Evaluating vestibular schwannoma size and volume on magnetic resonance imaging: An inter- and intra-rater agreement study

A multi-institutional machine learning algorithm for prognosticating facial nerve injury following microsurgical resection of vestibular schwannoma

Vestibular schwannomas (VS) are the most common tumor of the skull base with available treatment options that carry a risk of iatrogenic injury to the facial nerve, which can significantly impact patients' quality of life. As facial nerve outcomes remain challenging to prognosticate, we endeavored to utilize machine learning to decipher predictive factors relevant to facial nerve outcomes following microsurgical resection of VS. A database of patient-, tumor- and surgery-specific features was constructed via retrospective chart review of 242 consecutive patients who underwent microsurgical resection of VS over a 7-year study period. This database was then used to train non-linear supervised machine learning classifiers to predict facial nerve preservation, defined as House-Brackmann (HB) I vs. facial nerve injury, defined as HB II-VI, as determined at 6-month outpatient follow-up. A random forest algorithm demonstrated 90.5% accuracy, 90% sensitivity and 90% specificity in facial nerve injury prognostication. A random variable (rv) was generated by randomly sampling a Gaussian distribution and used as a benchmark to compare the predictiveness of other features. This analysis revealed age, body mass index (BMI), case length and the tumor dimension representing tumor growth towards the brainstem as prognosticators of facial nerve injury. When validated via prospective assessment of facial nerve injury risk, this model demonstrated 84% accuracy. Here, we describe the development of a machine learning algorithm to predict the likelihood of facial nerve injury following microsurgical resection of VS. In addition to serving as a clinically applicable tool, this highlights the potential of machine learning to reveal non-linear relationships between variables which may have clinical value in prognostication of outcomes for high-risk surgical procedures.

An External Validation Study for Automated Segmentation of Vestibular Schwannoma

OBJECTIVE

To validate how an automated model for vestibular schwannoma (VS) segmentation developed on an external homogeneous dataset performs when applied to internal heterogeneous data.

PATIENTS

The external dataset comprised 242 patients with previously untreated, sporadic unilateral VS undergoing Gamma Knife radiosurgery, with homogeneous magnetic resonance imaging (MRI) scans. The internal dataset comprised 10 patients from our institution, with heterogeneous MRI scans.

INTERVENTIONS

An automated VS segmentation model was developed on the external dataset. The model was tested on the internal dataset.

MAIN OUTCOME MEASURE

Dice score, which measures agreement between ground truth and predicted segmentations.

RESULTS

When applied to the internal patient scans, the automated model achieved a mean Dice score of 61% across all 10 images. There were three tumors that were not detected. These tumors were 0.01 ml on average (SD = 0.00 ml). The mean Dice score for the seven tumors that were detected was 87% (SD = 14%). There was one outlier with Dice of 55%-on further review of this scan, it was discovered that hyperintense petrous bone had been included in the tumor segmentation.

CONCLUSIONS

We show that an automated segmentation model developed using a restrictive set of siloed institutional data can be successfully adapted for data from different imaging systems and patient populations. This is an important step toward the validation of automated VS segmentation. However, there are significant shortcomings that likely reflect limitations of the data used to train the model. Further validation is needed to make automated segmentation for VS generalizable.

Growth potential of small residual tumors after vestibular schwannoma surgery: comparison between remnants and the natural history of small tumors

OBJECTIVE

Due to the heterogeneous definitions of tumor regrowth and various tumor volume distributions, the nature of small remnants after vestibular schwannoma (VS) surgery and the appropriate timing of adjuvant stereotactic radiosurgery for these remnants remain unclear. In this study, the growth potential of small remnants (< 1 cm3) after VS surgery was compared with that of treatment-naïve (TN) small VSs.

METHODS

This retrospective single-center study included 44 patients with VS remnants following subtotal resection (STR) of a large VS (remnant group) and 75 patients with TN VS (< 1 cm3; TN group). A 20% change in tumor volume over the imaging interval indicated radiographic progression or regression. Tumor progression-free survival (TPFS) rates were estimated using the Kaplan-Meier method.

RESULTS

In the remnant group, the mean preoperative tumor volume was 13.8 ± 9.0 cm3 and the mean tumor resection rate was 95% ± 5%. The mean tumor volume at the start of the observation period did not differ significantly between the two groups (remnant vs TN: 0.41 ± 0.29 vs 0.34 ± 0.28 cm3, p = 0.171). The median periods until tumor progression was detected were 15.1 (range 4.9-76.2) months and 44.7 (range 12.6-93.2) months in the TN and remnant groups, respectively. In the remnant group, the TPFS rates were 74% and 70% at 3 and 5 years after the surgery, respectively, compared with 59% and 47% in the TN group. The log-rank test demonstrated a significant difference (p = 0.008) in the TPFS rates between the two groups. Furthermore, 42 patients each from the remnant and TN groups were matched based on tumor volume. TPFS was significantly longer in the remnant group than in the TN group (3-year rates, 77% vs 62%; 5-year rates, 73% vs 51%; p = 0.02). In the remnant group, 18% of the tumor remnants demonstrated regression during follow-up, compared with 9% in the TN group, but this intergroup difference was not significant (p = 0.25).

CONCLUSIONS

This study demonstrated that the growth potential of small VS remnants was lower than that of TN tumors. Observing for small remnants may be appropriate after STR of a large VS. Given the risk of tumor regrowth, careful observation using MRI should be mandatory during follow-up.

