William E. Hitselberger

Auditory Brainstem Implant: I. Issues in Surgical Implantation:

Most patients with neurofibromatosis type 2 (NF2) are totally deaf after removal of their bilateral acoustic neuromas. Twenty-five patients with neurofibromatosis type 2 have been implanted with a brainstem electrode during surgery to remove an acoustic neuroma. The electrode is positioned in the lateral recess of the fourth ventricle, adjacent to the cochlear nuclei. The present electrode consists of three platinum plates mounted on a Dacron mesh backing, a design that has been demonstrated to be biocompatible and positionally stable in an animal model. Correct electrode placement depends on accurate identification of anatomic landmarks from the translabyrinthine surgical approach and also on Intrasurglcal electrophysiologic monitoring. Some tumors and their removal can result in significant distortion of the brainstem and surrounding structures. Even in the absence of Identifiable anatomic landmarks, electrode location can be adjusted during surgical placement to find the location that maximizes the auditory evoked response and minimizes activation of other monitored cranial nerves. Stimulation of the electrodes produces auditory sensations in most patients, with results similar to those of single-channel cochlear Implants. A coordinated multldlscipllnary team is essential for successful application of an auditory brainstem implant.

Middle fossa acoustic tumor surgery: results in 106 cases.

Although the middle cranial fossa approach has been used less frequently in recent years than in the past, it continues to be a useful technique for the removal of small acoustic tumors with possible hearing preservation. The approach provides complete exposure of the contents of the internal auditory canal, thus allowing positive facial nerve identification and facilitating total tumor removal.

Auditory brainstem implants

SummaryThe development of cochlear implantation has allowed the majority of patients deafened after the development of language to regain significant auditory benefit. In a subset of patients, however, loss of hearing results from destruction of the cochlear nerves, rendering cochlear implantation ineffective. The most common cause of bilateral destruction of the cochlear nerves is neurofibromatosis type 2 (NF2). The hallmark of this genetic disorder is the development of bilateral acoustic neuromas, the growth or removal of which causes deafness in most patients. Patients with NF2 may benefit from direct stimulation of the cochlear nucleus. We describe the development, use, and results of the auditory brainstem implant (ABI), which is typically implanted via craniotomy at the time of tumor removal. Most patients with the implant have good appreciation of environmental sounds, but obtain more modest benefit with regard to speech perception. The majority of patients make use of the implant to facilitate lip reading; some can, to varying degrees, comprehend speech directly. We discuss future directions in central implants for hearing, including the penetrating ABI, the use of ABI in nontumor patients, and the auditory midbrain implant.

Cochlear nucleus implants.

The case of a 51-year-old woman with an acoustic neuroma in her only hearing ear is presented. At the time the tumor was removed, May 24, 1979, a depth electrode was implanted In the cochlear nucleus. This worked for 2 months, allowing her to perceive sound in her environment. On March 12, 1981, the depth electrode was replaced with a surface electrode. Since that time her hearing has been as good as that of a patient with a cochlear implant. It has now been over 2 years since her last surgery and she continues to do well.

Surgical Salvage after Failed Irradiation for Vestibular Schwannoma

Objectives/Hypothesis: Compare vestibular schwannoma (VS) surgical outcome between patients with prior irradiation and those not previously treated.

Surgery of the Skull Base: Transcochlear Approach to the Petrous Apex and Clivus

The Transcochlear approach is described for resection of lesions arising anterior or medial to the internal auditory canal as well as for those arising directly from the clivus. Through an extended complete mastoidectomy the facial nerve is totally decompressed and rerouted posteriorly from the stylomastoid foramen to the internal auditory canal. The fallopian canal, promontorium, and cochlea are removed anteriorly and medially as far as the internal carotid artery, obtaining exposure to a triangular area limited by the superior petrosal sinus, inferior petrosal sinus, carotid, and internal auditory canal, giving adequate exposure to the structures of the clivus and the midline (basilar artery, vertebral arteries, and the sixth cranial nerves).

Long-term hearing preservation after middle fossa removal of vestibular schwannoma.

OBJECTIVE: We sought to determine long-term hearing preservation in vestibular schwannoma patients after undergoing middle fossa resection. STUDY DESIGN, SETTING, AND OUTCOME MEASURES: We conducted a retrospective chart review of patients undergoing middle fossa resection from 1990 to 1995 at a tertiary care center. Pure-tone thresholds, before resection and at least 5 years after resection, and speech discrimination scores are reported. RESULTS: Seventy percent of patients with immediate postoperative hearing maintained serviceable hearing at more than 5 years after surgery. Pure-tone average in the operative ear changed at the same rate as hearing in the unoperated ear during this follow-up period. CONCLUSIONS: More than two thirds of patients who underwent middle fossa resection of a vestibular schwannoma with some hearing postoperatively maintain that hearing at greater than 5 years of follow-up. Surgery alone does not have a negative impact on long-term hearing preservation. (Otolaryngol Head Neck Surg 2003;129:660-5.)

