Marcus André Acioly

Facial Nerve Monitoring During Cerebellopontine Angle and Skull Base Tumor Surgery: A Systematic Review from Description to Current Success on Function Prediction

BACKGROUND Intraoperative neuromonitoring has been established as one of the methods by which modern neurosurgery can improve surgical results while reducing morbidity. Despite routine use of intraoperative facial nerve (FN) monitoring, FN injury still is a complication of major concern due to severe negative impact on patients quality of life. METHODS Through searches of PubMed, we provided a systematic review of the current literature up to February, 2011, emphasizing all respects of FN monitoring for cerebellopontine angle and skull base tumor surgery from description to current success on function prediction of standard and emerging monitoring techniques. RESULTS Currently, standard monitoring techniques comprise direct electrical stimulation (DES), free-running electromyography (EMG), and facial motor evoked potential (FMEP). We included 62 studies on function prediction by investigating DES (43 studies), free-running EMG (13 studies), and FMEP (6 studies) criteria. DES mostly evaluated postoperative function by using absolute amplitude, stimulation threshold, and proximal-to-distal amplitude ratio, whereas free-running EMG used the train-time criterion. The prognostic significance of FMEP was assessed with the final-to-baseline amplitude ratio, as well as the event-to-baseline amplitude ratio and waveform complexity. CONCLUSIONS Although there is a general agreement on the satisfactory functional prediction of different electrophysiological criteria, the lack of standardization in electrode montage and stimulation parameters precludes a definite conclusion regarding the best method. Moreover, studies emphasizing comparison between criteria or even multimodal monitoring and its impact on FN anatomical and functional preservation are still lacking in the literature.

Quantitative parameters of facial motor evoked potential during vestibular schwannoma surgery predict postoperative facial nerve function

BackgroundFacial motor evoked potential (FMEP) amplitude ratio reduction at the end of the surgery has been identified as a good predictor for postoperative facial nerve outcome. We sought to investigate variations in FMEP amplitude and waveform morphology during vestibular schwannoma (VS) resection and to correlate these measures with postoperative facial function immediately after surgery and at the last follow-up.MethodsIntraoperative orbicularis oculi and oris muscles FMEP data from 35 patients undergoing surgery for VS resection were collected, then analysed by surgical stage: initial, dural opening, tumour dissection (TuDis), tumour resection (TuRes) and final.FindingsImmediately after surgery, postoperative facial function correlated significantly with the FMEP amplitude ratio during TuDis, TuRes and final stages in both the orbicularis oculi (p = 0.003, 0.055 and 0.028, respectively) and oris muscles (p = 0.002, 0.104 and 0.014, respectively). At the last follow-up, however, facial function correlated significantly with the FMEP amplitude ratio only during the TuDis (p = 0.005) and final (p = 0.102) stages for the orbicularis oris muscle. At both time points, postoperative facial paresis correlated significantly with FMEP waveform deterioration in orbicularis oculi during the final stage (immediate, p = 0.023; follow-up, p = 0.116) and in orbicularis oris during the TuDis, TuRes and final stages (immediate, p = 0.071, 0.000 and 0.001, respectively; follow-up, p = 0.015, 0.001 and 0.01, respectively).ConclusionsFMEP amplitude ratio and waveform morphology during VS resection seem to represent independent quantitative parameters that can be used to predict postoperative facial function. Event-to-baseline FMEP monitoring is quite useful to dictate when intraoperative changes in surgical strategy are warranted to reduce the chances of facial nerve injury.

Prognostic factors for hearing loss following the trigeminocardiac reflex

The recent letter by Schaller et al. [1] illustrates a progressing consideration of the trigeminocardiac reflex (TCR) during skull base surgery. The impact of the TCR on postoperative auditory function has already been studied prospectively during vestibular schwannoma surgery, revealing the hypotension following TCR to be a negative prognostic factor for hearing preservation [2]. Schaller et al. [1] suggest preoperative serum biomarkers and radiological markers as future prognostic factors for both the occurrence of and the potential recovery from the TCR while noticing that ‘‘we are far away from a clinical application of this knowledge.’’ In fact, the pathophysiological mechanism of hearing loss after the TCR is unknown yet. We are convinced that the appropriate detection and management of the TCR is determined by the surgery itself rather than by a specific preoperative patient profile as this phenomenon is induced by intraoperative manipulations of the trigeminal nerve. Therefore, we believe that future research focusing on questions such as tumor characteristics (size, entity), eliciting surgical maneuvers (e.g. traction), or intraoperative changes of auditory evoked potentials will lead more successfully to clinical application than serum or radiological markers. The parallels to the history of and previous efforts in the preservation of auditory function in vestibular schwannoma surgery are too obvious to be neglected. Continuous intraoperative monitoring of hemodynamic parameters has been shown to allow the surgeon to interrupt surgical maneuvers immediately upon the occurrence of the TCR [3]. This technique has been proven sufficient for the heart rate and the arterial blood pressure to return to normal levels. Nonetheless, the reaction of the surgeon to hemodynamic changes may be too late to prevent postoperative neurological deficits. Therefore, we have conducted a prospective study to analyze electrophysiological changes of auditory evoked potentials (AEP) during the TCR in cerebellopontine angle surgery. Preliminary results indicate that intraoperative AEP changes related to the TCR predict postoperative hearing function and may serve as a valuable prognostic tool. Future studies will have to show whether this tool might also be applied to prevent the occurrence of the TCR.

