OP12.07: Revisiting the pathophysiology of intracranial hemorrhage in fetuses with Chiari II malformation: novel imaging biomarkers of disease severity?

Intracranial hemorrhage (ICH) has emerged as a notable concern in Chiari II malformation (CM II), yet its origins and clinical implications remain elusive. This study aims to validate the prevalence of ICH in CM II, investigate contributing factors to ICH, and visualise the findings in a network format. A single-centre retrospective review of fetal MRI scans obtained in fetuses with CM II was performed to identify ICH utilising EPI-T2* blood-sensitive sequence. Fetuses with aqueduct stenosis (AS) were included as a control group. The incidence of ICH and corresponding gestational ages were compared between CM II and AS cases, and morphometric measurements (inner/outer CSF spaces, posterior fossa, venous structure) were compared among the three 1:1 age-matched groups: CM II+ICH, CM II-ICH, and AS+ICH. Additionally, a co-occurrence network analysis (NA) was constructed to visualise associations between phenotypic features in ICH cases. A total of 101 fetuses with CM II and 90 controls with AS at a median gestational age of 24.4 weeks and 22.8 weeks were included. Prevalence of ICH in fetuses with CM II was higher compared to the AS cases (28.7% vs 18.9%), accompanied by congested veins (deep vein congestion mainly in young fetuses, and cortical veins may also be affected in older fetuses). ICH was notably correlated with extremely reduced outer cerebrospinal fluid spaces and clivus-supraocciput angle. NA spotlighted spinal bony defects, small posterior fossa dimensions, and vermis ectopia as central elements, as well as venous congestion and venous sinus stenosis as pivotal components within the network. The high prevalence of ICH – detected by fetal MRI - among fetuses with CM emphasises the pathophysiological importance of venous congestion, ICH, and vasogenic edema. As indicators of disease severity, these features may serve as helpful additional imaging biomarkers for the identification of potential candidates for fetal surgery.