in detail, hereby stressing the advantages of the lateral suboccipital approach in microneurosurgery.

Neuro-otological findings in patients with small acoustic neuromas

The method of choice for the diagnosis of even the smallest acoustic neuromas is CT gas cisternography. Lumbar puncture and gas insufflation, however, is an intervention demanding strict indication. Neuro-otological examinations should lead to this indication. The aim of this paper is to demonstrate neuro-otological findings on 19 patients presenting small acoustic neuromas. These neuro-otological findings are not necessarily comparable to earlier reports in the literature dealing with mainly larger tumours at a time when early diagnosis was not so advanced.

Acoustic neuroma surgery. Translabyrinthine-transtentorial approach via the middle cranial fossa

In our approach for acoustic tumors, the method of Morrison and King and that of Bochenek and Kukwa have been modified into one method. This modified method is basically a neuro-otological-neurosurgical team approach, extending the operative field by drilling the temporal bone and cutting the superior petrosal sinus, tentorium, and posterior fossa dura according to the size of the tumor. Therefore, for tumors slightly protruding into the posterior fossa from the prous of the internal auditory canal, only the bone adjacent to it is removed (Bochenek et al's method). For larger tumors, labyrinthectomy and mastoidectomy with the separation of the superior petrosal sinus and the tentorium and posterior fossa dura are also performed. In Morrison et al.'s method, the translabyrinthine approach is done first and the middle cranial fossa approach is performed thereafter. In contrast, in the modified method, drilling the bone from the middle cranial fossa to the tip of the mastoid--labyrinthectomy and mastoidectomy--is the first thing done after elevating the temporal lobe and revealing the middle cranial fossa, and the internal auditory canal is opened thereafter. Thirty-five cases of acoustic tumors and other cerebello-pontine angle tumors were operated on during the past 3.5 years through the middle cranial fossa. Among 30 cases of acoustic tumors, eight cases in which the tumors were confined to the internal auditory canal were operated on through the middle cranial fossa. In four cases, Bochenek et al's method was performed in which bones adjacent to the internal auditory canal and a part of the labyrinth are removed without cutting the superior petrosal sinus. In 23 cases including five cerebellopontine angle tumors, the modified translabyrinthine-transtentorial approach through the middle cranial fossa was done. This modification has the advantage that severe postoperative complications are less frequent. The surgical technique and the results are discussed.

Audiologic findings after stereotactic radiosurgery in nine cases of acoustic neurinomas

Nine cases of acoustic neurinoma were treated by stereotactic radiosurgery between 1969 and 1974. The follow-up period can now be regarded as sufficiently long for a preliminary evaluation of the results. An arrest of growth or shrinkage of the tumour was observed in 8 of the 9 cases. In one case open surgery was performed 2 years after irradiation and histological examination showed regressive changes of the type expected after irradiation. Audiological examination revealed that in the majority of cases radiosurgery could be performed without causing serious damage to the hearing function. The average hearing loss present before treatment increased on average only 20.0 dB in the most successful 7 cases. None of the patients suffered facial nerve involvement. In small and medium-sized acoustic tumours this method offers a satisfactory therapeutic alternative worthy of consideration.

Translabyrinthine surgery of acoustic neurinoma

In translabyrinthine and translabyrinthine-suboccipital removal of 47 acoustic tumours, the mortality rate was 2.1%; among 18 large tumours, 5.6%. The facial nerve was preserved in 89%, and 80% had normal facial nerve function. 98% of the tumours were removed in toto, including 17% where the tumour remnant was removed by the suboccipital approach one week after the translabyrinthine operation.

Facial nerve function after suboccipital removal of acoustic neurinoma

The recovery of facial nerve function after suboccipital removal of 91 acoustic neurinomas is presented. The results after anatomical preservation of the nerve (60 cases), direct anastomosis of the nerve (7 cases), nerve grafting (16 cases), and facial hypoglossal anastomosis (8 cases) are presented after a follow-up period of 31.2 months. A simplified classification was used to describe motor function. The results are compared to those in the literature.