Surgical exposure of the fundus of the internal auditory canal: anatomic limits of the middle fossa versus the retrosigmoid transcanal approach

Retrosigmoid Approach for Sporadic Vestibular Schwannoma: Patient Selection, Technical Pearls, and Hearing Results

The retrosigmoid corridor provides the most broadly applied approach for resection of sporadic vestibular schwannoma. It may be utilized for any size tumor and for patients with intact hearing with the intention of hearing preservation. For larger tumors, the skull base surgeon must weigh the benefits the retrosigmoid approach against those of the translabyrinthine route. For smaller tumors where hearing preservation is a goal, the retrosigmoid approach is contrasted to the middle fossa route. Hearing preservation is most likely for patients with small and medially located intracanalicular tumors with minimal extension into the cerebellopontine angle, and excellent preoperative hearing.

Internal Auditory Canal Variability: Anatomic Variation Affects Cisternal Facial Nerve Visualization

BACKGROUND

The internal auditory canal (IAC) is an important landmark during surgery for lesions of the cerebellopontine angle. There is significant variability in the position and orientation of the IAC radiographically, and the authors have noted differences in surgical exposure depending on the individual anatomy of the IAC.

OBJECTIVE

To test the hypothesis that IAC position and orientation affects the surgical exposure of the IAC and facial nerve, especially when performing the translabyrinthine approach.

METHODS

The authors retrospectively reviewed magnetic resonance imaging studies of 50 randomly selected patients with pathologically confirmed vestibular schwannomas. Measurements, including the anterior (APD) and posterior (PPD) petrous distances, the anterior (APA) and posterior (PPA) petro-auditory angles, and the internal auditory angle (IAA), were obtained to quantify the position and orientation of the IAC within the petrous temporal bone.

RESULTS

The results quantitatively demonstrate tremendous variability of the position and orientation of the IAC in the petrous temporal bone. The measurement ranges were APD 10.2 to 26.1 mm, PPD 15.1 to 37.2 mm, APA 104 to 157°, PPA 30 to 96°, and IAA –5 to 40°.

CONCLUSION

IAC variability can have a substantial effect on the surgical exposure of the IAC and facial and vestibulocochlear nerves. Specifically, a horizontally oriented IAC with a small IAA may have significant impact on visualization of the facial nerve within its cisternal segment with the translabyrinthine approach. The retrosigmoid approach is less affected with IAC variability in position and angle.

Anatomical study of presigmoid-retrolabyrinthine approach based on temporal bone high-resolution CT

BACKGROUND

The surgical approach of acoustic neuroma includes translabyrinthine, transcranial fossa, suboccipital retrosigmoid sinus, and presigmoid retrolabyrinthine approach. Aims/Objective: To provide the anatomical basis for the surgical selection of presigmoid retrolabyrinthine approach by measuring the anatomical parameters of retrolabyrinthine space of the petrous bone by high-resolution CT.

MATERIAL AND METHODS

A retrospective study of 208 high-resolution CT (HRCT) images of 104 patients examined in our hospital were analyzed retrospectively. Forty-nine males and 55 females were included in this study. Lines were drawn on the HRCT to measure the morphological data for pre-operational assessment.

RESULT

Morphological data were retracted from HRCT, for preoperational assessment.

CONCLUSION AND SIGNIFICANCE

Using the standard postprocessing images of temporal bone HRCT can predict the size of the retrolabyrinthine space and the degree of exposure to the inner auditory canal, providing an important anatomical index for the choice of presigmoid retrolabyrinthine approach.

Exposing the Fundus of the Internal Acoustic Meatus without Entering the Labyrinth Using a Retrosigmoid Approach: Is It Possible?

OBJECTIVES

To evaluate the feasibility of performing a labyrinth-sparing neuronavigation-assisted retrosigmoid approach to the fundus of the internal acoustic meatus (IAM) and to describe the anatomy of the structures embedded in the posterior meatal wall.

METHODS

Ten surgical dissections were performed bilaterally on 5 fresh cadavers. Cadavers were subjected to preoperative computed tomography scans and spatial coordinates of inner ear structures were recorded. A retrosigmoid craniectomy was performed. The IAM was drilled towards the fundus until no more than 1 mm of bone covered the labyrinthine structures. Specimens underwent a new computed tomography scan to verify the length of opened IAM and the status of the labyrinth. We then opened the labyrinthine structures and recorded their coordinates using navigation. These were compared with the radiologic coordinates to verify the neuronavigation accuracy.

RESULTS

In 9 sides, the IAM was opened to the fundus without injuring the labyrinth; in 1 side, the vestibule was opened. The mean residual bone on the fundus was 0.97 mm. The average length of the accessible IAM was 88.95%. The best accuracy of the navigation was for the identification of the common crus, with a mean value of 0.73 mm.

CONCLUSIONS

This surgical technique could facilitate the opening of the IAM with preservation of inner ear structures. We opened a mean of 88.95% of the IAM without entering the labyrinthine structures in 90% of cases. These results confirm the feasibility of the retrosigmoid approach for the exposure of the IAM fundus with preservation of labyrinthine structures.

