Uncrossed Cerebellar Diaschisis in Hemimegalencephaly: Evaluated by FDG-PET and Diffusion Tensor Tractography

Background: This study aimed to assess cerebrocerebellar connectivity in patients with hemimegalencephaly (HME) using ¹⁸F-fluorodeoxyglucose positron emission tomography (FDG-PET) and diffusion tensor imaging (DTI), as uncrossed cerebellar diaschisis is often observed in patients with HME. Methods: Thirty-one patients with HME underwent FDG-PET and magnetic resonance imaging. Cerebellar and cerebral cortical uptake was measured using FDG-PET, and the cerebellar diaschisis index was calculated. Fractional anisotropy (FA) values for crossed and uncrossed cortico-ponto-cerebellar (CPC) fibres were obtained via DTI. Correlation between the cerebellar diaschisis index and FA values, seizure onset, frequency and developmental quotient scores were analysed. Results: Uncrossed cerebellar diaschisis was present in 68% of patients, whereas crossed diaschisis was identified in 32% of patients. A significant positive correlation was found between the cerebellar diaschisis index and the FA values of uncrossed CPC fibres on HME and contralateral sides. No significant correlation was noted between the index and the FA values of crossed CPC fibres or clinical outcomes. Conclusion: Uncrossed CPC fibres play a more significant role in cerebrocerebellar connectivity in the HME than crossed fibres. Our results provide valuable insights into the neural fibre development in HME.