Microsurgical anatomy and pathoanatomy of the outer arachnoid membranes in the cerebellopontine angle: cadaveric and intraoperative observations

PURPOSE

The cerebellopontine angle (CPA) is a frequent region of skull base pathologies and therefore a target for neurosurgical operations. The outer arachnoid is the key structure to approach the here located lesions. The goal of our study was to describe the microsurgical anatomy of the outer arachnoid of the CPA and its pathoanatomy in case of space-occupying lesions.

METHODS

Our examinations were performed on 35 fresh human cadaveric specimens. Macroscopic dissections and microsurgical and endoscopic examinations were performed. Retrospective analysis of the video documentations of 35 CPA operations was performed to describe the pathoanatomical behavior of the outer arachnoid.

RESULTS

The outer arachnoid cover is loosely attached to the inner surface of the dura of the CPA. At the petrosal surface of the cerebellum the pia mater is strongly adhered to the outer arachnoid. At the level of the dural penetration of the cranial nerves, the outer arachnoid forms sheath-like structures around the nerves. In the midline, the outer arachnoid became detached from the pial surface and forms the base of the posterior fossa cisterns. In pathological cases, the outer arachnoid became displaced. The way of displacement depends on the origin of the lesion. The most characteristic patterns of changes of the outer arachnoid were described in case of meningiomas, vestibular schwannomas, and epidermoid cysts of the CPA.

CONCLUSION

The knowledge of the anatomy of the outer arachnoid of the cerebellopontine region is essential to safely perform microsurgical approaches as well as of dissections during resection of pathological lesions.

Is Preoperative Facial Palsy a Deterrent to Facial Nerve Preservation after Gross-Total Removal of Giant Vestibular Schwannomas?

Background Although rare in small vestibular schwannomas, preoperative facial nerve paresis is often present in giant schwannomas. Preserving facial nerve function in these cases remains a herculean task. This study evaluates the facial functions after complete tumor removal and whether preoperative facial nerve involvement affects postoperative functional status.

Methods This retrospective study from January 2014 to August 2021 excluded nongiant tumors (< 4 cm), neurofibromatosis type 2 cases, incomplete removals, redo surgeries, deaths, and cases done without nerve monitoring. These were grouped into preoperative facial palsy present (PFP) and no preoperative facial palsy (NFP). Facial nerve functions were assessed on first postoperative day, at the time of discharge, and at last follow-up and dichotomized into two groups: nondisfiguring (House–Brackmann [HB] grades I–III) and disfiguring (HB grades IV–VI). The cohort outcomes of patients with nondisfiguring PFP (HB grades I–III) were also analyzed.

Results There were 88 cases (PFP, n = 57; NFP, n = 31). Facial nerve was preserved anatomically in 62 (70.45%) patients (PFP, n = 38; NFP, n = 24) without any statistical difference (p = 0.29). Statistically significant disfiguring facial outcomes (HB IV, V, VI) were seen in patients with preoperative facial palsy (p = 0.01); however, a comparison of facial functions in patients with only nondisfiguring PFP with those in NFP group did not show the statistical difference (p = 0.12).

Conclusions Facial nerve palsy present before surgery does not seem to be a deterrent to intraoperative preservation of facial nerve during complete removal of giant vestibular schwannomas. Patients with nondisfiguring facial palsies have postoperative facial functions comparable to those without facial palsy.

Hypervascularized Large Vestibular Schwannomas: Single-Center Experience in a Series of Forty Cases

Background

Vestibular schwannomas (VS) are usually hypovascularized benign tumors. Large VS (Koos grade IV) with unusual vascular architecture are defined as hypervascular (HVVS); the excessive bleeding during microsurgery has a negative impact on results.

Methods

Forty consecutive patients were operated on for HVVS (group A). A tendency to bleed and adherence of capsule to nervous structures were evaluated by reviewing intraoperative video records. The cisternal facial nerve (FN) position was reported. Microsurgical removal was classified as total, near-total, subtotal, or partial and the MIB-1 index was evaluated in all. FN results were classified according to the House-Brackmann scale.

Results

Results of Group A were compared with those of 45 patients operated on for large low-bleeding VS (group B). Mean tumor diameter was 3.81 cm in group A and 3.58 cm in group B; the mean age was 42.4 and 56.3 years, respectively. The mean American Society of Anesthesiologists Physical Status Scale class of group A was 1.67 versus 2.31 of group B (P < 0.01). Total or near-total resection was accomplished in 76.5% of group A versus 73.3% of group B. Tight capsule adhesion was observed in 67.5% of group A versus 57.8% of group B. Mean MIB-1 was 1.25% and 1.08%, respectively.

