Preservation of hearing in neurofibromatosis 2

Endoscopy in neuro-otologic surgery

Endoscopy offers several distinct advantages over the operating microscope during neuro-otologic surgery that make it an excellent adjunctive tool to the microscope or independent modality during cranial base surgery. The high magnification gives excellent definition of perforating blood vessels, cranial nerves, and neural structures, which in many cases is superior to that achieved with the microscope. Furthermore, the use of angled or flexible endoscopes allows one to look around corners and behind anatomic structures blocking the view seen via a 0 degree microscope. Endoscopy also has the theoretical advantage that a less invasive operative procedure is required, which should reduce the operative morbidity. Several notable disadvantages of endoscopy include the problems associated with blood soiling the endoscope, making visualization difficult or impossible, the lack of readily available instrumentation designed specifically for endoscopic neuro-otology, and the poor overview of the operative field. This last point is an important one because the endoscope is placed adjacent to the lesion and does not allow one to look backward to prevent [figure: see text] injury to structures next to the shaft of the telescope. Furthermore, the surgeon must be cognizant of potential thermal injury to structures caused by the heat generated by the light source. The present endoscopic technology limits the image that the surgeon sees to two dimensions, which results in certain unique problems when operating in a three-dimensional milieu. Because of this, there is a steep learning curve to acquire endoscopic dexterity and three-dimensional orientation. Finally, bimanual operation requires the use of an articulated endoscope holder or the commitment of the co-surgeon to hold the endoscope. One of the limitations of the operative microscope is that the angle of view is determined by the distance of the lens to the skull, retractor, or obstructing tissue, which is a function of the lens focal length; the longer the focal length, the narrower the viewing angle. During most microsurgical procedures, the focal distance varies between 200 and 400 mm. Using a previous analogy, if one looks through a door's keyhole at close range, nearly the entire room on the opposite side of the door can be seen, although nothing can be seen when the hole is viewed from a long distance. This is similar to what happens when using the endoscope with focal lengths ranging from 5 to 20 mm: a wider angle of view can be achieved. Based on their, experience the authors believe that endoscopes can be used safely during neuro-otologic surgery. As an adjunct to or substitution for the operative microscope, this modality does improve visualization of bony, neural, and vascular structures while minimizing cerebellar retraction.

Paediatric presentation of type 2 neurofibromatosis

BACKGROUND

Neurofibromatosis type 2 (NF2) is a highly penetrant autosomal dominant condition predisposing affected individuals to schwannomas and meningiomas. The proportion of children presenting with meningioma or schwannoma who have NF2 is not well described, and neither is the mode of presentation in most children with the inherited disease.

AIMS

To determine the frequency of childhood meningioma and schwannoma cases caused by NF2 and the mode of presentation.

METHODS

The records of the Manchester Children's Tumour Registry from 1954 were searched for cases of meningioma and schwannoma. Paediatric presentation in a large UK series of NF2 was also studied.

RESULTS

18% (61/334) of patients with NF2 on the UK database presented in the paediatric age group (0-15 years), frequently with the symptoms of an isolated tumour. More than half had no family history to alert the clinician to their susceptibility. Three of 22 children presenting with a meningioma on the Manchester Children's Tumour Registry have gone on to develop classic features of NF2.

CONCLUSIONS

Clinicians should suspect NF2 in children presenting with meningioma, schwannoma, and skin features, such as neurofibromas/schwannomas, but fewer than 6 café au lait patches, who thus fall short of a diagnosis of neurofibromatosis type 1.

Evaluation of surgical approaches to endoscopic auditory brainstem implantation

OBJECTIVES

This study investigates the use of endoscopy for the placement of an auditory brainstem implant by translabyrinthine, retrosigmoid (suboccipital), and middle cranial fossa approaches.

STUDY DESIGN

Cadaver dissection and endoscope-assisted placement of the auditory brainstem implant.

METHODS

Translabyrinthine, retrosigmoid, and middle cranial fossa dissections were performed bilaterally in five cadaveric heads. An auditory brainstem implant was placed within the lateral recess of the fourth ventricle under endoscopic visualization. The implantation was performed with all approaches and documented by digital image capture followed by production of dye-sublimation photographic prints.

