# Spatial distribution of cerebral microbleeds and FLAIR hyperintensities on follow-up MRI after radiotherapy for lower grade glioma

## TL;DR

This study examines how cerebral microbleeds and FLAIR hyperintensities appear and spread in brain scans of lower grade glioma patients after radiotherapy.

## Contribution

The study reveals that cerebral microbleeds and FLAIR hyperintensities do not spatially overlap in patients after radiotherapy for lower grade glioma.

## Key findings

- Cerebral microbleeds increase with time after radiotherapy completion.
- FLAIR hyperintensities appear earlier and are dose-dependent.
- Cerebral microbleeds and FLAIR hyperintensities are generally not spatially overlapping.

## Abstract

•The longer the time between the completion of RT and the scan, the more CMBs appear.•The higher the dose, the more FLAIR hyperintensities are generally observed.•Compared to CMBs, FLAIR hyperintensities appear early after completion of RT.•CMBs and FLAIR hyperintensities do not generally spatially overlap.

The longer the time between the completion of RT and the scan, the more CMBs appear.

The higher the dose, the more FLAIR hyperintensities are generally observed.

Compared to CMBs, FLAIR hyperintensities appear early after completion of RT.

CMBs and FLAIR hyperintensities do not generally spatially overlap.

Cerebral microbleeds (CMBs) and fluid-attenuated-inversion recovery (FLAIR) hyperintensities on brain MRI scans after radiotherapy (RT) are considered markers for microvascular damage and related cognitive changes. However, the spatial distribution using existing scoring systems as well as colocation of these imaging biomarkers remain unclear, hampering clinical interpretation. This study aims to elucidate the distribution and colocation of these markers in patients with lower grade glioma (LGG).

CMBs were spatially classified on retrospective 1.5 T susceptibility weighted MRI scans according to the existing Microbleed Anatomical Rating Scale (MARS) and were additionally scored for being located in hippocampus, amygdala, cortex, white matter (WM), grey matter (GM), WM/GM junction and for their spatial relation to FLAIR hyperintensities. Scoring was performed for whole, ipsilateral and contralateral cerebrum (with respect to tumour bulk).

Fifty-one scans were included of which 28 had at least one CMB. The majority of CMBs were localized in the lobar area and in deep and periventricular white matter (DPWM) - generally in WM. Only few CMBs were found in GM. In scans obtained up to 7 years after RT completion the majority of CMBs were not colocalized with FLAIR hyperintensities.

CMBs and FLAIR hyperintensities appear to be separate imaging biomarkers for radiation therapy induced microvascular damage, as they are not colocalized in patients with LGG, especially not early on after completion of RT.