Proton beam radiosurgery for vestibular schwannoma: tumor control and cranial nerve toxicity

OBJECTIVE: We sought to determine the tumor control rate and cranial nerve function outcomes in patients with vestibular schwannomas who were treated with proton beam stereotactic radiosurgery. METHODS: Between November 1992 and August 2000, 88 patients with vestibular schwannomas were treated at the Harvard Cyclotron Laboratory with proton beam stereotactic radiosurgery in which two to four convergent fixed beams of 160-MeV protons were applied. The median transverse diameter was 16 mm (range, 2.5-35 mm), and the median tumor volume was 1.4 cm(3) (range, 0.1-15.9 cm(3)). Surgical resection had been performed previously in 15 patients (17%). Facial nerve function (House-Brackmann Grade 1) and trigeminal nerve function were normal in 79 patients (89.8%). Eight patients (9%) had good or excellent hearing (Gardner-Robertson [GR] Grade 1), and 13 patients (15%) had serviceable hearing (GR Grade 2). A median dose of 12 cobalt Gray equivalents (range, 10-18 cobalt Gray equivalents) was prescribed to the 70 to 108% isodose lines (median, 70%). The median follow-up period was 38.7 months (range, 12-102.6 mo). RESULTS: The actuarial 2- and 5-year tumor control rates were 95.3% (95% confidence interval [CI], 90.9-99.9%) and 93.6% (95% CI, 88.3-99.3%). Salvage radiosurgery was performed in one patient 32.5 months after treatment, and a craniotomy was required 19.1 months after treatment in another patient with hemorrhage in the vicinity of a stable tumor. Three patients (3.4%) underwent shunting for hydrocephalus, and a subsequent partial resection was performed in one of these patients. The actuarial 5-year cumulative radiological reduction rate was 94.7% (95% CI, 81.2-98.3%). Of the 21 patients (24%) with functional hearing (GR Grade 1 or 2), 7 (33.3%) retained serviceable hearing ability (GR Grade 2). Actuarial 5-year normal facial and trigeminal nerve function preservation rates were 91.1% (95% CI, 85-97.6%) and 89.4% (95% CI, 82-96.7%). Univariate analysis revealed that prescribed dose (P = 0.005), maximum dose (P = 0.006), and the inhomogeneity coefficient (P = 0.03) were associated with a significant risk of long-term facial neuropathy. No other cranial nerve deficits or cancer relapses were observed. CONCLUSION: Proton beam stereotactic radiosurgery has been shown to be an effective means of tumor control. A high radiological response rate was observed. Excellent facial and trigeminal nerve function preservation rates were achieved. A reduced prescribed dose is associated with a significant decrease in facial neuropathy.     

Radiosurgery for acoustic neuromas: results of low-dose treatment

OBJECTIVE: The results of radiosurgical treatment of acoustic neuromas have improved by reducing the tumor marginal doses. We report relatively long-term follow-up results (>5 yr) for patients who underwent low-dose radiosurgery. METHODS: We treated and followed 51 consecutive patients with unilateral acoustic neuromas who were treated from January 1994 to December 1996 by gamma knife radiosurgery at low doses (20 dB of improvement) were noted in 9% of the patients with any hearing. Hearing was preserved at a useful level (Gardner-Robertson Classes 1 and 2) in 56% of patients. Although preexisting trigeminal neuropathy worsened in 4% of the patients, our patients did not experience new facial palsies or trigeminal neuropathies after radiosurgery. Facial spasm occurred in 6% of the patients, and intratumoral bleeding occurred in 4% of patients. CONCLUSION: Low-dose radiosurgery (相似文献   

Fractionated stereotactic radiotherapy for acoustic neuromas

Fractionated stereotactic radiotherapy (FSR) for acoustic neuromas offers both higher tumor dose and potential sparing of the facial and auditory cranial nerve functions. Eighty consecutive patients (45 males and 35 females; age 56.8 +/- 1.7 years) received FSR for acoustic neuromas and had a median follow-up of 2.9 years (range 2.3-6.5 years). For FSR, 70 patients had 5 daily fractions of 5 Gy (25 Gy total) and 10 patients had 10 daily fractions of 3 Gy (30 Gy total). Volume decreased by an average of 18%. No tumor increased in size, no patient developed facial weakness, and hearing was preserved.     

