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Kajetan L. von Eckardstein, Charles W. Beatty, Colin L. W. Driscoll and Michael J. Link

The authors report on 2 patients with bilateral vestibular schwannomas (VSs) who underwent unilateral surgical tumor removal. One patient was followed up for 4 years, the other for 9; in both cases, the contralateral VS regressed markedly without any additional treatment during the follow-up period. Serial MR imaging was performed to monitor the untreated tumor, which in both cases involved the only hearing ear. The tumors were assessed volumetrically. The contralateral tumors appeared to enlarge mildly at initial follow-up and then, with no treatment, regressed (to 23% of the original maximum volume in Case 1 and to 15% of the original maximum in Case 2). The largest posterior fossa diameter decreased from 30.1 mm to 18.6 mm in Case 1 over 4 years and from 27 mm to 16 mm over 8 years in Case 2. Hearing declined only mildly during follow-up in both patients.

These cases demonstrate the first well-documented, long-term, spontaneous VS regressions in patients with neurofibromatosis Type 2. They underline the importance of careful observation of VS involving the only hearing ear in the management of bilateral VS to determine the natural growth pattern of the tumors. The mechanism of the dramatic spontaneous tumor regression is uncertain.

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William R. Copeland, Grant W. Mallory, Brian A. Neff, Colin L. W. Driscoll and Michael J. Link

OBJECT

The following study was conducted to identify risk factors for a postoperative CSF leak after vestibular schwannoma (VS) surgery.

METHODS

The authors reviewed a prospectively maintained database of all patients who had undergone resection of a VS at the Mayo Clinic between September 1999 and May 2013. Patients who developed a postoperative CSF leak within 30 days of surgery were compared with those who did not. Data collected included patient age, sex, body mass index (BMI), tumor size, tumor side, history of prior tumor treatment, operative time, surgical approach, and extent of resection. Both univariate and multivariate regression analyses were performed to evaluate all variables as risk factors of a postoperative CSF leak.

RESULTS

A total of 457 patients were included in the study, with 45 patients (9.8%) developing a postoperative CSF leak. A significant association existed between increasing BMI and a CSF leak, with those classified as overweight (BMI 25–29.9), obese (BMI 30–39.9), or morbidly obese (BMI ≥ 40) having a 2.5-, 3-, and 6-fold increased risk, respectively. Patients undergoing a translabyrinthine (TL) approach experienced a higher rate of CSF leaks (OR 2.5, 95% CI 1.3–4.6; p = 0.005), as did those who had longer operative times (OR 1.04, 95% CI 1.02–1.07; p = 0.0006). The BMI, a TL approach, and operative time remained independent risk factors on multivariate modeling.

CONCLUSIONS

Elevated BMI is a risk factor for the development of a postoperative CSF leak following VS surgery. Recognizing this preoperatively can allow surgeons to better counsel patients regarding the risks of surgery as well as perhaps to alter perioperative management in an attempt to decrease the likelihood of a leak. Patients undergoing a TL approach or having longer operative times are also at increased risk of developing a postoperative CSF leak.

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Vini G. Khurana, Michael J. Link, Colin L. W. Driscoll and Charles W. Beatty

✓ The authors report on a patient with a rare schwannoma that arose from the cochlear division of the vestibulocochlear nerve. Distinctively, the lesion appeared to arise from the cochlea itself and was monitored with clinical and neuroimaging studies for 12 years before it was diagnosed and treated. The atypical occurrence of schwannomas of the vestibulocochlear nerve originating in the inner ear structures underscores the high level of clinical suspicion required for the diagnosis of these lesions in patients presenting with persistent auditory and vestibular symptoms.

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Michelle A. Holman, William R. Schmitt, Matthew L. Carlson, Colin L. W. Driscoll, Charles W. Beatty and Michael J. Link

Object

The aim in this study was to describe the clinical presentation, differential diagnosis, and risk for neurofibromatosis Type 2 (NF2) in pediatric patients presenting with cerebellopontine angle (CPA) and internal auditory canal (IAC) tumors.

