Intra-operative monitoring in acoustic neuroma surgery.

Intra-operative neurophysiologic monitoring (IOM) is rapidly evolving as an important adjunct during acoustic neuroma surgery to reduce the incidence of neurologic deficits. Monitoring alerts the surgeon to ongoing changes in neural function. The benefit of facial nerve monitoring in reducing the incidence of facial palsy during acoustic tumor resection appears clear and is now recommended by the National Institutes of Health (Consensus Development Conference on Acoustic Neuroma, 1991). Auditory monitoring is not as effective as facial monitoring but hearing preservation can be enhanced particularly if used with facial monitoring because the latter alerts the surgeon to traumatic manipulations that may affect both facial and cochlear nerves. Monitoring is not a replacement for surgical experience. 'Poor monitoring is worse than no monitoring'.

Smoking and tympanoplasty: implications for prognosis and the Middle Ear Risk Index (MERI).

OBJECTIVES/HYPOTHESIS: The objectives of this study are to review the effects of smoking on preoperative middle ear disease severity, long-term surgical outcome, type and extent of surgery required, the need for ossicular chain reconstruction, and the long-term hearing results. STUDY DESIGN: A retrospective chart review. MATERIALS AND METHODS: The charts of 74 smokers and non-smokers who underwent over-under tympanoplasty were reviewed. An analysis of the disease severity (using the Middle Ear Risk Index [MERI]) at presentation and type of surgery was performed. A review of graft take and delayed failure (late perforation or atelectasis after 6 mo) and audiologic data were performed. RESULTS: Fifteen patients smoked a mean of 20 cigarettes daily for a mean of 15 years. The MERI was well matched for both groups. There was a trend toward smokers having a higher incidence of otorrhea preoperatively and requiring a more extensive surgical procedure. All patients had full take of the tympanic membrane graft at 6 months; however, delayed surgical failure was seen in 20% of non-smokers compared with 60% of smokers (P = .050). No statistically significant difference was seen in hearing outcome. CONCLUSIONS: Cigarette smoking is associated with more severe middle ear disease preoperatively. More extensive surgery is often needed in smokers to eradicate the disease. Most significantly, smoking is associated with a threefold increase in the chance of long-term graft failure. Based on the results of this study, the MERI has been revised to include smoking as a risk factor.

Posterior semicircular canal occlusion for benign paroxysmal positional vertigo--CO2 laser-assisted technique: preliminary results.

Benign paroxysmal positional vertigo (BPPV) is a common vestibular end-organ disorder that in the majority of patients resolves with conservative management. In the occasional patient who has unremitting BPPV despite conservative treatment, posterior semicircular canal occlusion (PCO) may be effective in eliminating symptoms. In an attempt to minimize the risk of hearing loss, a modified procedure was developed that uses the CO2 laser to shrink the membranous vestibular posterior semicircular canal prior to mechanically plugging the canal. Preliminary results of this CO2 laser-assisted occlusion technique used in four patients are presented.

Salivary gland choristoma of the middle ear: a case report and review of the literature.

Salivary gland choristomata are heterotopic rests which have rarely been reported in the middle ear. A case report of a salivary gland choristoma of the middle ear is presented and the literature reviewed. The frequent association of ossicular chain and facial nerve anomalies is emphasized.

Intraparotid facial nerve neurofibroma.

Neurogenic neoplasms of the intraparotid facial nerve are uncommon and are usually diagnosed intraoperatively by tissue biopsy. Fifty-six cases of primary neurogenic neoplasms involving the facial nerve have been reported. The majority of these have been schwannomas. A case of a solitary neurofibroma involving the main trunk of the facial nerve is presented. Schwannomas and neurofibromas have distinct histological features which must be considered prior to the management of these tumors. The management of neurogenic tumors associated with normal facial function is a particularly difficult problem. A new approach for the diagnosis and management of neurogenic neoplasms is described utilizing electroneurography.

Patterns of vestibular function following vestibular nerve section.

Bithermal caloric irrigations, low-frequency rotational chair stimulation, and posturography were performed on 20 patients before and after vestibular nerve section. Twelve patients demonstrated acute postoperative spontaneous nystagmus and rotational vestibulo-ocular reflex (VOR) asymmetry. Eight patients demonstrated minimal acute postoperative spontaneous nystagmus and VOR asymmetry. Four patients had suppression of all vestibular function characterized by an absent contralateral caloric response, low VOR gain, and falls on posturography when required to rely solely on vestibular input to maintain posture. Four patients had a severe preoperative vestibular loss and no acute change in vestibular function following surgery. Over time, 5 patients continued to manifest elevated spontaneous nystagmus, 2 patients manifested a persistent rotational VOR asymmetry, and 5 patients exhibited a return of caloric function in the operated ear. It is suggested that multiple clinical factors contributed to the variable vestibular responses demonstrated in this study.