Guiding Patients Through Decision-Making in Management of Sporadic Vestibular Schwannoma

Decision-making in management of sporadic vestibular schwannoma aims to identify the most appropriate options based on tumor characteristics, symptoms, health, and goals for each patient. Advances in knowledge of tumor natural history, improvements in radiation techniques, and achievements in neurologic preservation with microsurgery have shifted emphasis toward maximizing quality of life using a personalized approach. To empower patients to make informed decisions, we present a framework to help match patient values and priorities with reasonable expectations from modern management options. Introduced herein are practical examples of communication strategies and decision aids to support shared decision-making in modern practice.

Confrontation of endolymphatic hydrops diagnosis on 3-Tesla MRI to clinical and audiovestibular findings in Meniere's disease

Objective

The aim of this study was to compare different MRI diagnostic criteria for endolymphatic hydrops (EH) and to investigate the relation between audiovestibular and MRI findings in Meniere's disease (MD).

Materials and methods

Prospective cross-sectional cohort study in 2 referral centers included 76 patients with unilateral (n = 62) or bilateral (n = 14) MD. All patients underwent inner ear 3T-MRI 4 h (n = 52) or >24H (n = 24) following audiovestibular tests. T2-CISS and 3D-FLAIR images 4H after gadolinium were obtained. EH diagnosis was based on saccular morphology on coronal views (T2 and 3D-FLAIR), semi quantitative estimation of endolymphatic space enlargement, and saccule utricle ratio inversion (SURI) on 3D-FLAIR axial views.

Results

SURI was the best criterion related to the disease side (43 SURI+ on symptomatic ears, n = 77, vs. 6 SURI+ on asymptomatic ears, n = 53, p < 0.0001, Chi-2). Same-day MRI revealed relation between EH, hearing loss and caloric weakness which could not be detected on delayed MRI: SURI was associated with a higher pure-tone average (43 ± 4.1 dB in SURI+ ears, n = 42 vs. 23 ± 2.6 SURI-, n = 62, p < 0.0001, unpaired t-test,), and a higher proportion of vestibular caloric weakness (23/46 SURI+ ears vs. 4/62 SURI-, p < 0.001, Chi-2). Among all criteria, SURI combined to caloric weakness was the best predictor of the affected side in a logistic regression model.

Conclusion

SURI had the strongest relation to the side the disease and audio vestibular findings for unilateral, probable and definite meniere disease. A short delay between MRI and audio vestibular tests improved the coherence between the findings.

Machine Learning for Automated Calculation of Vestibular Schwannoma Volumes

HYPOTHESIS

Machine learning-derived algorithms are capable of automated calculation of vestibular schwannoma tumor volumes without operator input.

BACKGROUND

Volumetric measurements are most sensitive for detection of vestibular schwannoma growth and important for patient counseling and management decisions. Yet, manually measuring volume is logistically challenging and time-consuming.

METHODS

We developed a deep learning framework fusing transformers and convolutional neural networks to calculate vestibular schwannoma volumes without operator input. The algorithm was trained, validated, and tested on an external, publicly available data set consisting of magnetic resonance imaging images of medium and large tumors (178-9,598 mm 3 ) with uniform acquisition protocols. The algorithm was then trained, validated, and tested on an internal data set of variable size tumors (5-6,126 mm 3 ) with variable acquisition protocols.

RESULTS

The externally trained algorithm yielded 87% voxel overlap (Dice score) with manually segmented tumors on the external data set. The same algorithm failed to translate to accurate tumor detection when tested on the internal data set, with Dice score of 36%. Retraining on the internal data set yielded Dice score of 82% when compared with manually segmented images, and 85% when only considering tumors of similar size as the external data set (>178 mm 3 ). Manual segmentation by two experts demonstrated high intraclass correlation coefficient (0.999).

CONCLUSION

Sophisticated machine learning algorithms delineate vestibular schwannomas with an accuracy exceeding established norms of up to 20% error for repeated manual volumetric measurements-87% accuracy on a homogeneous data set, and 82% to 85% accuracy on a more varied data set mirroring real world neurotology practice. This technology has promise for clinical applicability and time savings.

Spontaneous Volumetric Tumor Regression During Wait-and-Scan Management of 952 Sporadic Vestibular Schwannomas

OBJECTIVE

Spontaneous tumor shrinkage during wait-and-scan management of sporadic vestibular schwannoma is generally considered an uncommon phenomenon. However, most data informing this understanding stem from single-slice linear tumor measurements taken in the axial imaging plane. The objective of the current work was to characterize the regression capacity of sporadic vestibular schwannomas using volumetric tumor measurements.

STUDY DESIGN

Retrospective cohort study using slice-by-slice, three-dimensional volumetric tumor measurements.

SETTING

Three tertiary referral centers.

PATIENTS

Patients with sporadic vestibular schwannoma.

INTERVENTIONS

Wait-and-scan.

MAIN OUTCOME MEASURES

Regression-free survival rates with regression defined as a decrease of at least 20% of the tumor volume.

RESULTS

Among 952 patients undergoing a total of 3,505 magnetic resonance imaging studies during observation, 123 experienced volumetric tumor regression after diagnosis at a median of 1.2 years (interquartile range, 0.6-2.9 yr). Volumetric regression-free survival rates (95% confidence interval; number still at risk) at 1, 3, and 5 years after diagnosis were 94% (92-95%; 662), 86% (83-89%; 275), and 78% (73-82%; 132), respectively. Among 405 patients who demonstrated an initial period of tumor growth but continued wait-and-scan management, 48 experienced volumetric regression at a median of 1.2 years (interquartile range, 0.8-2.6 yr) after initial growth. Volumetric regression-free survival rates at 1, 3, and 5 years after initial growth were 94% (92-97%; 260), 84% (79-89%; 99), and 75% (67-83%; 43), respectively. Ultimately, only 82 of the 952 patients studied showed exclusively volumetric tumor regression (i.e., without any periods of tumor growth) by the time of last follow-up.