FN anatomic preservation was possible in 84.6% of group A versus 95.5% of group B; 67.5% of group A had HB grade I or II FN outcome versus 93.3% of group B (P < 0.001). In group A, 8 patients (20.0%) experienced transient postoperative complications versus 4.4% of group B. Recurrence/regrowth was observed in 4 patients in group A versus 1 in group B.

Conclusions

Intraoperative video for classification of HVVS was used. Microsurgery of large HVVS was associated with higher (usually transient) complications and recurrence/regrowth rates and poorer FN outcome, especially in patients with tight capsule adhesion.

Application of Subperineural Resection Technique in Vestibular Schwannomas: Surgical Efficacy and Outcomes in 124 patients

Objective

We aimed to explore the application and prospects of the subperineural resection technique for tumor separation and removal under the perineurium during surgery for vestibular schwannomas (VSs).

Methods

This study retrospectively analyzed 124 patients with VSs who underwent surgery via a retrosigmoid approach from July 2015 to October 2020 in the Department of Neurosurgery, Tangdu Hospital, Air Force Military Medical University. The data will be discussed with regard to the following aspects: clinical features, surgical strategies, tumor resection extent, facial–acoustic function preservation, and postoperative complications.

Results

Gross total resection (GTR) of the tumor was achieved in 104 patients, with a GTR rate of 83.9%, and subtotal resection (STR) of the tumor was achieved in 20 patients. There was no significant difference in facial and acoustic nerve functional preservation between GTR and STR, as well as in tumor resection between solid and cystic tumors. The retention rate reached 97.6% in terms of complete anatomical facial nerve preservation. Facial nerve function was assessed using the House–Brackmann (HB) grading score. Consequently, HB grades of I–II, III–IV, and V–VI were determined for 96 (77.4%), 25 (20.2%), and 3 (2.4%) cases, respectively, 1 week postoperatively and accounted for 110 cases (88.7%), 13 cases (10.5%), and 1 case (0.8%), respectively, at 6 months. Fifteen of 35 (42.9%) patients with serviceable hearing before the operation still had serviceable hearing at 6 months postoperatively. There were 5 cases of cerebellar or brainstem bleeding after the operation, and one patient died. Multivariate logistic regression analysis showed that older age (≥60 years, p = 0.011), large tumor (>3 cm, p = 0.004), and cystic tumor (p = 0.046) were independent risk factors associated with the extent of adhesion between the tumor and the brainstem and facial–acoustic nerve.

Conclusion

We successfully applied the subperineural resection technique to a large series of patients with VSs and achieved satisfactory results. Accurate identification of the perineurium and subperineural resection of the tumor can effectively reduce the disturbance of the facial–acoustic nerve during the operation and provide an intuitive basis for judging the tumor boundary. The subperineural resection technique may be conducive to improving the rate of total tumor resection and facial–acoustic nerve functional preservation in the surgical treatment of VSs.

Microsurgical treatment of symptomatic vestibular schwannomas in patients under 40: different results before and after age of 30

In 10-15% of cases of vestibular schwannoma (VS), age at diagnosis is 40 years or less. Little is known about the differences in natural history, surgical findings, and postoperative outcomes of such younger patients as compared to those of greater age. To analyze clinical and surgical and imaging data of a consecutive series of n = 50 patients with unilateral sporadic VS, aged 40 years or younger - separated in a very young group (15-30 years) and a moderately young group (31-40 years). Retrospective case series. Fifty consecutive patients under 40 years of age underwent microsurgical resection of unilateral sporadic VS via the retrosigmoid approach. The study cohort was subdivided into two groups according to the age range: group A, age range 15-30 years (n = 23 patients), and group B, age range 31-40 years (n = 27 patients). The adherence of VS capsule to surrounding nervous structures and the tendency of the tumors to bleed were evaluated by reviewing video records; the course of the FN in relation to the tumor's surface was assessed in each case. Microsurgical removal of tumor was classified as total (T), near total (residual tumor volume < 5%), subtotal (residual tumor volume 5-10%), or partial (residual tumor volume > 10%). Mean tumor size of entire cohort was 2.53 (range: 0.6-5.8) cm: 2.84 cm in group A and 2.36 cm in group B (p = NS). Facial nerve course and position within the cerebellopontine angle did not differ significantly between the two groups. At 6-month follow-up, FN functional outcome was HBI-II in 69.5% in group A, versus 96.3% in group B (p < .001). Hearing preservation was achieved in 60.0% of patients of group A and in 58.3% of group B (p = NS). Total and near-total resection was feasible in 95.6% of cases of group A and in 88.9% of group B (p = NS). Tumor capsule was tightly adherent to nervous structures in 69.6% patients of group A and in 22.2% of group B (p < .05). Significant bleeding was encountered in 56.5% of group A tumors, and in 29.6% of group B tumors (p < .01). Microsurgery of VS in patients aged 40 or less is associated with good functional results, and with high rates of total and near total tumor removal. Patients < 30 years of age have more adherent tumor capsules. Furthermore, their tumors exhibit a tendency to larger sizes, to hypervascularization, to profuse intraoperative bleeding and they present worse long-term functional FN results when compared to patients in their fourth decade of life. Our limited experience seems to suggest that a near total resection in very young VS patients with large tumors should be preferred in adherent and hypervascularized cases, in order to maximize resection and preserve function.