Clinical assessment of postural stability following vestibular nerve section.

Little is known about the recovery of postural control in patients following acute vestibular loss. This paper reports on the results of moving-platform posturography to assess the recovery of postural stability in 24 patients following vestibular nerve section. Posturography was abnormal prior to surgery in 17% of the patients. Seven days following surgery, 44% of the patients demonstrated vestibular deficit patterns, while 56% of the patients had normal posturography. Posturography was normal in all patients 1 month following surgery. Abnormal posturography was subsequently noted in 21% of the patients between 3 and 20 months following surgery. Each of the patients with abnormal preoperative posturography subsequently demonstrated abnormal late postoperative posturography. These results suggest that perioperative posturography may be useful in the evaluation and counseling of patients considering ablative vestibular surgery.

Intraoperative facial nerve monitoring: a comparison of stimulating electrodes.

Preservation of the facial nerve during acoustic neuroma resection may be enhanced by the use of intraoperative electrical stimulation. Although stimulation of the extratemporal facial nerve is an effective and established procedure, anatomic differences of the intradural facial nerve and its microenvironment demand more exacting stimulus protocols. The absence of epineurium may make the intradural nerve more susceptible to mechanical or electrical trauma while intermittent pooling of cerebrospinal fluid (CSF) at the cerebellopontine angle may shunt current away from nerve. Four stimulus configurations were examined under varying conditions simulating CSF pooling. The results indicated that: 1. insulation of stimulating electrodes prevents CSF current shunting and allows utilization of a constant current source, and 2. monopolar and bipolar configurations demonstrate significantly different electrical characteristics which may be employed selectively based upon specific clinical goals.

The giant cholesterol cyst of the petrous apex: a distinct clinical entity.

The giant cholesterol cyst (GCC) of the petrous apex may now be considered a distinct clinical entity and should be considered in the differential diagnosis of lesions of the midcranial skull base. This benign cystic lesion of the petrous apex gradually enlarges and may produce progressive bone erosion and serial neurologic deficits of the cranial nerves within the temporal bone and jugular foramen. We report here five instances of this lesion (3 patients with unilateral and 1 patient with bilateral petrous apex lesions) and describe the natural history, diagnostic evaluation, pathology, and surgical management.

Promontory stimulation following labyrinthectomy: implications for cochlear implantation.

Transtympanic electric promontory stimulation is a psychoacoustic test used to assess residual acoustic neurons in profound sensorineural hearing loss. The test was performed in six patients who had previously undergone transmastoid (N = 5) or transcanal-oval window (N = 1) labyrinthectomy as a means of determining the feasibility of future cochlear implantation. Four patients had unilateral Meniere's disease, one had labyrinthitis, and one had delayed onset vertigo. All patients perceived a definite auditory sensation in the labyrinthectomized ear during stimulation. The results of threshold, dynamic range, and difference limen testing were similar to those obtained during preoperative stimulation of cochlear implant candidates (N = 12) who subsequently became successful users. There was no evidence of response degradations as the time following labyrinthectomy increased. The results of this study suggest the possibility of successful cochlear implantation following labyrinthectomy. Supporting histologic data are reviewed.

Anatomic basis for labyrinthine preservation during posterior fossa acoustic tumor surgery.

Earlier diagnosis of acoustic tumors promises to increase our opportunity to identify patients with serviceable hearing. Critical to a posterior fossa transmeatal approach for acoustic tumor resection is preservation of the underlying labyrinth. Although the labyrinth has been recognized as a limiting factor in exposure of tumor in the internal auditory canal, few reports have detailed the microscopic surgical anatomy posterior to the internal auditory canal. An anatomic study was undertaken to determine consistent relationships between critical structures within the temporal bone relevant to hearing preservation surgery. The results of this study indicate that, whereas topographic landmarks are helpful for orientation, the more consistent relationship of the labyrinth to the vestibular aqueduct and singular canal allows a more accurate localization of the underlying labyrinth. Although the vestibule frequently prevents direct visualization of the transverse crest, a dissection based upon the microsurgical anatomy will maximize visualization of the lateral fundus while preserving the integrity of the labyrinth.

Bioactive glass ceramic in ossicular reconstruction: a preliminary report.

