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Parthasarathy Thirumala, Andrew M. Frederickson, Jeffrey Balzer, Donald Crammond, Miguel E. Habeych, Yue-Fang Chang and Raymond F. Sekula Jr.

OBJECT

Microvascular decompression is a safe and effective procedure to treat hemifacial spasm, but the operation poses some risk to the patient’s hearing. While severe sensorineural hearing loss across all frequencies occurs at a low rate in experienced hands, a recent study suggests that as many as one-half of patients who undergo this procedure may experience ipsilateral high-frequency hearing loss (HFHL), and as many as one-quarter may experience contralateral HFHL. While it has been suggested that drill-related noise may account for this finding, this study was designed to examine the effect of a number of techniques designed to protect the vestibulocochlear nerve from operative manipulation on the incidence of HFHL.

METHODS

Pure-tone audiometry was performed both preoperatively and postoperatively on 67 patients who underwent microvascular decompression for hemifacial spasm during the study period. A change of greater than 10 dB at either 4 kHz or 8 kHz was considered to be HFHL. Additionally, the authors analyzed intraoperative brainstem auditory evoked potentials from this patient cohort.

RESULTS

The incidence of ipsilateral HFHL in this cohort was 7.4%, while the incidence of contralateral HFHL was 4.5%. One patient (1.5%; also included in the HFHL group) experienced an ipsilateral nonserviceable hearing loss.

CONCLUSIONS

The reduced incidence of HFHL in this study suggests that technical modifications including performing the procedure without the use of fixed retraction may greatly reduce, but not eliminate, the occurrence of HFHL following microvascular decompression for hemifacial spasm.

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Parthasarathy Thirumala, Kristin Meigh, Navya Dasyam, Preethi Shankar, Kanika R. K. Sarma, Deepika R. K. Sarma, Miguel Habeych, Donald Crammond and Jeffrey Balzer

OBJECT

The primary aim of this study was to evaluate the incidence and discuss the pathogenesis of high-frequency hearing loss (HFHL) after microvascular decompression (MVD) for trigeminal neuralgia (TGN), glossopharyngeal neuralgia (GPN), or geniculate neuralgia (GN).

METHODS

The authors analyzed preoperative and postoperative audiogram data and brainstem auditory evoked potentials (BAEPs) from 93 patients with TGN, 6 patients with GPN, and 8 patients with GN who underwent MVD. Differences in pure tone audiometry > 10 dB at frequencies of 0.25, 0.5, 1, 2, 4, and 8 kHz were calculated preoperatively and postoperatively for both the ipsilateral and the contralateral sides. Intraoperative monitoring records were analyzed and compared with the incidence of HFHL, which was defined as a change in pure tone audiometry > 10 dB at frequencies of 4 and 8 kHz.

RESULTS

The incidence of HFHL was 30.84% on the side ipsilateral to the surgery and 20.56% on the contralateral side. Of the 47 patients with HFHL, 20 had conductive hearing loss, and 2 experienced nonserviceable hearing loss after the surgery. The incidences of HFHL on the ipsilateral side at 4 and 8 kHz were 17.76% and 25.23%, respectively, and 8.41% and 15.89%, respectively, on the contralateral side. As the audiometric frequency increased, the number of patients with hearing loss increased. No significant postoperative difference was found between patients with and without HFHL in intraoperative BAEP waveforms. Sex, age, and affected side were not associated with an increase in the incidence of hearing loss.

CONCLUSIONS

High-frequency hearing loss occurred after MVD for TGN, GPN, or GN, and the greatest incidence occurred on the ipsilateral side. This hearing loss may be a result of drill-induced noise and/or transient loss of cerebrospinal fluid during the course of the procedure. Changes in intraoperative BAEP waveforms were not useful in predicting HFHL after MVD. Repeated postoperative audiological examinations may be useful in assessing the prognosis of HFHL.

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Jeffrey R. Balzer, Nestor D. Tomycz, Donald J. Crammond, Miguel Habeych, Parthasarathy D. Thirumala, Louisa Urgo and John J. Moossy

Object

Spinal cord stimulation (SCS) is being currently used to treat medically refractory pain syndromes involving the face, trunk, and extremities. Unlike thoracic SCS surgery, during which patients can be awakened from conscious sedation to confirm good lead placement, safe placement of paddle leads in the cervical spine has required general anesthesia. Using intraoperative neurophysiological monitoring, which is routinely performed during these cases at the authors' institution, the authors developed an electrophysiological technique to intraoperatively lateralize lead placement in the cervical epidural space.