Endoscopic-Assisted Middle Fossa Craniotomy for Resection of Vestibular Schwannoma

Background Rates of hearing preservation following surgery via middle fossa craniotomy in patients harboring tumors with unfavorable characteristics are significantly lower than for those patients with “favorable” tumors.

Objectives We will present two cases both with unfavorable conditions, which underwent endoscopic-assisted middle fossa craniotomy (MFC) resection of intracanalicular vestibular schwannomas with preserved postoperative hearing.

Methods Chart reviews were conducted on both patients. Their presentation, intraoperative details, and techniques, pre- and postoperative audiograms, and facial nerve outcomes are presented.

Results Patient A had 5.6 × 6.8 × 13.2 mm intracanalicular tumor with unserviceable hearing (pure tone audiometry [PTA], 41; speech determination score [SDS], 47%; class D) but was blind so hearing preservation was attempted. Postoperative hearing was preserved (PTA, 47; SDS, 60%; class B). Patient B had a 5 mm round intracanalicular tumor immediately adjacent to the vestibule and cochlea without any fundal fluid present. Preoperative audiogram showed serviceable hearing (PTA, 48; SDS, 88%; class B). Postoperatively, aidable hearing was preserved (PTA, 51; SDS, 76%; class C).

Conclusion Hearing preservation surgery via MFC can be enhanced with endoscopic-assisted dissection, especially in the lateral internal auditory canal. The superior optical view allows for preservation of cochlear nerve function and removal of residual tumor not otherwise seen on microscopy.

Preoperative identification of facial nerve in vestibular schwannomas surgery using diffusion tensor tractography

OBJECTIVE

Facial nerve palsy is a common complication of treatment for vestibular schwannoma (VS), so preserving facial nerve function is important. The preoperative visualization of the course of facial nerve in relation to VS could help prevent injury to the nerve during the surgery. In this study, we evaluate the accuracy of diffusion tensor tractography (DTT) for preoperative identification of facial nerve.

METHODS

We prospectively collected data from 11 patients with VS, who underwent preoperative DTT for facial nerve. Imaging results were correlated with intraoperative findings. Postoperative DTT was performed at postoperative 3 month. Facial nerve function was clinically evaluated according to the House-Brackmann (HB) facial nerve grading system.

RESULTS

Facial nerve courses on preoperative tractography were entirely correlated with intraoperative findings in all patients. Facial nerve was located on the anterior of the tumor surface in 5 cases, on anteroinferior in 3 cases, on anterosuperior in 2 cases, and on posteroinferior in 1 case. In postoperative facial nerve tractography, preservation of facial nerve was confirmed in all patients. No patient had severe facial paralysis at postoperative one year.

CONCLUSION

This study shows that DTT for preoperative identification of facial nerve in VS surgery could be a very accurate and useful radiological method and could help to improve facial nerve preservation.

Rate of recurrent vestibular schwannoma after total removal via different surgical approaches

OBJECTIVES

The objective of this study was to assess the differences in the recurrence rates of vestibular schwannoma (VS) after total tumor removal through enlarged translabyrinthine (ETL), retrosigmoid (RS), and middle cranial fossa (MCF) approaches. Our results were compared with previously published data, and literature reviews were done to identify the possible causes for the recurrence of VS.

METHODS

We performed a retrospective analysis of 2,400 cases of VS that underwent removal at the Gruppo Otologico, Piacenza, Italy, from 1983 until 2010. The minimum postoperative follow-up was 12 months. We also reviewed the previously published data on recurrence rates of VS after ETL, RS, and MCF approaches.

RESULTS

Total tumor removal was achieved in 2,252 cases (93.8%). The recurrence rate was 0.05% for the ETL approach, 0.7% for the RS approach, and 1.8% for the MCF approach. Literature reviews of 3 previously published case series utilizing the translabyrinthine approach showed that none of the primary tumors were less than 2.0 cm in size. Recurrences were seen between 1 and 13 years after the initial surgery.

CONCLUSIONS

The rate of VS recurrence after total removal is exceptionally low in experienced hands. Undetected microscopic deposits left on crucial points such as the facial nerve, the preserved cochlea nerve, or the fundus of the internal auditory canal could be possible causes for the recurrence. A definite advantage of an ETL approach is the excellent internal auditory canal exposure, resulting in an extremely low rate of VS recurrence. The patients should be followed up to 15 years with gadolinium-enhanced magnetic resonance imaging (with fat suppression sequence in ETL approach cases). Recurrent VS may exhibit a faster growth rate than primary VS.

Dural Landmark to Locate the Internal Auditory Canal in Large and Giant Vestibular Schwannomas: The Tübingen Line

BACKGROUND:

In cases of large and giant vestibular schwannomas (VS), the visualization of the internal auditory canal (IAC) opening is difficult or impossible.

OBJECTIVE:

To describe the Tübingen line and explore its relationships with the IAC as a landmark to help locate the IAC.

METHODS:

Ten cadaveric heads were used in this study. Between 2004 and 2009, the senior author (M.T.) used the Tübingen line as a landmark to recognize the IAC in 300 consecutive patients with VS. To locate the Tübingen line, the initial step was to identify several vertical foldings of dura located around the area of the vestibular aqueduct. After this, foldings upward consistently reached a linear level where all of the foldings ended and the dura tightly adhered to the bony surface in a smooth, foldless shape.

