A modified extended middle cranial fossa approach for acoustic nerve tumors. Results of 125 operations

Comprehensive review of the extended middle cranial fossa approach

PURPOSE OF REVIEW

To review the current literature on the extended middle cranial fossa (xMCF) approach and to provide a comprehensive description of the relevant anatomy, indications, surgical technique, results, and complications.

RECENT FINDINGS

The xMCF approach expands the surgical exposure provided by the sMCF approach, allowing access to the internal auditory canal, cerebellopontine angle, prepontine cistern, anterior petrous apex, petrous carotid artery, Meckel's cave, cavernous sinus, mid and upper clivus, and posterior lesions approaching the jugular foramen. Preservation of serviceable hearing is possible with success rates approximating 50% in vestibular schwannoma and meningioma resection, and facial nerve outcome is excellent.

SUMMARY

The xMCF is an important approach for difficult to access lesions that additionally offers the possibility of hearing preservation. This approach is also useful for vascular lesions, auditory brainstem implantation, and lesions of mid-brainstem.

Anatomic Assessment of Petrous Internal Carotid Artery, Facial Nerve, and Cochlea Through the Anterior Transpetrosal Approach

The aim of this study was to measure the related parameters of the cochlea, so as to allow preoperative assessment of the anatomic relationship of the petrous internal carotid artery (ICA), the facial nerve (FN), and the cochlea during skull base surgery. Seven parameters of these 3 structures were examined in the computed tomographic scan of 120 patients. The shortest distance from the cupula cochleae to the petrous ICA and the FN is as follows: 19.39 (1.01) mm to the stylomastoid foramen (D2), 10.27 (0.80) mm to the midpoint of the genu of FN canal (D3), 13.66 (0.88) mm to the exocranial opening of the carotid canal (D4), and 5.64 (1.03) mm to the midpoint of carotid knee (D5). The shortest distance between the mastoid segment of FN canal and the vertical segment of the petrous ICA (D6) was 13.33 (1.25) mm. The angle between D2 and D3 was measured at 45.66 (3.31)°, and the angle between D4 and D5 was measured at 41.08 (2.64)°. Clinically, it is relatively safe to work within the distances and angles measured in this research, and these results may give surgeons a practical and specific view of these 3 structures in the skull base approaches such as anterior transpetrosal approach to achieve the best possible surgical outcome and maximize safety.

Radiographic Assessment and Surgical Implications of Arcuate Eminence Pneumatization

BACKGROUND

The middle cranial fossa (MCF) approach is a valuable yet technically challenging technique. Identification of the superior semicircular canal (SCC) using the arcuate eminence (AE) was proposed as a surface landmark. However, the AE is sometimes absent, with inconsistent relationship to the SCC. Air cells in the AE area facilitate safer identification of the SCC. The aim of this study is to determine the radiographic prevalence of AE pneumatization.

METHODS

Two hundred consecutive fine-cut temporal bone CT scans were retrospectively reviewed. The region of the petrosal bone at and above the level of the SCC dome was assessed for the presence of air cells, and graded 0 (no pneumatization) to 2 (well pneumatized).

RESULTS

Four hundred temporal bones were studied. The average age was 49 years (range 18-89). Of all AE assessments, 47 (12%) were nonpneumatized, 62 (15%) partially pneumatized, and 291 (73%) well pneumatized. There was no significant correlation between patient age and pneumatization grade (p = 0.72).

CONCLUSION

The SCC is a valuable landmark in MCF surgery as it holds consistent relationships to adjacent critical structures. Surrounding air cells should facilitate safer initial identification of the SCC, as the AE region is well pneumatized in 73% of patients.

The intracranial facial nerve as seen through different surgical windows: an extensive anatomosurgical study

BACKGROUND

The facial nerve has a short intracranial course but crosses critical and frequently accessed surgical structures during cranial base surgery. When performing approaches to complex intracranial regions, it is essential to understand the nerve's conventional and topographic anatomy from different surgical perspectives as well as its relationship with surrounding structures.