Methods

Data from 44 patients undergoing median and tibial nerve somatosensory evoked potential (SSEP) monitoring during cervical laminectomy or hemilaminectomy for placement or replacement of dorsal column stimulators were retrospectively reviewed. Paddle leads were positioned laterally or just off midline and parallel to the axis of the cervical spinal cord to effectively treat what was most commonly a predominant unilateral pain syndrome. During SSEP recording, the spinal cord stimulator was activated at 1.0 V and increased in increments of 1.0 V to a maximum of 6.0 V. A unilateral reduction or abolishment of SSEP amplitude was regarded as an indicator of lateralized placement of the stimulator. A bilateral diminutive effect on SSEPs was interpreted as a midline or near midline lead placement.

Results

Epidural stimulation abolished or significantly reduced SSEP amplitudes in all patients undergoing placement for a unilateral pain syndrome. In 15 patients, electrodes were repositioned intraoperatively to achieve the most robust SSEP amplitude reduction or abolishment using the lowest epidural stimulation intensity. In all cases in which a significant unilateral reduction in SSEP was observed, the patient reported postoperative sensory alterations in target locations predicted by intraoperative SSEP changes. Placement of cervical spinal cord stimulators for bilateral pain syndromes often resulted in bilateral but asymmetrical SSEP changes. In no cases were significant SSEP changes, other than those induced using the device to directly stimulate the dorsal surface of the spinal cord, observed. No case of new postoperative neurological deficit was observed.

Conclusions

Somatosensory evoked potentials can be used safely and successfully for predicting the lateralization of cervical spinal cord stimulator placement. Moreover, they can also intraoperatively alert the surgical team to inadvertent displacement of a lead during anchoring. Further studies are needed to determine whether apart from assisting with proper lateralization, SSEP collision testing may help to optimize electrode positioning and improve pain control outcomes.

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Parthasarathy D. Thirumala, Preethi Ilangovan, Miguel Habeych, Donald J. Crammond and Jeffrey Balzer

Object

Microvascular decompression (MVD) of the facial nerve is an effective treatment for patients with hemifacial spasm. Intraoperative monitoring of brainstem auditory evoked potentials (BAEPs) during MVD can reduce the incidence of hearing loss. In this study the authors' goal was to evaluate changes in interpeak latencies (IPLs) of Waves I–V, Waves III–V, and Waves I–III of BAEP Waveforms I, III, and V during MVD and correlate them with postoperative hearing loss. To date, no such study has been performed. Hearing loss is defined as nonuseful hearing (Class C/D), which is a pure tone average of more than 50 dB and/or speech discrimination score of less than 50%.

Methods

The authors performed a retrospective analysis of IPLs of BAEPs in 93 patients who underwent intraoperative BAEP monitoring during MVD. Patients who did not have hearing loss were in Class A/B and those who had hearing loss were in Class C/D.

Results

Binary logistic regression analysis of independent IPL variables was performed. A maximum change in IPLs of Waves I–III and Waves I–V and on-skin change in IPLs of Waves I–V increases the odds of hearing loss. However, on adjusting the same variables for loss of response, change in IPLs did not increase the odds of hearing loss.

Conclusions

Changes in IPL measurements did not increase the odds of postoperative hearing loss. This information might be helpful in evaluating the value of IPLs as alarm criteria during MVD to prevent hearing loss.

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Parthasarathy D. Thirumala, Donald J. Crammond, Yoon K. Loke, Hannah L. Cheng, Jessie Huang and Jeffrey R. Balzer

OBJECTIVE

The goal of this study was to evaluate the efficacy of intraoperative transcranial motor evoked potential (TcMEP) monitoring in predicting an impending neurological deficit during corrective spinal surgery for patients with idiopathic scoliosis (IS).

METHODS

The authors searched the PubMed and Web of Science database for relevant lists of retrieved reports and/or experiments published from January 1950 through October 2014 for studies on TcMEP monitoring use during IS surgery. The primary analysis of this review fit the operating characteristic into a hierarchical summary receiver operating characteristic curve model to determine the efficacy of intraoperative TcMEP-predicted change.