CONCLUSION

Spontaneous volumetric tumor shrinkage during wait-and-scan management occurs more frequently than suggested by previous studies using linear tumor measurements and can even occur after previous episodes of documented tumor growth. These data further highlight the dynamic nature of vestibular schwannoma growth. To this end, the application of natural history data to patient management requires a nuanced approach that parallels the complex tumor behavior of vestibular schwannoma.

A Subset of Intracanalicular Vestibular Schwannomas Demonstrates Minimal Growth Over a 10-Year Period

OBJECTIVE

Vestibular schwannomas (VS) commonly undergo magnetic resonance imaging (MRI) surveillance, but long-term data to support the ideal frequency is limited. Herein, we aim to investigate intracanalicular VS growth predictors and long-term growth rates (GR).

STUDY DESIGN

Retrospective chart review.

SETTING

Two tertiary care centers.

PATIENTS

Sporadic intracanalicular VS with initial conservative management and at least two sequential MRIs.

INTERVENTION

Serial MRI.

MAIN OUTCOME MEASURES

VS were categorized by baseline internal auditory canal tertile sublocalization (fundus, midpoint, porus) and size (≤100, 100-200, >200 mm3). Throughout follow-up, volumetric GR (mm3/yr) were determined (baseline-3 yrs, 3-5 yrs, 5-10 yrs) and treatment rates were assessed.

RESULTS

Ninety-nine intracanalicular VS were identified (mean follow-up of 6.1 ± 4.5 yrs). Mean GR before 5-year follow-up were comparable for baseline tertile involvement and size. After 5-year follow-up, mean GR of VS involving the fundus at baseline were lower than those involving the midpoint and fundus (6.17 ± 21.16 and 119.74 ± 117.57 mm3/yr, respectively; p = 0.034). Mean GR of VS with less than or equal to 100 mm3 at baseline (-7.29 ± 25.44 mm3/yr) were lower than those with 100 to 200 mm3 (86.55 ± 103.99 mm3/yr; p = 0.011) and more than 200 mm3 (45.70 ± 35.71 mm3/yr; p = 0.031). Vestibular schwannomas involving the midpoint and fundus had greater treatment rates compared with VS involving only the fundus (p < 0.001).

CONCLUSIONS

Baseline tertile involvement and size may predict long-term intracanalicular VS growth where fundal tumors or those less than or equal to 100 mm3 exhibit little long-term growth. Extending surveillance after 5-year follow-up may be reasonable for fundal VS.

Comparing the Precision and Reliability Between Three Radiographic Techniques for Measuring Sporadic Vestibular Schwannomas

RATIONALE AND OBJECTIVES

Several methods exist for measuring vestibular schwannoma (VS) size radiographically. Our aim was to compare the precision and reproducibility of three different radiographic measurement techniques for assessing VS tumor size.

MATERIAL AND METHODS

Twenty patients with unilateral, sporadic VS previously untreated were identified. All patients had thin-slice T1 weighted, postcontrasted magnetization prepared rapid acquisition gradient echo images. Three measurement techniques were performed using within-subject and between-subject comparison. Experimental comparison of interobserver agreement between techniques was calculated. Interobserver intraclass correlation coefficients, repeatability coefficients, and relative smallest detectable difference were calculated and compared.

RESULTS

Mean tumor measurements were: 10.3 mm (maximum linear dimension, [MLD]), 495.9 mm³ (orthogonal volumetric analysis, [OVA]), and 572.1 mm³ (segmented volumetric analysis, [SVA]). Interobserver correlation coefficient was excellent for all measurement techniques, but highest for segmented volumetric analysis. Repeatability coefficient was 1.44 mm for MLD, 298.9 mm³ for OVA, and 174.8 mm³ for SVA. The smallest detectable difference was 13.9% for MLD, 60.2% for OVA, and 30.6% for SVA. A subgroup analysis was performed for small tumors (<14 mm) and large tumors (>14 mm) and demonstrated increased precision of segmented volumetric analysis for larger tumors.

CONCLUSION

Semi-automated segmented volumetric analysis appears more precise than either linear measurement or orthogonal volumetric analysis for reporting VS tumor size, and becomes increasingly precise for larger tumors. Tumor volume and tumor volume change over time using SVA may be more sensitive in surveilling VS than current measurement techniques.

Long-term natural history and patterns of sporadic vestibular schwannoma growth: A multi-institutional volumetric analysis of 952 patients

BACKGROUND

The current study aims to characterize the natural history of sporadic vestibular schwannoma volumetric tumor growth, including long-term growth patterns following initial detection of growth.

METHODS

Volumetric tumor measurements from 3505 serial MRI studies were analyzed from unselected consecutive patients undergoing wait-and-scan management at three tertiary referral centers between 1998 and 2018. Volumetric tumor growth was defined as a change in volume ≥20%.