OBJECTIVE

To describe the entire intracranial course of the facial nerve as observed via different neurosurgical approaches and to provide an analytical evaluation of the degree of nerve exposure achieved with each approach.

METHODS

Anterior petrosectomies (middle fossa, extended middle fossa), posterior petrosectomies (translabyrinthine, retrolabyrinthine, transcochlear), a retrosigmoid, a far lateral, and anterior transfacial (extended maxillectomy, mandibular swing) approaches were performed on 10 adult cadaveric heads (20 sides). The degree of facial nerve exposure achieved per segment for each approach was assessed and graded independently by 3 surgeons.

RESULTS

The anterior petrosal approaches offered good visualization of the nerve in the cerebellopontine angle and intracanalicular portion superiorly, whereas the posterior petrosectomies provided more direct visualization without the need for cerebellar retraction. The far lateral approach exposed part of the posterior and the entire inferior quadrants, whereas the retrosigmoid approach exposed parts of the superior and inferior quadrants and the entire posterior quadrant. Anterior and anteroinferior exposure of the facial nerve was achieved via the transfacial approaches.

CONCLUSION

The surgical route used must rely on the size, nature, and general location of the lesion, as well as on the capability of the particular approach to better expose the appropriate segment of the facial nerve.

Surgical management of petroclival chordomas: report of eight cases

In the management of skull base chordomas, surgical treatment is essential to achieve long-term control. A petroclival chordoma growing laterally in the skull base is one of the most challenging tumors for neurosurgeons. We have treated petroclival chordomas based on the principle of maximal surgical resection of the tumor with minimal morbidity. Lateral skull base approaches were used to approach petroclival chordomas in eight patients. The surgical procedure involved removal of soft tumor tissue and extensive drilling of adjacent bony structures. Gross total resection of the tumor was achieved in six patients. Subtotal resection in the remaining two patients was associated with acceptable morbidity. In cases of petroclival chordomas, lateral skull base approaches can be used as a primary procedure, although those approaches may be associated with high rates of morbidity and mortality.

Anatomo-radiological evaluation of lateral approaches to the skull base

Our objective is to correlate the anatomical exposure provided by complex skull base approaches to the lateral skull base with their CT and MRI scans counterparts and to introduce a modular concept emphasizing the derivation of complex skull base approaches from simpler ones.We executed 10 lateral approaches to the skull base in 20 embalmed cadaveric heads (40 sides). Each approach was executed a minimum of three times on each specimen. These approaches were the pterional and its modifications, the subtemporal and its modifications, and the suboccipital and its modifications. We correlated the approaches and the areas of the skull base exposed by scanning the surgical cavity filled with material imageable by CT and MRI and throughly surveying the operative field.Visualization of the area of the skull base exposed was excellent using our CT-MRI imageable cadaveric preparation. The topographic areas of the skull base exposed correlated well with their radiological counterparts.The areas of the skull base exposed by each of the complex surgical approaches to the skull base were clearly delineated by using our anatomo-radiological correlation. Complex approaches to the skull base are formed by simple neurosurgical approaches (building blocks) to which different modules are added.

Prediction of facial nerve function after surgery for cerebellopontine angle tumors: use of a facial nerve stimulator and monitor