The facial nerve in medial acoustic neuromas

OBJECT: Functional results after surgery for acoustic neuromas that have little or no growth within the internal auditory canal are controversial, because these medial tumors can grow to a considerable size within the cerebellopontine angle (CPA) before symptoms occur. METHODS: A prospective study was designed to evaluate the surgical implications of the course of the facial nerve within the CPA on medial acoustic neuromas. This study included a consecutive series of 22 patients with medial acoustic neuromas (mean size 32 mm, range 17-52 mm) who underwent surgery via a suboccipitolateral approach between 1997 and 2001. All patients underwent pre- and postoperative magnetic resonance imaging and preoperative electromyography (EMG). Evaluation was based on continuous intraoperative EMG monitoring and video recordings of the procedure. All patients were reevaluated at a mean of 19 months (6-50 months) postsurgery. Preoperative evaluation of facial nerve function revealed House-Brackmann Grade I in six, Grade II in 14, and Grade III in two patients. During surgery a distinct splitting of the nerve at the root exit zone through its intracisternal course was seen in eight patients and documented by selective electrical stimulation. The facial nerve was separated into a smaller portion that ran cranially and parallel to the trigeminal nerve, and a larger portion on the anterior tumor surface. Both components joined anterior to the porus without major spreading of the nerve bundle. In two cases the nerve was found on the posterior surface of the cranial tumor. In one case the facial nerve entered the porus of the canal at its lower part, obtaining the expected anatomical position proximally within the middle portion of the canal. An anterior cranial, middle (five cases each), or caudal course (two cases) was seen in the remaining patients. After surgery, facial nerve function deteriorated in most cases; on follow-up evaluation House-Brackmann Grade I was found in 11, Grades II and III in 10, and Grade V in one patient. CONCLUSIONS: The facial nerve requires special attention in surgery for medial acoustic neuromas, because an atypical course of the nerve can be expected in the majority of cases. A split course of the nerve was found in 36% of the cases presented. Meticulous use of intraoperative facial nerve stimulation and continuous monitoring ensures facial nerve integrity and offers good functional results in patients with medial acoustic neuromas.     

Immediate neurological deterioration after gamma knife radiosurgery for acoustic neuroma. Case report

The authors describe acute deterioration in facial and acoustic neuropathies following radiosurgery for acoustic neuromas. In May 1995, a 26-year-old man, who had no evidence of neurofibromatosis Type 2, was treated with gamma knife radiosurgery (GKS; maximum dose 20 Gy and margin dose 14 Gy) for a right-sided intracanalicular acoustic tumor. Two days after the treatment, he developed headache, vomiting, right-sided facial weakness, tinnitus, and right hearing loss. There was a deterioration of facial nerve function and hearing function from pretreatment values. The facial function worsened from House-Brackmann Grade 1 to 3. Hearing deteriorated from Grade 1 to 5. Magnetic resonance (MR) images, obtained at the same time revealed an obvious decrease in contrast enhancement of the tumor without any change in tumor size or peritumoral edema. Facial nerve function improved gradually and increased to House-Brackmann Grade 2 by 8 months post-GKS. The tumor has been unchanged in size for 5 years, and facial nerve function has also been maintained at Grade 2 with unchanged deafness. This is the first detailed report of immediate facial neuropathy after GKS for acoustic neuroma and MR imaging revealing early possibly toxic changes. Potential explanations for this phenomenon are presented.     

Fractionated stereotactic radiosurgery for treatment of acoustic neuromas

BACKGROUND: Microsurgery and single-fraction radiosurgery for acoustic neuromas are associated with high rates of control, but can result in facial palsy and trigeminal neuropathy. To reduce the morbidity of treatment for acoustic neuromas while maintaining efficacy, we explored fractionated stereotactic radiosurgery (FSR). METHODS: We reviewed data for 31 acoustic neuromas in 30 patients treated with 25 Gy (linear accelerator) given in 5 consecutive daily fractions. The minimum follow-up was 6 months (6-44 months). The mean tumor volume was 1.1 cm(3) (0.1-8.74 cm(3)). RESULTS: All tumors remain controlled (9 smaller, 22 unchanged). No patient has experienced post-radiosurgery facial motor dysfunction. Two patients developed new trigeminal neuropathy; 2 patients with preexisting trigeminal nerve symptoms had improvement after FSR. Balance improved in 3 patients, was unchanged in 20 and worsened in 7 patients. Of the 12 patients with useful hearing (PTA < or = 50 dB) prior to treatment, 9 patients retained useful hearing following FSR. Subjectively, of 25 patients with any hearing prior to treatment, 2 had improvement, 10 remained unchanged and 13 had worsening. CONCLUSIONS: Short course FSR for acoustic neuromas results in acceptable toxicity and may provide high control of tumors. Longer follow-up is needed to assess outcomes.     

