Combined retrolabyrinthine-retrosigmoid approach for improved exposure of the posterior fossa without cerebellar retraction.

The combined retrolabyrinthine-retrosigmoid (CRR) approach utilizes anterior retraction of the sigmoid sinus to improve exposure of the posterior fossa without cerebellar retraction. The CRR was initially used for vestibular neurectomy but is now utilized for acoustic neuroma excision with hearing preservation and exposure for clipping of basilar and vertebrobasilar aneurysms. This excellent exposure of the cerebellopontine angle without cerebellar retraction can be used for all posterior fossa exposures.

Microsurgical posterior fossa vestibular neurectomy: an evolution in technique.

Between 1925 and 1945, Walter Dandy and Kenneth McKenzie performed more than 700 posterior fossa eighth nerve sections and vestibular neurectomies, treating the intractable vertigo accompanying Meniere's disease. During the past 10 years, using microsurgical techniques and reaching the posterior fossa through the temporal bone, vestibular neurectomy has enjoyed a resurgence of popularity. When hearing is to be preserved, vestibular neurectomy is the surgical treatment of choice, if the patient fails to undergo a remission of the vertigo of Meniere's disease. This report reviews 115 consecutive vestibular neurectomies performed for the treatment of Meniere's disease from 1978 to 1988.In 1978, the retrolabyrinthine vestibular neurectomy (RVN) was introduced, a procedure in which the posterior fossa is entered anterior to the sigmoid sinus and behind the labyrinth. During the last three years, the approach to the posterior fossa has been a small dural opening behind the sigmoid sinus, the combined retrolabyrinthine-retrosigmoid (R-R) approach. There have been no cases of facial paralysis and no serious complications. A high incidence of headache (75%) resulted when the posterior wall of the internal auditory canal was drilled away for better exposure. Transient cerebrospinal fluid (CSF) leaks occurred in 7% of the patients having the RVN, the incidence was 3% when the combined R-R approach was used. In the RVN series, wound infection occurred in 20% of cases until perioperative antibiotics reduced the rate to 3%. The results in curing or improving vertigo have been excellent (94%), and hearing has been preserved to within 20 dB of the preoperative levels in 76%. Until a cure for Meniere's disease is found, microsurgical posterior fossa vestibular neurectomy remains the best treatment.

The resurrection of vestibular neurectomy: a 10-year experience with 115 cases.

Between 1925 and 1945, Walter Dandy and Kenneth McKenzie performed more than 700 posterior fossa eighth nerve sections and vestibular neurectomies to treat the intractable vertigo accompanying Ménière's disease. During the past 10 years, with the aid of microsurgical techniques and the approach to the posterior fossa through the temporal bone, vestibular neurectomy has undergone a resurgence of popularity. When hearing is to be preserved, vestibular neurectomy is the surgical treatment of choice for patients who fail to undergo a remission of the vertigo attacks of Ménière's disease. This report reviews 115 consecutive vestibular neurectomies performed from 1978 to 1988 for the treatment of Ménière's disease. In 1978, retrolabyrinthine vestibular neurectomy (RVN), a procedure in which the posterior fossa is entered anterior to the sigmoid sinus and behind the labyrinth, was introduced. During the last 3 years, the approach to the posterior fossa has been a small dural opening behind the sigmoid sinus; this approach is known as the combined retrolabyrinthine retrosigmoid approach. There have been no cases of facial paralysis and no serious complications connected with this technique. A high incidence of headache (50%) resulted when the posterior wall of the internal auditory canal was drilled away for better exposure. Transient cerebrospinal fluid (CSF) leaking occurred in 7% of the patients undergoing RVN; however, no CSF leaks occurred when the combined retrolabyrinthine retrosigmoid approach was used. In the RVN series, wound infection occurred in 20% of the cases until perioperative antibiotics reduced the rate to 3%. The results in terms of curing or improving vertigo have been excellent (94%), and hearing has been preserved to within 20 dB preoperative levels in 76% of the cases. Until a cure for Ménière's disease is found, microsurgical posterior fossa vestibular neurectomy remains the best treatment.

An evolution of approach in vestibular neurectomy.

Since introducing the retrolabyrinthine vestibular neurectomy in 1978, we have performed 78 procedures with good results. In 1985 we introduced the retrosigmoid-IAC vestibular neurectomy, which allows a more complete transection of the vestibular nerves within the internal auditory canal (IAC). Vertigo control has been excellent; however, in 75% of patients, postoperative headaches have been a significant problem. In 1987, the best aspects of the two procedures were incorporated and the combined retrolab-retrosigmoid vestibular neurectomy was developed. The procedure is similar to the RVN in that all bone covering the lateral venous sinus is removed. It differs from the RVN in that a limited mastoidectomy is performed and the dura is opened just behind the LVS. The LVS is retracted forward, exposing the cerebellopontine angle. This allows the surgeon the option to section the vestibular nerve in either the CP angle or the IAC, depending upon the presence or absence of a cochieovestibular cleavage plane in the CP angle. The results have been good and the incidence of headache has been reduced to 10%. The technique, results, and complications are reported here.