A series of 18 patients undergoing surgery for cerebellopontine angle tumors is reported. Patients were grouped according to size of tumor (0 to 2.5 cm, 11 cases; more than 2.5 cm, 7 cases). In all, the facial nerve was identified and conductance assessed by monitoring the facial electromyographic response to facial nerve stimulation. Postoperative facial nerve function was graded clinically after 3 months according to the House scale. Tumor removal was complete in all cases. In patients with tumors up to 2.5 cm the facial nerve was intact to visual inspection at the end of the procedure in all but one, where partial division was evident. In this group intraoperative facial nerve stimulation indicated electrical integrity in 8 of the 11 cases, all of which regained good facial nerve function postoperatively (House grades I and II). Nerve conduction was lost during the operation in the remaining three patients with small tumors; two subsequently developed a moderately severe (grade IV) dysfunction and the third, a total paralysis (grade VI). In the large (more than 2.5 cm) tumor group the facial nerve was anatomically intact in five of the seven cases, partially divided in one, and completely sectioned in the remaining case. Facial nerve stimulation indicated functional integrity in three patients, two of whom developed moderate (grade III) and the third a severe (grade V) dysfunction. In the other four cases nerve function could not be detected at operation; three of these developed a moderate facial nerve dysfunction (grade III/IV) and the final case a complete paralysis (grade VI). Intraoperative facial nerve monitoring appeared to predict eventual facial function accurately in the small tumor group, but did not predict facial nerve recovery reliably following surgery for larger tumors.

Beyond audiofacial morbidity after vestibular schwannoma surgery

Object

Outcomes following vestibular schwannoma (VS) surgery have been extensively described; however, complication rates reported in the literature vary markedly. In addition, the majority of reports have focused on outcomes related to cranial nerves (CNs) VII and VIII. The objective of this study was to analyze reported morbidity unrelated to CNs VII and VIII following the resection of VS.

Methods

The authors performed a comprehensive search of the English language literature, identifying and aggregating morbidity and death data from patients who had undergone microsurgical removal of VSs. A subgroup analysis based on surgical approach and tumor size was performed to compare rates of CSF leakage, vascular injury, neurological deficit, and postoperative infection.

Results

One hundred articles met the inclusion criteria, providing data for 32,870 patients. The overall mortality rate was 0.2% (95% CI 0.1–0.3%). Twenty-two percent of patients (95% CI 21–23%) experienced at least 1 surgically attributable complication unrelated to CNs VII or VIII. Cerebrospinal fluid leakage occurred in 8.5% of patients (95% CI 6.9–10.0%). This rate was markedly increased with the translabyrinthine approach but was not affected by tumor size. Vascular complications, such as ischemic injury or hemorrhage, occurred in 1% of patients (95% CI 0.75–1.2%). Neurological complications occurred in 8.6% of cases (95% CI 7.9–9.3%) and were less likely with the resection of smaller tumors (p < 0.0001) and the use of the translabyrinthine approach (p < 0.0001). Infections occurred in 3.8% of cases (95% CI 3.4–4.3%), and 78% of these infections were meningitis.

Conclusions

This study provides statistically powerful data for practitioners to advise patients about the published risks of surgery for VS unrelated to compromised CNs VII and VIII.

The relationship between the zygomatic arch and the floor of the middle cranial fossa: a radiographic study

OBJECTIVE

Access to the floor of the middle cranial fossa (MCF) is often required for approaches to cranial base lesions. This study measures the craniocaudal distance between the zygomatic arch (ZA) and the floor of the MCF from a random sample of high-resolution computed tomography scans of the cranial base.

METHODS

Forty computed tomography scans were imported into an OsiriX station and reconstructed in multiple planes. The most caudal point of the MCF was determined in each computed tomography scan. The distances between that point and the root of the zygoma and the middle point of the ZA were calculated. The thickness of the temporalis muscle and the vertical height of the zygoma were also calculated. A 2-tailed, paired Student t test was used to compare right and left measurements with a 95% confidence interval and P value <.05 as statistically significant.

RESULTS

The foramen ovale was consistently the lowest point of the MCF. The average root-to-floor measurement was 5.05 +/- 0.42 mm above the floor of the MCF and distance of the mid-zygoma to the floor was 1.94 +/- 0.61 mm above the floor of MCF. The average temporalis muscle thickness and vertical height of the ZA were 22.22 +/- 0.36 mm and 8.10 +/- 0.13 mm, respectively. The muscle-to-floor measurement (muscle thickness + mid-zygoma-to-floor measurement) was 24.16 +/- 0.74 mm.