Stereotactic radiosurgery in the management of acoustic neuromas associated with neurofibromatosis Type 2

OBJECT: Stereotactically guided radiosurgery is one of the primary treatment modalities for patients with acoustic neuromas (vestibular schwannomas). The goal of radiosurgery is to arrest tumor growth while preserving neurological function. Patients with acoustic neuromas associated with neurofibromatosis Type 2 (NF2) represent a special challenge because of the risk of complete deafness. To define better the tumor control rate and long-term functional outcome, the authors reviewed their 10-year experience in treating these lesions. METHODS: Forty patients underwent stereotactic radiosurgery at the University of Pittsburgh, 35 of them for solitary tumors. The other five underwent staged procedures for bilateral lesions (10 tumors, 45 total). Thirteen patients (with 29% of tumors) had undergone a median of two prior resections. The mean tumor volume at radiosurgery was 4.8 ml, and the mean tumor margin dose was 15 Gy (range 12-20 Gy). The overall tumor control rate was 98%. During the median follow-up period of 36 months, 16 tumors (36%) regressed, 28 (62%) remained unchanged, and one (2%) grew. In the 10 patients for whom more than 5 years of clinical and neuroimaging follow-up results were available (median 92 months), five tumors were smaller and five remained unchanged. Surgical resection was performed in three patients (7%) after radiosurgery; only one showed radiographic evidence of progression. Useful hearing (Gardner-Robertson Class I or II) was preserved in six (43%) of 14 patients, and this rate improved to 67% after modifications made in 1992. Normal facial nerve function (House-Brackmann Grade 1) was preserved in 25 (81%) of 31 patients. Normal trigeminal nerve function was preserved in 34 (94%) of 36 patients. CONCLUSIONS: Stereotactically guided radiosurgery is a safe and effective treatment for patients with acoustic tumors in the setting of NF2. The rate of hearing preservation may be better with radiosurgery than with other available techniques.     

Facial nerve neuromas: report of 10 cases and review of the literature

OBJECTIVE: This study reviewed the management and outcomes of facial neuromas during the past decade at our institution. The goal was to analyze differences in presentation on the basis of location of the facial neuroma, review facial nerve function and hearing preservation postoperatively, and understand the characteristics of patients with tumors limited to the cerebellopontine angle or internal auditory canal. We also report an unusual case of a facial neuroma limited to the nervus intermedius. METHODS: Nine patients with facial neuromas and one with Jacobson's nerve neuroma underwent surgery, and total resection was accomplished in nine patients. A chart review for pre- and postoperative data was performed, after which all patients were evaluated on an outpatient basis. RESULTS: The mean age of the patients was 47 years; mean follow-up time was 33.1 months. The most common presenting symptoms were hearing loss (six patients) and facial paresis (five patients). A total of five patients had progressive (four patients) or recurrent (one patient) facial paresis. No patient experienced worsened hearing as a result of surgery, and one experienced improvement in a conductive hearing deficit. Five patients required cable graft repair of the facial nerve; four improved to House-Brackmann Grade 3 facial paresis. Four of five patients with preserved anatomic continuity of the facial nerve regained normal facial function. There were no surgical complications. No tumors have recurred during follow-up. We report the second nerve sheath tumor limited to the nervus intermedius. CONCLUSION: This series documents that facial neuromas can be resected safely with preservation of facial nerve and hearing function. Preservation of anatomic continuity of the facial nerve should be attempted, and it does not seem to lead to frequent recurrence. Tumors limited to the cerebellopontine angle/internal auditory canal are a unique subset of facial neuromas with characteristics that vary greatly from facial neuromas in other locations, and they are indistinguishable clinically from acoustic neuromas.     

