Best Practices in Facial Nerve Monitoring.

OBJECTIVES/HYPOTHESIS: Facial nerve monitoring (FNM) has evolved into a widely used adjunct for many surgical procedures along the course of the facial nerve. Even though majority opinion holds that FNM reduces the incidence of iatrogenic nerve injury, there are few if any studies yielding high-level evidence and no practice guidelines on which clinicians can rely. Instead, a review of the literature and medicolegal cases reveals significant variations in methodology, training, and clinical indications. STUDY DESIGN: Literature review and expert opinion. METHODS: Given the lack of standard references to serve as a resource for FNM, we assembled a multidisciplinary group of experts representing more than a century of combined monitoring experience to synthesize the literature and provide a rational basis to improve the quality of patient care during FNM. RESULTS: Over the years, two models of monitoring have become well-established: 1) monitoring by the surgeon using a stand-alone device that provides auditory feedback of facial electromyography directly to the surgeon, and 2) a team, typically consisting of surgeon, technologist, and interpreting neurophysiologist. Regardless of the setting and the number of people involved, the reliability of monitoring depends on the integration of proper technical performance, accurate interpretation of responses, and their timely application to the surgical procedure. We describe critical steps in the technical set-up and provide a basis for context-appropriate interpretation and troubleshooting of recorded signals. CONCLUSIONS: We trust this initial attempt to describe best practices will serve as a basis for improving the quality of patient care while reducing inappropriate variations. LEVEL OF EVIDENCE: 4 Laryngoscope, 131:S1-S42, 2021.

Laryngeal nerve monitoring.

Intraoperative neurophysiological monitoring of the vagus and recurrent laryngeal nerves is increasingly used during thyroidectomy, parathyroidectomy, skull base surgery, and cervical discectomy with fusion. Monitoring can assist in nerve localization and in reducing the incidence of neural trauma. To be effective, however, monitoring must be correctly implemented and the results interpreted based on an in-depth understanding of technique and the surgical structures at risk. Because "poor monitoring is worse than no monitoring" all members of the surgical monitoring team must have training specific to laryngeal recording to maximize its benefit and minimize pitfalls. This publication will review pertinent anatomy and neurophysiology as well as technical and interpretative factors.

Round window reinforcement for superior semicircular canal dehiscence: a retrospective multi-center case series.

PURPOSE: To evaluate the outcome of round window (RW) tissue reinforcement in the management of superior semicircular canal dehiscence (SSCD). MATERIALS AND METHODS: Twenty-two patients with confirmed diagnosis of SSCD by clinical presentation, imaging, and/or testing were included in the study. Six surgeons at four institutions conducted a multicenter chart review of patients treated for symptomatic superior canal dehiscence using RW tissue reinforcement or complete RW occlusion. A transcanal approach was used to reinforce the RW with various types of tissue. Patients completed a novel postoperative survey, grading preoperative and postoperative symptom severity. RESULTS: Analysis revealed statistically significant improvement in all symptoms with the exception of hearing loss in 19 patients who underwent RW reinforcement. In contrast, 2 of 3 participants who underwent the alternate treatment of RW niche occlusion experienced worsened symptoms requiring revision surgery. CONCLUSION: RW tissue reinforcement may reduce the symptoms associated with SSCD. The reinforcement technique may benefit SSCD patients by reducing the "third window" effect created by a dehiscent semicircular canal. Given its low risks compared to middle cranial fossa or transmastoid canal occlusion, RW reinforcement may prove to be a suitable initial procedure for intractable SSCD. In contrast, complete RW occlusion is not advised.

Improved facial nerve outcomes using an evolving treatment method for large acoustic neuromas.

OBJECTIVE: To describe a successful paradigm for the treatment of large acoustic neuromas (vestibular schwannomas). STUDY DESIGN: Retrospective case review. SETTING: Tertiary referral center. PATIENTS: The charts of 2,875 acoustic neuroma patients at Michigan Ear Institute were reviewed to identify 153 patients who underwent surgical resection for large acoustic neuromas (>=3 cm) between 2000 and 2009. INTERVENTION(S): Staged surgical resection or single stage surgery with or without adjuvant stereotactic radiosurgery. MAIN OUTCOME MEASURE(S): Postoperative facial nerve outcomes are reported using the House-Brackmann (HB) facial nerve grading scale and compared with historical controls from a literature review. Rates of adverse outcomes are also reported. RESULTS: Seventy-five patients underwent staged surgical resection of their tumors, whereas 78 patients underwent either single stage surgery or surgery with subsequent stereotactic radiosurgery. Eighty-one percent of patients in the staged surgical resection group had a postoperative HB Grade I or II facial nerve function compared with 75% in the single stage surgical group. Overall, 78% of patients in the current study had HB Grade I or II after treatment compared with a mean of 53% in the literature for similar sized tumors. Our methods including the decision to use staged surgery when necessary, dissection of tumor with stimulating dissector-directed intraoperative monitoring, and use of adjuvant stereotactic radiosurgery are described. CONCLUSION: Using the described paradigm, large acoustic neuromas can be successfully treated with either staged or single-stage surgical resection with or without adjuvant radiosurgery to obtain more favorable facial nerve outcomes than historically reported controls while minimizing morbidity for the patient.