Combined retrolab-retrosigmoid vestibular neurectomy. An evolution in approach.

Since introducing the retrolabyrinthine vestibular neurectomy (RVN) in 1978, we have performed 78 procedures with good results. In 1985, we introduced the retrosigmoid-internal auditory canal vestibular neurectomy (RSG-IAC), which allowed a more complete transection of the vestibular nerves in the IAC. Vertigo control has been excellent. However, in 50% of cases postoperative headaches have been a significant problem. In 1987, we combined these two approaches into one procedure, the combined retrolab-retrosigmoid vestibular neurectomy (RSG-RVN). The procedure is similar to a RVN, in that all bone covering the lateral venous sinus (LVS) is removed. It differs from the RVN in that the dura is opened just behind the LVS. The LVS is retracted forward, thereby exposing the cerebellopontine (CP) angle. This allows the surgeon the option to sever the vestibular nerve either in the CP angle or in the IAC, depending on the presence or absence of a cochleovestibular (CV) cleavage plane in the CP angle. The technique, results, and complications will be reported in this article.

The singular canal: a valuable landmark in surgery of the internal auditory canal.

The singular canal transmits the posterior ampullary nerve between the inferior part of the internal auditory canal (IAC) and ampulla of the posterior semicircular canal. The anatomy of the singular canal was studied in temporal bone dissections, in surgical dissections, and in high-resolution computerized tomography scans. Measurements were taken for distances between the origin of the singular canal in the IAC, the porus acousticus, the vestibule, and posterior canal ampulla. The location and importance of the singular canal are demonstrated for retrosigmoid-IAC vestibular neurectomy, retrosigmoid acoustic neuroma surgery, and transcochlear cochleovestibular neurectomy. The main purpose for the use of the retrosigmoid approach to the internal auditory canal during vestibular neurectomy and excision of acoustic neuromas is preservation of hearing. A major concern when the contents of the internal auditory canal are exposed through this approach is fenestration of the labyrinth, which results in sensorineural hearing loss. In the retrosigmoid approach, the singular canal has been found to be a vital landmark in prevention of fenestration during surgery of the internal auditory canal.

Retrolabyrinthine or retrosigmoid vestibular neurectomy: indications.

Selective vestibular nerve section is indicated for the treatment of vertigo in unilateral Meniere's disease or other inner ear disorders, in patients with salvageable hearing. Since 1978, the retrolabyrinthine approach to the vestibular nerve in the cerebellopontine angle has been used extensively with good success and minimal morbidity. In an attempt to obtain more complete section of the vestibular nerve, the retrosigmoid-internal auditory canal approach was developed in 1985 and has been employed in 13 patients, all of whom obtained complete control of vertigo. The surgical techniques are presented with emphasis on the advantages and disadvantages of each approach. Relative indications and contraindications are suggested.

Retrosigmoid-internal auditory canal approach vs. retrolabyrinthine approach for vestibular neurectomy.

A new procedure, the retrosigmoid-internal auditory canal (RSG-IAC) vestibular neurectomy, has been developed, presented, and compared with the retrolabyrinthine vestibular neurectomy (RVN). The RSG-IAC involves a 3 cm retrosigmoid craniotomy removal of the posterior wall of the internal auditory canal (IAC) to the singular canal, with transection of the superior vestibular nerve and the posterior ampullary nerve. This effects a complete denervation of the vestibular labyrinth and preserves the patient's hearing. All 11 patients with Meniere's disease were cured of vertigo. Hearing was preserved to within 10 dB of the preoperative pure-tone average (PTA) in 9 of 11 cases. There were no serious complications and no cases of facial paralysis or total hearing loss. The major postoperative problem is persistent headache that necessitates medication. These results compare favorably with--and may be better than those noted after--the RVN procedure. The RSG-IAC vestibular neurectomy is an important improvement in the evolution of vestibular neurectomy for the treatment of vertigo. A prospective study is now in progress to determine which procedure--the RSG-IAC or RVN--best fulfills the goals of vestibular neurectomy.

A comparison of retrosigmoid IAC, retrolabyrinthine, and middle fossa vestibular neurectomy for treatment of vertigo.