Methods

The authors conducted a retrospective study at a tertiary care academic referral center. All patients with an age ≤ 18 years who had presented with an extraaxial CPA or IAC tumor between 1987 and 2012 were included in the study cohort. Data regarding symptoms, diagnosis, tumor characteristics, and NF2 status were collected and analyzed.

Results

Sixty patients (55% female, 45% male) harboring 87 tumors were identified. The mean age at diagnosis was 12.8 years (median 14.0 years, range 0.9–18.9 years). Schwannomas were the most commonly identified lesions (57 of 87 tumors, including 52 vestibular, 3 facial, and 2 trigeminal schwannomas), followed by meningiomas (5 of 87) and epidermoid cysts (4 of 87). Six malignant tumors were diagnosed, including small-cell sarcoma, squamous cell carcinoma, malignant meningioma, atypical rhabdoid-teratoid tumor, endolymphatic sac tumor, and malignant ganglioglioma. Headache, followed by hearing loss and imbalance, was the most common presenting symptom, whereas dysphagia, otalgia, and facial pain were uncommon.

Neurofibromatosis Type 2 was diagnosed in 20 (61%) of 33 patients with vestibular schwannoma (VS), while the other 13 patients (39%) had sporadic tumors. Nineteen of the 20 patients with NF2 met the diagnostic criteria for that disorder on initial presentation, and 15 of them presented with bilateral VS. At the last follow-up, 19 of the 20 patients subsequently diagnosed with NF2 demonstrated bilateral VSs, whereas 1 patient with a unilateral VS and multiple other NF2-associated tumors has yet to demonstrate a contralateral VS to date. Only 1 patient presenting with an isolated unilateral VS and no family history of NF2 demonstrated a contralateral VS on subsequent radiological screening.

Conclusions

Cerebellopontine angle and IAC tumors in the pediatric population are rare. There are several noteworthy differences between the adult and pediatric populations harboring these lesions. While VS is the most common pathology in both age groups, the lesion was found in only 60% of the pediatric patients in the present study. Unlike in adults, VSs in the pediatric population were associated with NF2 in over one-half of all cases. The majority of pediatric patients with NF2 fulfilled the diagnostic criteria at initial presentation; however, approximately 7% of patients presenting with a seemingly sporadic (no family history of NF2) unilateral VS will meet the criteria for NF2 later in life. Finally, malignancies account for a significantly higher percentage (10%) of cases among pediatric patients. These findings underscore the importance of early screening and close radiological follow-up and may be helpful in patient counseling.

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Matthew L. Carlson, Jeffrey T. Jacob, Bruce E. Pollock, Brian A. Neff, Nicole M. Tombers, Colin L. W. Driscoll and Michael J. Link

Object

The goals of this retrospective cohort study were as follows: 1) to describe the long-term prevalence and timing of hearing deterioration following low-dose (12- to 13-Gy marginal dose) stereotactic radiosurgery (SRS) for vestibular schwannoma (VS); and 2) to identify clinical variables associated with long-term preservation of useful hearing following treatment.

Methods

Patients with serviceable hearing who underwent SRS for VS between 1997 and 2002 were studied. Data including radiosurgery treatment plans, tumor characteristics, pre- and posttreatment pure tone average, speech discrimination scores, and American Academy of Otolaryngology–Head and Neck Surgery hearing class were collected. Time to nonserviceable hearing was estimated using the Kaplan-Meier method. Univariate and multivariate associations with time to nonserviceable hearing were evaluated using Cox proportional hazards regression models.