RESULTS

Twelve studies, with a total of 2102 patients with IS were included. Analysis found an observed incidence of neurological deficits of 1.38% (29/2102) in the sample population. Of the patients who sustained a neurological deficit, 82.8% (24/29) also had irreversible TcMEP change, whereas 17.2% (5/29) did not. The pooled analysis using the bivariate model showed TcMEP change with sensitivity (mean 91% [95% CI 34%–100%]) and specificity (mean 96% [95% CI 92–98%]). The diagnostic odds ratio indicated that it is 250 times more likely to observe significant TcMEP changes in patients who experience a new-onset motor deficit immediately after IS correction surgery (95% CI 11–5767). TcMEP monitoring showed high discriminant ability with an area under the curve of 0.98.

CONCLUSIONS

A patient with a new neurological deficit resulting from IS surgery was 250 times more likely to have changes in TcMEPs than a patient without new deficit. The authors' findings from 2102 operations in patients with IS show that TcMEP monitoring is a highly sensitive and specific test for detecting new spinal cord injuries in patients undergoing corrective spinal surgery for IS. They could not assess the value of TcMEP monitoring as a therapeutic adjunct owing to the limited data available and their study design.

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Marion A. Hughes, Ronak H. Jani, Saeed Fakhran, Yue-Fang Chang, Barton F. Branstetter IV, Parthasarathy D. Thirumala and Raymond F. Sekula Jr.

OBJECTIVE

The aim of this study was to identify preoperative imaging predictors of surgical success in patients with classic trigeminal neuralgia (cTN) undergoing microvascular decompression (MVD) via retrospective multivariate regression analysis.

METHODS

All included patients met criteria for cTN and underwent preoperative MRI prior to MVD. MR images were blindly graded regarding the presence and severity (i.e., mild or severe) of neurovascular compression (NVC). All patients were contacted by telephone to determine their postoperative pain status.

RESULTS

A total of 79 patients were included in this study. Sixty-two patients (78.5%) were pain-free without medication following MVD. The following findings were more commonly observed with the symptomatic nerve when compared to the contralateral asymptomatic nerve: NVC (any form), arterial compression alone, NVC along the proximal trigeminal nerve, and severe NVC (p values < 0.0001). The only imaging variable that was a statistically significant predictor of being pain-free without medication following MVD was severe NVC. Patients with severe NVC were 6.36 times more likely to be pain-free following MVD compared to those without severe NVC (p = 0.007).

CONCLUSIONS

In patients with cTN undergoing MVD, severe NVC on preoperative MRI is a strong predictor of an excellent surgical outcome.

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Cheran Elangovan, Supriya Palwinder Singh, Paul Gardner, Carl Snyderman, Elizabeth C. Tyler-Kabara, Miguel Habeych, Donald Crammond, Jeffrey Balzer and Parthasarathy D. Thirumala

OBJECT

The aim of this study was to evaluate the value of intraoperative neurophysiological monitoring (IONM) using electromyography (EMG), brainstem auditory evoked potentials (BAEPs), and somatosensory evoked potentials (SSEPs) to predict and/or prevent postoperative neurological deficits in pediatric patients undergoing endoscopic endonasal surgery (EES) for skull base tumors.

METHODS

All consecutive pediatric patients with skull base tumors who underwent EES with at least 1 modality of IONM (BAEP, SSEP, and/or EMG) at our institution between 1999 and 2013 were retrospectively reviewed. Staged procedures and repeat procedures were identified and analyzed separately. To evaluate the diagnostic accuracy of significant free-run EMG activity, the prevalence of cranial nerve (CN) deficits and the sensitivity, specificity, and positive and negative predictive values were calculated.

RESULTS

A total of 129 patients underwent 159 procedures; 6 patients had a total of 9 CN deficits. The incidences of CN deficits based on the total number of nerves monitored in the groups with and without significant free-run EMG activity were 9% and 1.5%, respectively. The incidences of CN deficits in the groups with 1 staged and more than 1 staged EES were 1.5% and 29%, respectively. The sensitivity, specificity, and negative predictive values (with 95% confidence intervals) of significant EMG to detect CN deficits in repeat procedures were 0.55 (0.22–0.84), 0.86 (0.79–0.9), and 0.97 (0.92–0.99), respectively. Two patients had significant changes in their BAEPs that were reversible with an increase in mean arterial pressure.

CONCLUSIONS

IONM can be applied effectively and reliably during EES in children. EMG monitoring is specific for detecting CN deficits and can be an effective guide for dissecting these procedures. Triggered EMG should be elicited intraoperatively to check the integrity of the CNs during and after tumor resection. Given the anatomical complexity of pediatric EES and the unique challenges encountered, multimodal IONM can be a valuable adjunct to these procedures.

