Hemispheric differences in brain function account for the differential effects of stroke laterality on various domains of cognition, sensory-motor function, and decision making. Similarly, the size and location of stroke have been shown to determine the type and severity of bladder dysfunction in stroke survivors with neurogenic lower urinary tract (LUT) dysfunction. However, the changes in functional brain activity patterns in relation to the side of stroke are yet to be understood. This study aimed to determine the differential patterns of micturition-related neural activity in right- versus left-sided strokes.

The protocol of this prospective study was approved by our Institutional Review Board, and all research participants provided informed consent prior to enrollment. Adult patients with a history of chronic (>12 months) ischemic or hemorrhagic strokes and neurogenic LUT dysfunction were enrolled. Subjects were placed in a 3T magnetic resonance imaging (MRI) machine and underwent urodynamic assessment while micturition-related brain activity was simultaneously measured using functional MRI with the blood-oxygen-level-dependent (BOLD) technique. Statistical parametric mapping (SPM) was used to assess the changes in BOLD signal during a 10-second period of maximum urgency. The signal intensity was subsequently compared between the patients with left- versus right-sided strokes. Age, gender, and time since stroke were used as covariates to account for any potential confounding effects. Based on the simulations, a sample size of 12 patients would be typically required to achieve 80% power at single-voxel level. Statistically significant clusters were identified using a conservative p value threshold of <0.001 and cluster size of >25 voxels.

A total of 23 patients, including 16 men (69.57%), with an average age of 53.61±9.82 years were enrolled. Among those, 16 patients (69.57%) suffered from right-sided strokes. Our analysis of the BOLD signal changes during the period of maximum urgency yielded increased intensity in patients with left-sided strokes in eight areas spanning the anterior cingulate (Brodmann area 32), inferior frontal gyrus, middle frontal gyrus, and limbic area (cingulate gyrus) on the left hemisphere; frontal sub-gyral area on the right; and superior frontal gyrus (Brodmann area 8) bilaterally. In contrast, two clusters that were located in the left cerebellar anterior lobe and right limbic lobe (posterior cingulate) showed decreased BOLD signal in left-sided strokes compared to the right- sided counterparts.

The present study is the first to demonstrate the differences in micturition-related brain activity between left- and right-sided strokes. Through simultaneous urodynamic-functional MRI studies, we identified ten areas of differential activity. Compared to left- sided strokes, patients with right-sided strokes demonstrated markedly diminished brain activity in several regions of the brain that are known to play a role in LUT control. Consistent with the inherent functional differences across the brain hemispheres, laterality of the lesion is correlated with the changes in brain activation during micturition.

The results of this study provide important insights into the neural mechanisms underlying the LUT dysfunction in stroke patients. The differential patterns of micturition-related neural activity in right- versus left-sided strokes identified in this study expand our understanding of the hemispheric differences in brain function that may in part explain the variability in the effects of stroke on LUT function. These findings lay the groundwork for further research into the pathophysiology of neurogenic LUT dysfunction, as the urodynamic-functional MRI paradigm continues to serve as a valuable tool for exploring the intricate interplay between the brain and bladder.