Vestibular schwannoma: care for soft tissues and subperineural dissection: how I do it

BACKGROUND

Recognition of the right surgical cleavage plane of a vestibular schwannoma is mandatory to preserve the facial nerve function.

METHOD

We describe here our surgical technique that is focused on soft tissues preservation and on subperineural dissection, avoiding direct exposure of the acoustico-facial complex in order to preserve facial nerve function.

CONCLUSION

Soft tissue dissection helps in reducing patient's postoperative discomfort. Meticulously keeping a subperineural plan of dissection enables to preserve facial nerve function while offering satisfying resection rates.

Arachnoid and dural reflections

The dura mater is the major gateway for accessing most extra-axial lesions and all intra-axial lesions of the central nervous system. It provides a protective barrier against external trauma, infections, and the spread of malignant cells. Knowledge of the anatomical details of dural reflections around various corners of the skull bases provides the neurosurgeon with confidence during transdural approaches. Such knowledge is indispensable for protection of neurovascular structures in the vicinity of these dural reflections. The same concept is applicable to arachnoid folds and reflections during intradural excursions to expose intra- and extra-axial lesions of the brain. Without a detailed understanding of arachnoid membranes and cisterns, the neurosurgeon cannot confidently navigate the deep corridors of the skull base while safely protecting neurovascular structures. This chapter covers the surgical anatomy of dural and arachnoid reflections applicable to microneurosurgical approaches to various regions of the skull base.

Koos grade IV vestibular schwannomas: considerations on a consecutive series of 60 cases-searching for the balance between preservation of function and maximal tumor removal

Koos grade IV vestibular schwannomas (VS) (maximum diameter > 3 cm) compress the brainstem and displace the fourth ventricle. Microsurgical resection with attention to the right balance between preservation of function and maximal tumor removal is the treatment of choice. Our series consists of 60 consecutive patients with unilateral VS, operated on from December 2010 to July 2019. All patients underwent microsurgical removal via the retrosigmoid approach. The adherence of VS' capsule to the surrounding nervous structures and the excessive tendency of tumor to bleed during debulking, because of a redundant vascular architecture, was evaluated by reviewing video records. Microsurgical removal of tumor was classified as total (T), near-total (NT: residue < 5%), subtotal (ST: residue 5-10%), or partial (P: residue > 10%). Maximal mean tumor diameter was 3,97 cm (SD ± 1,13; range 3,1-5,8 cm). Preoperative severely impaired hearing or deafness (AAO-HNS classes C-D) was present in 52 cases (86,7%). Total or NT resection was accomplished in 46 cases (76,7%), 65,8% in cases with, and 95,4% without tight adhesion of capsule to nervous structures (p < 0,001). Endoscopic-assisted microsurgical removal of VS in the IAC was performed in 23 patients: in these cases, a T resection was obtained in 78,3% versus 45,9% of microsurgery only (p < 0,001). The capsule of VS was tightly adherent to nervous structures in 63,3% of patients, whereas hypervascular high-bleeding tumors represented 56,7%. Hearing preservation was possible in 2 out of 8 patients with preoperative class B hearing. At last follow-up, 34 (56,7%) patients had a normal postoperative FN outcome (HBI), 9 (15,0%) were HBII, 8 (13,3%) HBIII, and 9 (15,0%) HBIV. The total NT resection of solid and low-bleeding VS, without tight capsule adhesion, was associated with better FN outcome. Mortality was zero; permanent complications were observed in 2 cases (diplopia, hydrocephalus), transient in 9. Microsurgery of Koos grade IV VS seems to be associated with more than acceptable functional results, with high rate of T and NT removal of tumor. Long-term FN results seem to be worse in patients with cystic Koos grade IV VS, in cases with tight capsule adherences to nervous structures and in high-bleeding tumors.