RESULTS

Among 952 patients undergoing observation, 622 experienced tumor growth with initial growth-free survival rates (95% CI) at 1, 3, and 5 years following diagnosis of 66% (63-69), 30% (27-34), and 20% (17-24). Among 405 patients who continued to be observed despite demonstrating initial growth, 210 experienced subsequent tumor growth with subsequent growth-free survival rates at 1, 3, and 5 years following initial growth of 77% (72-81), 37% (31-43), and 24% (18-31). Larger tumor volume at initial growth (HR 1.13, P = .02) and increasing tumor growth rate (HR 1.31; P < .001) were significantly associated with an increased likelihood of subsequent growth, whereas a longer duration of time between diagnosis and detection of initial growth was protective (HR 0.69; P < .001).

CONCLUSIONS

While most vestibular schwannomas exhibit an overall propensity for volumetric growth following diagnosis, prior tumor growth does not perfectly predict future growth. Tumors can subsequently grow faster, slower, or demonstrate quiescence and stability. Larger tumor size and increasing tumor growth rate portend a higher likelihood of continued growth. These findings can inform timing of intervention: whether upfront at initial diagnosis, after detection of initial growth, or only after continued growth is observed.

Association of Metformin With Volumetric Tumor Growth of Sporadic Vestibular Schwannomas

OBJECTIVE

Recent research demonstrates a potential association between metformin use and reduced sporadic vestibular schwannoma (VS) growth in patients undergoing conservative observation. The current study was designed to elucidate the effect of metformin on tumor growth in sporadic VS using volumetric analyses.

STUDY DESIGN

Retrospective cohort.

SETTING

Tertiary referral center.

PATIENTS

Patients with sporadic VS who elected initial conservative treatment with at least two serial magnetic resonance imaging (MRI) scans were included.

INTERVENTIONS

Metformin use among patients with observed sporadic VS.

MAIN OUTCOME MEASURES

Tumor growth, defined as an increase in volume of at least 20% from the initial MRI.

RESULTS

A total of 361 patients were evaluated. Thirty-four patients (9%) had a diagnosis of diabetes at baseline. Nineteen patients (5%) were taking metformin at the time of the initial MRI. Metformin use was not significantly associated with a reduced risk of volumetric tumor growth in a univariable analysis in all patients undergoing observation for VS (hazard ratio [HR] 0.75; 95% confidence intervals [CI] 0.40-1.42; p = 0.38) or within the diabetic subset (HR 0.79; 95% CI 0.34-1.83; p = 0.58). Additionally, diabetes status, insulin dependence, hemoglobin A1c value, and metformin dose were not significantly associated with volumetric tumor growth.

CONCLUSION

Despite promising initial results in several previous studies, our data suggest that metformin use does not significantly reduce the risk of volumetric tumor growth in sporadic VS.

Vestibular Schwannoma Measurements-Is Volumetric Analysis Clinically Necessary?

OBJECTIVE

1) To compare vestibular schwannoma maximum linear dimensions and calculated volume with measured volume in accurately determining tumor volume and growth. 2) To determine natural growth history of vestibular schwannomas utilizing volumetric measurements in an observed patient population.

STUDY DESIGN

Retrospective chart review.

SETTING

Tertiary academic referral.

PATIENTS

One hundred fifty two adults with a vestibular schwannoma who underwent observational management with sequential magnetic resonance imaging (MRI) scans (496 scans).

INTERVENTION

MRI scans.

MAIN OUTCOME MEASURES

Tumor volume calculated from linear dimensions compared with measured volume. The percentage change in tumor size (linear or volume) between consecutive MRI scans.

RESULTS

The percentage change in tumor size between consecutive MRIs is significantly different between maximum linear dimension (MLD) and measured tumor volume (p = 0.03), but no difference exists in the percentage change between measured and calculated tumor volume (p = 0.882 for three linear measurements, p = 0.637 for two linear measurements). The overall number of growing tumors is 57.2% (n = 87) with an average growth rate of 62.6%. If a criterion for growth of 20% change is used, 32.2% of tumors monitored by linear volume would have demonstrated growth while 57.2% of tumors with measured volume demonstrated growth.

CONCLUSION

Maximum linear dimensions are a significantly less sensitive measure of tumor growth compared with measured volumes. Calculated tumor volume utilizing three linear measurements is an accurate predictor of both measured tumor volume and tumor growth.

Postural Sway Predicts Growth in Untreated Vestibular Schwannoma: A Retrospective Volumetric Study

BACKGROUND

One in three vestibular schwannomas (VS) will grow within 3 years after diagnosis, but no reliable baseline parameter has been found to predict such growth.

OBJECTIVE

To determine if postural sway is associated with growth of untreated VS.

METHODS

Patients with newly diagnosed sporadic VS assigned to a wait-and-scan protocol were identified from a prospectively maintained database. Postural sway was measured by posturography at baseline and patients were classified as steady or unsteady. Observer-blinded volumetric tumor measurements were performed on the diagnostic MRI and a 3-year control MRI. Tumor growth quantified as relative growth (%) and volume-doubling time (VDT and VDT-1) were investigated as dependent variables against baseline parameters.

RESULTS

Out of 204 VS patients, 53 (26%) were classified as unsteady on the platform at baseline. Median tumor volume was 0.32 cm3 (range 0.02-4.79), and 51% demonstrated significant growth within 3 years. Unsteady patients had significantly faster-growing tumors, with a mean relative growth of 172.5% compared to 79.5% in steady patients (p < 0.006). Seventy-seven percent of unsteady patients had >20% volume increase, compared to 42% in steady patients (p < 0.001). Mean VDT-1 was 0.65 doublings per year for unsteady patients, and 0.22 for steady patients (p < 0.001). Multivariate regression analysis including demographic and clinical parameters showed an OR of 5.6 (95% CI 2.6, 11.8) for growth in unsteady patients.

