Hans-Peter Schlake

Acoustic neuroma surgery as an interdisciplinary approach: a neurosurgical series of 508 patients

OBJECTIVES To evaluate an interdisciplinary concept (neurosurgery/ear, nose, and throat (ENT)) of treating acoustic neuromas with extrameatal extension via the retromastoidal approach. To analyse whether monitoring both facial nerve EMG and BAEP improved the functional outcome in acoustic neuroma surgery. METHODS In a series of 508 patients consecutively operated on over a period of 7 years, functional outcome of the facial nerve was evaluated according to the House/Brackmann scale and hearing preservation was classified using the Gardner/Robertson system. RESULTS Facial monitoring (396 of 508 operations) and continuous BAEP recording (229 of 399 cases with preserved hearing preoperatively) were performed routinely. With intraoperative monitoring, the rate of excellent/good facial nerve function (House/Brackmann I-II) was 88.7%. Good functional hearing (Gardner/Robertson 1–3) was preserved in 39.8%. CONCLUSION Acoustic neuroma surgery via a retrosigmoidal approach is a safe and effective treatment for tumours with extrameatal extension. Functional results can be substantially improved by intraoperative monitoring. The interdisciplinary concept of surgery performed by ENT and neurosurgeons was particularly convincing as each pathoanatomical phase of the operation is performed by a surgeon best acquainted with the regional specialties.

Intra-operative electromyographic monitoring of the lower cranial motor nerves (LCN IX–XII) in skull base surgery

The functional preservation of lower (motor) cranial nerves (LCN) is endangered during skull base surgery. Intra-operative EMG monitoring of the LCN IX-XII was investigated in 78 patients undergoing 80 operations on various skull base tumors with regard to technical feasibility and clinical efficacy. Ongoing spontaneous muscle activity (SMA) and compound muscle action potentials (CMAP) following supramaximal bipolar stimulation were intra-operatively recorded applying needle electrodes into the soft palate (CN IX: n=76), the vocal cord (CN X: n=72), the trapezius muscle (CN XI: n=18), and the tongue (CN XII: n=71). From 24/22/8 cases with LCN IX/X/XII deficits (despite monitoring) only 5/6/4 remained unchanged (3-6 months postoperative). An irreversible plegia of the LCN IX/X/XII occurred in three (1/1/1) patients. In 7/6/1 patients postoperative (3-6 months) LCN IX/X/XII function was better than preoperatively. In all patients accessory nerve function remained unchanged. Pathological SMA of the LCN IX/X/XII occurred in 12/16/8 cases, but in only 6/5/3 cases corresponded to postoperative LCN deficits. Corresponding pathological SMA patterns were found in 18/17/5 out of 24/22/8 cases with postoperative LCN IX/X/XII dysfunction. Reproducible CMAP of LCN IX/X/XI/XII could be recorded in 59/56/11/32 patients. Approximate normal values were calculated and compared to (very few) data so far given in the literature. Electromyographic monitoring proved to be a safe tool for the intra-operative identification and localization of the LCN contributing to their anatomical and functional preservation. The predictive value of standard neurophysiological parameters for functional outcome, however, is limited.

Quantitative Parameters of Intraoperative Electromyography Predict Facial Nerve Outcomes for Vestibular Schwannoma Surgery

OBJECTIVEnFacial nerve monitoring is an established method that is routinely used during cerebellopontine angle tumor surgery. The aim of this study was to determine quantitative electromyographic (EMG) parameters that were predictive of facial nerve outcomes.nnnMETHODSnIn 137 patients with intra-/extrameatal vestibular schwannomas, the most proximal (the exit from the brainstem) and distal (the fundus of the internal auditory canal) parts of the facial nerve were stimulated after total tumor removal. A quantitative analysis of absolute values and ratios (proximal/distal) of evoked EMG parameters (amplitude, latency, and duration) was performed, and parameters were correlated with postoperative (1 and 6 wk and 6 mo) facial nerve function (FNF).nnnRESULTSnAbsolute values of EMG amplitudes were statistically correlated with FNF (P < 0.05). Amplitude ratios (proximal/distal) demonstrated an even greater predictive power. The risk of exhibiting facial palsy 6 months after surgery increased from 1.6% (amplitude ratio of >0.8) to 75% (ratio of <0.1). For EMG latencies, only the ratios revealed a significant correlation with FNF. The latency ratio-dependent risk of facial palsy after 6 months increased from 2.9% (ratio of <1.05) to 33% (ratio of >1.35). The durations of the muscle responses were not significantly correlated with clinical outcomes.nnnCONCLUSIONnThe predictive power of the amplitudes and latencies of electrically evoked muscle responses could be improved by calculating proximal/distal ratios. The proximal/distal amplitude ratio proved to be the most powerful parameter for intraoperative assessment of postoperative FNF.