Surgery combined with radiosurgery of large acoustic neuromas

The treatment of acoustic neuromas has been improved by advancements in microsurgical techniques and in radiosurgery. To further elucidate the degree of clinical improvement, we evaluated the treatment results of a combination of surgery and radiosurgery for large acoustic neuromas. METHODS: From January 1994 through December 2000, we treated 14 patients with large acoustic neuromas using a combination of surgery and radiosurgery. Of these, 8 were male and 6 were female patients, with an average age of 47 years (range, 18-64). The average maximum diameter of the tumor was 42 mm (range, 30-58 mm). All patients underwent operations using the retrosigmoid approach, and one patient was retreated using the transpetrosal transtentorial approach. The tumors were removed subtotally in thirteen patients and partially in one who had a very large hypervascular acoustic neuroma. There were no mortality and no surgical complications, such as hemorrhage or CSF leakage. Postoperative facial palsy was avoided in 10 patients (71%). Radiosurgery was performed 1 to 6 months (mean, 2.9 months) after surgery. At the time of radiosurgery, the treatment size (mean diameter) became 19.2 mm (range, 9.8-36.1 mm). The average tumor marginal dose was 12.1Gy (range, from 10-14 Gy). The mean follow-up period was 32 months after radiosurgery. RESULTS: The tumor size decreased in 6 patients, unchanged in 5 patients, and increased in 3 patients. Only 1 patient (7%) with extra large tumor needed surgical resection 1 year after radiosurgery. Excellent facial nerve function (House & Brackmann Grade I or II) was preserved in 12 patients (85.7%) in the final follow-up. CONCLUSIONS: In the case of large acoustic neuromas, subtotal removal and subsequent radiosurgery is one option for maintaining cranial nerve function and long-term tumor growth control.     

Facial Nerve Neuroma: Surgical Concept and Functional Results

This study reviewed the management and outcomes of 11 facial nerve neuromas treated in our institution during the past two decades with particular emphasis on surgical concepts and functional outcomes. All patients underwent complete surgical resection of their tumor. Eight patients (73%) were followed on an outpatient basis. A retrospective chart review for pre- and postoperative clinical and radiological data was performed. All facial neuromas were multi-segment tumors. All segments of the facial nerve were represented, but 54% involved the geniculate ganglion and 45% involved the labyrinthine or tympanic portions of the nerve, or both. Depending on the extent of sensorineural hearing loss, surgical removal was performed through the middle cranial fossa or translabyrinthine approach. To obtain adequate nerve reconstruction, we combined intra- and extracranial approaches (e.g., the transmastoidal and transtemporal routes). Regardless of the type of nerve reconstruction, the best recovery achieved was moderate facial weakness (House-Brackmann Grade III) in 75% of the patients, even in a patient who was Grade IV preoperatively. The choice of treatment for facial neuromas and surgical approach depends on the extent of tumor, grade of facial palsy, and hearing function. When facial palsy is present, complete resection is clearly indicated. In patients without facial dysfunction, a conservative strategy consisting of clinical and radiological observation should be considered as a treatment option.     

Cranial Nerve Preservation in Surgery for Large Acoustic Neuromas

Facial nerve outcomes and surgical complication rates for other cranial nerves were evaluated retrospectively after the resection of large acoustic neuromas. The charts of all patients who underwent surgical removal of an acoustic neuroma between 1992 and 2001 at New York University Medical Center were reviewed. Fifty-four patients with tumors measuring 3 cm or larger were included in the study. Four patients had neurofibromatosis type 2, two of whom underwent bilateral removal of acoustic neuromas. Translabyrinthine microsurgical removal of tumor was performed in 47 of 56 cases (84%). In all cases, EMG monitoring, improved sharp microdissection, and ultrasonic aspiration were employed. Facial nerve function was assessed using the House-Brackmann facial nerve grading system immediately after surgery and at follow-up visits. A House-Brackmann grade III or better was achieved in 90% of patients, and a grade II or better was achieved in 84% of patients. Ultimate facial nerve outcome was excellent after the surgical resection of large acoustic neuromas. Preoperative cranial nerve palsies also improved after surgery. The translabyrinthine approach for tumor removal is our treatment of choice for acoustic neuromas 3 cm or larger.     

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.     

Long-term hearing preservation after surgery for vestibular schwannoma

OBJECT: Vestibular schwannomas (VSs) are now amenable to resection with excellent hearing preservation rates. It remains unclear whether immediately postoperative hearing is a durable result and will not diminish over time. The aim of this study was to determine the rate of long-term preservation of functional hearing following surgery for a VS and to examine factors influencing hearing preservation. METHODS: All patients eligible for hearing preservation (Gardner-Robertson Class I or II) who had undergone resection of a VS by a single surgeon were reviewed retrospectively. Follow-up audiograms and magnetic resonance images were obtained. Of 142 patients deemed eligible for hearing preservation surgery, 38 had immediate postoperative hearing confirmed by an audiogram. In these patients with preserved hearing, the audiographic results demonstrated functional hearing in 30 (85.7%) of 35 patients who underwent repeated testing at a mean follow-up time of 7 years. Delayed hearing loss occurred in five (14.3%) of the 35 patients and did not correlate significantly with the size of the tumor. Hearing improved one Gardner-Robertson class postoperatively in three (7.9%) of the 38 patients. CONCLUSIONS: Long-term functional hearing was maintained in 85.7% of patients when it was preserved immediately postoperatively and the result was independent of tumor size. The results of this study emphasize that long-term preservation of functional hearing is a realistic goal following VS surgery and should be attempted in all patients in whom preoperative hearing is determined to be Gardner-Robertson Class I or II.     

