Intraoperative Transcranial Motor-Evoked Potential Monitoring of the Facial Nerve during Cerebellopontine Angle Tumor Resection

Objective To determine whether transcranial motor-evoked potential (TCMEP) monitoring of the facial nerve (FN) during cerebellopontine angle (CPA) tumor resection can predict both immediate and long-term postoperative FN function.Design Retrospective review.Setting Tertiary referral center.Main Outcome Measures DeltaTCMEP (final-initial) and immediate and long-term facial nerve function using House Brackmann (HB) rating scale.Results Intraoperative TCMEP data and immediate and follow-up FN outcome are reported for 52 patients undergoing CPA tumor resection. Patients with unsatisfactory facial outcome (HB >2) at follow-up had an average deltaTCMEP of 57 V, whereas those with HB I or II had a mean deltaTCMEP of 0.04 V (t = -2.6, p < 0.05.) Intraoperative deltaTCMEP did not differ significantly between groups with satisfactory (HB I, II) and unsatisfactory (HB > 2) facial function in the immediate postoperative period.Conclusion Intraoperative TCMEP of the facial nerve can be a valuable adjunct to conventional facial nerve electromyography during resection of tumors at the CPA. Intraoperative deltaTCMEP >57 V may be worrisome for long-term recovery of satisfactory facial nerve function.     

Radiologic Assessment of the Paranasal Sinuses after Endoscopic Skull Base Surgery

Objectives To identify sinuses demonstrating postoperative radiographic mucosal thickening after endoscopic exposure of the cranial base through the transsphenoidal corridor. Design Retrospective review. Setting University-based medical center. Participants Patients undergoing endoscopic transnasal transsphenoidal approaches to the skull base who had both preoperative and postoperative imaging. Main Outcome Measures Change in preoperative and postoperative imaging scores for each sinus and side at 3 and 6 months. The left-sided undissected sinuses served as internal controls for comparison. Results Fifty-one patients were identified with the aforementioned inclusion and exclusion criteria. The mean difference in preoperative and postoperative imaging scores for the right anterior ethmoid sinus was significantly different from the left-sided equivalents (p = 0.0020). The difference in the frontal sinuses approached significance (p = 0.0625). Conclusions Resection of the lower half of the middle turbinate and maxillary antrostomy and harvest of a nasoseptal flap are associated with an increased radiographic incidence of mucosal thickening of the ipsilateral anterior ethmoids compared with the undissected contralateral side. When accessing the transnasal transsphenoidal corridor for skull base surgery, preservation of native anatomy is associated with a lower incidence of mucosal thickening on postoperative imaging.     

A New Segment of the Trochlear Nerve: Cadaveric Study with Application to Skull Base Surgery

Objectives The trochlear nerve is important to preserve during approaches to the skull base. Traditionally, this nerve has been divided into cisternal, cavernous, and orbital segments. However, the authors anecdotally observed an additional segment during routine cadaveric dissections. Therefore, they performed this study to better elucidate this anatomy. Design Twenty latex-injected cadaveric sides (10 adult cadavers) were dissected with the aid of an operating microscope. Standard microdissection techniques were used to examine the course of the distal cisternal and precavernous segments of the trochlear nerve. Setting Cadaver laboratory. Main Outcome Measures Measurements were made using a microcaliper. Digital images were made of the dissections. Results The authors identified a previously undescribed segment of the trochlear nerve in all specimens. This part of the nerve coursed between the entrance of the trochlear nerve into the posterior corner of the oculomotor trigone to the posterior wall of the cavernous sinus. This segment of trochlear nerve was, on average, 4 mm in length. Conclusions The authors have identified a new segment of the trochlear nerve not previously described. They propose that this be referred to as the trigonal segment. Knowledge of the microanatomy of the trochlear nerve is useful to skull base surgeons.     

