# Notch appearance as a novel radiological predictor of transient expansion and good outcome of expanding schwannoma after radiotherapy

## TL;DR

This study identifies a new radiological sign, a notch, that predicts temporary tumor growth and better outcomes in schwannomas after radiotherapy.

## Contribution

The appearance of a notch is introduced as a novel predictor for transient schwannoma expansion and improved long-term outcomes after radiotherapy.

## Key findings

- Approximately 28% of schwannomas showed transient expansion, with 75% displaying a new notch appearance.
- Tumors with a notch showed significant regression 5 years after radiation, indicating better outcomes.
- A notch appearance was associated with a higher local control rate in expanding schwannomas.

## Abstract

Schwannoma expansion after radiotherapy has not been well-studied despite the clinical importance of distinguishing transient increase from permanent expansion. Thus, this study aimed to identify the underlying mechanism and novel radiological predictors of schwannoma expansion after radiotherapy.

We retrospectively examined the therapeutic effects of radiotherapy on schwannomas and magnetic resonance images of 43 patients with vestibular schwannomas who underwent stereotactic radiotherapy or radiosurgery at our facility between June 1, 2012 and September 1, 2018. Based on the size change pattern, the treated tumors were classified into six groups, including transient-expansion and consistent-increase groups. The apparent diffusion coefficient (ADC) ratio and appearance of any notch were included as evaluation items based on our hypothesis that transient expansion is due to edema with increased extracellular free water. A log-rank test was performed to evaluate the relationship between the local control rate and radiological signs.

The mean overall 5-year local control rate was 90%, and the median follow-up period was 62 (24–87) months. Approximately 28% of the tumors showed transient expansion; all ADC ratios synchronized with size change, and 75% showed a new notch appearance. Approximately 9% of tumors showed consistent increase, with no notch on the outline. The log-rank test revealed a difference in the local control rate with or without notch appearance in expanding irradiated schwannomas. All tumors with notch appearance showed a significant regression 5 years after radiation.

New notch appearance on the outline could indicate favorable long-term outcomes of expanding schwannomas post-treatment.

Notch appearance can help differentiate a transient schwannoma from a real tumor expansion, and it is a novel predictor of better outcomes of expanding schwannomas after radiotherapy.

The online version contains supplementary material available at 10.1007/s12672-024-00936-y.