CONCLUSIONS

This is the first demonstrated association between a measurable parameter and future growth in untreated VS. Our findings may help clinicians identify patients with a higher risk for tumor growth and provide closer monitoring or early treatment.

Predicting Potential of Rapid Tumor Growth in Small to Medium Vestibular Schwannomas on the Basis of Sway Assessed Using Posturography

OBJECTIVE

The relationship between quantitative posturography results and growth of vestibular schwannomas (VSs) during conservative management has not been studied. We aimed to clarify the relationship between the presence of disequilibrium based on posturographic measurement and VS growth.

METHODS

This retrospective, single-center study included 53 patients with VSs (Koos stage I or II) managed conservatively after initial diagnosis. Radiographic progression was considered present if 20% volumetric growth was observed over the imaging interval. Posturography was performed at initial diagnosis, and sway velocity (SV) and sway area were calculated. Tumor growth-free survival was estimated using the Kaplan-Meier method.

RESULTS

Mean follow-up period was 2.87 ± 2.58 years, up to tumor growth detection or last follow-up magnetic resonance imaging. Tumor growth incidence was 40.8% and 61.2% at 2 and 5 years, respectively. Cerebellopontine angle extension and SV with eyes open were related to tumor growth. Tumor growth-free survival of patients with cerebellopontine angle extension and patients with intracanalicular tumor at 2 years was 37.3% and 76.4%, respectively. Tumor growth-free survival of patients with SV >2.06 cm/second and patients with SV ≤2.06 cm/second at 2 years was 30.8% and 68.9%, respectively. The Cox hazard model demonstrated a significant risk for future tumor growth with SV >2.06 cm/second (relative risk, 2.475; 95% confidence interval, 1.11-5.37, P = 0.027).

CONCLUSIONS

We demonstrated a positive correlation between SV with eyes open and future tumor growth. Posturographic data are objective and quantitative; thus, SV may be a potential predictor of future growth of VSs.

Vestibular schwannomas with spontaneous shrinkage: about 35 cases

PURPOSES

The first aim is to describe the epidemiological, clinical, and radiological characteristics of regressive vestibular schwannomas (VS), based on volumetric measurements on MRI to define which regressions are significant. The secondary aim is to look for a correlation between a shrinkage of the tumor and the medical history, and the presence of clinical symptoms.

METHODS

We first selected all patients presenting with a VS who underwent two or more MRI of the internal auditory canal on the same 3 T MRI machine retrospectively between January 2013 and June 2018. All MRI images were evaluated independently by two radiologists. The volumetric analysis was performed contrast-enhanced 2D spin-echo T1-weighted sequence and expressed in cubic centimeters.

RESULTS

Thirty-five patients presented with a regressive VS on MRI (14%). The annual mean shrinkage rate was 0.08 cm³/year. Eighty percent of the patients present both a shrinkage by more than 0.01 cm³/year and a decrease of the initial tumor volume by more than 20%. The majority of patients are asymptomatic or presented moderate balance disorders, which remained stable or improved over time. Tinnitus was observed in 47% and was stable or improved in the majority of cases and the mean annual mean hearing loss was by < or = 4 dB/year.

CONCLUSION

Out of 247 VS, 14% decreased using follow-up (by > or = 2 MRI), and a spontaneous shrinkage greater than 0.01 cm³/year and greater than 20% could be considered significant.

MRI based volumetric measurements of vestibular schwannomas in patients with neurofibromatosis type 2: comparison of three different software tools

Neurofibromatosis type 2 is a neurogenetic disorder with an incidence of about 1:33.000. Hallmarks are bilateral benign vestibular schwannomas, which can lead to deafness or brainstem compression. Volumetric tumor measurements are essential to assess the efficacy of new therapies. We present a statistical and methodical comparison of three volumetric image analysis tools. We performed volumetric measurements on phantoms with predefined volumes (0.1 to 8.0 ml) and tumors seen on 32 head MRI scans from eight NF2 patients with BrainLab, ITK-Snap, or OsiriX. The software was compared with regard to accuracy and reproducibility of the measurements and time required for analysis. The mean volume estimated by all three software programs differed significantly from the true volume of the phantoms, but OsiriX and BrainLab gave estimates that were not significantly different from each other. For the actual tumors, the estimated volumes with all three software tools showed a low coefficient of variability, but the mean volume estimates differed among the tools. OsiriX showed the shortest analysis time. Volumetric assessment of MRI images is associated to an intrinsic risk of miscalculation. For precise volumes it is mandatory to use the same volumetric tools for all measurements.

Association of Metformin With the Growth of Vestibular Schwannomas

Objective

To assess whether medication use, specifically statin, metformin, and aspirin, affects the growth of vestibular schwannomas (VSs).

Study Design

Retrospective case series.

Setting

Single tertiary care academic hospital.

Subjects and Methods

Patients were enrolled if they were diagnosed with sporadic VS and had at least 2 magnetic resonance imaging (MRI) studies at a minimum of 6 months apart prior to any intervention. Electronic medical records were reviewed for demographic and medication data. Tumor volumes on MRI studies were assessed via BrainLab iPlan. The primary endpoint was VS tumor growth, defined as a 20% increase in tumor volume, between consecutive MRI studies or between the first and last available MRI study. Predictors of volumetric growth, specifically statin, aspirin, or metformin use, were analyzed with t tests, chi-square test, univariate logistic regression, and multivariate logistic regression.