RESULTS

The lateral recess was visualized with the endoscope in all three approaches to the brainstem. The 30 degrees endoscope provided the best visualization by translabyrinthine and retrosigmoid dissection and was essential for the middle cranial fossa approach. Refinement of implant position was readily achieved, as even the deepest portion of the recess could be seen with all three approaches.

CONCLUSIONS

This study finds that endoscopy provides superior visualization of the lateral recess of the fourth ventricle than the operating microscope with all approaches. The retrosigmoid approach is recommended, as it provides the best view of the implantation site and the easiest angle for placement of the prosthesis. The use of the endoscope may allow for a smaller craniotomy than with conventional microscopic techniques, depending on tumor size. The translabyrinthine approach provides a good view of the lateral recess but had no advantage over other approaches. The middle cranial fossa approach is only possible with angled endoscopes; however, it is technically the most difficult and places the facial nerve at greatest risk.

Hearing preservation in patients undergoing vestibular schwannoma surgery: comparison of middle fossa and retrosigmoid approaches

OBJECT

The goal of this retrospective study was to evaluate hearing preservation after surgery for vestibular schwannoma in which the middle fossa (MF) or retrosigmoid (RS) approaches were used. Hearing preservation in vestibular schwannoma surgery can be achieved by using either the MR or RS approach. Comparative outcome data between these approaches are lacking, and, as a result, selection has generally been determined by the surgeon's preference.

METHODS

The authors have compared removal of small vestibular schwannomas via MF and RS approaches with regard to hearing preservation and facial nerve function. The study group was composed of consecutively treated patients with vestibular schwannoma, 48 of whom underwent operation via an MF approach and 50 of whom underwent the same number of RS operations. Tumors were divided into size-matched groups. Hearing results were recorded according to the American Academy of Otolaryngology-Head and Neck Surgery criteria, and facial nerve outcome was recorded as the House-Brackmann grade. Overall, 26 (52%) of the patients treated via the MF approach achieved a Class B or better hearing result compared with seven (14%) of the RS group. Some hearing was preserved in 32 (64%) of the patients in the MF group and in 17 (34%) of the RS group. The results obtained by using the MF approach were superior for intracanalicular tumors (p=0.009, t-test), and for tumors with a cerebellopontine angle (CPA) component measuring 0.1 to 1 cm (p=0.006, t-test). For tumors in the CPA that were 1.1 to 2 cm in size, our data were inconclusive because of the small sample size. Facial weakness was seen more frequently after MF surgery in the early postoperative period, but results were equal at 1 year.

CONCLUSIONS

The results of this study have demonstrated a more favorable hearing outcome for patients with intracanalicular tumors and tumors extending up to 1 cm into the CPA that were removed via the MF when compared with the RS approach.

Retinal changes associated with neurofibromatosis 2

INTRODUCTION

Neurofibromatosis (NF) is now known to be more than one disease. NF2, formerly classified as central neurofibromatosis, is characterized by bilateral vestibular schwannomas, previously termed "acoustic neuromas", and is much less common than NF1. Lens opacities at an early age have been described in approximately 85% of NF2 patients.

PURPOSE

To determine the frequency of retinal abnormalities in NF2 patients.

METHODS

We prospectively examined 15 consecutive patients who met the diagnostic criteria of NF2.

RESULTS

We observed an epiretinal membrane in the macular or paramacular area in 12 of 15 patients, and a combined pigment epithelial and retinal hamartoma in the macula of one patient who also had an epiretinal membrane in the macula of the other eye. Additionally, 11 patients had central posterior cortical, subcapsular, or peripheral cortical lens opacities.

CONCLUSIONS

Children or young patients with epiretinal membranes, combined pigment epithelial retinal hamartoma, and lens opacities that are not the result of other ocular disorders should have a neurologic evaluation and a careful family history for NF2.

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.