Value of Free-Run Electromyographic Monitoring of Lower Cranial Nerves in Endoscopic Endonasal Approach to Skull Base Surgeries

Objective The main objective of this study was to evaluate the value of free-run electromyography (f-EMG) monitoring of cranial nerves (CNs) VII, IX, X, XI, and XII in skull base surgeries performed using endoscopic endonasal approach (EEA) to reduce iatrogenic CN deficits.Design We retrospectively identified 73 patients out of 990 patients who had EEA in our institution who had at least one CN monitored. In each CN group, we classified patients who had significant (SG) f-EMG activity as group I and those who did not as group II.Results We monitored a total of 342 CNs. A total of 62 nerves had SG f-EMG activity including CN VII = 18, CN IX = 16, CN X = 13, CN XI = 5, and CN XII = 10. No nerve deficit was found in the nerves that had significant activity during procedure. A total of five nerve deficits including (CN IX = 1, CN X = 2, CN XII = 2) were observed in the group that did not display SG f-EMG activity during surgery.Conclusions f-EMG seems highly sensitive to surgical manipulations and in locating CNs. It seems to have limited value in predicting postoperative neurological deficits. Future studies to evaluate the EMG of lower CNs during EEA procedures need to be done with both f-EMG and triggered EMG.     

Skull Base Meningiomas and Cranial Nerves Contrast Using Sodium Fluorescein: A New Application of an Old Tool

Objective The identification of cranial nerves is one of the most challenging goals in the dissection of skull base meningiomas. The authors present an application of sodium fluorescein (SF) in skull base meningiomas with the purpose of improving the identification of cranial nerves. Design A prospective study within-subjects design. Setting Hospital Ernesto Dornelles, Porto Alegre, Brazil. Participants Patients with skull base meningiomas. Main Outcomes Measures Cranial nerve identification. Results The group of nine meningiomas was composed of one cavernous sinus, three petroclival, one tuberculum sellae, two sphenoid wing, one olfactory groove, and one temporal floor meningioma. The SF enhancement in all tumors was strong, and the contrast with cranial nerves clearly evident. There were one definite olfactory nerve deficit, one transient abducens deficit, and one definite hemiparesis. All lesions were resected (Simpson grades 1 and 2). The analysis of the difference of the delta SF wavelength between the meningiomas and cranial nerve contrast was performed by the Wilcoxon signed rank test and showed p = 0.011. Conclusions The contrast between the enhanced meningiomas and cranial nerves was evident and assisted in the visualization and microsurgical dissection of these structures. The anatomical preservation of these structures was improved using the contrast.     

Intraoperative electrophysiologic monitoring of cranial motor nerves in skull base surgery

BACKGROUND Intraoperative cranial nerve monitoring has been applied for the preservation of nerve function during skull base surgery. However, its usefulness is controversial because clinical results reported are limitedMETHODS We evaluated the usefulness of intraoperative electro-physiologicmonitoring of the third to seventh cranial motor nerves in 15 patients undergoing skull base surgery intracranial bipolar electrical stimulation of each nerve was performed and compound muscle action potentials (CMAP) were recorded from the innervated musclesRESULTS CMAP's were successfully recorded form 23 of the innervated muscles. The loss of the CMAP response during the manipulation of lesions or high stimulos intensity at the end of manipulations seem to be related to the postoperative beats of nerve functionCONCLUSIONS The results suggest that intraoperative electrophysiologic monitoring of cranial motor nerves is useful for prediction of postoperative nerve function     

A Novel Graft Material for Preventing Cerebrospinal Fluid Leakage in Skull Base Reconstruction: Technical Note of Perifascial Areolar Tissue