Combined Intra-Operative Monitoring of Hearing by Means of Auditory Brainstem Responses (ABR) and Transtympanic Electrocochleography (ECochG) During Surgery of Intra- and Extrameatal Acoustic Neurinomas

Summary.Summary.Background: Although being established as a standard procedure in intra-operative monitoring in acoustic neurinoma surgery, auditory brainstem responses (ABR) represent a far-field technique bearing some technical limitations. This prospective study was designed to evaluate electrocochleography (ECochG) as a supplementary tool for hearing preservation.Method: 84 patients with unilateral intra-/extrameatal acoustic neurinomas (extrameatal diameter: 5–55 mm) preserving serviceable hearing, were operated on using a combined (neuro-/otosurgical) suboccipital approach. ECochG was recorded simultaneously to ABR following transtympanic insertion of a steel needle electrode into the promontory under otoscopic view.Findings: Serviceable hearing (Class 1–3 according to Gardner/Robertson) was preserved in 43 out of 84 patients (51.2%), of whom 40 showed both ECochG and ABR being preserved. All 24 patients with loss of both modalities became deaf. Hearing preservation was observed in 4 out of 12 patients with preserved ECochG but loss of ABR (waves III–V). The reverse was observed in 2 cases with postoperative deafness. While both ECochG and ABR amplitudes were significantly correlated with pre- and postoperative hearing, latencies of ECochG summating (SP) and action potential (AP) proved to be more reliable indicators for preserved hearing than ABR (peak I/III/V) latencies. The predictive value of baseline ABR amplitudes for postoperative hearing, however, was superior to ECochG parameters. Only in large neurinomas (extrameatal diameter: >2 cm) tumour size was found to be a significant predictor for the preservation of hearing. Apart from three cases with postoperative otoliquorrhea and one further case presenting with local bleeding within the external acoustic meatus, no side effects were observed.Conclusions: In combination with ABR monitoring, ECochG proved to be a useful supplementary tool for hearing preservation in acoustic neurinoma surgery. It is particularly helpful during electrocautery and drilling, since no averaging is required. Special applications are: (1) small tumours with good serviceable hearing; (2) and/or a large intrameatal portion; (3) cases with lost or endangered contralateral hearing (e.g. bilateral acoustic neurinomas), when the preservation of poor or even non-functional hearing is desirable.

“De novo” formation of intracranial aneurysms: who is at risk?

Abstract Although aneurysms are widely considered to be of congenital origin there is still debate as to whether some at least might be formed de novo during life. A review of all 49 reported cases plus one previously unpublished case reveals common clinical features and might aid in the management of this group of patients. Statistical analysis of all 50 cases of de novo aneurysms discloses a more frequent history of smoking (P = 0.0007) and arterial hypertension (P = 0.0026) than in a control cohort. Patients with de novo aneurysms are younger (P < 0.0001); the proportion with multiple aneurysms was 28 %. Of de novo aneurysms 44 % became symptomatic 3–6 years after the first subarachnoid haemorrhage (SAH), and the interval was significantly shorter in hypertensive patients. We suggest that young patients with a history of SAH and arterial hypertension and nicotine abuse should therefore be considered for conventional angiography after a 5-year interval. MRA might not be useful due to clip artefacts from even nonferromagnetic clips. Close control of blood pressure is essential in these patients.

Intra-Operative Electromyographic Monitoring of Extra-Ocular Motor Nerves (Nn. III, VI) in Skull Base Surgery

Summaryu2003Background. Extraocular motor nerves (Nn. III, IV, VI) are at risk of damage during skull base surgery. A new recording technique was employed in 18 patients suffering from various skull base tumours in order to extend intra-operative EMG monitoring to the extra-ocular muscles.u2003Methods. Selective intra-operative EMG recordings were obtained from extra-ocular muscles by placement of single-shafted bipolar needle electrodes under the guidance of B-mode ultrasound to visualise the needle tip within the target muscle in the orbital cavity.u2003Findings. Following bipolar electrical stimulation, the oculomotor nerve (N.III) was intra-operatively identified in 5 out of 7 cases, and the abducens nerve (N.VI) in 12 out of 18 cases. Postoperative (3–6 months) oculomotor nerve function remained unchanged in 5 and improved in 2 patients. No permanent deterioration was observed. Abducens nerve function deteriorated in two patients and improved in one case, but remained unchanged in 15 cases. No side effects occurred. There was neither any distinct relation of ocular motor nerve function to the kind and extent of SMA (“spontaneous muscle activity”) patterns, nor could such relationship be detected with concern to neurophysiological parameters (latencies, amplitudes) of electrically evoked CMAP (“compound muscle action potentials”).u2003Interpretation. The EMG technique proposed proved to be mainly effective as a mapping tool for intra-operative localisation and identification of ocular motor nerves in skull base surgery. However, the predictive value of conventional neurophysiological parameters for clinical outcome, seems to be rather poor. Further studies on a larger number of patients are therefore required to develop new quantification techniques which enable an intra-operative prediction of ocular motor nerve deficits. Further efforts are also necessary to extend this technique to the trochlear nerve.

