Abstracts DGNC

(Abstract ID: 40) S. K. Rosahl 1 , J. Lehmberg 2 1 Helios-Klinik Erfurt 2 Städtisches Klinikum München GmbH Background: Compared to far-field registration, near-field recording of cochlear and brainstem auditory potentials significantly reduces acquisition time during surgery around the cochlear nerve. We have designed and tested new tympanic and brainstem electrodes to monitor the functional integrity of the lower auditory pathway. Materials and methods: Stainless-steel, ball-shaped electrodes were developed in co-operation with inomed Medizintechnik GmbH (Emmendingen, Germany). The first of these electrodes was connected to a stainless-steel spring running through an insert earphone. It attaches to the tympanic membrane to record a peripheral auditory evoked potential (ECoG). A second mini ball electrode with a diameter of 1.6 mm was placed either on the cochlear nerve or at the dorsal cochlear nucleus of the brainstem to record a central auditory brainstem response (CABR). Dual near-field recording (DNF) with both electrodes in place was applied in a series of 589 patients with lesions in the CPA and internal auditory canal during microsurgery. Near-field potentials have been compared to the far-field Auditory Brainstem Response (ABR, Cz-A1/A2, band-pass 100 - 3000 Hz). Click stimuli were applied at 13.2 Hz. Data processing was carried out with a commercially available electrophysiological monitoring system (ISIS®, inomed). Waveforms were injected into the visual field of the operating microscope. Results: Waves I and II of the BAEP were best identified in recordings at the tympanic membrane, wave III to V were largest in recordings at the brainstem or with electrodes places on the cochlear nerve. Compared to far-field recordings, amplitudes were 3 - 4 times larger for ECoG, and 2 - 20 times larger for CABR in patients with functional hearing. CABR was more variable than the ECoG, depending mostly on electrode location relative to the brainstem generators. In patients with good pre-operative hearing acquisition time for reliable averages were 40 seconds in far-field, and as low as two seconds in near-field recordings. Conclusion: Non-invasive electrodes have rendered near-field recording of electrophysiological responses to auditory stimuli the gold standard in hearing-preserving surgery in lesions around the cochlear nerve. In lesions located intradurally around the petrous bone, dual near-field recording adds safety and significantly shortens feedback time to the surgeon, especially with video microscope injection of waveforms. Fig.1 ECoG electrode in the outer ear canal (A), CABR mini-ball electrode (B), and recording site near the brainstem entry zone of the cochlear nerve (Abstract ID: 737) R. Behr 1 , K. Schwager 1 , E. Hofmann 1 1 Klinikum Fulda Background: The treatment of vestibular Schwannomas (VS) changed over the last decades. Initially patients were diagnosed mostly with large tumors. The operation was the only treatment modality. With availability of CT and MRI, diagnosis was made earlier and treatment strategies changed. Nowadays 3 modalities are accepted: wait and scan, microsurgical operation and radiotherapy. We add a forth, the interdisciplinary counseling in a skull base center and operation by an oto-and neurosurgical team. This "forth way" provides an optimum in pretherapeutic management and counseling by a peer group of neuro- and otosurgeons, neuroradiologists, neurologists, oncologistc, radiotherapists and an experienced team of neuro- and oto-surgeons, performing the operation together. This concept was started in 1992 at Würzburg University "Kopfklinik" and continued by the authors at different institutions since now. Materials and methods: 125 patients, including 7 recurrencies (5.6%), were retrospectively analyzed. The operative concept is a retrosigmoid approach in semi sitting position. IOM was intensively used by SSEP, MEP, direct facial monitoring, facial MEP and BERA. The extrameatal tumor was removed by the neurosurgeon and the intrameatal by the otosurgeon. All tumor sizes and recurrencies were evaluated, only intrameatal location was excluded. The House-Brackmann (HB) scale was slightly modified as to grade 1 comprises HB 1 and 2, grade 2 HB 3 and grade 3 HB 4-6. For hearing evaluation the Gardner-Robinson (GR) scale was used. Results: Of all tumor sizes, 7 patients (5.6%) had a grade 3 facial paresis, most of them with large tumors and recurrency. 116 patients (92.8%) had grade 1, excellent to good results, HB 1-2, one year after the operation. Only a few patients were in grade 2, equivalent HB 3. In all but 2 recurrent tumors the HB grade remained the same as preoperatively. In 3 grade 1, in 2 grade 2 and in 1 grade 3. Facial outcome was related to extrameatal tumor size. In tumors larger than 3.1 cm diameter facial function was in 23% grade 3. Also the rate of hearing preservation was clearly related to tumor size. In 88 patients, 70.4%, there was a preoperative hearing according to GR of 1-3. Which means not in every case a servicable hearing but an augmentable hearing with appropriate hearing aids. Over all tumor sizes the postoperative hearing was in 42 patients, 47.8%, GR 1-3. An interesting parameter was the feasibility of reproducible BERA recordings. In patients with extrameatal tumors of up to 20mm and a preoperative hearing of GR 1-2 and reliable recordings of BERA, the hearing outcome in the same GR scale of 1-2 was 68% (15/22). Including patients with the same Tumor size and preop hearing but worse BERAs, the result was 53.84% (21/39). There were 5 subctaneous CSF pouches and 2 liquorrhea, 1 superficial wound infection and one transient hemiparesis due to pneumatocephalus. Conclusion: The interdisciplinary treatment of VS provides a safe and effective treatment of this disease. The rates of facial nerve and hearing preservation are in the same range