RESULTS:

The Tübingen line was identified in all temporal bones studied and in all 300 patients operated on, with the exception of 2 cases (<1%). Removal of the bone just above the Tübingen line located the IAC in all temporal bone specimens studied. Similarly, the surgical cases showed that the Tübingen line helped locate the IAC in all patients.

CONCLUSION:

The Tübingen line is an easy, consistent, and safe method to locate the projection of the IAC along the posterior surface of the temporal bone.

Image-guided, endoscopic-assisted drilling and exposure of the whole length of the internal auditory canal and its fundus with preservation of the integrity of the labyrinth using a retrosigmoid approach: a laboratory investigation

OBJECTIVE

Hearing loss after removal of vestibular schwannomas with preservation of the cochlear nerve can result from labyrinthine injury of the posterior semicircular canal and/or common crus during drilling of the posterior wall of the internal auditory meatus. Indeed, there are no anatomic landmarks that intraoperatively identify the position of the posterior semicircular canal or of the common crus. We investigated the usefulness of image guidance and endoscopy for exposure of the internal auditory canal (IAC) and its fundus without labyrinthine injury during a retrosigmoid approach.

METHODS

A retrosigmoid approach to the IAC was performed on 10 whole fresh cadaveric heads after acquiring high-resolution computed tomographic scans (120 kV; slice thickness, 1 mm; field of vision, 40 cm; matrix, 512 x 512) with permanent bone-implanted reference markers. Drilling of the posterior wall of the IAC was executed with image guidance. Its most lateral area was visualized using endoscopy.

RESULTS

Target registration error for the procedure was 0.28 to 0.82 mm (mean, 0.46 mm; standard deviation, 0.16 mm). The measured length of the IAC along its posterior wall was 9.7 +/- 1.6 mm. The angle of drilling (angle between the direction of drill and the posterior petrous surface) was 43.3 +/- 6.0 degrees, and the length of the posterior wall of the IAC drilled without violating the integrity of the labyrinth was 7.2 +/- 0.9 mm. The surgical maneuvers in the remaining part of the IAC, including the fundus, were performed using an angled endoscope.

CONCLUSION

Frameless navigation using high-resolution computed tomographic scans and bone-implanted reference markers can provide a "roadmap" to maximize safe surgical exposure of the IAC without violating the labyrinth and leaving a small segment of the lateral IAC unexposed. Further exposure and surgical manipulation of this segment, including the fundus without additional cerebellar retraction and labyrinthine injury, can be achieved using an endoscope. Use of image guidance and an endoscope can help in exposing the entire posterior aspect of the IAC including its fundus without violating the labyrinth through a retrosigmoid approach. This technique could improve hearing preservation in vestibular schwannoma surgery.

Facial nerve function and hearing preservation acoustic tumor surgery: does the approach matter?

OBJECTIVE

The retrosigmoid and middle fossa approaches to acoustic tumor excision allow for hearing preservation but differ in the angle of approach to the facial nerve. The authors comparatively examined facial nerve results of each approach.

STUDY DESIGN

Case series with chart review.

SETTING

Multiple physician subspecialty practice.

SUBJECTS AND METHODS

The authors reviewed facial nerve outcomes of patients undergoing acoustic tumor excision at a single subspecialty practice that had used a hearing preservation approach for the past 15 years. The retrosigmoid and middle fossa approaches were compared. Hearing results and recurrence rates were also examined.

RESULTS

One hundred thirty-eight patients had adequate data for inclusion in this study. Of the patients undergoing a middle fossa approach, 80 percent had a House-Brackmann (HB) grade I-II outcome, whereas 90 percent of patients undergoing the retrosigmoid approach had an HB grade I-II. When classifying HB I and II outcomes together, we did not find a statistically different result between the surgical groups. Upon more critical analysis, however, facial function recovered faster and there were more long-term HB grade I function results in the retrosigmoid group. There were more recurrent/residual tumors in the retrosigmoid group and better hearing preservation in the middle fossa group.

CONCLUSION

There are small but important functional outcome differences between the retrosigmoid and middle fossa approach for acoustic tumors. The clinician needs a working understanding of these differences so that the correct approach can be used to produce the best results for each patient.

Sporadic unilateral vestibular schwannoma in the pediatric population. Clinical article

OBJECT

Vestibular schwannomas (VSs) are rare in the pediatric population. Most often, these lesions manifest as a bilateral disease process in the setting of neurofibromatosis Type 2. Even in the absence of additional clinical diagnostic criteria, the presentation of a unilateral VS in a young patient may be a harbinger of future penetrance for this hereditary tumor syndrome.

METHODS

The authors retrospectively reviewed the charts of a cohort of 7 patients who presented with apparently sporadic, unilateral VSs. These patients had previously undergone surgery via translabyrinthine, retrosigmoid, or combined approaches. Clinical outcomes were reviewed with emphasis on facial nerve function and follow-up for signs and symptoms of a heritable disorder.