Current techniques for ossicular reconstruction include ossicular autografts and homografts, and plastic and ceramic prostheses. Experimental testing of ceramic materials has led to the development of a nonporous, bioactive form of glass ceramic (Ceravital) for tympanoplastic reconstruction. To determine the clinical usefulness of these implants, Ceravital ossicular reconstructions were evaluated in 37 patients treated at the University of Michigan Medical Center during an 18-month period. Thirty-two patients (86%) with chronic ear disease underwent Ceravital ossicular reconstruction with tympanoplasty with or without mastoidectomy. Five other patients (14%) underwent ossicular reconstruction--2 for congenital anomalies, 2 for temporal bone trauma, and 1 patient for glomus tympanicum removal. Patient follow-up ranged from 2.2 to 3.8 years, with a mean follow-up period of 2.9 years. Prosthesis extrusion occurred in one case (3%). Mean preoperative and postoperative (2-year) pure tone air-bone gaps were 41.6 dB and 21.3 dB, respectively. Hearing was improved in 35 of 37 patients (95%). Postoperative pure tone air-bone gap was closed to 20 dB or less in 23 patients (62%). Hearing gains were greater with partial rather than total reconstructions (p = 0.14) and significantly greater with intact canal wall rather than canal wall down tympanoplasties (p less than 0.05). Initial results obtained with the Ceravital ossicular prosthesis compare favorably with those obtained using other methods of alloplastic reconstruction. These preliminary data suggest that Ceravital is an effective alternative prosthetic material for ossicular reconstruction.

Use of bacitracin for neurotologic surgery.

Wound infection, cerebrospinal fluid leak, and meningitis are serious potential complications of neurotologic procedures that transgress the posterior cranial fossa dura. A study of 236 patients was made to determine the effect of perioperative intravenous antibiotics and topical bacitracin irrigation on the incidence of these complications. Of the 236 patients, 170 (72%) underwent translabyrinthine resection of acoustic tumors, while 66 (28%) underwent retrolabyrinthine vestibular nerve section. Patients were divided into four groups: those who received no antibiotics, those who received perioperative intravenous antibiotics only, those who received topical bacitracin irrigation only, and those who received a combination of perioperative intravenous antibiotics and topical bacitracin irrigation. There were no untoward effects of either perioperative intravenous antibiotics or topical bacitracin. The results indicate that bacitracin irrigation reduced the incidence of wound infection from 9% to 2% (p less than 0.05); of cerebrospinal fluid leak from 12% to 5% (p less than 0.04); and of all targeted complications combined from 22% to 9% (p less than 0.006). Furthermore, the topical bacitracin irrigation only group showed a statistically significant reduction in wound infections compared to the perioperative intravenous antibiotic only group (p less than 0.02). The incidence of meningitis was statistically unaffected by any of our treatment protocols.

Electromagnetic semi-implantable hearing device: phase I. Clinical trials.

Conventional hearing aids have improved significantly in recent years; however, amplification of sound within the external auditory canal creates a number of intrinsic problems, including acoustic feedback and the need for a tight ear mold to increase usable gain. Nonacoustic alternatives which could obviate these encumbrances have not become practical due to inefficient coupling (piezoelectric techniques) or unfeasible power requirements (electromagnetic techniques). Recent technical advances, however, prompted a major clinical investigation of a new electromagnetic, semi-implantable hearing device. This study presents the details of clinical phase I, in which an electromagnetic driver was coupled with a target magnet temporarily affixed onto the lateral surface of the malleus of six hearing aid users with sensorineural losses. The results indicate that the electromagnetic hearing device provides sufficient gain and output characteristics to benefit individuals with sensorineural hearing loss. Significant improvements compared to conventional hearing aids were noted in pure-tone testing and, to a lesser degree, in speech discrimination. Subjective responses were quite favorable, indicating that the electromagnetic hearing device 1. produces no acoustic feedback; 2. works well in noisy environments; and 3. provides a more quiet, natural sound than patients' conventional hearing aids. These favorable results led to phase II of the project, in which patients with surgically amendable mixed hearing losses were implanted with the target magnet incorporated within a hydroxyapatite ossicular prosthesis. The results of this second-stage investigation were also encouraging and will be reported separately.

Spontaneous encephalocele of the temporal bone.

Postsurgical and posttraumatic encephaloceles of the tegmen tympani and tegmen mastoideum are well-recognized occurrences. Less frequently recognized, however, is the spontaneous occurrence of an encephalocele associated with cerebrospinal fluid otorrhea or rhinorrhea. This cerebral herniation into the middle ear and the mastoid cavity in adults is associated with a loss of both bony and dural support, and surgical management must deal with both the cerebrospinal fluid leak and herniation of the brain.

