# Structural Fiber Tract Alterations in Relation to Surgery in Children With a Posterior Fossa Tumor

## TL;DR

This study examines how surgery for posterior fossa tumors in children affects brain fiber tracts, particularly the dentato-rubro-thalamic tract, which may be linked to post-surgery speech issues.

## Contribution

The study introduces a method to assess macro- and microstructural changes in the DRTT during surgery using intraoperative diffusion MRI tractography.

## Key findings

- Intraoperative reductions in DRTT and AF tract volumes and diameters were observed during posterior fossa tumor surgery.
- Patients with postoperative speech disturbances showed higher variability in microstructural measures along the DRTT.
- Microstructural changes in the DRTT near the resection cavity were more pronounced compared to the arcuate fasciculus.

## Abstract

Cerebellar mutism syndrome (CMS) is a potential complication of pediatric posterior fossa tumor (pPFT) resection and may be related to disruption of the dentato‐rubro‐thalamic tract (DRTT). Intraoperative tractography allows assessment of changes to the DRTT during surgery. We evaluated macro‐ and microstructural changes of the DRTT by comparing pre‐ and intraoperative diffusion MRI (dMRI) tractography in patients with pPFT. Pre‐ and intraoperative T1‐weighted and dMRI data were acquired to reconstruct the DRTT, while the arcuate fasciculus (AF) was reconstructed as a control tract. To evaluate macrostructural intraoperative alterations, tract volume and diameter were calculated. Microstructural changes were assessed using fractional anisotropy (FA) and mean diffusivity (MD), both globally and along the tract. Speech disturbances, as a characteristic symptom of CMS, were scored preoperatively and at hospital discharge, based on retrospective neurological reports. In 30 patients (aged > 21 months) with sufficient data quality, intraoperative reductions in tract volumes and diameters were observed (p < 0.05) in the decussating DRTT (d‐DRTT) (−45.4% to −10%) and AF (−9.9% to −5.1%), while the non‐decussating DRTT (nd‐DRTT) remained stable. Right d‐DRTT volume loss correlated with ventricular enlargement (r = −0.476, p = 0.022). Whole‐tract analyses revealed increased FA in the AF and increased MD in the nd‐DRTT and AF. Along‐tract analyses demonstrated high variance of the MD in the DRTT cerebellar segments. Patients with postoperative speech disturbances showed higher variance of FA and MD along the DRTT, particularly in the left cerebellar segment. pPFT surgery affected the variation of the DRTT microstructure near the resection cavity, whereas the AF remained relatively stable. Although we did not find significant differences in patients with postoperative speech disturbances, we observed a much higher variability in MD in this group, suggesting a potential effect of DRTT disruption in these symptoms.

Children that undergo posterior fossa tumor resection may experience post‐surgery neurological symptoms related to disruption of the dentato‐rubro‐thalamic tract (DRTT). By comparing pre‐ and intraoperative diffusion MRI tractography, we observed more variation in microstructural measures in the DRTT near the resection cavity, which were more pronounced in patients with postoperative speech disturbances.