Hearing preservation in patients with vestibular schwannoma treated with Gamma Knife surgery.

OBJECT: Hearing loss after Gamma Knife surgery (GKS) in patients with vestibular schwannoma has been associated with radiation dose to the cochlea. The purpose of this study was to evaluate serviceable hearing preservation in patients with VS who were treated with GKS and to determine if serviceable hearing loss can be correlated with the dose to the cochlea. METHODS: Forty patients with vestibular schwannoma with serviceable hearing were treated using GKS with a median marginal dose of 12.5 Gy (range 12.5-13 Gy) to the 50% isodose volume. Audiometry was performed prospectively before and after GKS at 1, 3, and 6 months, and then every 6 months thereafter. Hearing preservation was based on pure tone average (PTA) and speech discrimination (SD). Serviceable hearing was defined as PTA less than 50 dB and SD greater than 50%. RESULTS: The median cochlear maximum and mean doses were 6.9 Gy (range 1.6-16 Gy) and 2.7 Gy (range 0.7-5.0 Gy), respectively. With a median audiological follow-up of 35 months (range 6-58 months), the 1-, 2-, and 3-year actuarial rates of maintaining serviceable hearing were 93%, 77%, and 74%, respectively. No patient who received a mean cochlear dose less than 2 Gy experienced serviceable hearing loss (p = 0.035). Patients who received a mean cochlear dose less than 3 Gy had a 2-year hearing preservation rate of 91% compared with 59% in those who received a mean cochlear dose of 3 Gy or greater (p = 0.029). Those who had more than 25% of their cochlea receiving 3 Gy or greater had a higher rate of hearing loss (p = 0.030). There was no statistically significant correlation between serviceable hearing loss and age, tumor size, pre-GKS PTA, pre-GKS SD, pre-GKS Gardner-Robertson class, maximum cochlear dose, or the percentage of cochlear volume receiving 5 Gy. On multivariate analysis there was a trend toward significance for serviceable hearing loss with a mean cochlear dose of 3 Gy or greater (p = 0.074). Local control was 100% at 24 months. No patient developed facial or trigeminal nerve dysfunction. CONCLUSIONS: With a median mean cochlear dose of 2.7 Gy, the majority of patients with serviceable hearing retained serviceable hearing 3 years after GKS. A mean cochlear dose less than 3 Gy was associated with higher serviceable hearing preservation.

Pitfalls in intraoperative nerve monitoring during vestibular schwannoma surgery.

Despite the widespread acceptance of intraoperative neurophysiological monitoring in skull base surgery over the last 2 decades, surgeon training in the technical and interpretive aspects of nerve monitoring has been conspicuously lacking. Inadequate fundamental knowledge of neurophysiological monitoring may lead to misinterpretations and an inability to troubleshoot system errors. Some surgeons perform both the technical and interpretive aspects of monitoring themselves while others enjoin coworkers (surgical residents, nurses, anesthetists, or a separate monitoring service) to perform the technical portion. Regardless, the surgeon must have a thorough understanding to avoid potential medical and legal pitfalls because poor monitoring is worse than no monitoring. A structured curriculum and protocol in both the technical and interpretive aspects of monitoring is recommended for all personnel involved in the monitoring process. This paper details the technical, interpretive, and surgical correlates necessary for optimal intraoperative nerve monitoring during vestibular schwannoma surgery with an emphasis on electromyographic monitoring for facial and recurrent laryngeal nerves. Just as the American Society of Anesthesiologists' 1986 "Standards for Basic Anesthetic Monitoring" became a useful tool for both patients and anesthesiologists, impending guidelines in intraoperative neurophysiological monitoring should likewise become an important instrument for optimizing intraoperative neurophysiological monitoring.