Results

A total of 387 patients met inclusion criteria, 53.5% of whom were women. For all patients, the mean age was 60.6 years (range, 18.2-89.2 years); the mean axial tumor diameter, 11.9 mm (range, 1.7-32.0 mm); and the mean tumor volume, 0.85 cm3 (range, 0.01-13.1 cm3). In review of the electronic medical record, 46 patients (11.9%) were taking metformin; 145 (37.5%), a statin; and 117 (30.2%), aspirin. Among patients taking metformin, 39.1% (18/46) exhibited volumetric growth, as opposed to 58.2% (198/340) of nonusers ( P = .014). Metformin (odds ratio, 0.497; P = .036) is significantly associated with reduced VS growth when controlling for aspirin, statin, and tumor size on multivariate logistic regression.

Conclusion

Metformin use is associated with reduced volumetric VS growth.

The Influence of Vestibular Schwannoma Tumor Volume and Growth on Hearing Loss

OBJECTIVE

To ascertain the relationship among vestibular schwannoma (VS) tumor volume, growth, and hearing loss.

STUDY DESIGN

Retrospective cohort study.

SETTING

Single tertiary center.

SUBJECTS AND METHODS

Adults with observed VS and serviceable hearing at diagnosis were included. The primary outcome was the development of nonserviceable hearing as estimated using the Kaplan-Meier method. Associations of tumor volume with baseline hearing were assessed using Spearman rank correlation coefficients. Associations of volume and growth with the development of nonserviceable hearing over time were assessed using Cox proportional hazards models and summarized with hazard ratios (HRs).

RESULTS

Of 230 patients with VS and serviceable hearing at diagnosis, 213 had serial volumetric tumor data for analysis. Larger tumor volume at diagnosis was associated with increased pure-tone average (PTA) (P < .001) and decreased word recognition score (WRS) (P = .014). Estimated rates of maintaining serviceable hearing at 6 and 10 years following diagnosis were 67% and 49%, respectively. Larger initial tumor volume was associated with development of nonserviceable hearing in a univariable setting (HR for 1-cm³ increase: 1.36, P = .040) but not after adjusting for PTA and WRS. Tumor growth was not significantly associated with time to nonserviceable hearing (HR, 1.57; P = .14), although estimated rates of maintaining serviceable hearing during observation were poorer in the group that experienced growth.

CONCLUSION

Larger initial VS tumor volume was associated with poorer hearing at baseline. Larger initial tumor volume was also associated with the development of nonserviceable hearing during observation in a univariable setting; however, this association was not statistically significant after adjusting for baseline hearing status.

Impact of Aspirin and Other NSAID Use on Volumetric and Linear Growth in Vestibular Schwannoma

Objectives

Conflicting research exists surrounding the utility of aspirin to prevent tumor growth in the medical management of vestibular schwannoma (VS). Recent studies demonstrated no association between aspirin and VS growth using linear tumor measurements. Given the heightened sensitivity of volumetric analyses to monitor tumor growth, the current study was conceived with the chief objective of assessing the association between aspirin or other nonsteroidal anti-inflammatory drug (NSAID) use and VS growth using volumetric analyses.

Study Design

Retrospective review.

Setting

Tertiary referral center.

Subjects and Methods

A total of 361 patients totaling 1601 volumetrically analyzed magnetic resonance imaging studies who underwent initial observation since January 1, 2003.

Results

In total, 123 (35%) patients took 81 mg aspirin daily, 23 (7%) took 325 mg aspirin daily, and 41 (11%) reported other NSAID use. Among those taking aspirin, 112 (72%) exhibited volumetric tumor growth during observation compared to 33 (80%) among other NSAID users and 137 (67%) among nonaspirin users. Patients taking aspirin or other NSAIDs were significantly older at time of diagnosis (median, 66 vs 56 years; P < .001). Neither aspirin use (hazard ratio [HR], 0.96; P = .73) nor other NSAID use (HR, 1.39; P = .081) was significantly associated with a reduced risk of volumetric tumor growth. These results were similar following age adjustment ( P = .81 and .087, respectively). When separating aspirin users by 81-mg or 325-mg dosing, neither group exhibited a reduced risk of growth ( P = .95 and .73, respectively).

Conclusion

Despite promising initial results, the preponderance of existing literature suggests that aspirin and other NSAID use does not prevent tumor growth in VS.

Natural History of Sporadic Vestibular Schwannoma: A Volumetric Study of Tumor Growth

Objective

(1) Assess 3-dimensional volumetric growth of untreated sporadic vestibular schwannomas (VSs) in a large cohort of patients treated with conservative observation. (2) Compare volumetric and conventional linear diameter measurements for detecting tumor growth.

Study Design

Case series with chart review.

Setting

Tertiary skull base referral center.

Subjects and Methods

Patients with sporadic VS who elected initial conservative treatment with at least 2 serial magnetic resonance imaging (MRI) scans were included. Tumor volume was determined with 3-dimensional segmentation of MRI sequences. The volumetric threshold for tumor growth was an increase ≥20% from baseline tumor volume. Tumor size based on linear diameter was assessed with the 1995 American Academy of Otolaryngology—Head and Neck Surgery Foundation guidelines for VS outcome reporting, with growth defined as an increase ≥2 mm.