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Xuhui Wang, Parthasarathy D. Thirumala, Aalap Shah, Paul Gardner, Miguel Habeych, Donald J. Crammond, Jeffrey Balzer and Michael Horowitz

Object

The objective of this study was to investigate the clinical characteristics, intraoperative findings, complications, and outcomes after the first microvascular decompression (MVD) in patients with and without previous botulinum neurotoxin treatment for hemifacial spasm (HFS).

Methods

The authors analyzed 246 MVDs performed at the University of Pittsburgh Medical Center between January 1, 2000, and December 31, 2007. One hundred and seventy-six patients with HFS underwent botulinum neurotoxin injection treatment prior to first MVD (Group I), and 70 patients underwent their first MVD without previous botulinum neurotoxin treatment (Group II). Clinical outcome data were obtained immediately after the operation, at discharge, and at follow-up. Follow-up data were collected from 177 patients with a minimum follow-up period of 9 months (mean 54.48 ± 27.84 months).

Results

In 246 patients, 89.4% experienced immediate postoperative relief of spasm, 91.1% experienced relief at discharge, and 92.7% experienced relief at follow-up. There was no significant difference in outcomes and complications between Group I and Group II (p > 0.05). Preoperatively, patients in Group I had higher rates of facial weakness, tinnitus, tonus, and platysmal involvement as compared with Group II (p < 0.05). The posterior inferior cerebellar artery and vertebral artery were intraoperatively identified as the offending vessels in cases of vasculature compression in a significantly greater number of patients in Group II compared with Group I (p = 0.008 and p = 0.005, respectively, for each vessel). The lateral spread response (LSR) disappeared in 60.48% of the patients in Group I as compared with 74.19% in Group II (p > 0.05). No significant differences in complications were noted between the 2 groups.

Conclusions

Microvascular decompression is an effective and safe procedure for patients with HFS previously treated using botulinum neurotoxin. Intraoperative monitoring with LSR is an effective tool for evaluating adequate decompression.

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Tingting Ying, Parthasarathy Thirumala, Aalap Shah, Tara Nikonow, Kelley Wichman, Maura Holmes, Barry Hirsch, Yuefang Chang, Paul Gardner, Miguel Habeych, Donald J. Crammond, Lois Burkhart, Michael Horowitz and Jeffrey Balzer

Object

The primary aim of this study was to evaluate the incidence and discuss the pathogenesis of high-frequency hearing loss (HFHL) after microvascular decompression (MVD) for hemifacial spasm (HFS).

Methods

Preoperative and postoperative audiogram data and brainstem auditory evoked potentials (BAEPs) from 94 patients who underwent MVD for HFS were analyzed. Pure tone audiometry at 0.25–2 kHz, 4 kHz, and 8 kHz was calculated for all individuals pre- and postoperatively ipsilateral and contralaterally. Intraoperative neurophysiological data were reviewed independently. An HFHL was defined as a change in pure tone audiometry of more than 10 dB at frequencies of 4 and 8 kHz.

Results

The incidence of HFHL was 50.00% and 25.53% ipsilateral and contralateral to the side of surgery, respectively. The incidence of HFHL adjusted for conductive and nonserviceable hearing loss was 26.6% ipsilaterally. The incidence of HFHL at 4 and 8 kHz on the ipsilateral side was 37.23% and 45.74%, respectively, and it was 10.64% and 25.53%, respectively, on the contralateral side. Maximal change in interpeak latency Waves I–V compared with baseline was the only variable significantly different between groups (p < 0.05). Sex, age, and side did not increase the risk of HFHL. Stepwise logistic regression analysis did not find any changes in intraoperative BAEPs to increase the risk of HFHL.

Conclusions

High-frequency hearing loss occurs in a significant number of patients following MVD surgery for HFS. Drill-induced noise and transient loss of CSF during surgery may impair hearing in the high-frequency ranges on both the ipsilateral and contralateral sides, with the ipsilateral side being more affected. Changes in intraoperative BAEPs during MVD for HFS were not useful in predicting HFHL. Follow-up studies and repeat audiological examinations may be helpful in evaluating the time course and prognosis of HFHL. Prospective studies focusing on decreasing intraoperative noise exposure, as well as auditory shielding devices, will establish causation and allow the team to intervene appropriately to decrease the risk of HFHL.