CONCLUSION

The routine use of a zygomatic osteotomy in approaches to the MCF does not provide very much increased exposure. However, in patients with exceptionally thick temporalis muscles or a high ZA, a zygomatic osteotomy may be helpful in providing exposure of the floor of the MCF.

An anatomical and radiological study of the high jugular bulb on high-resolution CT scans and alcohol-fixed skulls of adults

Although many reports mention a "high jugular bulb" (HJB), it is often not clearly defined. We examined the relationship between the jugular bulb (JB) and the internal auditory canal (IAC) in 200 temporal bones on high resolution CT scans and alcohol-fixed skull bases of adults. The average distance (+/-standard deviation) between the IAC and the JB was 7.5+/-2.3mm (range, 1-16 mm). The JB was higher on the right side than its companion in 53.3% of patients (left side only in 22%; no side dominance in 23.7% of bases). When the JB reached or exceeded the floor of the IAC (16.5%), it was defined as a HJB; 61% of HJB were found in females. Bilateral HJB was found in 0.5% of patients. The HJB was not associated with a contralateral flat JB. Preoperative multiplanar high resolution CT reconstructions make the most detailed assessment of structural topography.

Assessment of the anatomical relationship between the arcuate eminence and superior semicircular canal by computed tomography

The anatomical relationship between the arcuate eminence (AE) and the superior semicircular canal (SSC) was examined by computed tomography (CT) in 52 petrous bones of 26 patients. After acquiring volume data by multidetector CT, 1-mm thick oblique bone window images perpendicular to the SSC were obtained from the axial images. The distances between the AE and the SSC, and the SSC and the superior surface of the petrous bone were measured. The AE corresponded exactly with the SSC in only 2/52 petrous bones, and corresponded well in 7/52. The AE was lateral to the SSC in 25/52 cases, medial to the SSC in 6/52 cases, intersected in 3/52 cases, and was indiscernible in 9/52 cases. The distance between the SSC and the petrous surface was 0 mm in 45/52 petrous bones, 1 mm in 5/52, 2 mm in 1/52, and 3 mm in 1/52. The SSC typically does not correspond exactly with the AE, and is generally located just under the surface of the petrous bone. Planning of the middle cranial fossa approach requires location of the SSC by CT.

Enlarged entry space for the transpetrosal approach

This report describes the removal of the roof of the external auditory meatus in approaching the tentorial edge, the cerebropontine angle, hippocampal brainstem lesions, and upper clival lesions. This procedure not only provides more space in approaching the tentorial edge or upper brainstem, it also provides a wider entry space for approaching posterior fossa lesions. This approach is also for lesions located lower than the tentorium or in the upper clivus. There is still some confusion about the method for removing the roof of the external auditory canal. We describe the clinical experience and comprehensive surgical procedures used on cadavers. Our extended temporal craniotomy technique using the removal of the roof of the external auditory meatus is a simple, safe, and useful method for obtaining a wider entry space to approach deep perimesencephalic lesions and the posterior fossa.

[High jugular bulb and its relationship with acoustic neurinoma surgery]

The jugular bulb is formed by the junction of the sigmoid sinus, inferior petrous sinus and the jugular vein. It is housed in the jugular fossa of the petrous pyramid. Variations in its size, location and relationship to the internal acoustic canal (IAC) have been reported. When the jugular bulb is located medial and less than 2 mm from the posterior wall of the internal acoustic canal, it is named as high jugular bulb. If the surgeon is not aware of this variation, damage to this structure can result in profuse haemorrhage and air embolism. This anatomical change also makes difficult the access to the intracanalicular portion of acoustic neurinomas when these tumours are excised by a retrosigmoid approach. We present the case of a patient with an acoustic schwannoma in whom a preoperative axial cranial CT revealed a high jugular bulb. To control this venous structure, we opened the IAC in a longitudinal manner achieving a total excision of the lesion preserving the function of the facial nerve. We conclude that preoperative radiological investigations in acoustic schwannomas surgery should include cranial MR and TC, to rule out the presence of a high jugular bulb. Cranial axial CT including bony windows and slices of 1.5 mm thick, should be carried out to exclude a high jugular bulb.

