Predicting the Consistency of Vestibular Schwannoma and Its Implication in the Retrosigmoid Approach: A Single-Center Analysis

TL;DR

This study explores how MRI scans can predict the texture of vestibular schwannomas, which could help surgeons plan operations to better protect facial nerves and improve patient outcomes.

Contribution

The study introduces a novel method using MRI parameters like ADC to predict tumor consistency, which could influence surgical planning.

Findings

Normalized ADC values (N-ADCmin) showed a significant association with tumor consistency and postoperative facial nerve outcomes.

Firmer tumors may transmit more shock waves during surgery, potentially impairing facial nerve function.

The study found that MRI-based parameters could help differentiate tumor types and guide surgical techniques.

Abstract

Vestibular schwannomas (VSs) are benign brain tumors that can affect hearing and facial nerve function. Their surgical removal can be challenging, as tumors can vary in texture and consistency. These characteristics act as mechanical factors that can influence facial nerve function and impact the patient’s quality of life. Specifically, while firmer tumors may have clearer dissection planes, they could transmit more shock waves to the facial nerve, affecting its electrical response and limiting the extent of resection. Currently, it is challenging to determine a tumor’s consistency prior to surgery. In this study, we examine the role of specific measurements from a standard MRI scan, namely the Apparent Diffusion Coefficient (ADC), in predicting the consistency of VSs. The possibility to easily anticipate tumor consistency allows surgeons to better plan their operations, potentially adjusting their technique to better protect the facial nerve during surgery, which could lead to improved patient outcomes.

To explore the relationship between magnetic resonance imaging (MRI) parameters, including T2-weighted intensity and apparent diffusion coefficient (ADC), and intraoperative tumor characteristics, particularly consistency, in vestibular schwannomas (VSs). The association between tumor consistency, facial nerve (FN) function, and postoperative outcomes was analyzed. A single-center retrospective analysis included newly diagnosed VS cases (2020–2023) with cisternal involvement (Samii T3a; volume ≥ 0.7 cm3). T2 and ADC maps from the perimetral region of interest were normalized, and tumors were categorized into 3 classes by combining qualitative consistency (soft, fibrous, or fibrous/hard), ultrasonic aspirator power, and adherence to neurovascular structures. FN function was assessed using the House–Brackmann scale at the immediate postoperative period and 12-month follow-up. MRIs of 33 VSs (18 solid and 15 cystic) were analyzed. Normalized values of both T2 (N-T2mean) and ADC (N-ADCmin) maps predicted the classical radiological differentiation. N-ADCmin may have some role in predicting consistency (value 1.361, p = 0.017, accuracy 0.48) and demonstrated a significant association (p = 0.04) with the FN outcome in the immediate postoperative period. An augmented consistency could impair FN function by increasing the intrameatal pressure related to greater transmission of shocks derived from the dissection maneuvers of the cisternal component of the tumor. The possibility of non-invasively exploring VS consistency with a parameter easily calculable on MRI might be beneficial in surgical planning, modifying the timing of the opening of the meatus with respect to what could be the surgical routine in some centers.

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