Results

A total of 361 patients were included with a median radiologic follow-up of 4.1 years (interquartile range [IQR], 2.5-6.8). At diagnosis, 232 VSs (64%) were purely intracanalicular, and 129 (36%) extended into the cerebellopontine angle. The median baseline tumor volume was 0.161 cm3 (IQR, 0.054-0.418). Overall, 69% of tumors demonstrated volumetric growth at a median of 1.1 years (IQR, 0.6-2.1) after initial MRI. In contrast, based on linear measurement assessment, 48% of tumors demonstrated growth at a median of 1.8 years (IQR, 0.8-3.1) from first MRI scan. Disequilibrium, facial hypoesthesia, aural fullness, initial tumor size, and nonincidental diagnosis were associated with tumor growth.

Conclusion

Three-dimensional volumetric assessment of VS provides a more sensitive measure of tumor growth when compared with linear diameter assessment. Through volumetric analysis, the current study revealed that a significant proportion of VSs demonstrate growth during observation.

A Comparison of Repeatability and Usability of Semi-Automated Volume Segmentation Tools for Measurement of Vestibular Schwannomas

OBJECTIVE

Semi-automated volume segmentation tools (SAVST) offer a less time consuming technique compared with manual volume segmentation method. No data exists to suggest which of the available applications are optimal for use with vestibular schwannomas (VS). This study aims to compare repeatability and usability of three different SAVST for measurement of VS.

STUDY DESIGN

Experimental comparison of three SAVST.

SETTING

Tertiary skull base unit.

PATIENTS

Twenty-four patients with a unilateral VS imaged with T1-weighted Gadolinium enhanced MRI.

INTERVENTION

Repeated measurements made to determine intra and inter-observer agreement. This was repeated using three different SAVST.

MAIN OUTCOME MEASURES

1) Intra- and inter-observer intraclass correlation coefficients (ICC), repeatability coefficients (RC), and relative smallest detectable differences (%SDD).2) Usability as determined by the mean number of steps and time required per tumor measurement and the proportion of cases where manual editing was required.

RESULTS

Intra-observer ICCs were significantly better for SliceOmatic and OleaSphere than AW VolumeShare (0.998 versus 0.994, p < 0.05). Inter-observer ICCs were also better for SliceOmatic (0.994) and OleaSphere (0.989) compared with AW VolumeShare (0.976), however, this was only significant for SliceOmatic (p = 0.012). SliceOmatic had a poorer usability profile requiring more manual editing, time, and individual steps per measurement but its "watershed segmentation" algorithm was better at measuring cystic or heterogenous tumors.

CONCLUSIONS

This is the first study to compare three SAVST for measurement of VS. While SliceOmatic had the highest repeatability, Olea Sphere combined comparable repeatability with improved usability and a greater degree of automation and was, therefore, deemed optimal for use in routine clinical practice.

Vestibular schwannomas: Accuracy of tumor volume estimated by ice cream cone formula using thin-sliced MR images

PURPOSE

We estimated the volume of vestibular schwannomas by an ice cream cone formula using thin-sliced magnetic resonance images (MRI) and compared the estimation accuracy among different estimating formulas and between different models.

METHODS

The study was approved by a local institutional review board. A total of 100 patients with vestibular schwannomas examined by MRI between January 2011 and November 2015 were enrolled retrospectively. Informed consent was waived. Volumes of vestibular schwannomas were estimated by cuboidal, ellipsoidal, and spherical formulas based on a one-component model, and cuboidal, ellipsoidal, Linskey's, and ice cream cone formulas based on a two-component model. The estimated volumes were compared to the volumes measured by planimetry. Intraobserver reproducibility and interobserver agreement was tested. Estimation error, including absolute percentage error (APE) and percentage error (PE), was calculated. Statistical analysis included intraclass correlation coefficient (ICC), linear regression analysis, one-way analysis of variance, and paired t-tests with P < 0.05 considered statistically significant.

RESULTS

Overall tumor size was 4.80 ± 6.8 mL (mean ±standard deviation). All ICCs were no less than 0.992, suggestive of high intraobserver reproducibility and high interobserver agreement. Cuboidal formulas significantly overestimated the tumor volume by a factor of 1.9 to 2.4 (P ≤ 0.001). The one-component ellipsoidal and spherical formulas overestimated the tumor volume with an APE of 20.3% and 29.2%, respectively. The two-component ice cream cone method, and ellipsoidal and Linskey's formulas significantly reduced the APE to 11.0%, 10.1%, and 12.5%, respectively (all P < 0.001).

CONCLUSION

The ice cream cone method and other two-component formulas including the ellipsoidal and Linskey's formulas allow for estimation of vestibular schwannoma volume more accurately than all one-component formulas.

A comparison of semi-automated volumetric vs linear measurement of small vestibular schwannomas

Objective

Accurate and precise measurement of vestibular schwannoma (VS) size is key to clinical management decisions. Linear measurements are used in routine clinical practice but are prone to measurement error. This study aims to compare a semi-automated volume segmentation tool against standard linear method for measuring small VS. This study also examines whether oblique tumour orientation can contribute to linear measurement error.

Study design

Experimental comparison of observer agreement using two measurement techniques.

Setting

Tertiary skull base unit.

Participants

Twenty-four patients with unilateral sporadic small (< 15 mm maximum intracranial dimension) VS imaged with 1 mm-thickness T1-weighted Gadolinium enhanced MRI.

Main outcome measures

(1) Intra and inter-observer intraclass correlation coefficients (ICC), repeatability coefficients (RC), and relative smallest detectable difference (%SDD). (2) Mean change in maximum linear dimension following reformatting to correct for oblique orientation of VS.