Subtemporal keyhole approach to the suprasellar and petroclival region: microanatomic considerations and clinical application

OBJECTIVE

To minimize surgical invasiveness, the keyhole concept is applied to the subtemporal approach.

METHODS

Anatomic features were studied in 14 sides of adult cadaver heads, and the technique was used in 162 interventions. Although most of the lesions treated were 3 cm in size or smaller, larger lesions were also treated using this technique. In some cases, if needed, an endoscope-assisted microsurgical technique was used.

RESULTS

The cadaveric study provided intimate experience with the microsurgical anatomy of the approach. The 162 consecutive patients who were operated on harbored various types of lesions; the most recent 43 consecutive interventions were investigated in detail. The complications encountered included five cases of permanent cranial nerve palsy, two cases of cerebrospinal leakage, two cases of short memory disturbance, two cases of seizure, and one case each of hemiplegia and incoordination, transient hearing loss and tinnitus, and consciousness deterioration and hemiplegia.

CONCLUSION

With careful patient selection, the subtemporal keyhole approach diminishes tissue traumatization considerably and has proven to provide sufficient operating space in the suprasellar area. When this approach is combined with the cranial base technique, the petroclival region can also be treated. However, the subtemporal keyhole approach requires deliberate preoperative planning for each patient, as well as for each surgeon.

The widened retrolabyrinthe approach: a new concept in acoustic neuroma surgery

For many years, the retrolabyrinthine approach has been limited to functional surgery of the cerebellopontine angle (CPA). As a result of the increased surgical exposure, particularly the opening of the internal auditory meatus (IAM), the widened retrolabyrinthine technique permits tumor excision from both the CPA and the IAM, regardless of the histological nature of the tumor. The authors have treated 60 acoustic neuromas of varying sizes via this approach (6% intrameatal tumors; 30% > 25 mm in diameter). The postoperative mortality rate was 0%. The risk of fistula formation was 3.3%, and 3.3% of the patients suffered from postoperative meningitis. The results for facial nerve function were equivalent to those obtained previously via a widened translabyrinthine approach and those in a series treated via a suboccipital approach (80% with Grades I and II, 15% with Grade III, and 5% with Grades V and VI). One patient (1.7%) required a secondary hypoglossal-facial nerve anastomosis and had attained a Grade IV result 6 months later. Postoperatively 21.7% of these patients maintained socially useful hearing and 20% had mediocre hearing. Socially useful hearing was preserved in 50% of a subgroup of 20 patients who had both good preoperative hearing and a tumor that involved less than half of the IAM regardless of its volume. Additionally, 15% had mediocre hearing that could be improved with hearing aids. Because of its efficacy in preserving hearing, the authors favor the retrolabyrinthine over the occipital approach, with the latter being considered less subtle and more aggressive.

Staged removal of acoustic tumors: techniques and lessons learned from a series of 83 patients