Acoustic neuroma neurophysiologic correlates: facial and recurrent laryngeal nerves before, during, and after surgery.

This article focuses on the facial nerve with additional comments on the recurrent laryngeal nerve as a proxy for the lower cranial nerves. Methods, advantages and disadvantages, and techniques are listed. The article addresses the anatomy of the facial nerve, discusses neurophysiologic testing, the role of electroneurography in preoperative, intraoperative, and postoperative testing, and presents 7 steps to set up for and perform facial nerve monitoring. Details are provided on interpretation of testing, and the pitfalls of interpretation are discussed. Studies are reviewed presenting outcomes of testing.

Longitudinal assessment of quality of life and audiometric test outcomes in vestibular schwannoma patients treated with gamma knife surgery.

OBJECTIVE: To prospectively assess the quality of life (QOL) and hearing acuity in vestibular schwannoma (VS) patients after gamma knife surgery (GKS). PATIENTS: Fifty-nine VS patients. INTERVENTION: GKS. MAIN OUTCOME MEASURES: Prospective follow-up algorithm included 36-item Short Form Health Survey (SF-36), Hearing Handicap Inventory (HHI), Dizziness Handicap Inventory (DHI), Tinnitus Handicap Inventory (THI), pure-tone average, and speech discrimination hearing scores (Gardner-Robertson and American Academy of Otolaryngology), performed before and after GKS at 1-, 3-, 6-, 12-, and 18-month posttreatment intervals. RESULTS: From December 2006 to November 2008, 59 VS patients were treated with a median follow-up of 15 months. At baseline, mean scores for SF-36, HHI, DHI, and THI were 73, 37, 17, and 23, respectively. Median baseline Gardner-Robertson and American Academy of Otolaryngology hearing acuity scores were 2 and B, respectively. No significant decline in SF-36 health survey was noted after GKS. Mean SF-36 score at baseline was 73, compared with a range of 70 to 77 at predetermined posttreatment intervals. Similarly, no significant changes in DHI, HHI, and THI were noted. Approximately 47% of patients with baseline serviceable hearing maintained serviceable hearing at 12 months. Significant acute and chronic worsening in hearing acuity were noted at 1 and 18 months, respectively. No correlative decline in QOL was noted as assessed by SF-36 or HHI. CONCLUSION: No significant decline in global QOL occurred after GKS with relatively short follow-up and approximately 50% survey completion. When discussing therapy options with VS patients, anticipated treatment-related QOL outcomes should be considered.

Successful treatment of glomus jugulare tumours with gamma knife radiosurgery: clinical and physical aspects of management and review of the literature.

PURPOSE: To demonstrate the feasibility of treatment and early outcomes for patients treated with gamma knife radiosurgery (GKR), with or without surgical resection, for glomus jugulare tumours. METHODS: Between January 2007 and November 2008, 10 patients with glomus jugulare tumours were treated with GKR. Eight had prior surgical resection, seven subtotal resection and one total resection. In two cases GKR was the only definitive therapy. Baseline neurological deficits were prospectively recorded and present in 90% prior to GKR. The median tumour size and volume were 4 cc (0.7-10.9 cc). The median marginal tumour dose was 14 Gy (12-16 Gy). Clinical and radiographic outcomes are reported with a median follow-up of 9.7 months. RESULTS: Stereotactic frame placement allowed treatment of all 10 lesions, although 3-point fixation was sometimes required to avoid collisions. No patients developed worsening of symptoms or new neurological complaints after GKR; symptom relief was achieved in 50% of cases. No cases of clinical or radiographic progression were identified. Radiographically, 80% of lesions were stable and 20% showed significant shrinkage. CONCLUSIONS: GKR is an excellent option for patients with glomus jugulare tumours after complete or subtotal resection or at recurrence. Appropriately planned frame placement allows successful treatment delivery without difficulty. GKR improved symptoms, prevented neurological progression and achieved radiographic stability or regression in all cases.

Otologic effects of topical mitomycin C: phase I-evaluation of ototoxicity.