Objectives Perifascial areolar tissue (PAT), a layer of loose connective tissue on the deep fascias with a rich vascular plexus, serves as a vital cover over defects with scarce vascularity. We report the usefulness of PAT as a nonvascularized alternative to flaps for reconstruction of dural defects in skull base surgery and transsphenoidal surgery while evaluating its effect on control of cerebrospinal fluid (CSF) leakage. Design A retrospective chart analysis was performed on patients who had undergone repair of a dural defect with PAT during skull base surgery or transsphenoidal surgery between December 2004 and October 2011. Results Twenty-one patients were included: 11 patients had received surgical treatment and/or irradiation. Fourteen of the 21 patients had pre- and/or intraoperative CSF leakage. Only one patient (4.8%) had postoperative CSF leakage requiring additional surgical repair. Ten patients underwent postoperative irradiation from 1 to 15 months after transplant of the PAT. None of the patients had postoperative CSF leakage after irradiation. Conclusion We successfully repaired dural defects using PAT in skull base surgery and transsphenoidal surgery, even in patients with a history of multiple operations and radiotherapy. PAT may serve as a valuable tool for skull base reconstruction.     

Facial Nerve Function after the Extended Translabyrinthine Approach

Objective To evaluate facial nerve function after excision of petroclival/anterior cerebellopontine angle (CPA) meningiomas by the extended translabyrinthine (EXTL) approach and compare these with outcomes after the transcochlear and transotic approaches. Design Retrospective chart review. Setting/Participants A search of archived surgical cases at a single institution between January 1, 1995, and January 1, 2012. Main Outcome Measures Facial function measured on the House-Brackmann (HB) scale. Results A total of 16 patients underwent the EXTL approach for primary excision of petroclival meningiomas. Average tumor size was 4.6 cm, and six patients had gross total resection. Average length of follow-up was 36.4 months. Two patients required reoperation for tumor regrowth. Preoperative facial function was HB I or II in all patients with available examinations. Immediate postoperative facial nerve function ranged from HB I to HB VI. In patients with an intact facial nerve at surgery, all but one had long-term facial function of HB I or II. A robust response on intraoperative facial nerve monitoring was prognostic of favorable long-term facial function. Facial function declined in some patients after postoperative radiation or revision surgery. Conclusions The EXTL approach allows excellent exposure of petroclival/anterior CPA lesions and should be favored to improve facial outcomes.     

A Linear Variant of Segmental Schwannomatosis Localized to the Upper Extremity

Introduction  Schwannomas represent benign peripheral nerve sheath tumors. Their phenotypic presentations in schwannomatosis and segmental schwannomatosis have been well described. To date, however, cases of schwannomatosis or multiple schwannomas localized to a single nerve fascicle have been limited in the literature. Case Presentation  In this study, we identify a case of a 48 year-old non-neurofibromatosis male who presented with symptomatic schwannomas localized to a single nerve fascicle of the upper extremity. Intraoperative exploration revealed four schwannomas arising from a 15-cm segment of ulnar nerve fascicle. Surgical excision was successful, without neurological deficit or recurrence. Conclusion  This study identifies a case of schwannomatosis localized to a single nerve fascicle that may represent a linear variant of segmental schwannomatosis. The presentation may represent a temporary linear appearance in progression to “nonlinear” segmental variant; however, a molecularly distinct subset of schwannomas cannot be excluded.     

Intraoperative cranial nerve monitoring during posterior skull base surgery

Intraoperative monitoring of neurophysiologic function is rapidly evolving as an important adjunct during skull base surgery to reduce the incidence of neurologic deficit. Facial nerve monitoring is an excellent model, since electrical and mechanical evoked potentials can be directly presented to the surgeon in real-time through an acoustic loudspeaker display. The lower cranial nerves may also be monitored using similar electromyographic techniques. Auditory system monitoring is more difficult due to the low amplitude response that requires averaging and filtering to extract the evoked potential. In conjunction with auditory monitoring, improved hearing preservation may be further enhanced by concomitant facial nerve monitoring, since the surgeon is alerted to traumatic manipulations that may affect both facial and cochlear nerves. Techniques and interpretative issues are presented to maximize the efficacy and safety of cranial nerve monitoring.     