The removal of large acoustic tumors is associated with increased mortality and cranial nerve injury. One method for treating these difficult lesions is staged resection. Between 1972 and 1992, more than 600 acoustic tumors were resected at our institution. Of these, 83 were removed in stages. This represents the largest series of staged acoustic tumor resections reported to date. A review of available films and patient records was performed for all acoustic tumors resected in stages between 1972 and early 1993 to analyze demographic information, tumor size, operative technique, outcome, and complications. The information was collected on standardized data sheets and entered into a computer database. Virtually all tumors were large, with the average size being 4 cm in greatest diameter. The average patient age was 41 years, and there was a slight preponderance of female patients. Ten patients had neurofibromatosis Type 2. The suboccipital approach was used in most patients. Anatomic preservation of the VIIth cranial nerve was achieved in > 72% of patients, with an average House-Brackmann score of Grade 3 at the longest follow-up (mean, 43 mo). Facial reanimation was performed in 19 of 23 patients with transected VIIth cranial nerves. Complications included cerebrospinal fluid fistulas in 11 patients, with 8 of 11 fistulas resolving after lumbar drainage. Six patients had meningitis (bacterial in three and aseptic in three). Two patients developed wound infections, and 10 patients developed exposure keratitis. There were two documented recurrences. There were no operative deaths. In most series, the incidence of cranial nerve deficits as well as morbidity and mortality is directly related to tumor size. Our operative strategy involved debulking the lateral aspect of large tumors during Stage I. Second stage removal is performed after the remaining tumor is shown to decompress out of the pons on computed tomographic or magnetic resonance images. During the second procedure, the residual tumor is less vascular and no longer densely adherent to the brain stem. Although staged removal is not without risk, there seems to be no apparent increase in morbidity when these results are compared with the results of series from the literature. Although there remain no absolute indications for staged resection of acoustic tumors, we think that it may represent the safest option for these difficult lesions.

Unilateral acoustic tumors: how often do they recur after translabyrinthine removal?

Unilateral acoustic tumors rarely recur after total translabyrinthine removal. Review of the patient records of the House Ear Clinic revealed five recurrent tumors, for an approximate incidence of 0.3%. A questionnaire was mailed to 857 patients who were at least 9 years postoperative and failed to find any additional recurrent tumors. No preoperative or intraoperative factors were identified to predict recurrence. The average time interval from initial removal to recurrence was approximately 10 years. Flow cytometric analysis did not reveal any fundamental differences between the recurrent acoustic tumor group and a larger group of 112 acoustic tumors. Based on observed growth rates of the recurrent acoustic tumors, a single gadolinium-enhanced magnetic resonance image 5 years after surgery is advised. To prevent recurrence, a margin of normal-appearing proximal eighth cranial nerve should be removed and the nerve stump cauterized.

The retrosigmoid approach to acoustic neurinomas: technical, strategic, and future concepts

The retrosigmoid approach continues to be the most widely employed strategy for the surgical resection of acoustic neuromas. The results with respect to facial nerve function are uniformly reported to be quite high. The great emphasis currently is upon improving results with regard to the conservation of useful hearing. This paper focuses on the anatomical and strategic surgical factors that we currently consider to be important to maximizing our current results. The future aspects of this trend toward improved success in conserving hearing in these patients is also discussed.

Extended middle fossa approach for petroclival lesions

A modification of the previously described transcochlear approach to extra- and intradural petroclival and clival lesions is described in this report. It is an approach from the middle cranial fossa. It involves unroofing and depression of the external ear canal, removal of the glenoid cavity of the temporo-mandibular joint, exentration of the middle ear ossicles, posterior mobilization of labryrinthine and tympanic segments of the facial nerve, and drilling of the petrous bone from an entirely lateral perspective. An extensive and low exposure of the petroclival region, posterior aspect of the cavernous sinus, upper and mid clivus and the cerebellopontine angle is obtained. The anterior surface of the brain stem upto the pontomedullary junction is exposed with minimal or no retraction of the temporal lobe of the brain. The vein of Labbe and sigmoid sinus drainage is unhampered. Anterior and posterior extension of the exposure is possible. Only a limited mastoidectomy and labyrinthectomy, necessary to facilitate exposure and mobilization of the facial nerve is necessary. The inferior limit of the exposure is set by the dome of the jugular bulb. Hearing is sacrificed. The technique and merits of the procedure are discussed in this report. The study is based on surgical experience of 4 cases.

