Effect of BAEP monitoring on hearing preservation during acoustic neuroma resection.

We measured the effect of brainstem auditory evoked potential (BAEP) monitoring on hearing preservation in acoustic neuroma resection in 90 consecutive patients with monitoring compared with 90 historical controls matched for tumor size and preoperative hearing status. In small tumors (less than 2 cm), BAEP monitoring was associated with a higher rate of hearing preservation and a greater chance that the hearing preserved was clinically useful. Changes in the BAEP intraoperatively showed a good correlation with postoperative hearing status.

Stereotactic radiosurgery using the gamma knife for acoustic neuromas.

PURPOSE: To assess the efficacy and toxicity of stereotactic radiosurgery using the gamma knife for acoustic neuromas. METHODS AND MATERIALS: Between January 1990 and January 1993, 36 patients with acoustic neuromas were treated with stereotactic radiosurgery using the gamma knife. The median maximum tumor diameter was 21 mm (range: 6-32 mm). Tumor volumes encompassed within the prescribed isodose line varied from 266 to 8,667 mm3 (median: 3,135 mm3). Tumors < or = 20 mm in maximum diameter received a dose of 20 Gy to the margin, tumors between 21 and 30 mm received 18 Gy, and tumors > 30 mm received 16 Gy. The dose was prescribed to the 50% isodose line in 31 patients and to the 45%, 55%, 60%, 70%, and 80% isodose line in one patient each. The median number of isocenters per tumor was 5 (range: 1-12). RESULTS: At a median follow-up of 16 months (range: 2.5-36 months), all patients were alive. Thirty-five patients had follow-up imaging studies. Nine tumors (26%) were smaller, and 26 tumors (74%) were unchanged. No tumor had progressed. The 1- and 2-year actuarial incidences of facial neuropathy were 52.2% and 66.5%, respectively. The 1- and 2-year actuarial incidences of trigeminal neuropathy were 33.7% and 58.9%, respectively. The 1- and 2-year actuarial incidence of facial or trigeminal neuropathy (or both) was 60.8% and 81.7%, respectively. Multivariate analysis revealed that the following were associated with the time of onset or worsening of facial weakness or trigeminal neuropathy: (a) patients < age 65 years, (b) dose to the tumor margin, (c) maximum tumor diameter > or = 21 mm, (d) use of the 18 mm collimator, and (e) use of > five isocenters. The 1- and 2-year actuarial rates of preservation of useful hearing (Gardner-Robertson class I or II) were 100% and 41.7% +/- 17.3, respectively. CONCLUSION: Stereotactic radiosurgery using the gamma knife provides short-term control of acoustic neuromas when a dose of 16 to 20 Gy to the tumor margin is used. Preservation of useful hearing can be accomplished in a significant proportion of patients.

Clinical findings in patients with acoustic neurinoma.

Herein we review the symptoms, physical findings, and test results in 131 patients with acoustic neurinoma. The earliest symptoms are unilateral hearing loss, tinnitus, and dysequilibrium. As the disease progresses, facial numbness, facial weakness, and headaches become more prominent. Physical findings other than hearing loss are uncommon; the most frequently observed are a decreased corneal reflex, nystagmus, and facial hypoesthesia. Routine audiometry provides objective information about the hearing loss. Some degree of asymmetry is found in the pure-tone tests. In addition, the speech discrimination scores are frequently lower than expected. Special audiometric tests should be performed on those patients with residual hearing; at the present time, acoustic reflex tests and the brainstem-evoked response yield the most information. Computed tomography with dye enhancement with or without the use of air contrast has become the most accurate roentgenographic test. Our goal is to identify acoustic neurinomas sufficiently early so that surgical removal is safe and leaves minimal deficit.

Improved preservation of facial nerve function with use of electrical monitoring during removal of acoustic neuromas.

Continuous spontaneous electromyographic activity and responses to electrical stimulation of the facial nerve in the surgical field were monitored in 48 patients undergoing primary removal of an acoustic neuroma. The operative and postoperative results in these patients were compared with the results in 48 patients who were matched for age and size of tumor and who underwent the same surgical procedure without intraoperative monitoring. Eighty-three percent of the patients had preoperative evidence of facial neuropathy, which was more severe with larger tumors. Postoperative facial nerve function was most accurately predicted on the basis of the extent of facial neuropathy on preoperative electrophysiologic testing. Anatomic preservation of the facial nerve in patients with large tumors was substantially improved in the monitored patients (67%) in comparison with those without monitoring (33%). No difference was noted in facial nerve function in the two groups of patients immediately postoperatively. By 3 months, the degree of improvement in the monitored group exceeded that in those who were not monitored, particularly in patients with medium-sized and large tumors.

Lymphocytic lymphoma involving the middle ear.