Electroneurography and intraoperative facial monitoring in contemporary neurotology.

Electrodiagnostic testing of the facial nerve has evolved beyond prognostic and topognostic testing to include preoperative assessment and intraoperative monitoring. The state of the art in facial nerve testing is herein reviewed. Electroneurography is described as a means of preoperative assessment to detect subclinical neural degeneration for temporal bone tumors, malignant external otitis, and recurring facial paralysis. Techniques of intraoperative facial nerve monitoring are presented with clinical correlation of the facial evoked responses. Finally, recent advances in electrodiagnostic testing, including antidromic recording and transtemporal magnetic stimulation of the facial nerve, are discussed.

Implications of sound levels generated by otologic devices.

OBJECTIVE: Exposure to loud noise can result in sensorineural hearing loss. In otology, a wide variety of devices are used that have significant noise output, both to the operator and the patient. This study quantifies and compares the sound pressure levels (SPL) of a variety of otologic instruments. METHODS: Using a calibrated sound pressure level meter, the peak and impulse sound pressure levels of several otologic instruments were determined at 1 cm from their application to human temporal bones. Devices measured were an air-powered drill with a cutting burr, an electric micro-drill, and KTP, CO(2), and erbium lasers. RESULTS: Impulse sound pressure levels for the KTP laser, CO(2) laser, microdrill, air-powered drill and erbium laser were 67, 71, 90, 105, and 105 dBA, respectively. Peak sound pressure levels were 81, 89, 102, 118, and 132 dBA, respectively. CONCLUSIONS: Use of the KTP laser, CO(2) laser, and microdrill result in impulse levels of less than 100 dBA. Although the impulse levels of the erbium laser and the air-powered drill were equivalent, the peak sound pressure levels of the erbium laser were significantly higher. These high sound pressure levels may increase the chance for hearing loss. Like any tool, lasers and drills have benefits and risks. The results of this study demonstrate significant differences in SPLs of common otologic lasers and drills. Although noise-induced hearing loss is a function of both SPL and duration of exposure, surgeons should consider these differences when selecting and applying these tools, especially when used on or adjacent to the ossicular chain and stapes footplate.

Total facial nerve decompression for recurrent facial paralysis: an update.

Recurrent facial paralysis (RFP) is a rare disorder that in some individuals may lead to worsening sequelae. Melkersson-Rosenthal syndrome is a variant of RFP that is associated with recurrent facial edema. In the past, decompression of the mastoid segment of the facial nerve has not been successful in preventing recurrences. In 1981 we began performing total facial nerve decompression for RFP and in 1986 reported its efficacy in one patient with Melkersson-Rosenthal syndrome and in another in whom both nerves were decompressed for alternating bilateral paralysis. An additional four cases with 3 to 8 years of followup demonstrate no recurrences in any patient. Total facial nerve decompression for RFP in selected patients appears efficacious in preventing recurrences. Decompression will remain investigational until further followup is obtained. Furthermore, its salutary effect should not be extrapolated to Bell's palsy without further study.

Facial electroneurography: clinical and experimental investigations.

Facial electroneurography (ENoG) appears to be a reliable prognostic test for intratemporal facial nerve paralysis. ENoG is objective and allows a permanent record to be maintained. Nonetheless, occasional inconsistencies in clinical correlation may diminish the utility of ENoG. A qualitative study was undertaken to identify the possible reasons for the inaccuracy of ENoG in some patients. Four clinical groups and one experimental group were studied: (1) normal subjects, (2) patients with acute facial palsy, (3) patients with progressive facial palsy, (4) patients with temporal bone tumors and normal facial function, and (5) animals in which one facial nerve was crushed and repaired. The reliability of ENoG is dependent on careful interpretation of data obtained by optimal electrode placement and stimulus duration.

The role of KTP laser in revision stapedectomy.

In recent years, the safety and efficacy of revision stapedectomy has come under scrutiny. Experienced surgeons report that the results of such surgery are often worse than the results after primary surgery and that the risks of sensorineural hearing loss, tinnitus, and vertigo are increased. With the addition of laser technology to revision stapes surgery, the procedure to open the neomembrane over the oval window and gain access to the inner ear can now be performed safely. This allows positive identification of the oval window and assures placement of the prosthesis through the fenestra rather than on an intermediate segment of scar or bone in the region of the footplate. Our studies have shown the laser to be an important tool that enhances the safety and efficacy of revision stapedectomy.