Middle fossa transpetrosal-transtentorial approaches for petroclival meningiomas. Selective pyramid resection and radicality

Forty-two patients with petroclival meningioma were operated upon by the middle fossa transpetrosal-transtentorial approaches since 1977. Half of those showed tumour extension into the middle fossa and one-third in the cavernous sinus. Seventeen (40%) had a large tumour of 40 mm in diameter or larger, and 8 of those had a broad attachment from the clivus to petrous pyramid of the temporal bone. The site of pyramid resection was selected from three types, depending on the tumour location and the patients' pre-operative hearing. There was no surgical mortality. Significant risk of lower cranial nerves palsy was minimal and useful hearing was preserved in 18 out of 21 patients. The follow-up, an average of 4 and a half years, showed tumours were completely eradicated in 32 patients (76%) and there was regrowth in 3 (7%). Thirty-four patients (81%) were independent, 3 disabled and only one died of rapid tumour regrowth. The most influential factor on surgical results was the extent to which the tumour had invaded the brain stem. The presence or absence of arterial encasement and of peritumoural oedema on MRI were important in the selection for radical surgery.

Lateral approaches to the petroclival region

The microsurgical anatomy that provides the basis for dealing with lesions arising in the petroclival region was reviewed in 15 adult cadaver heads and 25 dry skulls. The eight surgical approaches studied were the retrosigmoid, extreme lateral transcondylar, translabyrinthine, transcochlear, combined supra and infratentorial presigmoid, subtemporal anterior transpetrosal, subtemporal preauricular infratemporal, and the postauricular transtemporal approach. Considerations important in the selection of these approaches are discussed. Special attention was directed to the course of the facial nerve and internal carotid artery in the temporal bone and the major venous pathways draining the region.

Transpetrosal approach: surgical anatomy and technique

Transpetrosal operations have been shown to offer distinct advantages over traditional operations in approaching lesions of the petroclival area. Confusion about these approaches exists due to the variety of names given to these procedures and the lack of detailed descriptions needed to perform them. After extensive review of the literature, we have determined that all transpetrosal techniques fall into one of two categories: anterior petrosectomy or posterior petrosectomy. Combining one of these procedures with existing conventional procedures accurately describes all existing transpetrosal operations and eliminates confusion over nomenclature. In addition, through a series of cadaveric dissections and operative experience, we have detailed each of these procedures as a series of steps that will enable the surgeon to understand the unfamiliar anatomy of the temporal bone and to perform these transpetrosal techniques.

The preservation of hearing and facial nerve function in a consecutive series of unilateral vestibular nerve schwannoma surgical patients (acoustic neuroma)

Between January 1981 and February 1992, 102 non-NF-2 patients underwent removal of a unilateral vesitbular schwannoma. There were 54 women and 48 men. Eighty-six percent of patients with normal facial function preoperatively retained normal function (House score 1 or 2) postoperatively. Of the 64 patients with a functional cochlear nerve preoperatively, five had normal hearing (PTA < 25 dB, SB > 70%), five had near normal hearing (PTA < 45 dB, SD > 70%), four patients had preserved hearing (PTA < 50 dB, SD > 50%), and three patients had preserved cochlear nerve function (PTA > 50 dB, SD < 50%) after surgery. Hearing preservation was obtained in patients whose tumors were larger than 3 cm. Radiological follow-up revealed 10 patients with recurrent tumor, all but one asymptomatic.

Preservation of hearing in surgery for acoustic neuromas

Preservation of hearing was attempted in 161 cases of histologically confirmed acoustic neuroma removed by the senior author between January 1, 1970, and September 30, 1991. There were 136 patients with unilateral tumors; 22 patients had bilateral tumors (neurofibromatosis 2) and underwent a total of 25 procedures. Hearing was initially preserved in 35% of patients with unilateral tumors and in 44% of those with bilateral tumors. Results are reported in terms of pre- and postoperative pure tone average and speech discrimination scores. Surgical access to the tumor was obtained via middle cranial fossa and suboccipital approaches. The latter has been used more often over the past 5 years because of a lower associated incidence of transient facial paresis. Persistent postoperative headaches have been the most common complication following the suboccipital approach. The results of preoperative brain-stem auditory evoked response (BAER) studies were useful in predicting the outcome of hearing preservation attempts. Patients with intact BAER waveform morphology and normal or delayed latencies had a higher probability of hearing preservation in comparison to those with abnormal preoperative BAER morphology.

