Specific Changes in Brain Activity during Urgency in Women with Overactive Bladder after Successful Sacral Neuromodulation: A Functional Magnetic Resonance Imaging Study

PURPOSE: The mechanism of sacral neuromodulation is poorly understood. We compared brain activity during urgency before and after sacral neuromodulation in women with overactive bladder and according to the response to treatment. MATERIALS AND METHODS: Women with refractory overactive bladder who elected sacral neuromodulation were invited to undergo functional magnetic resonance imaging before and after treatment. During imaging the bladder was filled until urgency was experienced. Regions of interest were identified a priori and brain activity in these regions of interest was compared before and after treatment as well as according to the treatment response. Whole brain exploratory analysis with an uncorrected voxel level threshold of p <0.001 was also performed to identify additional brain regions which changed after sacral neuromodulation. RESULTS: Of the 12 women who underwent a pretreatment functional magnetic resonance imaging examination 7 were successfully treated with sacral neuromodulation and underwent a posttreatment examination. After sacral neuromodulation brain activity decreased in the left anterior cingulate cortex, the bilateral insula, the left dorsolateral prefrontal cortex and the bilateral orbitofrontal cortex (each p <0.05). No new brain regions showed increased activity after sacral neuromodulation. Pretreatment brain activity levels in the bilateral anterior cingulate cortex, the right insula, the bilateral dorsolateral prefrontal cortex, the right orbitofrontal cortex, the right supplementary motor area and the right sensorimotor cortex were higher in women who underwent successful treatment (each p <0.05). CONCLUSIONS: Brain activity during urgency changes after successful sacral neuromodulation. Sacral neuromodulation may be more effective in women with higher levels of pretreatment brain activity during urgency.