Hearing preservation in vestibular schwannoma surgery via retrosigmoid transmeatal approach

BACKGROUND

Advances in various diagnostic and/or treatment modalities, including radiological imaging, neuromonitoring, and microsurgical techniques, have resulted in treatments of vestibular schwannomas being aimed at preserving facial and hearing functions while achieving optimal tumor control.

METHOD

We describe our surgical technique for hearing preservation in vestibular schwannoma surgery.

CONCLUSION

The retrosigmoid transmeatal approach under continuous neuromonitoring (auditory brainstem response, cochlear nerve action potentials, and continuous facial nerve monitoring) enables gross-total resection of vestibular schwannomas, while preserving hearing and facial functions. Radiological assessment and microsurgical techniques, such as meticulous tumor dissection, are also essential for functional preservation with sufficient tumor removal.

Cerebellopontine angle schwannomas arising from the intermediate nerve: a scoping review

Intermediate nerve schwannomas (INS) are extremely rare lesions in literature. They have been described mimicking facial nerve schwannomas, but not vestibular schwannomas (VS). We aimed to review the previously published cases, as well as the evidence to believe that they are far more common, though usually misdiagnosed as facial or VS. We performed a review of PubMed/Medline and Embase of "intermediate nerve schwannoma," "facial nerve schwannoma," "greater superficial petrosal nerve schwannoma," "geniculate ganglion schwannoma," and "chorda tympani schwannoma" to identify all cases of INS, following the Preferred Reporting Items for Systematic reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR) statement. Furthermore, 2 cases operated at our center are shown to exemplify the proposed hypotheses. No article was excluded from review. Thirteen cases of INS, 11 cases of chorda tympani schwannoma, and 18 cases of greater superficial petrosal nerve schwannoma were found in literature. In facial nerve schwannomas, the predilection of schwannomas for sensory nerves, and the ability to preserve the motor facial nerve during tumor resection support the hypothesis of intermediate nerve as the nerve of origin. For VSs, the different arachnoidal arrangement of medial VS, the sharing of pia mater by the intermediate nerve and vestibular nerve, and the medial Obersteiner-Redlich zone of the intermediate nerve, support the hypothesis of intermediate nerve origin of some VS. The correct identification of the intermediate nerve as a nerve of origin of cerebellopontine angle schwannomas is of uttermost importance, especially when mistaken for VS, as this may account for the heterogeneity of facial and cochlear outcomes after surgery.

The Method for Placement of an Intraoperative Continuous Facial Nerve Stimulating Electrode in Acoustic Neuroma Surgery: Technical Note

Preservation of facial nerve (FN) function is the most important goal in acoustic neuroma (AN) surgery. We have been using intraoperative continuous facial nerve monitoring (ICFNm) of evoked electromyography during AN surgery. ICFNm is very useful, and we can identify the real-time functions of the FN. Some surgeons have experienced difficulty with placing the ICFN stimulating electrode (SE). We therefore show how to place the ICFN SE. We mostly perform AN surgery with a retrosigmoid approach (RSA). A craniotomy with four burr holes is performed. We dissect the arachnoid membrane along the accessory nerve from the cisterna magna to the glossopharyngeal nerve. When we are able to identify the root exit zone (REZ) of the FN near the brainstem, we place the ICFN SE on it. However, when a large tumor covers the REZ, we have to debulk the tumor to create a space between the tumor and the glossopharyngeal nerve. After that, we can place the SE on the REZ. A method for placement of the ICFN SE is needed for some techniques of AN surgery. Once we learn how to place the SE, we can identify continuous FN function during AN surgery. This method is useful for the preservation of postoperative FN function in AN surgery.

Hypervascular Vestibular Schwannomas: Clinical Characteristics, Angiographical Classification, and Surgical Considerations

BACKGROUND

There is a rare type of vestibular schwannoma, scarcely discussed in the literature, known as a hypervascular vestibular schwannoma (HVS).

OBJECTIVE

To evaluate its biological characteristics, angiographical classification, surgical outcomes, and the significance for surgical consideration, using a large series of this clinical entity.