Acoustic tumour volume and the prediction of facial nerve functional outcome from intraoperative monitoring

The long-term facial function in 26 patients undergoing surgery to remove an acoustic neuroma has been related to the tumour volume (ml) estimated by computerized tomogram (CT) reconstruction techniques. Analysis of data allowed accurate categorization into 'small' (= < 5 ml) and 'large' (> 5 ml) tumours, which gave the maximum prognostic distinction between two groups for facial recovery. Thus, of the 14 patients with small volume tumours, 11 achieved a good (House grade I or II) facial outcome compared with 1 out of 12 patients with large tumours. Combined with the information derived from the assessment of intraoperative facial nerve electrical integrity using a combined nerve stimulator and EMG monitor, long-term facial function was predictable for all small tumours defined by volume. This represented a 15% improvement in prediction of facial recovery when defining tumour size by maximum linear dimension (small = < 2.5 cm, large > 2.5 cm). The calculations of volume obtained using a simplified ellipsoidal model compared well with CT reconstructed values (r2 = 0.85), and gave identical prediction and outcome comparisons.

Use of protein electrophoresis in the diagnosis of cerebrospinal fluid rhinorrhoea

The diagnosis of CSF rhinorrhoea on clinical grounds alone can be difficult. We describe how the use of non-invasive electrophoretic analysis of nasal secretions for tau protein (asialotransferrin) helped in the management of cases where the existence of a CSF leak was in doubt. Patients were thus saved unnecessary invasive investigations or surgery. A modification of the method of analysis, which improves diagnostic accuracy, is described.

Anatomical basis of the extended subtemporal approach to the cerebellopontine angle: its value and limitations

The cerebellopontine angle is an anatomic region situated deeply at the anterolateral aspect of the brainstem, access to which is complicated by the presence of neurovascular bundles. The functional importance of these cranial n. (trigeminal, facial, vestibulo = cochlear, glossopharyngeal, vagus and accessory) calls for the use of special surgical routes of access in certain cases. In particular, tumors situated between the vestibulocochlear-facial bundle behind and the trigeminal n. in front are difficult to reach by the suboccipital and subtemporal transmeatal routes. The endeavor to preserve hearing in particular situations, where the side opposite the tumor is no longer functional, justifies the use of a subtemporal transmeatal route extended by opening the tentorium cerebelli. This anatomic and experimental surgical study deals with the possibilities of this route of approach.

Hearing preservation in acoustic neuroma surgery and postoperative audiological findings

One hundred fifty-three cases of acoustic neuroma were treated surgically by the middle cranial fossa approach or extended middle cranial fossa approach. Attempts to preserve hearing were made in 30 cases with tumours extending 2.0 cm or less into the posterior fossa; successful hearing preservation was achieved in 12 cases. Among the 15 patients with preoperative hearing levels (HL) of 50 dB or lower and speech discrimination scores (SDS) of 50% or higher, hearing was preserved in 9 (60%) patients. A similar rate of hearing preservation was achieved among the patients with normal or near-normal hearing. Compared with those patients in whom hearing could not be preserved, those with hearing preservation had better HL, higher SDS, and less abnormal ABR findings preoperatively. Postoperatively, the HL and SDS deteriorated slightly. In addition, there was a marked prolongation of the IT5, and the incidence of absence of the stapedius reflex increased. Compared with the preoperative HL, the postoperative HL was unchanged in 5 cases; deteriorated temporarily and then improved in 5 cases; and deteriorated, though with hearing preserved, in 2 cases. Intraoperative monitoring was conducted by recording the ABR and VIII nerve compound action potentials and by electrocochleography. However, postoperative hearing could not always be predicted from the findings obtained at the end of the operation.