Auditory brainstem implant: I. Issues in surgical implantation

Most patients with neurofibromatosis type 2 (NF2) are totally deaf after removal of their bilateral acoustic neuromas. Twenty-five patients with neurofibromatosis type 2 have been implanted with a brainstem electrode during surgery to remove an acoustic neuroma. The electrode is positioned in the lateral recess of the fourth ventricle, adjacent to the cochlear nuclei. The present electrode consists of three platinum plates mounted on a Dacron mesh backing, a design that has been demonstrated to be biocompatible and positionally stable in an animal model. Correct electrode placement depends on accurate identification of anatomic landmarks from the translabyrinthine surgical approach and also on intrasurgical electrophysiologic monitoring. Some tumors and their removal can result in significant distortion of the brainstem and surrounding structures. Even in the absence of identifiable anatomic landmarks, electrode location can be adjusted during surgical placement to find the location that maximizes the auditory evoked response and minimizes activation of other monitored cranial nerves. Stimulation of the electrodes produces auditory sensations in most patients, with results similar to those of single-channel cochlear implants. A coordinated multidisciplinary team is essential for successful application of an auditory brainstem implant.

Ocular findings associated with neurofibromatosis type II

BACKGROUND

Neurofibromatosis has been recently acknowledged as consisting of a number of different diseases. Neurofibromatosis (NF) type I and NF type II are the most clearly defined. Type II is characterized by bilateral acoustic neuromas and is rare (its incidence is 1/50,000). The previously reported ocular associations of NF type II are posterior subcapsular cataracts, Lisch nodules, and combined hamartomata of the retinal pigment epithelium and retina. In this study, the authors attempt to define further the ocular manifestations of NF type II.

METHODS

The authors prospectively examined 9 patients who met the diagnostic criteria for NF type II (age, 18 to 38 years; mean, 25 years).

RESULTS

Seven of nine patients had epiretinal membranes in the posterior pole. None of these epiretinal membranes were visually significant. In addition, five patients had central posterior cortical cataracts and five had peripheral wedge-shaped cortical cataracts.

CONCLUSION

The presence of epiretinal membranes in young patients may represent another clinical finding associated with NF type II. Epiretinal membranes, central posterior cataracts, peripheral cortical cataracts, or combined hamartoma of the retinal epithelium and retina in young patients should alert the ophthalmologist to include NF type II in the differential diagnosis in patients with stigmata of NF type II.

Preservation of hearing in bilateral acoustic neurinomas by deliberate partial resection

With the aim of preserving hearing, 20 acoustic neurinomas in 17 patients with neurofibromatosis 2 were intentionally submitted to an incomplete (80%) tumour removal. In 12 cases this was an operation on the last hearing ear with total deafness of the contralateral ear. If an auditus existed in both ears the better hearing ear was selected for the primary intervention. Early audiological controls evidenced residual hearing in 19 of the 20 cases operated on by the enlarged middle fossa approach, which was utilized inspite of the tumour diameters being between 1 and 6 cm in the cerebello-pontine angle. The oncologic and functional follow-up over 1 to 7 years showed different patterns of slow progression of hearing loss and of persistent auditory function over 2 to 7 years. Facial nerve function was excellent in 16 of the 18 controlled cases. Continued CT or MRT imaging revealed no signaling in 2 cases, constant tumour sizes in 10 cases and slow progression in 3 cases. With regard to the importance of an auditory communication in the younger adult, the described treatment modality appears to be the first choice method.

Contemporary management of neurofibromatosis

The neurofibromatoses are two distinct entities with different genetic origins. The phenotypic expressions and required treatments are different. The devastating nature of neurofibromatosis-2 may be more effectively controlled through the application of advanced imaging techniques and contemporary neurotologic procedures. The most common manifestation of neurofibromatosis-2 is that of bilateral acoustic neuromas. The eventual total bilateral sensorineural deafness associated with this condition can be obviated in selected cases if the diagnosis is established early. Follow-up data are reported for three patients in whom hearing was preserved in at least one ear. When removal with hearing preservation is not possible, subtotal tumor removal with decompression of the internal auditory canals may delay progression of hearing loss. A new approach to tumors of the pterygomaxillary fossa that have extended to the middle cranial fossa has been successfully applied and is described.