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

OBJECT: To evaluate the possible prognostic factors for hearing preservation, the authors retrospectively reviewed the results of 30 consecutive acoustic neuroma operations in which hearing preservation was attempted, in a total series of 63 acoustic neuromas. METHODS: Intracanalicular tumors or those that extended less than 3 mm outside the porus acusticus (10 cases) were resected via the middle fossa approach. The retrosigmoid approach was used for tumors exceeding the limits for the middle fossa approach (20 cases). Overall, hearing was preserved (pure tone average < or = 50 dB and speech discrimination score > or = 50%) in 21 patients (70%). There were 11 patients with severe adhesion between the cochlear nerve and tumor capsule, and 19 without. Hearing was preserved postoperatively in only two (18.2%) of 11 patients with severe adhesion, whereas all 19 without severe adhesion had hearing preservation. CONCLUSIONS: The presence or absence of severe adhesion in the interface between the cochlear nerve and the tumor might be the most significant prognostic factor for hearing preservation postsurgery.     

Results of acoustic neuroma radiosurgery: an analysis of 5 years' experience using current methods

OBJECT: The goal of this study was to define tumor control and complications of radiosurgery encountered using current treatment methods for the initial management of patients with unilateral acoustic neuroma. METHODS: One hundred ninety patients with previously untreated unilateral acoustic neuromas (vestibular schwannomas) underwent gamma knife radiosurgery between 1992 and 1997. The median follow-up period in these patients was 30 months (maximum 85 months). The marginal radiation doses were 11 to 18 Gy (median 13 Gy), the maximum doses were 22 to 36 Gy (median 26 Gy), and the treatment volumes were 0.1 to 33 cm3 (median 2.7 cm3). The actuarial 5-year clinical tumor-control rate (no requirement for surgical intervention) for the entire series was 97.1+/-1.9%. Five-year actuarial rates for any new facial weakness, facial numbness, hearing-level preservation, and preservation of testable speech discrimination were 1.1+/-0.8%, 2.6+/-1.2%, 71+/-4.7%, and 91+/-2.6%, respectively. Facial weakness did not develop in any patient who received a marginal dose of less than 15 Gy (163 patients). Hearing levels improved in 10 (7%) of 141 patients who exhibited decreased hearing (Gardner-Robertson Classes II-V) before undergoing radiosurgery. According to multivariate analysis, increasing marginal dose correlated with increased development of facial weakness (p = 0.0342) and decreased preservation of testable speech discrimination (p = 0.0122). CONCLUSIONS: Radiosurgery for acoustic neuroma performed using current procedures is associated with a continued high rate of tumor control and lower rates of posttreatment morbidity than those published in earlier reports.     

Vasoactive treatment for hearing preservation in acoustic neuroma surgery.

OBJECT: Delayed hearing loss following surgery for acoustic neuroma indicates anatomical and functional preservation of the cochlear nerve and implies that a pathophysiological mechanism is initiated during surgery and continues thereafter. Intraoperative brainstem auditory evoked potentials (BAEPs) typically demonstrate gradual reversible loss of components in these patients. METHODS: Based on this BAEP pattern, a consecutive series of 41 patients with unilateral acoustic neuromas was recruited into a prospective randomized study to investigate hearing outcomes following the natural postoperative course and recuperation after vasoactive medication. Both groups were comparable in patient age, tumor size, and preoperative hearing level. Twenty patients did not receive postoperative medical treatment. In 70% of these patients anacusis was documented and in 30% hearing was preserved. Twenty-one patients were treated with hydroxyethyl starch and nimodipine for an average of 9 days. In 66.6% of these patients hearing was preserved and in 33.3% anacusis occurred. CONCLUSIONS: These results are statistically significant (p < 0.05, chi2 = 5.51) and provide evidence that these surgically treated patients suffer from a disturbed microcirculation that causes delayed hearing loss following removal of acoustic neuromas.     

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.     

