Volumetric Analysis of Deep Cerebellar and Thalamic Nuclei in Spastic Cerebral Palsy

Cerebral palsy (CP) encompasses various movement disorders, most commonly spasticity, although other motor phenotypes such as dystonia may occur. Certain structural magnetic resonance imaging (MRI) findings, such as periventricular leukomalacia, are strongly correlated with spasticity. Due to their contributions in motor system modulation, thalamic structures and deep cerebellar nuclei (DCN) are appealing volumes of interest for investigating spasticity and CP-related motor pathway injuries. The goal of this study is to determine the validity of using scaled volumetric analysis of thalamic and deep cerebellar nuclei for distinguishing patients with spastic cerebral palsy.

All MRI scans were processed with FreeSurfer's recon-any pipeline, which integrates the deep-learning tools SynthSeg and SynthSR to generate standardized 1 mm isotropic T1-weighted images and robust segmentations independent of input contrast or resolution. DCN volumes were obtained using the SUIT toolbox, which employs an atlas-based segmentation of the cerebellum. To account for individual differences in brain size, volumes were allometrically scaled relative to total brain volume (TBV). Age-matched healthy controls were used from the Calgary Preschool MRI Dataset to ensure that observed volumetric differences reflected pathology rather than typical developmental variation. Statistical analyses were performed using Welch t test to account for unequal variances and sample size, as well as Spearman rank correlation analyses to evaluate the monotonic relationship between DCN and Gross Motor Function Classification System (GMFCS) scores.

Relative to TBV, all 14 thalamic nuclei were significantly smaller in the spastic CP group. Scaled DCN volumes revealed a heterogeneous and lateralized pattern. Overall, this cohort demonstrated reduced left dentate volume and relative enlargement of the left interposed and bilateral fastigial nuclei. This enlargement was confined to individuals with mild motor impairment, while more severe impairment was associated with progressively reduced volumes.

Patients with spastic CP demonstrate widespread reductions in TBV-adjusted thalamic volumes and a lateralized pattern of DCN volume alterations, which may reflect compensatory or maladaptive plasticity following cerebellothalamic pathway injury. Allometrically scaled volumetric analysis of these subcortical structures may provide a reliable approach for characterizing CP-related movement disorders and identifying potential neuroanatomical targets for future surgical interventions, including deep brain stimulation.