RESULTS

All patients underwent microsurgical resection in a multidisciplinary effort by the senior authors. The average tumor size was 4.57 cm, with an average duration of symptoms prior to definitive diagnosis of 31.2 months. The tumor size at the time of presentation followed a trend different from reports in adults, while the duration of symptoms did not. At a follow-up average of 6.3 years (range 1-12 years), 100% of patients demonstrated good facial function (House-Brackmann Grade I or II). No patient in this cohort demonstrated symptoms, objective signs, or genetic analysis indicating the presence of neurofibromatosis Type 2.

CONCLUSIONS

Diagnosis and management of sporadic, unilateral VSs in children is complicated by clinical presentations and surgical challenges unique from their adult counterparts. Careful consideration should be given to a heritable genetic basis for sporadic unilateral VS in the pediatric population. Results of genetic testing do not preclude the necessity for long-term follow-up and systemic investigation. In patients who present with large tumors, preliminary experience leads the authors to suggest that a combined retrosigmoid-translabyrinthine approach offers the greatest opportunity for preservation of facial nerve function.

Guiding patients through the choices for treating vestibular schwannomas: balancing options and ensuring informed consent. 2007

Counseling patients who are diagnosed with vestibular schwannomas, formerly known as acoustic neuromas, can be challenging. The health care provider has the responsibility to explain, in understandable language, to the patient or legal representative the proposed treatment options, risks and complications associated with each form of treatment, and alternatives to treatment, including no therapy. Patients should be encouraged to gather information before making a treatment decision. For the physicians managing these patients, information should be delivered in a balanced way to ensure patient understanding of their options leading to adequate informed consent.

Guiding patients through the choices for treating vestibular schwannomas: balancing options and ensuring informed consent

Counseling patients who are diagnosed with vestibular schwannomas, formerly known as acoustic neuromas, can be challenging. The health care provider has the responsibility to explain, in understandable language, to the patient or legal representative the proposed treatment options, risks and complications associated with each form of treatment, and alternatives to treatment, including no therapy. Patients should be encouraged to gather information before making a treatment decision. For the physicians managing these patients, information should be delivered in a balanced way to ensure patient understanding of their options leading to adequate informed consent.

An Anatomic and Radiologic Evaluation of Access to the Lateral Internal Auditory Canal Via the Retrosigmoid Approach and Description of an Internal Labyrinthectomy

OBJECTIVE

The retrosigmoid approach to the posterior petrous bone may be used as a hearing preservation operation for extirpation of posterior fossa and internal auditory canal (IAC) lesions. However, it is usually not possible to remove tumor from the most lateral portions of the IAC even after removing the retrolabyrinthine bone down to the posterior semicircular canal. Our goal was to examine the advantages and disadvantages of the retrosigmoid approach with respect to approaching the lateral IAC, to find what is gained by drilling down the retrolabyrinthine bone, and to describe an internal labyrinthectomy whereby the labyrinth is removed via a retrosigmoid approach.

MATERIALS AND METHODS

Using a 3.5-cm craniotomy, a retrosigmoid approach was performed on one side in each of five whole fresh cadaveric heads. The IAC was identified, and the length of the IAC and the depth of the acoustic porus from the center of the craniotomy were measured. The bone posterior to the labyrinth was removed, and the length of the portion of the IAC still inaccessible was measured. These measurements were compared with measurements using computed tomography (CT) scans of each cadaveric head. Additionally, we present the findings of 11 patients who had an internal labyrinthectomy performed by the senior author.

RESULTS

The average length of the IAC based on CT scanning was 11.2 mm (SD, 0.84 mm; range, 10-12 mm, 95% confidence interval [CI], 9.44-12.96). The potential gain predicted by the CT scans was 8.4 mm (SD, 0.9 mm; range, 7-9 mm). In the anatomic study, the average length of the IAC was 11.0 mm (SD, 2.3 mm; range, 8.0-13.0 mm; 95% CI, 9.26-12.78). The average length of the IAC that was inaccessible after removing the retrolabyrinthine bone was 6.7 mm (SD, 1.5 mm; range, 5.0-7.8 mm), or 61%. The average gain in access to the lateral IAC was 4.3 mm (SD, 1.0 mm; range, 2.7-5.2 mm). After performing an internal labyrinthectomy, the fundus was accessible, as was the labyrinthine segment of Cranial Nerve VII and the geniculate ganglion.

CONCLUSION

The retrosigmoid approach provides access to the posterior petrous bone, and removal of the bone posterior to the labyrinth provides some additional access to the lateral IAC. However, an internal labyrinthectomy is necessary to provide access to the fundus of the IAC via the retrosigmoid approach.

Stereotactic radiosurgery, microsurgery, and expectant management of acoustic neuroma: basis for informed consent

There is diversity in the techniques and instrumentation used to perform stereotactic radiosurgery. The field continues to evolve rapidly, and improvements are being made in accuracy, effective radiation dose, and parameters necessary to maximize patient outcome. Stereotactic radio-surgery, like any other treatment modality, has advantages and disadvantages that must be discussed with a patient who has an acoustic neuroma or other skull base tumor. An informed decision to pursue observation,microsurgery, stereotactic radiosurgery, or a combination of these methods must be made, and it remains the responsibility of the surgeon to provide a balanced view of the relative advantages and disadvantages of each method.