Intraoperative Cranial Nerve Monitoring During Posterior Skull Base Surgery

Intraoperative monitoring of neurophysiologic function is rapidly evolving as an important adjunct during skull base surgery to reduce the incidence of neurologic deficit. Facial nerve monitoring is an excellent model, since electrical and mechanical evoked potentials can be directly presented to the surgeon in real-time through an acoustic loudspeaker display. The lower cranial nerves may also be monitored using similar electromyographic techniques. Auditory system monitoring is more difficult due to the low amplitude response that requires averaging and filtering to extract the evoked potential. In conjunction with auditory monitoring, improved hearing preservation may be further enhanced by concomitant facial nerve monitoring, since the surgeon is alerted to traumatic manipulations that may affect both facial and cochlear nerves. Techniques and interpretative issues are presented to maximize the efficacy and safety of cranial nerve monitoring.     

The Association of Meningitis with Postoperative Cerebrospinal Fluid Fistula

Objective To determine the risk factors for and the clinical course of postoperative meningitis following lateral skull base surgery and to determine its relationship to cerebrospinal fluid (CSF) fistula.Patients Patients undergoing lateral skull base surgery between July 1999 and February 2010 at an academic tertiary referral center. All subjects had culture-proven meningitis or suspected bacterial meningitis in the postoperative period. Medical records were compared with the lateral skull base patients who did not develop meningitis.Results Of 508 procedures, 16 patients developed meningitis (3.1%). The most common diagnosis was acoustic neuroma in 81.3%; 68.8% of patients had a CSF leak prior to onset of meningitis, and 50% received a lumbar drain. The median time from surgery to the onset of meningitis was 12 days with a range of 2 to 880 days. The relative risk of developing meningitis in the setting of postoperative CSF fistula is 10.2 (p < 0.0001). No meningitis-associated mortality was observed.Conclusions Postoperative meningitis occurred in a small number of patients undergoing lateral skull base surgery. A postoperative CSF fistula leads to an increased risk of meningitis by a factor of 10.2.     

Modifications to the Endoscopic Approach for Anterior Skull Base Lesions Improve Postoperative Sinonasal Symptoms

Background/Objective Our institution previously showed that patients experience significant postoperative sinonasal symptoms for the first few months after endoscopic transnasal transsphenoidal skull base surgery (eTNTS). Since our initial study we have modified our technique, discontinuing routine resection of the middle turbinate, maxillary antrostomies, and nasoseptal flaps. In this study, we analyze whether these technical modifications decrease postoperative sinonasal morbidity after eTNTS. Methods A retrospective review was performed of 93 consecutive patients who underwent eTNTS at a tertiary academic medical center from August 2011 to August 2012. Main Outcome Measures  Sino-Nasal Outcome Test (SNOT)-20 and SNOT-22 scores preoperatively and after surgery. Results Compared with our previous study, our new cohort experienced a significant improvement (p < 0.05) in SNOT scores for the need to blow nose, runny nose, postnasal discharge, thick nasal discharge, wake up at night, reduced concentration, and frustrated/restless/irritable. Within the new cohort, patients who did not have a nasoseptal flap or middle turbinate resection had less worsening and faster improvement of nasal symptom scores after surgery. Conclusions Preserving normal sinonasal physiology during eTNTS by limiting middle turbinate resections, avoiding unnecessary maxillary antrostomies, and reducing the use of nasoseptal flaps when feasible results in less sinonasal morbidity and more rapid recovery during the postoperative period.     

Image-Guided Robotic Skull Base Surgery

Objectives To describe the potential uses of computed tomography image guidance in concert with the surgical robot for skull base surgery. Design An anatomical study was conducted. Setting Tertiary academic center. Participants Cadaveric skull. Main Outcome Measures The primary outcome measure was to measure the accuracy of robotic arm positioning to anatomical landmarks on a skull using image guidance and the surgical robot synchronously. Instruments with different angles of rotations were used. Estimated systematic error was calculated and compared with achieved errors. Clinical applications of metachronous image guidance and robotic system were discussed. Results The skull model approximated < 1 mm accuracy using standard image guidance instruments and the 0-degree robotic arm positioning. Increased angles of instruments from 20 to 60 degrees on the robotic system revealed more significant increases in error than estimated. Conclusions Image guidance may be useful for transoral robotic approaches. Precise movements are improved by limiting the angle of deviation. Future studies will help optimize the combined technologies before validating the study in clinical settings.     