Translabyrinthine removal of large acoustic neuromas.

Several surgical approaches to the cerebellopontine angle and internal auditory canal have been developed for the removal of acoustic neuromas. The choice of an approach may be influenced by hearing levels and tumor size. We reviewed the records of the primary translabyrinthine removal of 167 large (> or = 4 cm) acoustic neuromas performed between 1982 and 1990. Patients ranged in age from 15 to 83 years, with a mean of 43 years (male, 49%; female, 51%). Total removal was achieved in 95%. The facial nerve was preserved anatomically intact in 91%. At follow-up (mean, 2.1 yr), facial nerve function was acceptable (Grades I-IV) in 75% and good (Grades I-II) in 42%. Vascular complications occurred in 4.8%; however, there were no deaths. A cerebrospinal fluid leak occurred in 9.6% of cases, and meningitis occurred in 8.3%. In patients with large tumors where there is little chance to preserve preoperative hearing, we have successfully used the translabyrinthine approach for total tumor removal. The advantages and disadvantages of both the translabyrinthine and suboccipital approaches are discussed.

Audiologic outcomes with the penetrating electrode auditory brainstem implant.

Objective: The penetrating electrode auditory brainstem implant (PABI) is an extension of auditory brainstem implant (ABI) technology originally developed for individuals deafened by neurofibromatosis type 2. Whereas the conventional ABI uses surface electrodes on the cochlear nuclei, the PABI uses 8 or 10 penetrating microelectrodes in conjunction with a separate array of 10 or 12 surface electrodes. The goals of the PABI were to use microstimulation to reduce threshold current levels, increase the range of pitch percepts, and improve electrode selectivity and speech recognition. Patients and Protocol: In a prospective clinical trial, 10 individuals, all with neurofibromatosis type 2, received a PABI after vestibular schwannoma removal via a translabyrinthine approach. All study participants met strict requirements for informed consent as part of a Food and Drug Administration clinical trial. Approximately 8 weeks after implantation, PABI devices were activated and tested at our tertiary clinical and research facility. Mean follow-up time was 33.8 months. Study Design: Using a single-subject design, we measured thresholds and dynamic ranges, electrode-specific pitch percepts, and speech perception performance at regular intervals. Results: Penetrating electrodes produced auditory thresholds at substantially lower charge levels than surface electrodes, a wide range of electrode-specific pitch sensations, and minimal cross-electrode interference and could be used in speech maps either alone or in combination with surface electrodes. However, less than 25% of penetrating electrodes resulted in auditory sensations, whereas more than 60% of surface electrodes were effective. Even after more than 3 years of experience, patients using penetrating electrodes did not achieve improved speech recognition compared with those using surface electrode ABIs. In patients with usable penetrating electrodes, City University of New York Sentence Test scores with sound and visual information were 61.6% in the PABI group and 64.7% in a surface ABI cohort (p = not significant). Conclusion: The PABI met the goals of lower threshold, increased pitch range, and high selectivity, but these properties did not result in improved speech recognition.

Early proactive management of vestibular schwannomas in neurofibromatosis type 2.

OBJECTIVEThe treatment of patients with neurofibromatosis Type 2 has always been challenging for neurosurgeons and neurotologists. Guidelines for appropriate management of this devastating disease are controversial. METHODSA retrospective study of 28 patients with neurofibromatosis Type 2 who underwent 40 middle fossa craniotomies for excision of their acoustic tumors is reported. Eleven patients underwent bilateral procedures. The study focused on hearing preservation and facial nerve results for this group of patients. The 16 male patients and 12 female patients ranged in age (at the time of surgery) from 10 to 70 years, with a mean age of 22.6 years. The mean tumor size was 1.1 cm (range, 0.5–3.2 cm), and the majority of tumors were less than 1.5 cm. RESULTSMeasurable hearing was preserved in 28 ears (70%), with 42.5% being within 15 dB pure-tone average and 15% speech discrimination score of preoperative levels. In 55% of cases there was no change in the hearing class, as defined by the American Academy of Otolaryngology-Head and Neck Surgery. Of the 11 patients who underwent bilateral operations, 9 (82%) retained some hearing bilaterally. After 1-year follow-up periods (mean, 12.8 mo), 87.5% of patients exhibited normal facial nerve function (House-Brackmann Grade I). CONCLUSIONEarly surgical intervention to treat acoustic tumors among patients with neurofibromatosis Type 2 is a feasible treatment strategy, with high rates of hearing and facial nerve function preservation.