Resection of large vestibular schwannomas: facial nerve preservation in the context of surgical approach and patient-assessed outcome

Object. Vestibular schwannoma surgery has evolved as new therapeutic options have emerged, patients' expectations have risen, and the psychological effect of facial nerve paralysis has been studied. For large vestibular schwannomas for which extirpation is the primary therapy, the goals remain complete tumor resection and maintenance of normal neurological function. Improved microsurgical techniques and intraoperative facial nerve monitoring have decreased the complication rate and increased the likelihood of normal to near-normal postoperative facial function. Nevertheless, the impairment most frequently reported by patients as an adverse effect of surgery continues to be facial nerve paralysis. In addition, patient assessment has provided a different, less optimistic view of outcome. The authors evaluated the extent of facial function, timing of facial nerve recovery, patients' perceptions of this recovery and function, and the prognostic value of intraoperative facial nerve monitoring following resection of large vestibular schwannomas; they then analyzed these results with respect to different surgical approaches.

Methods. The authors retrospectively reviewed a database of 67 patients with 71 vestibular schwannomas measuring 3 cm or larger in diameter. The patients had undergone surgery via translabyrinthine, retrosigmoid, or combined approaches. Clinical outcomes were analyzed with respect to intraoperative facial nerve activity, responses to intraoperative stimulation, and time course of recovery.

Eighty percent of patients obtained normal to near-normal facial function (House—Brackmann Grades I and II). Patients' perceptions of facial nerve function and recovery correlated well with the clinical observations.

Conclusions. Trends in the data lead the authors to suggest that a retrosigmoid exposure, alone or in combination with a translabyrinthine approach, offers the best chance of facial nerve preservation in patients with large vestibular schwannomas.

Preservation of hearing in patients undergoing microsurgery for vestibular schwannoma: degree of meatal filling

Object. Preservation of hearing has become a standard goal in selected patients undergoing surgery for a vestibular schwannoma (VS). This study was aimed at analyzing the role played by filling of the internal auditory canal (IAC) as well as those played by preoperative hearing quality, and tumor size in the postoperative preservation of serviceable hearing (SH).

Methods. Three hundred eighty-six patients with VS were treated. Hearing preservation was attempted in 128 cases (33.2%) by using intraoperative monitoring and following a retrosigmoid approach. The maximal extrameatal size of the tumor, its extension within the IAC, and pre- and postoperative hearing quality, according to the Gardner—Robertson classification, were evaluated. Preservation of SH was achieved in 24.2% of the 128 patients. With respect to tumor size, SH was preserved in 39% of 77 patients harboring a tumor 15 mm wide or smaller and in 2% of 51 patients with lesions 16 mm wide or larger (p < 0.001). With regard to filling of the IAC, among 63 patients harboring a tumor 15 mm or smaller, in whom magnetic resonance images were available, SH was preserved in 52.8% of 36 patients with partial filling and in 25.9% of 27 patients with complete filling (p = 0.032). Concerning preoperative hearing quality, in the patients with tumors 15 mm or smaller, SH was preserved in 46.5% of 43 patients with Gardner—Robertson Class I hearing and 29.4% of 34 patients with Class II hearing (p = 0.126). Both tumor size and the extent of IAC filling proved statistically significant in a multivariable analysis (p < 0.001 and p = 0.026, respectively).

Conclusions. Incomplete filling of the IAC and a tumor size of 15 mm or smaller are independent favorable factors in SH preservation. Excellent preoperative hearing appears to have a positive impact but does not have statistical significance. Intraoperative monitoring is useful in guiding the dissection; however, the surgeon's knowledge of topographical landmarks and meticulous surgical technique remain the essential factors of success.

B. Neto R, Bento RF, Ribas GC. Endoscopia do meato acústico interno pelo acesso retrolabiríntico

O acesso direto à região do ângulo pontocerebelar pela via retrolabiríntica é seguro, entretanto, não permite a visão direta de todo o meato acústico interno (MAI) pela otomicroscopia. Os endoscópios podem ser utilizados na exploração do MAI por esta via. OBJETIVO: Nosso objetivo é avaliar a capacidade de inspeção do MAI com endoscópios de diferentes angulações. FORMA DE ESTUDO: Estudo anatômico. MATERIAL E MÉTODO: Estudamos 40 ossos temporais humanos nos quais realizamos acessos retrolabirínticos. Nestes ossos, medimos as distâncias ocultas do MAI, em seus quatro quadrantes, utilizando o microscópio cirúrgico e os endoscópios de 0º, 30º e 70º. RESULTADOS: Observamos que as distâncias ocultas medidas foram diminuindo, com significância estatística, conforme o instrumento utilizado, nesta seqüência: microscópio, endoscópio de 0º, 30º e 70º. Somente o endoscópio de 70º permitiu a visão do fundo do MAI em todos os quadrantes, o que ocorreu em 27,5% dos casos. A visão parcial do fundo do MAI foi obtida em 67,5% dos ossos com o endoscópio de 70º e em 12,5% com o endoscópio de 30º, não tendo sido obtida em nenhum caso com o uso do endoscópio de 0º ou do microscópio. As médias de distâncias ocultas no quadrante ântero-superior, medidas com o microscópio e endoscópios de 0º, 30º e 70º foram respectivamente: 10,4mm, 7,3mm, 4,3mm e 1,1mm. CONCLUSÕES: O endoscópio de 70º demonstrou ser significativamente superior aos demais instrumentos na inspeção do MAI e sugerimos que ele seja considerado o instrumento de escolha na inspeção do MAI nos acessos retrolabirínticos.