METHODS

The definition for HVS in this study was the tumor stain from the vertebrobasilar system (VBS) in angiography. The authors conducted a retrospective analysis of 36 patients who were angiographically diagnosed with HVS and underwent surgery between 2008 and 2015. Their biological findings and their surgical outcomes were compared with non-HVS subjects. With regard to the tumor feeders and AV shunt, we classified HVS into 5 types.

RESULTS

HVS occurred more commonly in younger subjects (mean: 39.4 yr), as a larger solid tumor with multiple flow voids (mean: 34.1 mm), and involved higher levels of cerebrospinal fluid protein (mean: 202 mg/dl) and a higher MIB1-index (mean: 4.3%). The average resection rate for these 36 cases was 95.3%, and recurrence was seen in 6 cases (16.7%). Compared with non-HVS, the extent of tumor resection was significantly lower, and the recurrence rate was significantly higher. Especially in HVS type 2B (the tumor stain is fed by the VBS and the external carotid artery, with an arteriovenous shunt from the VBS), the recurrence-free survival duration was significantly shorter compared with other HVS types and non-HVS, and HVS type 2B exhibited an identifiable risk factor for recurrence.

CONCLUSION

HVS have the distinct clinical characteristics compared with those of non-HVS subjects.

The medium and long-term effect of electrophysiologic monitoring on the facial nerve function in minimally invasive surgery treating acoustic neuroma

The medium and long-term effects of electrophysiologic monitoring on the facial nerve function in minimally invasive surgery treating acoustic neuroma were studied. Sixty-two patients with acoustic neuroma taking minimally invasive surgeries in Dezhou Hospital from August 2014 to September 2015 were selected and randomly divided into 29 cases of the control group and 33 cases of the observation group. Intraoperative electrophysiologic monitoring was applied to the observation group, but not to the control group. The effects of the surgeries were compared. Comparisons on the surgical resection rate and the surgery length between two groups showed no statistical differences (P>0.05); the anatomical and functional preservation rate of facial nerves, as well as the score of survival quality in the observation group prominently proceeded that in the control group, and the differences were statistically significant (P>0.05). In conclusion, the application of the electrophysiologic monitoring on facial nerve function in minimally invasive surgery treating acoustic neuroma can effectively increase the anatomical and functional preservation rate of facial nerves, providing certain clinical significance to the improvement of living quality.

The outermost "dura-like membrane" of vestibular schwannoma

Background:

The membranous structure of vestibular schwannoma is an important factor in its surgical treatment. Herein, we report intraoperative and microscopic findings relating to an outermost dura-like membrane in cases of vestibular schwannoma and the importance of these findings.

Methods:

Intraoperative findings of 16 cases of vestibular schwannoma treated with an initial surgery were studied with an aim to determine if the cases had a dura-like membrane. Then we studied microscopic findings of the dura-like membrane using hematoxylin and eosin, Masson trichrome, and immunohistochemical staining in 2 cases.

Results:

The dura-like membrane was observed in 8 out of 16 cases. The average tumor size of the cases that had a dura-like membrane was 30 ± 8.1 mm, and Koos grading 4 was in 7 out of 8 cases, and one was grade 3. In cases without a dura-like membrane, these values were significantly smaller, with an average tumor size of 12.8 ± 5.2 mm, and Koos grading 4 was only in 1 of 8 cases, grade 3 was in 2 cases, and other 5 cases were grade 2. The outermost dura-like membrane enveloped the vestibular schwannoma around the internal acoustic meatus and was continuous with the dura mater. Reactive angiogenesis was observed in the dura mater. Microscopic findings proved its continuity with the dura mater. In one case, the facial nerve was damaged before it was identified during subcapsular dissection. In that case, the dura-like membrane negatively affected our ability to identify the facial nerve.

Conclusions:

A dura-like membrane sometimes envelops vestibular schwannoma around the internal acoustic meatus. Recognition of this membranous structure is important for the surgical preservation of facial and acoustic nerves.

The extracisternal approach in vestibular schwannoma surgery and facial nerve preservation

The classical surgical technique for the resection of vestibular schwannomas (VS) has emphasized the microsurgical anatomy of cranial nerves. We believe that the focus on preservation of the arachnoid membrane may serve as a safe guide for tumor removal. Method The extracisternal approach is described in detail. We reviewed charts from 120 patients treated with this technique between 2006 and 2012. Surgical results were evaluated based on the extension of resection, tumor relapse, and facial nerve function. Results Overall gross total resection was achieved in 81% of the patients. The overall postoperative facial nerve function House-Brackmann grades I-II at one year was 93%. There was no recurrence in 4.2 years mean follow up. Conclusion The extracisternal technique differs from other surgical descriptions on the treatment of VS by not requiring the identification of the facial nerve, as long as we preserve the arachnoid envelope in the total circumference of the tumor.