HYPOTHESIS: To determine ototoxicity of topical mitomycin C when placed in the middle ear at varying concentrations. BACKGROUND: Despite meticulous surgical technique and diligent postoperative care, some patients develop excessive scar and granulation tissue in the middle ear or mastoid cavity. Poor wound healing may result in infection, tympanic membrane perforation, or conductive hearing loss, which may necessitate further surgery. Use of topical mitomycin C in the ear may be beneficial in reducing scar and granulation tissue formation. This phase of the study was developed to determine the safety of topical mitomycin C in the rat model relative to ototoxicity. METHODS: Twelve Sprague-Dawley rats were evaluated with auditory brainstem response testing before and after treatments. Topical mitomycin C was injected in the middle ear of the right ear of eight animals. Varying concentrations of 0.125 to 0.5 mg/ml were used. Saline was injected in the left ear of each animal to serve as a control. Four separate animals were evaluated with placement of topical mitomycin C on Gelfoam into the middle ear. In two animals, Gelfoam was placed in the middle ear for 1 minute and then removed. In two animals, Gelfoam was placed in the middle ear and left in place. Auditory brainstem response testing was performed at 4 weeks and at 8 weeks. RESULTS: Using a high concentration of mitomycin C (>0.25 mg/ml) resulted in ototoxicity, with an increase in the auditory brainstem response threshold at 4 weeks and at 8 weeks. At low concentrations (<0.20 mg/ml), no change in auditory brainstem response threshold was noted. Animals treated with Gelfoam soaked in mitomycin C showed no change in auditory brainstem response threshold. CONCLUSION: The results of this study indicate that topical mitomycin C on Gelfoam applied in the middle ear appears safe when low concentrations are used, even in the rat, which has a higher susceptibility to gentamycin toxicity than humans. Higher concentrations may lead to ototoxicity based on changes in Wave V on auditory brainstem response. This treatment may prove to be an important option for patients suffering from chronic granulation tissue or scar tissue in the external or middle ear.

Staged resection of large acoustic neuromas.

OBJECTIVE: Surgical removal of large (>3 cm) acoustic neuromas is associated with poor long-term facial nerve function results and higher complication rates. This study analyzes whether long term facial nerve function and the incidence of neurological and vascular complications is improved by resection of large acoustic neuromas in 2 or 3 stages. PATIENTS AND METHODS: Among 660 patients who underwent surgical resection of acoustic neuromas between 1989 and 2002 by the senior author (J.M.K.), 34 (5%) patients underwent a staged resection of their large-sized tumors: stage I via a retrosigmoid craniotomy and stage II via a translabyrinthine approach. A retrospective chart review was performed. Tumor size, completeness of tumor removal, tumor recurrence, facial nerve function, and any complications were noted. RESULTS: The average tumor size was 4.4 cm with a mean postoperative length of follow-up of 6 years after the last surgery. Thirty-one patients underwent a 2-staged resection and 3 patients underwent a 3-staged resection. After their last surgery, 32 (94%) patients had excellent long-term facial function grades of House-Brackmann (H-B) I, one was H-B III, and one was H-B VI. All patients had a total or near-total (>98%) resection. There were no tumor recurrences on follow-up MRI scans. From these 71 operations, no patients required reoperation for a CSF leak. There were no deaths, strokes, hydrocephalus, or meningitis. CONCLUSION: In conjunction with the reported technical refinements, staged resection of large tumors significantly reduces morbidity and improves long-term facial nerve function. EBM RATING: C.

Oral dextromethorphan reduces perioperative analgesic administration in children undergoing tympanomastoid surgery.

OBJECTIVE: To determine whether oral dextromethorphan (1 mg/kg) given one hour prior to surgery decreases opioid administration in the perioperative period in children undergoing tympanomastoid surgery. METHODS: This was a prospective randomized double-blinded and placebo-controlled study in which 20 male and 18 female children (age 11.5 +/- 3.5 years) were enrolled. Nineteen children received dextromethorphan (DM), while the other 19 received placebos. Postoperative pain was assessed using a visual analogue scale and a pain score of > or =5 was treated with intravenous morphine sulfate. Patients were discharged home on oral oxycodone. RESULTS: The total doses of fentanyl administered during surgery were higher in the placebo group compared to the DM group (4.1 +/- 2 vs 2.6 +/- 1.4 microg/kg, P = 0.02) and the total doses of intravenous morphine administered in the postoperative period were also higher in the placebo group compared to the DM group (150 +/- 80 vs 73 +/- 56 microg/kg, P = 0.004). The placebo group had a higher pain score at the time of admission to the Day Surgery Unit (DSU) and a higher maximum pain score, compared to the DM group, during their combined stay in the Post-Anesthesia Care Unit and DSU (7.3 +/- 1.5 vs 3.1 +/- 2.6, P = 0.001). CONCLUSIONS: Premedication with DM reduces the need for opioid administration in the perioperative period in children undergoing tympanomastoid surgery. EBM RATING: A.