Modified translabyrinthine approach and hearing preservation

OBJECTIVES/HYPOTHESIS

In 1991, the translabyrinthine approach was modified by sealing the vestibule with bone wax, which allowed preservation of the hearing function in one patient. The present study aimed specifically at evaluating the effectiveness of the modified translabyrinthine approach in preserving hearing function in a group of patients with vestibular schwannoma that involved the internal auditory canal.

STUDY DESIGN

Prospective study.

METHODS

The series consisted of 12 patients with vestibular schwannoma (average age, 49.7 y). The schwannoma was smaller than 2 cm in all patients who had surgery. The patients accepted for the study were required to have preserved hearing function.

RESULTS

None of the patients has shown signs of persistence or tumoral relapse on postoperative magnetic resonance imaging. Immediately after surgery, the entire group had excellent facial functionality. Six patients had maintained their hearing function (four in Class 1 and two in Class 2 according to the Gardner-Robertson scale) at the last follow-up after surgery. A patient during follow-up noted fluctuating hearing contemporarily with a tinnitus in the ear that had maintained its hearing, which was attributable to an endolymphatic hydrops. Three of the six patients with preserved hearing complained of persistent tinnitus. None of the patients had any of the complications or consequences of cerebellopontine surgery.

CONCLUSION

In our patients, Class 1 or 2 hearing was preserved in 50% of the patients, with no persistence or tumoral relapse. The follow-up has obviously been short, but the first results are encouraging and deserve to be studied further in a more comprehensive survey.

Middle fossa versus retrosigmoid-transmeatal approach in vestibular schwannoma surgery: a prospective study

OBJECTIVE

To compare the advantages, disadvantages, and results obtained with the middle fossa and retrosigmoid-transmeatal approaches during pure intracanalar vestibular schwannoma surgery in an attempt to preserve hearing.

STUDY DESIGN

Prospective study of patients treated from 1998 to 2001.

SETTING

Tertiary care referral center.

PATIENTS

Patients with intracanalar vestibular schwannoma (size ranging from 4 to 12 mm), 25 operated on with the retrosigmoid-transmeatal technique and 25 via the middle fossa route.

MAIN OUTCOME MEASURES

Facial nerve and auditory function were examined at 1 year with both techniques. Auditory results were also evaluated as a function of tumor size, distance from the internal auditory canal fundus, and internal auditory canal enlargement.

RESULTS

The results indicated no significant difference in facial nerve and auditory function results between the two techniques. The retrosigmoid-transmeatal approach, however, yielded better facial nerve function results at discharge. Postoperative hearing was better when the distance from the fundus was greater than 3 mm, when the size of the vestibular schwannoma was equal to or less than 7 mm, and when the internal auditory canal enlargement was less than 3 mm.

CONCLUSIONS

The middle fossa approach does not afford any particular advantages over the retrosigmoid-transmeatal approach in terms of auditory results. Facial nerve function is less satisfactory in the short term, when the middle fossa route is used, but can be improved by decompression and gentle displacement of the facial nerve in its labyrinthine portion.

Management of acoustic schwannoma

PURPOSE

To discuss the optimal management for patients with acoustic schwannoma.

MATERIALS AND METHODS

Review of the pertinent literature.

RESULTS

Microsurgery, stereotactic radiosurgery, and fractionated radiotherapy result in cure rates that approximate 90% at 5 years. Depending on tumor extent and surgical approach, the morbidity of microsurgery may exceed that of stereotactic radiosurgery and fractionated radiotherapy. Patients with useful hearing before treatment may have a higher likelihood of hearing preservation after radiotherapy compared with radiosurgery.

CONCLUSION

Both microsurgery and radiosurgery are good options for patients with tumors less than 3 cm. Depending on tumor extent and the surgical approach, the morbidity of microsurgery may exceed that of radiosurgery. Patients with useful hearing may have a higher likelihood of hearing preservation after radiotherapy. Microsurgery is preferred for patients in whom the disease progresses after initial irradiation and in patients with tumors larger than 3 cm.

