Hypothesis / aims of study
Complex networks of neurons form cerebral control of the lower urinary tract (LUT). Several specific areas are known to play a role within the cortex and the brainstem. Cerebellum is also actively involved in the regulation of LUT, however, the cerebellum's contributions to LUT function is understudied, and its exact role in the working model of the brain-bladder network is poorly described [1]. Our team has identified three specific areas of interest (ROI) within the cerebellum (ROI1 and ROI2: right posterior lobe, ROI3: left tonsil) as playing a role in bladder filling in a cohort of healthy men and women[2].
Using tractography analysis with diffusion tensor imaging (DTI) targeting cerebellar white matter tracts (WMT), we sought to determine the anatomical structural connections linking these 3 ROIs and the rest of the brain.
Study design, materials and methods
We included healthy males and females with no reported history of neurological disease or LUT symptoms. They had a full 7Tesla MRI T1 weighted anatomical sequence, followed by functional MRI passive filling bladder protocol to determine the three relevant ROIs originated from the cerebellum. Then, we acquired an SMS2 diffusion-weighted image (DWI) sequence (64 directions, b-value: 1000s/mm2, slice thickness: 1.4mm).
Data were preprocessed with FSL (TOPUP, synthesized b0 reverse phase-encoding with Synb0-DISCO toolbox, and Eddy Current correction) and DSI Studio (motion correction, and normalization in the MNI space, diffusion data reconstruction). Then, we summed the subject's map to construct an average DTI [3]. A sampling length ratio of 1.25 was used, tensor metrics were calculated using DWI with a b-value lower than 1750s/mm2, and the three ROIs were added to filter and select only WMT passing through them. Finally, the ICMB 152 WMT template was used to compare the tracts shown by our individuals to the reference atlas.
Interpretation of results
The cerebellar ROIs with functional connectivity during bladder filling show lateralized, interhemispheric anatomical connectivity. These ROIs are also connected to the brain stem, the mesencephalon, and some cortical radiations. The cerebellum of healthy males and females is structurally highly connected to other cerebral structures, especially within the ROI involved in bladder filling and the brain bladder network.