Ambulatory tympanomastoid surgery in children: factors affecting hospital admission.

OBJECTIVE: To identify clinical factors associated with postoperative nausea and vomiting (PONV) and failure to discharge from the hospital on the day of surgery in children undergoing tympanomastoid surgery. DESIGN: Records of 144 children undergoing 152 tympanomastoid surgical procedures from July 1, 2001, through June 30, 2002, were retrospectively reviewed and the data analyzed. SETTING: A tertiary care university-affiliated hospital. RESULTS: The mean +/- SD age of the cases was 11 +/- 3.7 years. Sixty-eight cases (45%) were middle ear procedures, while 84 cases (55%) were mastoid procedures. Forty-three cases (28%) were discharged home from the postanesthesia care unit (PACU), 55 cases (36%) were discharged on the day of surgery, and 142 cases (92%) were discharged home from the day surgery unit (DSU) within 23 hours after surgery. Patients who underwent mastoid procedures were more likely to require intravenous (IV) morphine sulfate in the PACU (75% vs 56%; P = .02) and were less likely to be discharged from PACU (15% vs 44%; P<.001) compared with patients who had middle ear procedures. In patients who underwent mastoid procedures, the presence of cholesteatoma (odds ratio, 1.9; 95% confidence interval, 1.0-3.7; P = .04) was associated with a higher likelihood of PONV. In both groups, the need for IV morphine sulfate to control pain on admission to DSU was associated with a higher occurrence of PONV. Factors that were significantly associated with failure to discharge from the hospital on the day of surgery were a pain score of 5 or greater, the presence of PONV, and the requirement of IV morphine sulfate on admission to DSU. CONCLUSIONS: Factors associated with higher risks of PONV and failure to discharge from the hospital on the day of surgery include the presence of cholesteatoma, a pain score of 5 or greater, and the requirement of IV morphine sulfate at the time admission to the DSU.

Endolymphatic sac-vein decompression for intractable Meniere's disease: long term treatment results.

OBJECTIVES: We sought to determine the long-term efficacy of endolymphatic sac-vein decompression surgery on patients with classic Meniere's disease. STUDY DESIGN AND SETTING: Using the 1995 American Academy of Otolaryngology-Head and Neck Surgery Committee on Hearing and Equilibrium criteria, starting stage, functional level, vertigo class, and hearing results were addressed. We studied 68 patients with classic Meniere's disease from a tertiary, private otology-neurotology practice. Patient data were gathered by retrospective chart review, questionnaire, and patient interview. All patients underwent endolymphatic sac-vein decompression with an average follow-up period of 55 months. RESULTS: Median functional level before surgery was level 4, improving to level 2 after surgery. Eighty-one percent of patients showed improvement in functional level, 12% remained stable, and 7% declined. Long-term vertigo control was 47% in class A, 25% in class B, 9% in class C, 3% in class D, and 16% in class F. Twenty percent of patients were in hearing stage I Meniere's disease; 31%, stage II; 44%, stage III; and 5%, stage IV. Eighteen percent of patients showed improvement in hearing class, 64% were stable, and 18% declined. CONCLUSION: Endolymphatic sac-vein decompression surgery is a safe, nondestructive surgical option for Meniere's disease that offers durable control of vertigo and stabilization of hearing for the majority of symptomatic patients. SIGNIFICANCE: The beneficial long-term outcome of the endolymphatic sac-vein decompression supports its continued use as a first-line treatment option in intractable Meniere's disease.

Round window gentamicin absorption: an in vivo human model.

OBJECTIVE/HYPOTHESIS: Using a novel human labyrinthine sampling model, in vivo gentamicin absorption through the round window can be measured. STUDY DESIGN: A prospective study. METHODS: Gentamicin was delivered either transtympanically (preoperative) or through a facial recess approach (intraoperative). The lateral semicircular canal and vestibule were opened, and by means of a microsyringe, labyrinthine fluid was aspirated. A sample of serum was also drawn. In all patients cerebrospinal fluid was also drawn. The samples were analyzed using a standard chemistry analyzer. RESULTS: Intratympanic gentamicin diffused through the round window membrane and achieved concentrations in the labyrinthine fluid ranging from 0 to 16 mg/L. Intratympanic gentamicin was absorbed into the systemic circulation in 4 of 11 patients with serum levels ranging from 0.3 to 0.4 mg/L. No gentamicin was detected in the cerebrospinal fluid. CONCLUSIONS: Intratympanic gentamicin diffuses rapidly through the round window membrane and achieves significant levels in the inner ear. Thus, this new model can be used to assess round window permeability to clinically relevant medications such as steroids and ototopical antibiotics.