Cranial nerve preservation after radiosurgery of vestibular schwannomas

Radiosurgery is a management approach used to treat patients with vestibular schwannomas. The goals are long-term tumour growth control, maintenance of cranial nerve function and prevention of new deficiencies. We sought to determine long-term outcomes measuring the potential benefits against the neurological risks of primary radiosurgery. Gamma Knife radiosurgery was applied as a treatment modality for 289 patients with vestibular schwannomas from April 1992 to April 2002. The long-term results of 100 patients who underwent radiosurgery were evaluated. 60 patients received a primary treatment, 40 other cases presented with previously performed subtotal microsurgical resection or recurrence of disease (12-96 months, median 39). The median treatment volume was 3.4 ccm and the median dose to the tumour margin was 13 Gy. The median patient follow-up time was 76 months (range 60-120 months). Four tumours progressed after primary radiosurgery. Tumour control rate was 96%. Useful hearing (Gardner-Robertson I/II) was preserved in 16 patients (55%). Clinical neurological improvement occurred in 50%. Adverse effects comprised neurological symptoms (incomplete facial palsy) (House-Brackman II/III) in six cases (four recovered completely), mild transient trigeminal neuropathy in five cases, and morphological changes displaying rapid enlargement of preexisting macrocysts in two patients and tumour growth in two other patients. Microsurgical resection was performed in four cases (4%) and two patients underwent a shunting procedure because of hydrocephalus formation (2%). In patients who had undergone previous microsurgery, no new cranial nerve deficit was observed. Radiosurgery is an effective method for growth control of vestibular schwannomas and is associated with both a low mortality rate and a good quality of life. Accordingly, for the preservation of cranial nerve function radiosurgery is a useful method for the management of properly selected patients and is comparable to microsurgery.

Risk-benefit analysis of using the middle fossa approach for acoustic neuromas with >10 mm cerebellopontine angle component

OBJECTIVES

To evaluate hearing preservation and facial nerve (FN) outcome in the middle fossa (MF) approach for acoustic neuromas with a cerebellopontine angle (CPA) component >10 mm.

STUDY DESIGN

Retrospective review of 193 patients.

PATIENT POPULATION

Patients were grouped according to tumor size: intracanalicular tumors (IC; 64), 1 to 9 mm CPA extension (42), and 10 to 18 mm CPA extension (47). Additionally, a group of 40 patients (tumor size 10-18 mm CPA extension) who had undergone a translabyrinthine (TL) approach was studied to assess comparative FN outcome. Hearing and FN function were measured 1 year postoperatively. We defined the success at functional hearing preservation as AAO-HNS class B or better and good FN outcome as House-Brackmann grade II or better.

RESULTS

For IC tumors and those with up to 9-mm CPA extension, there was no significant difference in the rate of functional hearing preservation (62.2% vs. 63.1%, P =.931) and good FN outcome (93.7% vs. 97.6%, P =.358). For tumors of 10- to 18-mm CPA extension, the rate of hearing preservation (34%) was lower than the other groups (P =.006 and P =.009). In this group, the rate of good FN outcome was lower compared with the IC and 1- to 9-mm tumors (80.8% vs. 93.7%, P =.037 and 97.6%, P =.012). The rate of good FN outcome following the TL approach in a comparable cohort of patients was 100% (P =.003 in comparison with 10-18 mm tumor resected with the MF approach).

CONCLUSIONS

When considering surgical options, patients with >10-mm tumors should be advised that choosing the MF approach for hearing preservation carries a somewhat higher risk of persistent FN dysfunction.

Distance from acoustic neuroma to fundus and a postoperative facial palsy

OBJECTIVE/HYPOTHESIS

Generally, patients with small acoustic neuroma have less facial palsy after its removal. The middle cranial fossa approach is mainly applied to the small acoustic neuroma and tumor size does not influence the prognosis of facial palsy. The internal auditory canal cannot be fully opened in the middle cranial fossa approach, and the facial nerve is tightly attached in the fundus. According to these anatomical factors, we hypothesized that acoustic neuromas located away from the fundus might be removed with less facial nerve damage. We investigated the distance between the acoustic neuroma and fundus and its clinical relationship.

STUDY DESIGN

Retrospective study of 45 patients with acoustic neuroma who underwent a middle cranial fossa approach.

METHODS

The distance between the acoustic neuroma and fundus and the tumor diameter were measured on T2-weighted and contrast-enhanced magnetic resonance images, respectively. These data were compared with the postoperative facial nerve function.

RESULTS

The mean distance was 3.0 +/- 1.8 mm (range, 0-10 mm), and the mean diameter was 11.3 +/- 3.7 mm (means +/- standard deviation; range, 4-20 mm). Neither the distance nor the diameter had any correlation to the degrees of postoperative facial palsy either immediately or at 3 months after surgery.

CONCLUSIONS

As far as the nerve was anatomically preserved, postoperative facial nerve function seemed to be influenced by factors other than surgical manipulation among small acoustic neuromas. Although the tumor fills in the fundus, it may not influence postoperative facial nerve function and also may not interfere with indication of the middle cranial fossa approach for removal of the acoustic neuroma.

Enlarged middle fossa vestibular schwannoma surgery: experience with 735 cases

OBJECTIVE

To show the clinical outcome in patients with sporadic vestibular schwannoma (VS) operated on by the enlarged middle cranial fossa approach (EMFA).

STUDY DESIGN

Retrospective case review.

SETTING

A tertiary referral center with four neurotologists experienced in EMFA surgery.

PATIENTS

There were 376 women and 359 men, with a mean age of 51.1 years (range, 12-77).

INTERVENTION

Enlarged middle cranial fossa approach surgery.

MAIN OUTCOME MEASURES

Magnetic resonance imaging and computed tomography scans were used for follow-up and re-evaluation of the operative sites. Facial nerve function and hearing were tested.