A patient with lymphocytic lymphoma involving the middle ear had otalgia and facial palsy as his initial symptoms, and the definitive diagnosis was made by means of biopsy of the tumor in the middle ear. Review of the literature revealed only one other case with clinical involvement of the middle ear space.

Chondroblastoma of the skull and facial bones.

A series of 30 chondroblastomas was reviewed: 21 had occurred in the lateral part of the temporal bone, 6 in the mandible, 1 in the parietal bone, and 2 in the region that included the temporal bone and mandible. Of the 30 patients in the series, 20 were males and 9 were females; the sex of 1 patient was not stated. The ages of 29 patients ranged from 2 years 11 months to 70 years (mean, 43.5 years). Radiologic findings were not suggestive of a specific diagnosis, although the lesions appeared to be benign. Histologically, most tumors were classic chondroblastomas. However, some showed aneurysmal bone cyst-like areas and nodules of epithelioid cells without chondroid differentiation. Conservative reexcisions were usually curative. Approximately half of the patients had recurrence after curettage.

Diagnosis of acoustic neurinoma.

Seventy-six patients underwent the primary removal of an acoustic neurinoma at the Mayo Clinic from 1978 through 1980. Hearing loss was present in 97% of the patients, and tinnitus and dysequilibrium occurred in 70% of the patients. The most common signs were a decreased corneal reflex, nystagmus, and facial hypesthesia. In these patients, pure tone and speech audiometry are used to define the hearing loss. When hearing is still present, the speech discrimination is often disproportionately low. Acoustic reflex testing and brain stem evoked response are used to determine whether the hearing loss is cochlear or retrocochlear. When these tests could be performed in this series of patients, they were accurate in 85 to 95%. The vestibular response to caloric testing is expected to be decreased or absent in about 90% of patients, and this was so in 86% of our patients. Radiographic studies are the most important tests currently used for the diagnosis of acoustic neurinoma. Tomography of the internal auditory canal shows abnormalities in 80% of patients. Computed tomography with contrast enhancement demonstrates abnormalities in 90% of patients. The computed tomographic (CT) scan may reveal the location, the size, and often the consistency of the tumor. In cases still questionable after CT scanning, positive contrast rhombencephalography is used for clarification. In this series, no single symptom, sign, abnormal audiometric test result, or abnormal radiographic finding was present in all patients; therefore, the most important factor in diagnosis is an alert physician.

Impact of cranioplasty on headache after acoustic neuroma removal.

We reported previously the incidence of headache after the retrosigmoid removal of an acoustic neuroma as 23% at 3 months, declining to 9% at 2 years after surgery. In an attempt to reduce the incidence and the severity of these headaches, we made one change in our surgical procedure, which was to perform a cranioplasty with methyl methacrylate. Twenty-four patients underwent the cranioplasty and were followed for at least 3 months postoperatively. These patients were matched to 24 patients who did not undergo a cranioplasty. We found a 4% incidence of headache in the cranioplasty group and a 17% incidence in the matched group. No complications were related to this change in our procedure.

Venous air embolism in sitting and supine patients undergoing vestibular schwannoma resection.

OBJECTIVE: This study retrospectively compares the incidence of venous air embolism (VAE) detection and morbidity in the sitting and supine positions. All patients underwent vestibular schwannoma resection via the retrosigmoid approach by a single surgical team. METHODS: A total of 432 consecutive operations were reviewed, 222 of which were performed with the patients in the sitting position and 210 of which were performed with the patients in the supine position. Charts were reviewed for evidence of intraoperative VAE, intraoperative hypotension secondary to VAE, postoperative morbidity related to VAE, and other variables to compare the groups. RESULTS: This study demonstrated a 28% incidence of VAE detection when patients were in the sitting position compared to a 5% incidence of VAE detection when patients were in the supine position (P < 0.0001). Intraoperative hypotension secondary to VAE was noted in 1.8% of the sitting patients and 1.4% of the supine patients (P=0.72, no significant difference). Postoperative morbidity caused by VAE was noted in one sitting patient (0.5%) (pulmonary edema) and in no supine patients (P=0.48, no significant difference). Blood loss was slightly greater in the supine group, and operative times were similar in both groups, despite that the average tumor size of patients operated on in the sitting position was 2.8 cm versus 2.2 cm in the supine group (P < 0.0001). CONCLUSION: Our results indicate that although there is a higher incidence of VAE detection in sitting patients, the morbidity is not statistically greater. We conclude that because morbidity from VAE is similar in either position, patient positioning should be based on surgical team preference.

Conservative management of acoustic neuroma: an outcome study.