Results

Forty-four patients met the study criteria and were included. The median duration of audiometric follow-up was 9.3 years. Thirty-six patients developed nonserviceable hearing at a mean of 4.2 years following SRS. The Kaplan-Meier estimated rates of serviceable hearing at 1, 3, 5, 7, and 10 years following SRS were 80%, 55%, 48%, 38%, and 23%, respectively. Multivariate analysis revealed that pretreatment ipsilateral pure tone average (p < 0.001) and tumor size (p = 0.009) were statistically significantly associated with time to nonserviceable hearing.

Conclusions

Durable hearing preservation a decade after low-dose SRS for VS occurs in less than one-fourth of patients. Variables including preoperative hearing capacity and tumor size may be used to predict hearing outcomes following treatment. These findings may assist in pretreatment risk disclosure. Furthermore, these data demonstrate the importance of long-term follow-up when reporting audiometric outcomes following SRS for VS.

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Brian A. Neff, Matthew L. Carlson, Megan M. O'Byrne, Jamie J. Van Gompel, Colin L. W. Driscoll and Michael J. Link

OBJECTIVE

The aim of this study was to evaluate the incidence, presentation, and treatment outcomes of trigeminal nerve–mediated symptoms secondary to large vestibular schwannomas (VSs) with trigeminal nerve contact. Specifically, the symptomatic results of pain, paresthesias, and numbness after microsurgical resection or stereotactic radiosurgery (SRS) were examined.

METHODS

The authors conducted a retrospective review of a database for concomitant diagnosis of trigeminal neuralgia (TN) or trigeminal neuropathy and VS between 1994 and 2014 at a tertiary academic center. All patients with VS with TN or neuropathy were included, with the exception of those patients with neurofibromatosis Type 2 and patients who elected observation. Patient demographic data, symptom evolution, and treatment outcomes were collected. Population data were summarized, and outcome comparisons between microsurgery and SRS were analyzed at last follow-up.

RESULTS

Sixty (2.2%) of 2771 total patients who had large VSs and either TN or neuropathy symptoms met inclusion criteria. The average age of trigeminal symptom onset was 53.6 years (range 24–79 years), the average age at VS diagnosis was 54.4 years (range 25–79 years), and the average follow-up for the microsurgery and SRS groups was 30 and 59 months, respectively (range 3–132 months). Of these patients, 50 (83%) had facial numbness, 16 (27%) had TN pain, and 13 (22%) had paresthesias (i.e., burning or tingling). Subsequently, 50 (83%) patients underwent resection and 10 (17%) patients received SRS.

Treatment of VS with SRS did not improve trigeminal symptoms in any patient. This included 2 subjects with unimproved facial numbness and 4 patients with worsened numbness. Similarly, SRS worsened TN pain and paresthesias in 5 patients and failed to improve pain in 2 additional patients. The Barrow Neurological Institute neuralgia and hypesthesia scale scores were significantly worse for patients undergoing SRS compared with microsurgery.

Resection alleviated facial numbness in 22 (50%) patients, paresthesias in 5 (42%) patients, and TN in 7 (70%) patients. In several patients, surgery was not successful in relieving facial numbness, which failed to improve in 17 (39%) cases and became worse in 5 (11%) cases. Also, surgery did not change the intensity of facial paresthesias or neuralgia in 6 (50%) and 3 (25%) patients, respectively. Microsurgery exacerbated facial paresthesias in 1 (8%) patient but, notably, did not aggravate TN in any patient.

CONCLUSIONS

Overall, resection of large VSs provided improved outcomes for patients with concomitant TN, facial paresthesia, and numbness compared with SRS. However, caution should be used when counseling surgical candidates because a number of patients did not experience improvement. This was especially true in patients with preoperative facial numbness and paresthesias, who frequently reported that these symptoms were unchanged following surgery.

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Matthew L. Carlson, Kathryn M. Van Abel, William R. Schmitt, Colin L. W. Driscoll, Brian A. Neff, John I. Lane and Michael J. Link

Object

The authors describe the unique occurrence of nodular enhancement within the fundus of the internal auditory canal (IAC) lateral to the preoperative radiological tumor margin following gross-total vestibular schwannoma (VS) resection.