Spinal metastasis of endometrial stromal sarcoma: Clinicopathological features and management

BACKGROUND Endometrial Stromal Sarcoma (ESS) is a rare uterine malignancy which often metastasizes several years after initial diagnosis. Thoracic spine is a rare ESS metastatic site and its proper management is still not a consensus. We discuss the histopathological features and the management strategies through an illustrative case of a 77 year-old woman with metastasis to the thoracic spine 13 years after total hysterectomy for ESS. METHODS Review of the literature and identification of 5 patients, including our present case, with ESS involving the spinal cord. We discuss the outcomes achieved after each therapy. In our case, the patient presented a mass involving the thoracic spinal canal constricting the spinal cord at T7 level. A two-level decompression laminectomy was performed and the lesion was partially excised. RESULTS The histopathological along with the immunohistochemical profile mitotic rate indicated the endometrial stromal cells origin of the tumor, confirming the diagnosis of a low-grade ESS metastasis. The patient was managed with surgery in combination with postoperative radiation therapy. CONCLUSIONS The small number of published cases precludes definitive conclusions regarding standard management. However, it seems that treatment of metastatic ESS to the spine matches the same general concepts of spine metastasis, namely surgery followed by radiation therapy, due to clinical improvement and long-term disease control of the reported cases. Hormonal therapy may be considered in recurrent disease with strong expression of estrogen and progesterone receptors. However, these findings need confirmation in larger studies.

Magnetic resonance angiography of a complex occipital meningoencephalocele involving the confluence of sinuses. Case illustration.

occipital region in almost 70% of cases.2 These entities comprise complex intracranial anomalies usually associated with several other brain malformations.4 Among these anomalies, an abnormal venous system is frequently associated with occipital encephaloceles.4 This 2-day-old girl was admitted to our department after suffering from a closed complex occipital meningoencephalocele. Cranial magnetic resonance (MR) imaging revealed a complex meningoencephalocele containing prolapsed parts of the occipital and parietal lobes and portions of the third and lateral ventricles, as well as corpus callosum agenesis. On T2-weighted MR imaging, large abnormal veins could be seen. The venous phase of MR angiography showed large veins within the encephalocele but only 1 joining the transverse sinus (Fig. 1). This vein was interpreted as an anomaly of the vein of Galen draining the prolapsed brain. The straight sinus was atretic. During surgery, the malformation was mostly repaired, preserving all neural and vascular structures. The abnormal venous system of complex occipital meningoencephaloceles has been studied using conventional angiography.4 Due to the invasiveness and additional risks of using conventional angiography, however,3 MR angiography has become increasingly useful for studying the normal cerebral venous system in children.5 Concerning brain malformations, MR angiography has also been used twice to demonstrate an abnormal venous system in occipital encephaloceles,1,3 but only once for a large occipital meningoencephalocele involving the confluence of sinuses.3 The use of MR angiography instead of conventional angiography appears to be a reasonable option in surgical planning for large occipital meningoencephaloceles with a complex abnormal venous system, which can preclude additional risks for this group of patients. (DOI: 10.3171/PED/2008/1/3/261)

Continuous monitoring of evoked facial nerve electromyograms: a new device for an old concept

Dear Editor, We read with great interest the recent article by Amano et al. [3] about a novel strategy for facial nerve monitoring during vestibular schwannoma (VS) resection, namely the continuous monitoring of evoked facial nerve electromyograms (EMG). The authors claimed the advantages of such a method because of the capability of identifying real-time EMG changes. This is a very interesting device that surmounts one of the great challenges in facial nerve monitoring with direct electrical stimulation, specifically the intermittent use. The concept is presented for the first time for the facial nerve in their study, sharing the same principles previously used for direct brainstem auditory evoked potential (BAEP) recording [6, 8]. As such, effective monitoring can only be initiated following the identification of the nerve at the brainstem. This is particularly difficult in patients harbouring large tumours, in whom the adequate placement of the stimulation electrode is disturbed because of the anatomical distortion of the brainstem and late identification of the proximal facial nerve, which is inaccessible during most of the surgical procedure [1, 4]. Thus, as occurs with direct electrical stimulation [4], continuous monitoring of evoked facial EMG is highly dependent on the surgeons’ ability to locate the exit zone of the facial nerve at the brainstem correctly. Some studies have demonstrated that proximal facial nerve identification and the recording of the brainstem-to-distal internal auditory canal compound muscle action potential (CMAP) ratio cannot be performed in up to 35% of monitored patients owing to technical reasons, distorted anatomy or surgical approach [1, 4]. Moreover, a recurrent problem in applying direct electrodes to the root exit zone of the facial nerve is the movement of the electrode, which can be particularly disastrous for monitoring, delaying the surgical procedure [5]. We feel that the authors were very brief in their description of electrode dislocation by the identification of a decrease in the CMAP instead of a facial nerve injury [3]. Moreover, the dislocation rate was not reported, giving a certainly optimistic expectation for the technique. Another issue that should be addressed is the electrode placement for adequate recording of EMG monitoring. Amano et al. [3] referred to monopolar electrodes over the frontalis, orbicularis oculi and oris, as well as masseter muscles. Although it demonstrates the intention of multichannel monitoring, it is not clear for the reader whether it represents a narrow or wide interelectrode distance of the bipolar configuration. In this regard, it is worth emphasizing that a wide montage, as initially proposed by Moller and Jannetta [7], for direct electrical stimulation is more prone to artifacts and sacrifices the topographical resolution of facial muscles [9]. Thus, setups with a narrow interelectrode distance comprise the standard of care for continuous EMG monitoring [9]. Finally, transcranial electrocortical stimulation rendering facial motor evoked potentials is the most promising monitoring technique for facial function because of the recognition of the functional integrity of the motor cortex, the corticospinal tract, the alpha motor neurons, the peripheral nerve and the neuromuscular junction [1]. M. A. Acioly (*) :M. Tatagiba Department of Neurosurgery, University of Tübingen, Hoppe-Seyler-Strasse 3, 72076 Tübingen, Germany e-mail: marcusacioly@yahoo.com.br