Relationship of a "Fundal Fluid Cap" and Vestibular Schwannoma Volume: Analysis of Preoperative Radiographic Findings and Outcomes

Refining the predictive value of preoperative apparent diffusion coefficient (ADC) by whole-tumor analysis for facial nerve outcomes in vestibular schwannomas

BACKGROUND

Apparent diffusion coefficient (ADC) in MRI has been shown to correlate with postoperative House-Brackmann (HB) scores in patients with vestibular schwannoma despite limited methodology. To rectify limitations of single region of interest (ROI) sampling, we hypothesize that whole-tumor ADC histogram analysis will refine the predictive value of this preoperative biomarker related to postoperative facial nerve function.

METHODS

Of 155 patients who underwent resection of vestibular schwannoma (2014-2020), 125 patients were included with requisite clinical and radiographic data. After volumetric analysis and whole-tumor ADC histogram, regression tree analysis identified ADC cutoff for significant differences in HB grade. Outcomes were extent of resection, facial nerve function, hospital length of stay (LOS), and complications.

RESULTS

Regression tree analysis defined three quantitative ADC groups (× 10-6 mm2/s) as high (> 2248.77; HB 1.7), mid (1468.44-2248.77; HB 3.1), and low (< 1468.44; HB 2.3) range (p 0.04). The mid-range ADC group had significantly worse postoperative HB scores and longer hospital LOS. Large tumor volume was independently predictive of lower rates of gross total resection (p <0.0001), higher postoperative HB score (p 0.002), higher rate of complications (p 0.04), and longer LOS (p 0.003).

CONCLUSIONS

Whole-tumor histogram yielded a robust regression tree analysis that defined three ADC groups with significantly different facial nerve outcomes. This likely reflects tumor heterogeneity better than solid-tumor ROI sampling. Whole-tumor ADC warrants further study as a useful radiographic biomarker in patients with vestibular schwannoma who are considering surgical resection.

The value of radiographic features in predicting postoperative facial nerve function in vestibular schwannoma patients: A retrospective study and nomogram analysis

OBJECTIVE

The purpose of this study was to identify significant prognostic factors associated with facial paralysis after vestibular schwannoma (VS) surgery and develop a novel nomogram for predicting facial nerve (FN) outcomes.

METHODS

Retrospective data were retrieved from 355 patients who underwent microsurgery via the retrosigmoid approach for VS between December 2017 and December 2022. Univariate and multivariate logistic regression analysis were used to construct a radiographic features-based nomogram to predict the risk of facial paralysis after surgery.

RESULTS

Following a thorough screening process, a total of 185 participants were included. The univariate and multivariate logistic regression analysis revealed that tumor size (p = 0.005), fundal fluid cap (FFC) sign (p = 0.014), cerebrospinal fluid cleft (CSFC) sign (p < 0.001), and expansion of affected side of internal auditory canal (IAC) (p = 0.033) were independent factors. A nomogram model was constructed based on these indicators. When applied to the validation cohort, the nomogram demonstrated good discrimination and favorable calibration. Then we generated a web-based calculator to facilitate clinical application.

CONCLUSION

Tumor size, FFC and CSFC sign, and the expansion of the IAC, serve as good predictors of postoperative FN outcomes. Based on these factors, the nomogram model demonstrates good predictive performance.

Pathophysiology of Postoperative Hearing Disorders after Vestibular Schwannoma Resection: Insights from Auditory Brainstem Response and Otoacoustic Emissions

Background: In order to better understand the pathophysiology of surgically induced hearing loss after vestibular schwannoma (VS) surgery, we postoperatively analyzed the hearing status in a series of patients where hearing was at least partially preserved. Methods: Hearing was assessed through tonal audiometry, speech discrimination score, maximum word recognition score (dissyllabic word lists-MaxIS), otoacoustic emissions (OAEs), and auditory brainstem response (ABR). The magnetic resonance imaging (MRI) tumor characterization was also noted. Results: In a series of 24 patients operated on for VS over 5 years, depending on the results of this triple hearing exploration, we could identify, after surgery, patients with either a myelin alteration or partial damage to the acoustic fibers, others with a likely partial cochlear ischemia, and some with partial cochlear nerve ischemia. One case with persisting OAEs and no preoperative ABR recovered hearing and ABR after surgery. Long follow-up (73 ± 57 months) revealed a mean hearing loss of 30 ± 20 dB with a drastic drop of MaxIS. MRI revealed only 25% of fundus invasion. Conclusion: a precise analysis of hearing function, not only with classic audiometry but also with ABR and OEAs, allows for a better understanding of hearing damage in VS surgery.

Presence of a fundal fluid cap on preoperative magnetic resonance imaging may predict long-term facial nerve function after resection of vestibular schwannoma via the retrosigmoid approach

OBJECTIVE

Preservation of neurological function is a priority when performing a resection of a vestibular schwannoma (VS). Few studies have examined the radiographic value of a fundal fluid cap—i.e., cerebrospinal fluid in the lateral end of a VS within the internal auditory canal—for prediction of postoperative neurological function. The aim of this study was to clarify whether the presence of a fundal fluid cap on preoperative magnetic resonance images has a clinical impact on facial nerve function after resection of VSs.