Methods

The nature of the study was a retrospective chart review of records. The authors reviewed the cases of all patients who underwent microsurgical resection of a VS between January 2000 and January 2010 at a single tertiary referral center. Patients with incomplete resection, neurofibromatosis Type 2, and those with fewer than 2 postoperative MR images available for review were excluded.

Postsurgical patients with IAC enhancement located lateral to the preoperative imaging–delineated tumor margin were identified. Lesion morphology was characterized on serial MR imaging studies. Clinical follow-up and outcomes were recorded.

Results

Over the past decade, 350 patients underwent microsurgical VS resection. Of these, 16 patients met study criteria and were found to have postsurgical enhancement in the distal aspect of the IAC lateral to the imaging limits of the preoperative tumor margin on the first postoperative MR imaging study (37.5% women, median age 45 years). Initial MR imaging was performed at a mean of 3.1 months following surgery, and the mean radiological follow-up duration was 39.8 months (range 16.4–101.9 months). None of the 16 patients developed recurrence during the follow-up course.

Conclusions

In contrast to previous publications that have reported a high rate of recurrence in cases involving nodular enhancement within the original tumor bed, postoperative enhancement in the IAC lateral to the original tumor margin appears to carry much less risk for tumor recurrence. These findings may be helpful when counseling patients on the recommended frequency of postoperative follow-up imaging.

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Alexander P. Marston, Jeffrey T. Jacob, Matthew L. Carlson, Bruce E. Pollock, Colin L. W. Driscoll and Michael J. Link

OBJECTIVE

Over the last 30 years, stereotactic radiosurgery (SRS) has become an established noninvasive treatment alternative for small- to medium-sized vestibular schwannoma (VS). This study aims to further define long-term SRS tumor control in patients with documented pretreatment tumor growth for whom conservative observation failed.

METHODS

A prospective clinical database was queried, and patients with sporadic VS who elected initial observation and subsequently underwent SRS after documented tumor growth between 2004 and 2014 were identified. Posttreatment tumor growth or shrinkage was determined by a ≥ 2-mm increase or decrease in maximum linear dimension, respectively.

RESULTS

Sixty-eight patients met study inclusion criteria. The median pre- and posttreatment observation periods were 16 and 43.5 months, respectively. The median dose to the tumor margin was 13 Gy (range 12–14 Gy), and the median maximum dose was 26 Gy (range 24–28 Gy). At the time of treatment, 59 tumors exhibited extracanalicular (EC) extension, and 9 were intracanalicular (IC). Of the 59 EC VSs, 50 (85%) remained stable or decreased in size following treatment, and 9 (15%) enlarged by > 2 mm. Among EC tumors, the median pretreatment tumor growth rate was 2.08 mm/year for tumors that decreased or were stable, compared with 3.26 mm/year for tumors that grew following SRS (p = 0.009). Patients who demonstrated a pretreatment growth rate of < 2.5 mm/year exhibited a 97% tumor control rate, compared with 69% for those demonstrating ≥ 2.5 mm/year of growth prior to SRS (p = 0.007). No other analyzed variables were found to predict tumor growth following SRS.

CONCLUSIONS

Overall, SRS administered using a marginal dose between 12–14 Gy is highly effective in treating VSs in which initial observation fails. Tumor control is achieved in 97% of VSs that exhibit slow (< 2.5 mm/year) pretreatment growth; however, SRS is less successful in treating tumors exhibiting rapid growth (≥ 2.5 mm/year).

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William R. Schmitt, Jasper R. Daube, Matthew L. Carlson, Jayawant N. Mandrekar, Charles W. Beatty, Brian A. Neff, Colin L. Driscoll and Michael J. Link

Object

The goal of vestibular schwannoma surgery is tumor removal and preservation of neural function. Intraoperative facial nerve (FN) monitoring has emerged as the standard of care, but its role in predicting long-term facial function remains a matter of debate. The present report seeks to describe and critically assess the value of applying current at supramaximal levels in an effort to identify patients destined for permanent facial paralysis.