Endoscopic Resection of Vestibular Schwannomas

Objective To report our results and the technical details of fully endoscopic resection of vestibular schwannomas. Design Prospective observational study. Setting A single academic institution involving neurosurgery and neurotology. Participants Twelve consecutive patients who underwent fully endoscopic resection of a vestibular schwannoma. Main Outcome Measures Hearing preservation, based on the American Association of Otolaryngology-Head and Neck Surgeons (AAO-HNS) score as well as the Gardener and Robertson Modified Hearing Classification (GR). Facial nerve preservation based on the House-Brackmann (HB) score. Results All patients successfully underwent gross total resection. Facial nerve preservation rate was 92% with 11 of 12 patients retaining an HB score of 1/6 postoperatively. Hearing preservation rate was 67% with 8 of 12 patients maintaining a stable AAO-HNS grade and GR score at follow-up. Mean tumor size was 1.5 cm (range: 1–2 cm). No patients experienced postoperative cerebrospinal fluid leak, infection, or cranial nerve palsy for a complication rate of 0%. Mean operative time was 261.6 minutes with an estimated blood loss of 56.3 mL and average length of hospital stay of 3.6 days. Conclusion A purely endoscopic approach is a safe and effective option for hearing preservation surgery for vestibular schwannomas in appropriately selected patients.     

Harvey Cushing's Early Operative Treatment of Skull Base Fractures

Objectives To review Dr. Harvey Cushing''s early surgical cases at the Johns Hopkins Hospital, revealing details of his operative approaches to fractures of the skull base. Design Following institutional review board approval and through the courtesy of the Alan Mason Chesney Archives, we reviewed the Johns Hopkins Hospital surgical files. Setting The Johns Hopkins Hospital, 1896 to 1912. Participants A total of 24 patients underwent operative treatment for suspected fractures of the skull base. Main Outcome Measures The main outcome measure was operative approach, postoperative mortality, and condition recorded at the time of discharge. Results Overall, 23 patients underwent operative treatment for suspected skull base fractures. The mechanisms of injury were known for 22 patients and included work-related injuries (41%), falls (23%), vehicle injuries (32%), and other trauma (5%). One patient had no mechanism of injury specified in the file. The outcome at the time of discharge from the hospital was “well” or “improved” in 12 patients (52%). The remaining 11 patients died during their admission. Conclusions Although Cushing''s experience with selected skull base pathology has been previously reported, the breadth of his contributions to operative approaches to the skull base has been neglected.     

Endotracheal tube electrodes to map and monitor activities of the vagus nerve intraoperatively. Technical note

Difficulty swallowing due to damage of the vagus nerve is one of the most devastating complications of surgery in and around the medulla oblongata; therefore, intraoperative anatomical and functional evaluation of this nerve is crucial. The authors applied endotracheal tube surface electrodes to record electromyography (EMG) activity from vocal cords innervated by the vagus nerve. The vagal nucleus or rootlet was electrically stimulated during surgery and vocalis muscle EMG activities were displayed by auditory and visual signals. This technique was used successfully to identify the vagus motor nerve and evaluate its integrity during surgery. The advantages of this method compared with the use of needle electrodes include safe simple electrode placement and stable recording during surgery. In cases involving a pontine cavernoma pressing the nucleus or a jugular foramen tumor encircling the rootlet, this method would be particularly valuable. Additional studies with a larger number of patients are needed to estimate the significance of this method as a means of functional monitoring to predict clinical function.     