as in large other contemporary studies. If the BERA recordings are technically stable and free from artefact, excellent rates of hearing preservation were obtained. A highly sophisticated intraoperative monitoring is essential for good results. With our setup, the learning effect for both surgeons is maximized and the intraoperative discussion is fruitful for the operative team, the students, nurses as well as for the patients outcome. In addition, it bears an excellent possibility to simultaneously train younger skull base specialists from both fields. (Abstract ID: 758) R. Behr 1 , K. Schwager 1 , E. Hofmann 1 1 Klinikum Fulda Background: ABI is a generally accepted method to restore hearing after destruction of the cochlear nerve mostly in neurofibromatosis type 2 (NF-2) patients. In the early years however speech understanding was not possible especially not without visual cues as lipreading. Newer data in NF-2 showed that despite of large tumors a considerable percentage of patients achieved open set speech recognition and even telefone use. In this retrospective study we tried to find factors associated with higher levels, better than 30% open set sentence recognition, of prosthetic hearing. Materials and methods: All NF-2 patients from 6 ABI centers implanted from 1997-2011 with a Med-El ABI device and with at least 3 months of implant experience were evaluated. Only patients out of this group who scored better than 30% open set sentence recognition were investigated more closely. Surgical factors (the author is the main surgeon), patient and tumor characteristics, intraoperative electrophysiology, electrode placement, number of auditory electrodes and distinct pitches, device factors, stimulation strategy and fitting factors were studied. Results: Of 84 patients 26 scored better than 30% open set sentence recognition (31%). Neither patient age, tumor size or -stage influenced hearing outcome significantly. If deafness before implantation was less 1 year scores were over 65% sentence recognition compared to 45% (p=0.03). Patients operated in semi-sitting position scored significantly better than in lying position (p=0.04). 35.7% of semi-sitting vs 16.7% of lying operated patients scored better than 30%. MCL levels of less than 28nC correlated sign. better , 67.1% correct sentence recognition vs 47.2, p=0.04. Number of audible electrodes had no significant effect on outcome. However patients with average number of distinct pitches of 9.1 had scores over 60% and those with 7.4 had between 30-60% (p=0.01). In patients with high stimulation rates, 1200ppse, scores were 67.1% vs 45.7% in those below 1200ppse (p=0.03). Conclusion: In this selected group of excellent and top performing ABI patients it was possible to distinguish some parameters which are probably responsible for improved outcomes. The message is, that exact probe positioning is mandatory. Intraoperative mapping of the cochlear nucleus area by test electrodes and painstaking electrophysiological measurements will support optimal placement. This will cause low thresholds and MCL levels, high stimulation rates and many distinct pitches. Surgery must be as meticulous and atraumatic to the nervous tissue as possible, which is facilitated by semi-sitting position. If any possible, timing of implantation should not be postponed longer than one year after deafness. (Abstract ID: 761) R. Behr 1 , K. Schwager 1 , E. Hofmann 1 1 Klinikum Fulda Background: Endoscopic techniques took over an important place in surgery of skull base lesions. In the last 10 to 20 years significant steps forward could be achieved in surgical treatment of anterior skull base lesions. Especially pituitary adenomas and, with the extended approaches, meningeomas and craniopharyngeomas are now successfully treated with exclusively endoscopic approaches. In the posterior fossa the use of the endoscope is still limited. It is mostly used for exploration of hidden places, which are difficult to be disclosed by the microscope. The question therefore arises if the endoscope can be used more intensively also in lesions of the posterior fossa. Materials and methods: In a prospective analysis 8 female and 2 male patients (pat), with 2 meningeomas (M) and 8 vestibular schwannomas (VS) were operated only by using the endoscope as visualisation tool. A two dimensional Storz endoscope with 0 and 30 degree optics was used. The tumors should not exceed 20mm in extrameatal diameter. VS grew intra- and extrameatal, the M were located laterally to the IAC. Intensive intraoperative monitoring was used. The pat were positioned laterally with slightly elevated head. Follow up period is meanwhile between 42 and 100 months. All pat were revisited on a regular basis with yearly clinical and MRI investigations. Results: Pat mean age was 61.5 years (mean deviation 8.2), mean tumor diameter was 13.6 mm (3.4) largest area was 150 mm2 (79.3), mean operation time was 255.2 minutes (48.7). In all but one case the facial nerve could be preserved with normal function, in one pat the postop result was HB 3 with improvement to 2. The acoustic nerve was anatomically preserved in 8/10 cases. Hearing was preserved at the same level as preoperatively in 7/10 cases. Tumor resection was complete in 9/10 patients. In one pat a small contrast enhancing area is under control and stable. There were no surgical complications as CSF fistula or infections. Conclusion: Exclusively endoscopic resection of CPA tumors is feasible. Results are comparable to microscopic resections. Visualisation in the posterior fossa is excellent, especially in the rostral area of the lesion and in the IAC. Retractors are not always necessary. The size of the approch may be reduced and tailored to the size of the lesion. It remains open if in larger tumors this technique is also beneficial. Problems may occur with severe bleedings in the operating field.