RESULTS

Overall complete VS removal was achieved in 97.1% of patients. There were two recurrences (0.3%) after microscopically complete tumor removal. Depending on the tumor size, postoperative normal and near-normal facial outcome ranged from 83% to 99% (average, 92%), and hearing at or near the preoperative level (+/-15 dB pure-tone average or +/-15% speech discrimination) was preserved in 60.2%, 48.2%, 23.9%, and 17.6%, respectively.

CONCLUSIONS

The EMFA is an excellent low-morbidity approach for VS removal with limited cerebellopontine angle extension (2 cm). Specific advantages of the EMFA are the superior internal auditory canal exposure, resulting in an extremely low tumor recurrence rate; best capability for hearing preservation; and minimal incidence of cerebrospinal fluid leaks. Postoperative facial function outcome compares with that of other surgical approaches. The best results are achieved in subjects with small tumors and good hearing, advocating early diagnosis and treatment.

Modified retrolabyrinthine approach with partial labyrinthectomy: anatomic study

This study was undertaken to evaluate the feasability of the modified retrolabyrinthine approach (traditional retrolabyrinthine approach plus resection of the posterior semicircular canal) to expose the entire fundus of the internal auditory canal (IAC). This approach is advocated by its proponents to manage acoustic neuromas reaching the lateral IAC and with the preservation of hearing as the goal. Little anatomic data directly estimate the limitations of this exposure. Measurements were recorded from 25 cadaver temporal bones dissected with this modified approach. The distances were taken between the porus acousticus (inferior and superior portions), the dome of the jugular bulb, the midportion of the sigmoid sinus, and the fundus of the IAC (inferior and superior portions). All of the measurements were then compared with those of the translabyrithine approach. The current study shows that despite the sacrifice of the posterior semicircular canal, the superior lateral fundus cannot be completely visualized. There is a distance (on average 1.1 mm) that differentiates the superior area of the IAC accessible with translabyrithine and modified retrosigmoid techniques. This value is smaller than that observed in the classic retrosigmoid approach indicating that the modified technique affords a more adequate, even if not ideal, exposure to minimize the risk of recurrence. The modified retrolabyrinthine approach provided an optimal exposure of the inferior half of the IAC. A superior blind area, smaller than that of the traditional retrolabyrinthine technique, cannot be completely approached via this route. We believe that this approach can be considered as an alternative technique in selected cases especially for tumors involving the inferior vestibular nerve.

Navigation-guided opening of the internal auditory canal via the retrosigmoid route for acoustic neuroma surgery: cadaveric, radiological, and preliminary clinical study

OBJECTIVE

We investigated the usefulness of a microscope-based navigational system (Multi Koordinaten Manipulator; Zeiss, Oberkochen, Germany) for removal of the posterior wall of the internal auditory canal (IAC) via the retrosigmoid route.

METHODS

A cadaveric study was performed to assess the navigational localization error for the retrosigmoid approach to the IAC. Computed tomographic findings for 47 acoustic neuroma cases were divided into three groups, on the basis of the relationship between the labyrinth and the sigmoid-fundus line (medial, on the line, or lateral). Furthermore, the shortest distances between the most medial labyrinthine extension and the resection line were measured. In 20 acoustic neuroma operations, the different features and the practicality of the microscope-based navigational system for opening of the IAC were evaluated.

RESULTS

The mean anatomic localization errors were 0.67 +/- 0.2 mm (95th percentile, 1.32 mm) for navigation to the IAC and 0.71 +/- 0.37 mm (95th percentile, 1.68 mm) for navigation to the posterior semicircular canal. The average distances between the most medial labyrinthine extension and the resection line were 3.65, 3.36, and 2.0 mm for the lateral, on-the-line, and medial groups, respectively. Direct contouring of structures at risk does not take into account the localization error, nor does it provide reliable navigational information. A novel indirect contouring concept that takes into account the localization error (the safety corridor method) was therefore introduced.

CONCLUSION

The value of navigational assistance for opening of the IAC is promising but still limited. Further development is required before the clinical effects of this navigational approach can be evaluated.

Evaluating the role of magnetic resonance imaging scans in the surgical management of acoustic neuromas

OBJECTIVE

To assess the reliability of magnetic resonance imaging (MRI) in predicting the size and position of an acoustic neuroma, with particular reference to the intracanalicular portion.

STUDY DESIGN

Prospective study comparing the position of the tumor in the internal auditory canal on fast spin-echo MRI with the actual position measured intraoperatively.

METHODS

The study was performed in a tertiary referral neurotology center, encompassing both the public and private health care systems. Fifteen consecutive patients admitted for acoustic neuroma removal via the translabyrinthine approach were studied. The main outcome measure was tumor position in the internal auditory canal expressed in millimeters, accurate to the nearest 0.5 mm.

RESULTS

The fast spin-echo MRI was accurate within an error of 1 mm in predicting the lateral extent of the tumor in the internal auditory canal.

CONCLUSION

Fast spin-echo MRI can accurately predict the lateral extent of an acoustic neuroma and allow accurate planning of the surgical approach.