A new procedure, the retrosigmoid internal auditory canal (IAC) vestibular neurectomy has been developed and presented. It involves a 3-cm retrosigmoid craniotomy removing the posterior wall of the IAC to the singular canal, with transection of the superior vestibular nerve and posterior ampullary nerve. This produces a complete denervation of the vestibular labyrinth and preserves the patient's hearing. All ten patients with Meniere's disease had their vertigo cured. Hearing was preserved to within 11 dB of the preoperative pure tone average in 9 of 10 cases. There were no serious complications, no cases of facial paralysis, and no cases of total hearing loss. These results compare favorably with the MFVN and the RVN. The retrosigmoid IAC vestibular neurectomy is an important improvement in the evolution of vestibular neurectomy for the treatment of vertigo.

The unrecognized rotation of the vestibular and cochlear nerves from the labyrinth to the brain stem: its implications to surgery of the eighth cranial nerve.

The cochlear and vestibular nerves rotate 90 degrees from the inner ear to the brain stem. Most of the rotation occurs within the internal auditory canal (IAC); only minimal rotation occurs in the cerebellopontine (CP) angle. At the labyrinthine end of the IAC, the cochlear nerve--which at first lies anterior to the inferior vestibular nerve (saccular nerve)--rapidly fuses with the inferior vestibular nerve. It then rotates to become inferior as the nerves leave the porus acousticus. The cochleovestibular (C-V) cleavage plane lies in a superior-inferior direction in the lateral IAC and rotates to become anterior-posterior in the CP angle. In 25% of patients in whom no C-V cleavage plane can be seen, it is not possible to completely transect all vestibular fibers. The surgical implications are that the most complete vestibular neurectomy can be done only in the lateral IAC, the cochlear and inferior vestibular nerves, because of their intimate association, should not be separated in the mid-IAC, in order to prevent damage to the cochlear nerve, and to create a complete denervation of the vestibular labyrinth, only the posterior ampullary nerve along with the superior vestibular nerve should be transected.

Hearing preservation after acoustic neuroma surgery with intraoperative direct eighth cranial nerve monitoring: Part II. A classification of results.

Since the advent of brainstem auditory evoked response audiometry and computerized tomography, small acoustic neuromas are more frequently found. Often the patient has serviceable hearing, which we would like to preserve during complete tumor removal. Since 1978, sixteen patients with acoustic neuromas have been operated upon through the retrosigmoid suboccipital approach, with the goal of hearing preservation. In 1983, we began using intraoperative direct eighth nerve monitoring, which produced a rapid assessment of cochlear nerve function during the excision of small acoustic neuromas. The tumors varied in size from intracanalicular lesions to one lesion with a 3.0 cm protrusion medial to the porus acousticus. In eight of sixteen cases, intraoperative monitoring was used, and in four of the patients hearing was preserved. In eight cases, intraoperative monitoring was not used, and hearing was preserved in only two patients. The overall success rate--in total tumor removal with hearing preservation--was 37%. Hearing was preserved in six of eight patients who had tumors which measured less than 1.5 cm. In this group of cases, two of the patients had a Class I good hearing result (PTA 0 to 30 dB and 70 to 100% discrimination), one patient had Class III nonserviceable hearing, (PTA 65 to 75 dB and 25 to 45% discrimination), and three patients had Class IV poor hearing, (PTA 80 to 100 dB and 0 to 20% discrimination). We found that continuous monitoring of direct eighth-nerve-evoked action potentials were extremely valuable and rapidly indicated reversible cochlear nerve trauma.

Retrolabyrinthine vestibular neurectomy with simultaneous monitoring of eighth nerve and brain stem auditory evoked potentials.

We have used retrolabyrinthine vestibular neurectomy in 36 of 49 cases as the primary surgical procedure to relieve vertigo. Most of the patients (46 of 49) had Meniere's disease. Results indicate that 71% (35 of 49) of the patients had no vertigo after the operation, while 22% (11 of 49) had much improvement. Hearing was maintained within 20 dB of the preoperative level in 78% (38 of 49) of the patients. During surgery in the last 23 patients, direct nerve potentials were recorded from the middle ear promontory and the intracranial cochlear nerve. Brain stem auditory evoked responses were simultaneously recorded in the last 10 patients. It appears that the intraoperative direct cochlear nerve potentials can be used as a sensitive monitor of trauma to the cochlear nerve during and after vestibular neurectomy. If the latency of the eighth nerve action potential changes less than 0.3 msec and the waveform does not change after vestibular neurectomy, there is an excellent chance that hearing at 1 month after surgery will be within 15 dB of the level before surgery. The retrolabyrinthine vestibular neurectomy has replaced the middle fossa vestibular neurectomy and the endolymphatic subarachnoid shunt procedure in our clinic.

Retrolabyrinthine vestibular neurectomy with and without monitoring of eighth nerve potentials.