OBJECTIVE: This study analyzed selection criteria, clinical outcome, and tumor growth rates in patients with acoustic neuromas in whom the initial management strategy was observation. METHODS: A retrospective review of patients with conservatively managed unilateral acoustic neuromas was conducted. Minimum follow-up was 6 months. Patients with neurofibromatosis Type II were excluded. Differences in tumor growth rates were analyzed by use of the Wilcoxon rank sum test. RESULTS: Sixty-eight patients (31 men and 37 women) with a mean age of 67.1 years were followed for an average of 3.4 years after diagnosis. The reasons for a trial of observation included advanced age (55%), patient preference (21%), minimal symptoms (9%), poor general medical condition (7%), asymptomatic tumor (4%), and tumor in the only hearing ear (4%). Fifty-eight patients (85%) were successfully managed with observation alone. Ten patients (15%) ultimately required treatment (nine received microsurgical treatment and one patient underwent radiosurgical intervention) at a mean time interval of 4.0 years after diagnosis. Forty-eight tumors (71%) showed no growth and 20 (29%) enlarged during the study period. The mean tumor growth rate at the 1-year follow-up was significantly higher in the group requiring treatment (3.0 mm) than in the group not requiring treatment (0.36 mm) (P < 0.0001). Thus, the tumor growth rate at the 1-year follow-up was a strong predictor of the eventual need for treatment. CONCLUSION: Observation is a reasonable management strategy in carefully selected patients with acoustic neuromas. Diligent follow-up with serial magnetic resonance imaging is recommended, because some tumors will enlarge to the point at which active treatment is required.

Translabyrinthine repair for cerebrospinal fluid otorhinorrhea.

Cerebrospinal fluid (CSF) otorhinorrhea may occur as a complication of surgery for removal of acoustic neurinomas. The CSF leak usually appears within the first 2 weeks after surgery, and the diagnosis is obvious. The fistulous site is frequently inaccessible and may be difficult to repair by reexploring the suboccipital craniectomy. Successful closure of the fistula is accomplished by obliterating the space between the posterior fossa dura and the eustachian tube orifice with homograft muscle, using a radical translabyrinthine approach.

Management of acoustic neuromas, 1978-1983.

The surgical aspects of 162 consecutive procedures for removal of acoustic neuromas, performed from 1978 through 1983, are reviewed. Nearly all of the procedures were done through a retrosigmoid suboccipital craniectomy. Most used the combined skills of a neurosurgeon and an otological surgeon. Total tumor removal was accomplished in 98% of cases. There have been two recurrences and one postoperative death. The facial nerve was preserved in 81% of procedures. Facial function returned in nearly all of these patients, but the degree of return was variable. The cochlear nerve was preserved in 55 patients, but hearing was present in only 14. The most common complication was cerebrospinal fluid otorhinorrhea (12%); about half of these patients required a secondary procedure. Other complications were meningitis (5%), aspiration (3%), and hemorrhage (2%). During the period reviewed, several changes occurred in management of this disorder. These procedures are now being done by a surgical team. The neurosurgeon performs the intracranial work and the otological surgeon accomplishes the temporal bone dissection. Most patients undergo the operation in the supine rather than the sitting position. During the operation, the facial nerve is monitored continuously by electromyography with intermittent bipolar stimulation. There appears to be continuing improvement in the management of these patients.

Intracranial ceruminous gland adenocarcinoma.

Patients with adenocarcinoma of the ceruminous gland arising in the middle ear have a typical syndrome consisting of unilateral hearing loss, otalgia, facial paresis, and a middle-ear mass. Adjacent cranial nerves also may be affected. Some patients may have an ipsilateral cerebellar ataxia if the lesion extends into the cerebellopontine angle and compresses the cerebellar hemisphere. Obstructive hydrocephalus may occur secondary to obstruction of the aqueduct or fourth ventricle. The initial clinical findings may be those of a jugular foramen syndrome. These lesions are usually slow-growing and may be associated with a very prolonged clinical course. Although the tumors are rare, the physician should be aware of their existence if proper care is to be given.

Current results of the retrosigmoid approach to acoustic neurinoma.

Since 1984 when cranial nerve monitoring became routinely performed at the Mayo Clinic, 255 patients have undergone 256 procedures using the retrosigmoid approach for the removal of acoustic neurinomas. Of these, 221 patients had some hearing before surgery and 52 maintained hearing following surgery. The anatomical continuity of the facial nerve was preserved in 237 of these 256 procedures. It was possible to perform a primary end-to-end anastomosis in seven of the remaining 19 patients, and one patient had a cable graft inserted. Thus, 95.7% of these patients were believed to have potential for spontaneous facial nerve function. Of the 11 patients in whom this was not possible, seven underwent early spinal accessory facial anastomosis, in two hypoglossal-facial anastomosis was performed, and two had no facial nerve procedures and have paralysis of the facial nerve. There were two deaths from a pulmonary embolus in the early postoperative period, both 4 days following otherwise uneventful surgery. The most common postoperative complication was cerebrospinal fluid leakage, which has not resulted in significant permanent morbidity although early repair for this problem is now routinely recommended. Other complications were quite rare and have generally not resulted in any major change in patient lifestyle or activity level. This review reconfirms that the retrosigmoid surgical treatment of acoustic tumors continues to be an acceptable treatment option.