Intratympanic ciprofloxacin and the human labyrinthine sampling model.

OBJECTIVE: The aim of the study was to investigate the potential absorption of intratympanic ciprofloxacin through the human round window membrane. STUDY DESIGN: A prospective study. METHODS: Ciprofloxacin was instilled into the middle ear of 10 patients undergoing acoustic tumor removal. The lateral semicircular canal and vestibule were subsequently opened and, using a microsyringe, labyrinthine fluid was aspirated. A sample each of serum and cerebrospinal fluid was also drawn. RESULTS: Into each middle ear, 0.5 mL ciprofloxacin (0.3%) was instilled. The time interval between the ciprofloxacin application to the round window membrane and sampling of labyrinthine fluid and plasma ranged from 9 to 120 minutes. There was no measurable ciprofloxacin in the labyrinthine fluid, cerebrospinal fluid, or serum of 10 patients. CONCLUSION: The lack of measurable absorption of intratympanic ciprofloxacin into the inner ear indicates that the chance of ototoxicity when ciprofloxacin is used clinically, even in the presence of a tympanic membrane perforation, is low.

Over-under tympanoplasty.

OBJECTIVE: Common techniques of tympanic membrane repair include underlay and overlay grafting. The over-under tympanoplasty, an innovative method for tympanic membrane repair, will be described as a reliable alternative that has advantages over traditional procedures. STUDY DESIGN: This study was a retrospective case review. SETTING: Tertiary referral center with hospital-setting surgery and outpatient ambulatory patient visits. PATIENTS: One hundred twenty patients who underwent over-under tympanoplasty were included in this study. Average follow-up was 1.8 years. INTERVENTION: Over-under tympanoplasty is performed by placing the graft over the malleus and under the annulus. This technique was used for patients undergoing ear surgery for chronic otitis media, perforations, cholesteatoma, and/or conductive hearing loss. All degrees of ear pathology were included. MAIN OUTCOME MEASURES: Main outcome measures were graft success (no perforation, atelectasis, or lateralization within 6 mo) and improvement of hearing. Patients were stratified by severity of disease (according to the Middle Ear Risk Index), cholesteatoma presence, and type of mastoidectomy. RESULTS: All 120 patients had successful grafts. Lateralization of the grafted drum did not occur. Seventeen patients had late atelectasis, and 12 patients had late perforations; nearly all of these were noted more than 1 year after surgery and were attributed to persistent eustachian tube dysfunction or infections. Average improvement in air-bone gap for all patients was 5.3 dB, whereas speech reception threshold improved by 5.9 dB. CONCLUSION: Over-under tympanoplasty has an excellent success rate while being technically easier than lateral tympanoplasty. Thus, it is a useful method for practitioners of all levels.

Rapid elevation of gentamicin levels in the human labyrinth following intravenous administration.

HYPOTHESIS: Adequate quantities of labyrinthine fluid can be sampled from the human labyrinth to perform quantitative analysis of medications. A rapid elevation of intralabyrinthine gentamicin levels after intravenous administration can be measured. A model for the sampling of human inner ear fluid in this manner is described. BACKGROUND: The risk of aminoglycoside ototoxicity has been a long-standing concern. The kinetics of gentamicin diffusion into the inner ear have been extrapolated to humans from various animal models. The validity of extrapolation to humans is unknown. We have developed a new model to measure the uptake of gentamicin in vivo. METHODS: A single intravenous dose of gentamicin (80 mg) was given perioperatively to 13 patients undergoing translabyrinthine acoustic neuroma surgery. The lateral semicircular canal and vestibule were opened and a microsyringe was used to obtain a sample of labyrinthine fluid concomitant with a serum sample. The gentamicin concentration of the labyrinthine fluid and serum was analyzed using a standard chemistry analyzer. RESULTS: After parenteral administration of gentamicin, fluid was obtained from the inner ear of 13 acoustic neuroma patients. Inner ear concentrations were between 1.0 and 3.8 mg/L. Serum gentamicin levels ranged from 1.2 to 10.5 mg/L. CONCLUSIONS: This method allows the sampling of intralabyrinthine fluid in humans. Gentamicin was noted immediately in the labyrinth after intravenous administration. This model may be expanded to measure other compounds given either by intravenous or transtympanic routes.