Retrolabyrinthine vestibular neurectomy is a safe and effective treatment for Meniere's disease and inner ear vertigo. Hearing was maintained within 20 dB of the preoperative level in 83% of our patients and speech discrimination scores were preserved within 20% in 80%. Intraoperative monitoring of audiometric evoked potentials, employed to study the possible causes of hearing loss, provided rapid, sensitive detection of trauma to the auditory system. Our patients benefited from this technique--those who underwent retrolabyrinthine vestibular nerve section, as well as those who experienced acoustic neuroma surgery, where hearing preservation is a goal. Direct intraoperative monitoring of eighth nerve function continues to be a standard part of our surgical practice.

Hearing preservation after acoustic neuroma surgery using intraoperative direct eighth cranial nerve monitoring.

Since the advent of brainstem auditory evoked response audiometry and computerized tomography, small acoustic neuromas are found more frequently. The patients often have serviceable hearing and wish to preserve it during complete tumor removal. Since 1978, we operated on thirteen patients with acoustic neuromas using the retrosigmoid suboccipital approach. Our goal in these cases was to preserve hearing. We began using intraoperative direct eighth nerve monitoring in 1983. This allowed us to rapidly assess cochlear nerve function during excision of small acoustic neuromas. Intraoperative monitoring was used in 5 of 13 cases, and in three patients, hearing was preserved. In the 8 cases where intraoperative monitoring was not used, hearing was preserved in only two patients. Our overall success rate of simultaneous total tumor removal hearing preservation was 38%. Tumor size varied from intracanalicular to one with a 3.0 cm protrusion medial to the porus acousticus. Hearing was preserved in 54% of cases where tumor size was less than 1.5 cm. We find continuous monitoring of direct eighth nerve evoked action potentials to be extremely valuable and a rapid indication of reversible cochlear nerve trauma.

Conservative management of acoustic neuroma in the elderly patient.

A subtotal resection through the translabyrinthine approach should be used in the treatment of large symptomatic acoustic neuromas in patients over the age of 65. This approach will consistently relieve the patient's symptoms of brain stem compression, reduce postoperative morbidity and complications, and preserve facial nerve function. In the elderly, after subtotal resection, the remaining tumor in 80% of cases appears to remain dormant during the average six year follow-up (1-16 year range). Eighty percent of acoustic neuromas not operated upon, appear to grow at a slow rate (0.2 cm/yr) while 20% grow at a fast rate (1 cm/yr). Patients over the age of 65 with small acoustic neuromas do not need surgical intervention. Yearly CT scanning is recommended to determine the growth rate of the acoustic neuroma. A conservative approach should be used in the treatment of all acoustic neuromas in the elderly.

Preoperative and postoperative growth rates in acoustic neuromas documented with CT scanning.

Sequential computerized tomography (CT) allows us to determine the growth rate of acoustic neuromas. Prior to CT scanning, a variability in tumor growth rates was recognized on the basis of clinical signs. After incomplete tumor removal, some patients experienced rapid recurrence, whereas others lived many years without recurrence. We used CT scanning to study tumor growth rates in a heterogeneous group of 21 patients. Thirteen elderly patients were given annual scans after incomplete tumor removal, while eight patients who had not had surgery are likewise being followed up. Early detection and complete tumor removal with preservation of hearing and facial function remain the goal in vigorous and healthy patients. However, a large number of older, infirm patients with acoustic neuromas may not require surgery or be candidates for incomplete tumor removal. Because rapid tumor growth may necessitate total tumor removal even in older patients, a better understanding of the growth rates may permit us to take a more scientific approach in planning these patients' management.

Retrolabyrinthine vestibular neurectomy with simultaneous monitoring of eighth nerve action potentials and electrocochleography.

Since November 1978, we have used retrolabyrinthine vestibular neurectomy in 29 of 42 cases as the primary procedure to relieve vertigo in Meniere's disease. The results indicate that 67% of patients had no vertigo postoperatively, while 21% were much improved. Hearing was maintained within 20 dB of the preoperative level in 78%. Simultaneous intraoperative electrocochleography and eighth nerve action potentials were used to monitor auditory function in the last fourteen cases using an Amplaid Mark V evoked potential signal processor. It appears that the intraoperative electrocochleography after vestibular neurectomy can be used as an indicator of postoperative auditory function. The retrolabyrinthine vestibular neurectomy has replaced the middle fossa vestibular neurectomy and the endolymphatic subarachnoid shunt in our practice.

Retrolabyrinthine vestibular neurectomy.

Vestibular neurectomy performed through the middle fossa or retrolabyrinthine approach is an effective method of denervating the labyrinth while preserving residual hearing. In the authors' opinion, the retrolabyrinthine approach is easier to perform, takes less time, and places the facial nerve in less jeopardy than the middle fossa procedure. The results of 26 cases of retrolabyrinthine vestibular neurectomy followed from six to 26 months indicate an 85% (22/26) cure rate of vertigo and a 79% (21/26) rate of hearing unchanged or improved.