Cochlear function in chronic otitis media.

Otologic symptoms, audiometric data, and operative findings were reviewed in 200 consecutive patients who had surgically treated unilateral chronic otitis media. Bone conduction thresholds were analyzed in relation to extent of perforation, frequency of otorrhea, duration of disease, and extent of pathologic change. Median bone conduction threshold differences between diseased and uninvolved ears were within 5 dB at all frequencies. The mean speech discrimination score between affected and unaffected ears was equal. Patients with prolonged disease and more extensive pathologic alterations were more likely to experience cochlear changes and hence sensorineural hearing loss, though not to the extent others have described. Our findings indicate that chronic otitis media has little effect on cochlear function in the majority of patients.

Roentgenographic diagnosis of acoustic neurinoma.

This article reviews the roentgenographic studies performed in 131 patients who had surgically confirmed acoustic neurinomas. In this 5-year study (1978-1982), all patients had computed tomography (CT) and 82% had petrous apex tomography. Approximately 18% of patients underwent angiography, and 18% had positive contrast rhombencephalography. The diagnostic capability with CT scanning has improved remarkably. There were no false-negative results for scans obtained in 1981 and 1982. At the same time the accuracy of other radiographic and audiometric tests was decreasing. The proportion of small tumors diagnosed has increased 200%, with a corresponding decrease in medium and large tumors. Tumors can be diagnosed at an earlier stage; and, because of this, surgical results have improved. No surgical mortality occurred in this series, preservation of the facial nerve was excellent, and in some patients cochlear function was maintained.

Residual and recurrent acoustic neuromas.

A retrospective study was conducted on all 23 patients who underwent operation for residual or recurrent acoustic neuromas during the 10-year period January 1976 through December 1985. The most common symptoms at the time of reoperation were ataxia (16 patients), facial paresthesias (13 patients), and headaches (9 patients). Primary procedures had consisted of suboccipital posterior fossa approaches in 22 patients and a middle fossa approach in one. Reoperation for recurrent or residual tumor consisted of a retrosigmoid approach in 17 patients and a translabyrinthine or translabyrinthine/retrosigmoid approach in six patients. This study confirms that residual or recurrent acoustic tumors are not common. It also suggests that long-term follow-up, for at least 7 to 8 years, is indicated.

Hearing preservation after removal of acoustic neurinoma.

Between January 1, 1978, and July 1, 1983, 149 patients underwent acoustic neurinoma removal (151 procedures). Of these, 119 ears (118 patients) had had some degree of hearing on the affected side preoperatively, and in all of them the tumors had been removed by a posterior cranial fossa approach. Fourteen (12%) had measurable hearing preserved postoperatively--serviceable in eight ears and poor in six. The patients with preserved hearing had had their hearing loss for a shorter period, slightly better preoperative hearing levels, and a smaller tumor. The complications, morbidity, and mortality in this group were comparable to those in other series. It is concluded that preservation of hearing is a worthwhile goal that can be achieved without increased risk.

Electrophysiologic monitoring of facial nerve during temporal bone surgery.

Monitoring of peripheral nerves during surgical procedures decreases trauma to the nerve, which may preserve function. During 1984, electrophysiologic monitoring of the facial nerve was used during 32 operative procedures in and around the temporal bone. The largest group were for cerebellopontine angle tumors. Clinically, monitoring appeared to be helpful by providing objective evidence of trauma to the facial nerve and a method of demonstrating integrity of the nerve. However, review of this series did not reveal objective evidence of improved facial nerve preservation compared to results in a similar group of patients operated on without monitoring. We think that the monitoring is best done by personnel experienced with the technique.

Intraoperative monitoring of the facial nerve.

Anatomic preservation of the facial nerve, with maximal facial function, is one of the goals of acoustic neuroma surgery. Application of electrophysiologic monitoring techniques is useful in achieving this goal. Preoperative electromyography and nerve conduction studies provide important prognostic information for preservation of the nerve and postoperative function. Intraoperative electromyography alerts the surgeon to facial nerve proximity and potential injury. Direct nerve stimulation is utilized to confirm the location and integrity of the nerve. Matched-pair analysis of two groups of patients demonstrated an increased ability to preserve the facial nerve with less postoperative facial deformity.