METHODS

The presence of a fundal fluid cap and its prognostic impact on long-term postoperative facial nerve function were analyzed.

RESULTS

A fundal fluid cap was present in 102 of 143 patients who underwent resection of sporadic VSs via the retrosigmoid approach. Facial nerve function was acceptable (House-Brackmann grade I–II) immediately after surgery in 82 (80.4%) patients with a fundal fluid cap and in 26 (63.4%) of those without this sign. The preservation rate of facial nerve function increased in a time-dependent manner after surgery in patients with a fundal fluid cap but plateaued by 3 months postoperatively in those without a fundal fluid cap; the difference was statistically significant at 12 months (96.1% vs 82.9%, p = 0.013) and 24 months (97.1% vs 82.9%, p = 0.006) after surgery. The presence of a fundal fluid cap had a significantly positive effect on long-term facial nerve function at 24 months after surgery when tumor size and intraoperative neuromonitoring response were taken into account (OR 5.55, 95% CI 1.12–27.5, p = 0.034).

CONCLUSIONS

Neuromonitoring-guided microsurgery for total resection of VSs is more likely to be successful in terms of preservation of facial nerve function if a fundal fluid cap is present. This preoperative radiographic sign could be helpful when counseling patients and deciding the treatment strategy.

The Influence of Extent of Resection and Tumor Morphology on Facial Nerve Outcomes Following Vestibular Schwannoma Surgery

OBJECTIVE

To determine the influence extent of resection and tumor characteristics on facial nerve (FN) outcomes following microsurgical resection of vestibular schwannoma (VS).

STUDY DESIGN

Retrospective chart review.

SETTING

Tertiary referral center.

PATIENTS

Three hundred eighty-five patients who underwent VS microsurgical resection.

INTERVENTIONS

Microsurgical VS resection.

MAIN OUTCOME MEASURES

House-Brackmann (HB) scores postoperatively. Good FN function was defined as HB grade I and II and poor FN function was defined as HB grade III and VI. Gross total resection (GTR) versus subtotal resection (STR). Propensity-score matching was used in subset analysis to balance tumor volume between the surgical cohorts, followed by multivariable analysis.

RESULTS

Seventy-one patients (18%) underwent STR and 314 patients (82%) underwent GTR. Two hundred fourteen patients (63%) had good FN function at 2 to 3 weeks postoperatively, and 80% had good FN function at 1 year. In single predictor analysis, STR did not influence FN function at 2 to 3 weeks (p = 0.65). In propensity-score matched subset analysis (N = 178), patients with STR were less likely to have poor FN function at 2 to 3 weeks (p = 0.02) independent of tumor volume (p = 0.004), but there was no correlation between STR and FN function at 1 year (p = 0.09). Ventral extension of tumor relative to the internal auditory canal plane was associated with poor FN outcomes at 2 to 3 weeks (p = 0.0001) and 1-year postop (p = 0.002).

CONCLUSIONS

When accounting for tumor volume, STR is protective in immediate postoperative FN function compared to GTR. Ventral extension of the tumor is a clinical predictor of long-term FN outcomes.

Predicting Hearing Outcomes in Conservatively Managed Vestibular Schwannoma Patients Utilizing Magnetic Resonance Imaging

OBJECTIVE

Management of small vestibular schwannomas has evolved to where observation with interval imaging is an accepted treatment strategy. Loss of residual hearing is a known complication of observation. Magnetic resonance imaging (MRI) may provide critical information to assist in determining which tumors are at highest risk of hearing loss. We wished to determine what effect fundal cap size and cochlear fluid-attenuated inversion recovery (FLAIR) signal had on the progression of hearing loss in a large cohort of observed subjects.

STUDY DESIGN

Retrospective chart review.

SETTING

Tertiary academic referral center.

PATIENTS

Three hundred ninety-three adults with a vestibular schwannoma who underwent expectant management with serial audiograms and MRI.

INTERVENTIONS

Audiogram and MRI.

MAIN OUTCOME MEASURES

Hearing outcomes included pure-tone average and word discrimination score (WRS). Cochlear FLAIR signal was measured as a ratio between the affected and nonaffected cochlea. Cerebrospinal fluid fundal cap was measured from the most lateral aspect of the tumor to the fundus of the internal auditory canal.

RESULTS

An increased cochlear FLAIR ratio was associated with a worse initial WRS (p = 0.0001, β=-0.25). A multivariate regression analysis demonstrated the variables fundal cap and initial WRS to significantly predict change in WRS over time. The larger the fundal cap size, the smaller the change in the WRS (p = 0.047, β=-0.35).

CONCLUSIONS

Cerebrospinal fluid fundal cap size predicts the natural history of hearing in vestibular schwannoma patients. The presence of a smaller fundal cap is correlated with a greater risk of progression of hearing loss and should be a variable considered in the management of small vestibular schwannomas.