Embolisation of intracranial meningiomas without subsequent surgery

In an open, prospective study, we embolised intracranial meningiomas in seven patients, without subsequent surgery. Follow-up over a mean of 20xa0months included serial neurological examination, MRI and MR spectroscopy. Clinically, embolisation had no adverse effects. Symptomatic patients showed clinical improvement. On MRI marked tumour shrinkage occurred after embolisation in six patients, and was most pronounced during the first 6xa0months. In a young boy the tumour was unchanged despite complete angiographic devascularisation. Embolisation without subsequent surgery may cause substantial tumour shrinkage and thus be used in selected in patients. However, thorough follow-up is mandatory to ascertain the effects of embolisation.

Technical developments in intra-operative monitoring for the preservation of cranial motor nerves and hearing in skull base surgery

Although EMG recordings from mimic muscles have become the standard for intra-operative facial nerve monitoring, few data are available concerning other motor cranial nerves (MCN). Auditory brainstem responses (ABR) are a proven tool for intra-operative hearing preservation, but have their limitations, suggesting the application of supplementary methods. This paper describes new developments of MCN and cochlear nerve monitoring in skull base surgery. Up to 2 x 8 EMG channels were recorded after bipolar stimulation of MCN using concentric coaxial probes. A special software enabled event-dependent registrations of all signals exceeding a definable threshold level. Selective recordings from masticatory muscles (N.V) were obtained using rectangular Teflon-insulated needle electrodes. For oculomotor (Nn.III/ VI) nerve recordings bipolar needle electrodes were precisely placed by orbital ultrasound guidance. Lower cranial nerves were monitored inserting needle electrodes into the soft palate (N.IX), tongue (N.XII) and vocal muscles (N.X) during laryngoscopy using a special applicator. For ABR recordings, click stimuli (95 dB HL) were applied monaurally through insert earphones. Electrocochleography was simultaneously recorded as a near-field potential without averaging after promontory (transtympanic) electrode placement using otomicroscopy. Regarding the ABR biosignal, a characteristic response pattern was detected following bipolar electrical stimulation of the auditory nerve possibly useful for its intra-operative identification.

Acute systemic vanadate poisoning presenting as cerebrovascular ischemia with prolonged reversible neurological deficits (PRIND)

A 22-year-old woman is reported who attempted suicide by oral ingestion of approximately 10-15 g ammonium metavanadate (NH4VO3). A few hours later she developed gastrointestinal symptoms followed by a transient right sensomotor hemiparesis and aphasic disturbances. Brain MRI and SPECT with 99mTc-HMPAO revealed a lesion in the left parietal cortex. Plasmapheresis, ascorbic acid and desferoxamine led to a complete clinical recovery within a few days.

The influence of acetazolamide on cerebral low-flow regions in migraine--an interictal 99mTc-HMPAO SPECT study.

Acetazolamide, a carbonic anhydrase inhibitor, has proved to be useful in the assessment of “vasodilatory capacity” in cerebrovascular disease. To obtain further information on the nature of interictal low-flow regions in migraine, we reinvestigated 20 asymptomatic patients suffering from migraine with aura (n = 15) or without aura (n = 5) and who had either minor (n = 12) or marked (n = 8) regional hypoperfusion when examined in a previous 99mTc-HMPAO SPECT investigation. These patients received acetazolamide IV prior to tracer application. In 14/20 cases regional hypoperfusion resolved. Three patients with migraine with aura had less pronounced regional hypoperfusion compared to baseline. No change in baseline hypoperfusion was detectable in three older patients. No further decreases in flow were measured. In contrast to patients with cerebrovascular ischemia, in whom acetazolamide usually enhances low-flow regions, vasodilatory capacity appears intact in most migraine patients with interictal regional hypoperfusion. Thus, the “acetazolamide test” might be useful in the differential diagnosis of migraine with aura from transient cerebrovascular ischemia.