Methods

Over more than a decade, the protocol for stimulating and assessing the FN during vestibular schwannoma surgery at the authors' institution has consisted of applying pulsed constant-current stimulation at supramaximal levels proximally and distally following tumor resection to generate an amplitude ratio, which subtracted from 100% yields the degree to which the functional integrity of the FN “dropped off” intraoperatively. These data were prospectively collected and additional variables that might impact postoperative FN function were retrospectively reviewed from the medical record. Only patients with anatomically intact FNs and > 12 months of follow-up data were analyzed.

Results

There were 267 patients available for review. The average posterior fossa tumor diameter was 24 mm and the rate of long-term good (House-Brackmann Grade I–II) FN function was 84%. Univariate logistic regression analysis revealed that prior treatment, neurofibromatosis Type 2 status, tumor size, cerebellopontine angle extension, subjectively thinned FN at the time of operation, minimal stimulation threshold, percent dropoff by supramaximal stimulation (SMS), and postoperative FN function all correlated statistically (p < 0.05) with long-term FN function. When evaluating patients with significant FN weakness at the time of hospital discharge, only the percent dropoff by SMS remained a significant predictor of long-term FN function. However, the positive predictive value of SMS for long-term weakness is low, at 46%.

Conclusions

In a large cohort of patients, the authors found that interrogating intraoperative FN function with SMS is safe and technically simple. It is useful for predicting which patients will ultimately have good facial function, but is very limited in identifying patients destined for long-term facial weakness. This test may prove helpful in the future in tailoring less than gross-total tumor removal to limit postoperative facial weakness.

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Maria Peris-Celda, Avital Perry, Lucas P. Carlstrom, Christopher S. Graffeo, Colin L. W. Driscoll and Michael J. Link

OBJECTIVE

Middle fossa surgery is challenging, and reliable surgical landmarks are essential to perform accurate and safe surgery. Although many descriptions of the middle fossa components have been published, a clinically practical description of this very complex anatomical region is lacking. Small structure arrangements in this area are often not well visualized or accurately demarcated with neuronavigation systems. The objective is to describe a “roadmap” of key surgical reference points and landmarks during middle fossa surgery to help the surgeon predict where critical structures will be located.

METHODS

The authors studied 40 dry skulls (80 sides) obtained from the anatomical board at their institution. Measurements of anatomical structures in the middle fossa were made with a digital caliper and a protractor, taking as reference the middle point of the external auditory canal (MEAC). The results were statistically analyzed.

RESULTS

The petrous part of the temporal bone was found at a mean of 16 mm anterior and 24 mm posterior to the MEAC. In 87% and 99% of the sides, the foramen ovale and foramen spinosum, respectively, were encountered deep to the zygomatic root. The posterior aspect of the greater superficial petrosal nerve (GSPN) groove was a mean of 6 mm anterior and 25 mm medial to the MEAC, nearly parallel to the petrous ridge. The main axis of the IAC projected to the root of the zygoma in all cases. The internal auditory canal (IAC) porus was found 5.5 mm lateral and 4.5 mm deep to the lateral aspect of the trigeminal impression along the petrous ridge (mean measurement values). A projection from this point to the middle aspect of the root of the zygoma, being posterior to the GSPN groove, could estimate the orientation of the IAC.

CONCLUSIONS

In middle fossa approaches, the external acoustic canal is a reliable reference before skin incision, whereas the zygomatic root becomes important after the skin incision. Deep structures can be related to these 2 anatomical structures. An easy method to predict the location of the IAC in surgery is described. Careful study of the preoperative imaging is essential to adapt this knowledge to the individual anatomy of the patient.