Combined Subgaleal/Myocutaneous Technique for Temporalis Muscle Dissection

Background The frontal branch of the facial nerve (FBFN) is the most susceptible neural structure to injury during frontotemporal craniotomies. The balance between adequate temporalis muscle mobilization and frontal branch protection with minimal anatomical alteration is the philosophy behind our approach to temporalis muscle dissection.Objective To describe a combined subgaleal/myocutaneous technique for dissection and mobilization of the temporalis muscle in anterolateral cranial approaches.Methods Interdisciplinary literature review of the anatomical course of the FBFN was performed. Retrospective analysis of anterolateral craniotomies performed at our institution in which the combined subgaleal/myocutaneous (CSGMC) technique was performed.Results A total of 71 cases of anterolateral craniotomies (excluding full variant orbitozygomatic) were performed with the successful application of a CSGMC technique (36 pterional, 31 orbitopterional, and 4 fronto-orbital). Partial frontalis weakness was transient in one case.Conclusion The CSGMC technique provides sufficient protection for the FBFN and allows for adequate mobilization for a variety of skull base exposures while minimally violating myofascial anatomy. This is the first reported technique that allows both adequate temporalis muscle mobilization with performance of the one-piece orbitofrontal and orbitopterional approaches, without disruption of the superficial/deep temporalis fascia and fat-pad complex.     

Endoscopic Endonasal Transclival Approaches: Case Series and Outcomes for Different Clival Regions

Objective Transclival endoscopic endonasal approaches to the skull base are novel with few published cases. We report our institution''s experience with this technique and discuss outcomes according to the clival region involved. Design Retrospective case series. Setting Tertiary care academic medical center Participants All patients who underwent endoscopic endonasal transclival approaches for skull base lesions from 2008 to 2012. Main Outcome Measures Pathologies encountered, mean intraoperative time, intraoperative complications, gross total resection, intraoperative cerebrospinal fluid (CSF) leak, postoperative CSF leak, postoperative complications, and postoperative clinical course. Results A total of 49 patients underwent 55 endoscopic endonasal transclival approaches. Pathology included 43 benign and 12 malignant lesions. Mean follow-up was 15.4 months. Mean operative time was 167.9 minutes, with one patient experiencing an intraoperative internal carotid artery injury. Of the 15 cases with intraoperative cerebrospinal fluid (CSF) leaks, 1 developed postoperative CSF leak (6.7%). There were six other postoperative complications: four systemic complications, one case of meningitis, and one retropharyngeal abscess. Gross total resection was achieved for all malignancies approached with curative intent. Conclusions This study provides evidence that endoscopic endonasal transclival approaches are a safe and effective strategy for the surgical management of a variety of benign and malignant lesions. Level of Evidence 4.     

Assessment of recurrent laryngeal nerve function during thyroid surgery

Introduction

There is disparity in the reported incidence of temporary and permanent recurrent laryngeal nerve (RLN) palsy following thyroidectomy. Much of the disparity is due to the method of assessing vocal cord function. We sought to identify the incidence and natural history of temporary and permanent vocal cord palsy following thyroid surgery. The authors wanted to establish whether intraoperative nerve monitoring and stimulation aids in prognosis when managing vocal cord palsy.

Methods

Prospective data on consecutive thyroid operations were collected. Intraoperative nerve monitoring and stimulation, using an endotracheal tube mounted device, was performed in all cases. Endoscopic examination of the larynx was performed on the first postoperative day and at three weeks.

Results

Data on 102 patients and 123 nerves were collated. Temporary and permanent RLN palsy rates were 6.1% and 1.7%. Most RLN palsies were identified on the first postoperative day with all recognised at the three-week review. No preoperative clinical risk factors were identified. Although dysphonia at the three-week follow-up visit was the only significant predictor of vocal cord palsy, only two-thirds of patients with cord palsies were dysphonic. Intraoperative nerve monitoring and stimulation did not predict outcome in terms of vocal cord function.

Conclusions

Temporary nerve palsy rates were consistent with other series where direct laryngoscopy is used to assess laryngeal function. Direct laryngoscopy is the only reliable measure of cord function, with intraoperative monitoring being neither a reliable predictor of cord function nor a predictor of eventual laryngeal function. The fact that all temporary palsies recovered within four months has implications for staged procedures.