Failure to preserve hearing in acoustic neuroma surgery: experiences after introduction of MRI

This report elucidates our experiences on acoustic neuroma surgery, in which auditory function was lost postoperatively, although conservation of hearing had been intended preoperatively. Five ears from four patients (two ears: unilateral, three ears from bilateral acoustic neuromas) were operated on via standard retromastoid route, with monitoring of auditory evoked potentials. Abolition of ABR occurred when surgical manipulations were performed within the internal auditory canal. Pulling tumor tissue away from the cochlea toward the brain stem has proved to be a hazardous procedure. Recognizing the condition of tumor tissue within the internal auditory canal is prerequisite for hearing preservation. For this purpose, MRI is very useful because tumor tissue within the internal auditory canal can be clearly visualized. The preoperative criteria in selecting candidates for hearing preservation operations should be more strict because most acoustic neuromas with a diameter of more than 10mm cannot be resected without causing loss of hearing, and, even in such small tumors, the cochlear nerves are infiltrated by tumor cells. Most ABR changes during operations seem to be explicable from avulsion of the cochlear nerve fibers and/or the internal auditory artery from the fundus of the internal auditory canal-the tractus spiralis foraminosus. Postoperative recordings of ABR indicated that progression of degeneration of the cochlear nerve fibers occurred after surgery. This phenomenon may explain postoperative delayed hearing loss observed clinically.     

Preservation of hearing in patients undergoing excision of acoustic neuromas and other cerebellopontine angle tumors

Microsurgical techniques have made it possible to identify and preserve the cochlear nerve from its origin at the brain stem and along its course through the internal auditory canal in patients undergoing removal of small or medium-sized acoustic neuromas or other cerebellopontine angle (CPA) tumors. In a consecutive series of 100 patients with such tumors operated on between 1975 and 1981, an attempt was made to preserve the cochlear nerve in 23. The decision to attempt to preserve hearing was based on tumor size and the degree of associated hearing loss. In cases of unilateral acoustic neuroma, the criteria for attempted preservation of hearing were tumor size (2.5 cm or less), speech reception threshold (50 dB or less), and speech discrimination score (60% or greater). In patients with bilateral acoustic neuromas or tumors of other types, the size and hearing criteria were significantly broadened. All patients were operated on through a suboccipital approach. Hearing was preserved postoperatively in six (31.6%) of the 19 patients with unilateral acoustic neuromas, although the cochlear nerve was preserved in 16. Of the six patients with postoperative hearing, three retained excellent hearing, and the other three had only sound awareness and poor discrimination. Hearing was preserved in three cases with other CPA tumors, including an epidermoid cyst and small petrous meningiomas in the internal auditory canal. Of the two cases with bilateral tumors, hearing was preserved in one. Of the 23 patients in whom hearing preservation was attempted, nine (39.1%) had some postoperative hearing, which in six was equal to or better than the preoperative level. Thus, it is worthwhile to attempt hearing preservation in selected patients with CPA tumors.     

Reduced-dose radiosurgery for vestibular schwannomas

OBJECTIVE: To evaluate tumor control and complications associated with low-dose radiosurgery for vestibular schwannomas. METHODS: Between December 1993 and January 2000, 47 patients with vestibular schwannomas were treated at our center with gamma knife radiosurgery. The marginal tumor doses ranged from 7.5 to 14.0 Gy (median, 12.0 Gy) for patients treated after microsurgery and from 10.0 to 15.0 Gy (median, 12.0 Gy) for patients in whom radiosurgery was the primary treatment. The median maximum tumor diameter was 18 mm (range, 3-50 mm). Evaluation included audiometry, neurological examination, and serial imaging tests. A survey was conducted at the time of analysis. RESULTS: Follow-up data were available for 45 patients and ranged from 1 to 7 years (median, 3.6 yr). In 43 patients (96%), tumor control (no radiographic progression or surgical resection) was observed. All 33 previously untreated patients had tumor control. Transient facial weakness, experienced in two patients (4%), had resolved completely within 6 months. No patient developed trigeminal neuropathy. Hearing was diminished from baseline in 12% of patients with useful hearing (Gardner-Robertson Class III). However, all patients with pretreatment hearing Gardner-Robertson Class I or II maintained testable hearing (Class I to III) at the most recent examination. CONCLUSION: Low-dose radiosurgery in this series provided comparable local control and decreased incidences of complications in relation to other reports. Additional follow-up will allow more definitive conclusions to be reached regarding the ultimate rates of tumor control and hearing preservation. Nevertheless, the current dose used for vestibular schwannomas at the University of Maryland Medical Center is 12.0 Gy to the tumor periphery.