Results

Intra-observer ICC was higher for semi-automated volumetric when compared with linear measurements, 0.998 (95% CI 0.994–0.999) vs 0.936 (95% CI 0.856–0.972), p < 0.0001. Inter-observer ICC was also higher for volumetric vs linear measurements, 0.989 (95% CI 0.975–0.995) vs 0.946 (95% CI 0.880–0.976), p = 0.0045. The intra-observer %SDD was similar for volumetric and linear measurements, 9.9% vs 11.8%. However, the inter-observer %SDD was greater for volumetric than linear measurements, 20.1% vs 10.6%. Following oblique reformatting to correct tumour angulation, the mean increase in size was 1.14 mm (p = 0.04).

Conclusion

Semi-automated volumetric measurements are more repeatable than linear measurements when measuring small VS and should be considered for use in clinical practice. Oblique orientation of VS may contribute to linear measurement error.

Diagnostics and therapy of vestibular schwannomas - an interdisciplinary challenge

Vestibular schwannomas (VS) expand slowly in the internal auditory canal, in the cerebellopontine angle, inside the cochlear and the labyrinth. Larger tumors can displace and compress the brainstem. With an annual incidence of 1:100,000 vestibular schwannoma represent 6-7% of all intracranial tumors. In the cerebellopontine angle they are by far the most neoplasm with 90% of all lesions located in this region. Magnetic resonance imaging (MRI), audiometry, and vestibular diagnostics are the mainstays of the clinical workup for patients harboring tumors. The first part of this paper delivers an overview of tumor stages, the most common grading scales for facial nerve function and hearing as well as a short introduction to the examination of vestibular function. Upholding or improving quality of life is the central concern in counseling and treating a patient with vestibular schwannoma. Preservation of neuronal function is essential and the management options - watchful waiting, microsurgery and stereotactic radiation - should be custom-tailored to the individual situation of the patient. Continuing interdisciplinary exchange is important to monitor treatment quality and to improve treatment results. Recently, several articles and reviews have been published on the topic of vestibular schwannoma. On the occasion of the 88^th annual meeting of the German Society of Oto-Rhino-Laryngology, Head and Neck surgery a special volume of the journal "HNO" will be printed. Hence this presentation has been designed to deviate from the traditional standard which commonly consists of a pure literature review. The current paper was conceptually woven around a series of interdisciplinary cases that outline examples for every stage of the disease that show characteristic results for management options to date. Systematic clinical decision pathways have been deduced from our experience and from results reported in the literature. These pathways are graphically outlined after the case presentations. Important criteria for decision making are size and growth rate of the tumor, hearing of the patient and the probability of total tumor resection with preservation of hearing and facial nerve function, age and comorbidity of the patient, best possible control of vertigo and tinnitus and last but not least the patient's preference and choice. In addition to this, the experience and the results of a given center with each treatment modality will figure in the decision making process. We will discuss findings that are reported in the literature regarding facial nerve function, hearing, vertigo, tinnitus, and headache and reflect on recent studies on their influence on the patient's quality of life. Vertigo plays an essential role in this framework since it is an independent predictor of quality of life and a patient's dependence on social welfare. Pathognomonic bilateral vestibular schwannomas that occur in patients suffering from neurofibromatosis typ-2 (NF2) differ from spontaneous unilateral tumors in their biologic behavior. Treatment of neurofibromatosis type-2 patients requires a multidisciplinary team, especially because of the multitude of separate intracranial and spinal lesions. Off-label chemotherapy with Bevacizumab can stabilize tumor size of vestibular schwannomas and even improve hearing over longer periods of time. Hearing rehabilitation in NF2 patients can be achieved with cochlear and auditory brainstem implants.

Gender-specific growth dynamics of neurofibromatosis type-2-related tumors of the central nervous system

BACKGROUND

To date, few studies have been published about the growth dynamics of tumors associated with neurofibromatosis type-2 (NF2), none of which evaluated gender-specific differences. Our aim was to compare radiographic data of female and male patients with NF2.

METHODS

MR images of 40 patients (20 female, 20 male) from the regional NF2 referral center were included in this analysis. Tumor sizes were determined by semi-automated volumetric measurement. Intracranial tumors were measured on post-contrast T1-weighted MRI datasets and volumes of intramedullary spinal tumors were determined from sagittal T2-weighted MRI datasets.

RESULTS

The median follow-up time was 91 months (range, 16-199 months) per patient. Intracranial tumors: On average, female patients had 13.4 neoplasms, while male patients had 6.75 (p = 0.042). The overall median time to tumor progression of ≥20 % was 20 months for females and 18 months for males. Tumors of the cerebellopontine angle (CPA) that had undergone previous surgery had shorter progression-free intervals in females than in males (16 and 24 months, respectively; p = 0.012). The median 1-year growth rate was 17.5 ± 44.6 % in females compared to 12.5 ± 44.9 % in males (p = 0.625). Intramedullary spinal tumors: On average, females had 2.05 tumors and males had 1.75 tumors (p = 0.721). Median time to tumor progression was 21 months in females and 44 months in males (p = 0.204). After 2 years, the median growth rate was 24.4 ± 56.8 % in female and 13.5 ± 40.4 % in male patients (p = 0.813).

CONCLUSIONS

The radiographic data in this study suggest that female patients are affected by a greater number of tumors than male patients and that post-surgery tumors of the CPA grow faster in females than in males.