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.

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.

20 subjects underwent DWI acquisitions. Infratentorial wrapping artifacts during DWI acquisition required the subsequent exclusion of 12 individuals. Therefore, the average brain was made from 8 individuals (four males and four females) in the final analysis. 
The three ROIs show intense structural connectivity within the cerebellum, crossing the midline through the vermis to the contralateral hemisphere and connecting each other. WMTs from ROI1 and ROI2 also travel to the brainstem mainly via the right middle and upper cerebellar peduncle. Additionally, WMT originating mainly from ROI1 radiate to cortical regions potentially involved in lower urinary tract network control. A comparison with ICBM 152 showed that the WMT description was relevant, with fewer fibers due to our limiting number of individuals (Figure 1).

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.

We described for the first time the structural connectivity of the cerebellum associated with LUT control on 7Teslas MRI. A complex intracerebellar network and connectivity with the brainstem were revealed. Further analysis will be necessary to describe other localizations in the cortex.

Mehnert U, van der Lely S, Seif M, Leitner L, Liechti MD, Michels L. Neuroimaging in Neuro-Urology. European Urology Focus. 2020 Sep;6(5):826–37.
Mazeaud C, Bernard J, Salazar B, Su J, Rajab H, Karmonik C, et al. A closer look at the cerebellar regions involved in men and women lower urinary tract function:  a 7T functional MRI
Yeh FC. Population-based tract-to-region connectome of the human brain and its hierarchical topology. Nat Commun. 2022 Aug 22;13(1):4933.

Continence 7S1 (2023) 100757
DOI: 10.1016/j.cont.2023.100757