Medial acoustic neuromas: clinical and surgical implications

OBJECT

Medial acoustic neuroma is a rare entity that confers a distinct clinical syndrome. It is scarcely discussed in the literature and is associated with adverse features. This study evaluates the clinical and imaging features, pertinent surgical challenges, and treatment outcome in a large series of this variant. The authors postulate that the particular pathological anatomy with its arachnoidal rearrangement has a profound implication on the surgical technique and outcome.

METHODS

The authors conducted a retrospective analysis of 52 cases involving 33 women and 19 men who underwent resection of medial acoustic neuromas performed by the senior author (O.A.) over a 20-year period (1993-2013). Clinical, radiological, and operative records were reviewed, with a specific focus on the neurological outcomes and facial nerve function and hearing preservation. Intraoperative findings were analyzed with respect to the effect of arachnoidal arrangement on the surgeon's ability to resect the lesion and the impact on postoperative function.

RESULTS

The average tumor size was 34.5 mm (maximum diameter), with over 90% of tumors being 25 mm or larger and 71% being cystic. Cerebellar, trigeminal nerve, and facial nerve dysfunction were common preoperative findings. Hydrocephalus was present in 11 patients. Distinguishing intraoperative findings included marked tumor adherence to the brainstem and frequent hypervascularity, which prompted intracapsular dissection resulting in enhancement on postoperative MRI in 18 cases, with only 3 demonstrating growth on follow-up. There was no mortality or major postoperative neurological deficit. Cerebrospinal fluid leak was encountered in 7 patients, with 4 requiring surgical repair. Among 45 patients who had intact preoperative facial function, only 1 had permanent facial nerve paralysis on extended follow-up. Of the patients with preoperative Grade I-II facial function, 87% continued to have Grade I-II function on follow-up. Of 10 patients who had Class A hearing preoperatively, 5 continued to have Class A or B hearing after surgery.

CONCLUSIONS

Medial acoustic neuromas represent a rare subgroup whose site of origin and growth patterns produce a distinct clinical presentation and present specific operative challenges. They reach giant size and are frequently cystic and hypervascular. Their origin and growth pattern lead to arachnoidal rearrangement with marked adherence against the brainstem, which is critical in the surgical management. Excellent surgical outcome is achievable with a high rate of facial nerve function and attainable hearing preservation. These results suggest that similar or better results may be achieved in less complex tumors.

Prognosis of tinnitus after acoustic neuroma surgery--surgical management of postoperative tinnitus

OBJECTIVE

Tinnitus is a bothersome symptom for patients with acoustic neuroma. We studied the possibility of surgical control of postoperative tinnitus associated with acoustic neuroma.

METHODS

Postoperative changes and prognosis of tinnitus were studied in 367 patients treated surgically via a lateral suboccipital retrosigmoid approach.

RESULTS

Postoperative prognosis of tinnitus was as follows: resolved in 20%, improved in 22%, unchanged in 35%, changed in 10%, and worsened in 14% of 290 patients who had preoperative tinnitus, and no tinnitus in 78% and appeared in 22% of 77 patients without preoperative tinnitus. Prognosis of postoperative tinnitus was influenced by age, tumor size, preoperative hearing acuity, types of preoperative hearing disturbance, and conditions of the cochlear nerve after tumor resection. Worse prognosis of postoperative tinnitus in the preoperative tinnitus group was found in younger patients, smaller tumor size, better preoperative hearing function, and normal or retrocochlear type of hearing disturbance. Regarding the conditions of the cochlear nerve after tumor resection, prognosis of tinnitus was significantly worse in the group of anatomically preserved cochlear nerve without useful hearing than in the group of cut cochlear nerve.

CONCLUSIONS

Deciding whether to cut the cochlear nerve during acoustic neuroma surgery by referring to a flowchart, we proposed in cases where hearing preservation is not intended or judged less possible contributes to controlling postoperative tinnitus. However, regardless of whether the cochlear nerve was cut intraoperatively, tinnitus remained unchanged in 37% of patients, suggesting that their tinnitus originates in the brainstem or post-brainstem pathways before surgery, and it is considered difficult to control postoperative tinnitus in these cases.